Author Topic: A digital scope for audio circuits, what do i need?  (Read 18261 times)

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Offline MrSadman

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A digital scope for audio circuits, what do i need?
« on: May 31, 2013, 08:55:36 am »
Long story short - I want a new oscilloscope.
I currently have an old Soviet analog scope, 10MHz, single channel. While it sort of works, it simply doesn't compare to the gear I have access to at school and work and I have been thinking about upgrading.

Main use is audio, including tube designs. I do some repairs but mostly analyze and modify circuits and build DIY projects. Also dabble with small scale automation.

Option one would be to upgrade to a better analog scope, however there is one drawback with analog scopes.
I write about the schematics in a blog and also document some case studies for uni or myself. Getting images of signal shapes is a pain with analog scopes, atleast compared to the DSO's That is actually the main reason I am interested in a digital scope.
 
So, what would you say I need for working with audio?
Picoscope has some PC scopes that have a high vertical resolution, enough memory and decent sampling rates around the 1000euros price range. They also include a signal genertor(I currently use a PC soundcard as a signal source), and my workspace is small, so saving space would be a big plus. However if they are anything like the PC scopes I have used, they are more of a logging device then a scope for a workbench. The no buttons thing usually means it takes a long time to get the desired image on screen. Also I would be worried about working with tube designs and high voltage.
 
Should I spend some more serious cash on a higher end digital scope with some extras, like Agilent 2000 or 3000 series(We use Agilent at work, I could probably get more bang for buck from a different brand), or go for a Rigol 1052E etc. and a separate signal gen? How imortant it actually is to get vertical resolution higher then eight bits and are there any scopes in under 3000 euros pricerange that actually offer this without sacrificing other functions?
Or is the answer that there is no place for digital scopes in the world of audio?
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #1 on: May 31, 2013, 11:36:04 am »
For audio work, an analog scope is cheapest and best. They are almost impossible to damage with high voltage overloads at the input, can display magnified baseline views of waveforms that exceed the graticule limits that digital scopes cannot except by distorting them to give you a false display.

Analogs are quicker to set up to the right vert and horiz settings and trig with just knobs and switches, all around easier to use. What could you possibly want memory storage for if you are working with tube amps?

Analog scopes are even easier to trigger on signals, especially with low-level signals that are smaller than 3 sub grat lines, the lower trig limit of any waveform displayed. On the DS4024, when I use mains (line triggering) I can always get a stable display, but  unlike on the analog scope, the DS4024 does not allow me to adj the trig level with line triggering.

A good digital scope that can get close to match the displayed fidelity of the 20 dollar used 20-MHz dual-chan analog scope I bought cannot be found.

Digital scopes are easily overloaded and severely distort signals displayed that have an envelope outside their graticule range. You cannot get a clear magnified view of signals around the 0-V point when their amplitude is way off  the graticule range.

In audio work you may want to get a magnified view of crossover distortion, those signals so often seen in audio work that are most important. Digital scopes cannot do this if you try to magnify the crossover point.

No digital scope I have tried is able to show the true waveform shape with input overload.

 At the tiniest V. level, the signal you may want to see is hidden by HF noise and unexpected ground loop effects not seen on a low freq analog scope.

And playing around at the 450+ V of tube amps...one single mistake hitting the range switch of a 10/1 probe and that 3000 buck digital scope input is trashed.


Digital scopes for some strange custom, and in normal operation, will always display a ghost image of the last waveform that was Norm triggered until the next trigger and so you to have to be very careful to check if you are really watching a live waveform at all. This odd behavior perhaps pays homage to old sampling scopes, but it cannot be turned off. Digital scopes do not seem to obey their own persistence settings with NORM triggering. An analog scope displays a waveform only when there is a waveform to display in NORM trigger mode.

When trying to see some instantaneous slow phenomena, the digital scopes most often fail to do this, requiring that a full 14-div trace is processed by the scope before displaying. So what you see is history. Only with Roll sweep, and only at certain time/div settings can you hope to see instantaneous things like microphonic effects displayed in real time of a circuit you might be testing.

Digital scopes, except for the most expensive ones, do not have anywhere near the vertical and horizontal display resolution of a cheap analog scope(essentially infinite), so waveforms are misrepresented time and voltage-wise. Waveforms are distorted because firstly, the display horiz and vert resolution is too low and secondly by the 8-bit digitization vertical limitations of all but 6000 US buck + high end digital scopes. Some high-end digital scopes require you to jump through hoops to achieve a 10 to 12 bit by non-real time averaging or the most expensive offer higher vert resolution, but that requires a special setup and a fat wallet..who has the money in one case or the time in the other?
« Last Edit: May 31, 2013, 06:28:56 pm by Paul Price »
 

Offline zibadun

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Re: A digital scope for audio circuits, what do i need?
« Reply #2 on: May 31, 2013, 01:12:36 pm »
Paul

I think what you are saying is "the digital scopes have a limited dynamic range".   DS2072 is 8 bit which may be slightly low, but it has a hi-res mode at 12 bit.   If that is not enough there are some 16-bit scopes out there. 

but how about some waveform pictures showing an ancient 20 Mhz outperforming a modern DSO  :scared:
 

Offline jahonen

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Re: A digital scope for audio circuits, what do i need?
« Reply #3 on: May 31, 2013, 01:32:24 pm »
For audio work, an analog scope is cheapest and best. They are almost impossible to damage with high voltage overloads at the input, can display magnified baseline views of waveforms that exceed the graticule limits that digital scopes cannot except by distorting them to give you a false display.

Digital scopes are easily overloaded and severely distort signals displayed that have an envelop outside their graticule range. You cannot get a clear magnified view of signals around the 0-V point when their amplitude is way off  the graticule range.

In audio work you may want to get a magnified view of crossover distortion, those signals so often seen in audio work that are most important. Digital scopes cannot do this if you try to magnify the crossover point.

No digital scope I have tried is able to show the true waveform shape with input overload.

Jim Williams has a slightly different opinion on his AN74:

Quote
Analog and digital ‘scopes are susceptible to overdrive. The classical sampling ‘scope is the only architecture that is inherently immune to overdrive.
Thus, I wouldn't trust blindly overdrive behavior on any ordinary scope blindly, whether analog or digital.

Regards,
Janne
 

Offline Lightages

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Re: A digital scope for audio circuits, what do i need?
« Reply #4 on: May 31, 2013, 04:34:47 pm »
I would have both, an analog and a digital. Get a good used analog scope for cheap and something like the Rigol DS1052E tht is still fairly popular and very cheap. This way you get the best of both worlds. The analog scope will be more useable for its lower noise inputs and other reasons, and you will have the digital scope for its ain benefits. There is no need to choose only one type!
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #5 on: May 31, 2013, 05:22:36 pm »
Zimbadum:

Here are two traces, the first on a cheap Chinese knockoff 20MHz 2-chan scope displaying the baseline (0-v) part of a 15-V peak rectangular pulse with both scopes at 50uS/div and 200mV per division, all views are with DC coupled input, 10x probe.
At 5V/div both scopes display the same pulse correctly, but hiding the baseline important view of  diode conduction that I am interested in viewing. Both probes have been correctly adj'd for input x10 compensation using the built-in calib. out.

This is a view of the catch diode conduction in a SMPS right at the schottky diode and the inductor in a step-down convertor.

The 20-MHz scope trace is accurately displaying the diode conduction portion of the pulse near the baseline. The DS4024 also showed a 1cm displacement positive of the baseline, increasing the distortion and meas. error.

No happy with this, I thought it was because I didn't buy a Tektronix DPO4000 series, costing over twice as much. So I requested Tek tech support to send me a video of the same pulse simulated by a sig generator. They sent me a video and the result was another remarkably distorted but different exponentially decaying waveform that was nowhere close to the actual waveform shape displayed on the 20MHz analog scope. I then made a simple voltage  window clamping circuit and viewed the same trace with the same probe going to the input of the DS4024 at 200mV/div and then only saw the correct waveform, closely matching that on the 20-MHz scope. ( Both the analog and digital scopes are both set to 20mV/div but with 10x probe=200mV/div display.)

« Last Edit: May 31, 2013, 05:51:48 pm by Paul Price »
 

Offline free_electron

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Re: A digital scope for audio circuits, what do i need?
« Reply #6 on: May 31, 2013, 05:32:49 pm »
turn off interpolation and vectors. see what the pulse looks like then... what you are seeing is an artefact of the data processing.
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Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #7 on: May 31, 2013, 05:42:45 pm »
Turning off vectors and interpolation doesn't  change the waveform displayed.
I am not using averaging or any other special feature of the DS4024. The problem (as explained to me by both Rigol and Tektronix tech support engineers) was that with even high end digital scopes,when displaying signals beyond the graticule limits,  will overload and saturate. and then the input amp cannot recover in time to correctly display the baseline.
« Last Edit: May 31, 2013, 06:06:08 pm by Paul Price »
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #8 on: June 01, 2013, 04:20:45 am »
First of all, I would like to say that I am planning on doing as Lightages suggested. Get both. The problem is, that the used market here is rather thin, for 20 bucks I can't really get anything. A single trace dual channel 20MHz scope that is not broken costs in the ballpark of 200 bucks. For that price I could just go for GW Instek lower end scopes. Or spend some more and get a dual trace one.

So far I am getting a message from Paul, that I should forget digital and get a camera to record the waveforms.
 

Offline Lightages

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Re: A digital scope for audio circuits, what do i need?
« Reply #9 on: June 01, 2013, 05:12:13 am »
I think we need to make it mandatory for people to indicate where on the face of the earth they live. It is very hard to give advice about some things if we have no idea where you live!
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #10 on: June 01, 2013, 05:58:04 am »
Fixed that part of my profile. Location: Estonia, what we get in the used market is mostly old soviet scopes and some Velleman toys. Strangely the Soviet stuff that works costs quite a lot. The stuff that doesn't work or has no probes etc. is cheap or even free, but some suitable replacemenet parts are a pain to find and finding separate probes is close to impossible.

There is always the chance to go fishing on eBay but my final purchase shipped by a certain courier has left me a bit mistrusting when shipping something fragile.
 

Offline Pat Pending

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Re: A digital scope for audio circuits, what do i need?
« Reply #11 on: June 01, 2013, 06:16:36 am »
I work developing high performance audio encoders for BLU-RAY, DVD and CE goods - most likely, you've listened to audio 'manged' by my code,
I'd suggest what you really need is a good multi-channel sound card with S/PDIF  (TASCAM, RME, M-Audio), sound editing software and headphones. 
But even then FFTs and Matlab are your tools of choice - pro-audio has a lot to do with math and measurement.

The scope (any scope) is useful for checking sound card phase alignment - still, you'd be surprised at the time wasted by 'pro audio' sound cards that can't even get the basics right!
« Last Edit: June 01, 2013, 06:42:16 am by Pat Pending »
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #12 on: June 01, 2013, 12:29:30 pm »
MrSadmad,

Digital scopes have their good points, they are so good for storing a single trace onto a USB memory stick.

My DS4024 can save 70 mega-points of a single waveform trace to an USB stick in less than 2 1/2 hours in CSV format. Not a problem, once saved by the scope, my PC could get it into Excel in just a few seconds.

At first it was a problem that the instruction manual says don't use a memory stick with a capacity greater than 4GB, so I had to hunt in the attic to find one small enough to work.

Since I couldn't use the scope while it was saving to USB, I had a chance to go to lunch, take a nap and read the newspaper.

The ease of use of an analog scope has been lost with digital scope, with so many, less or unneeded functions crowding the controls of their face.

Any new digital scopes you buy will also  may also have the same chance of damage by that certain courier, so take a short vacation to the USA, Denmark, Britain, Germany or France.  The weather is nice and used scopes abound on local used-buy-sell websites in these countries, not to mention Ebay but be sure to email the seller and tell them how you want them to package this thing so it is not trampled by elephants on the way to you. Else, have a pleasant summer journey and carry one home as a souvenir.

The last analog models made by Tektronix, like those in their 2600 series are still the best scopes around.
« Last Edit: June 01, 2013, 01:33:37 pm by Paul Price »
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #13 on: June 01, 2013, 02:25:22 pm »
I actually agree with everything said in this topic about the analog vs digital subject. If you give me any analog scope, I can instantly use it and I know what most, if not all of the buttons do. I also know that most of the time what I see on the screen, is the actual waveform. For debugging I will most likely be using an analog scope for the foreseeable future.
With digital scopes there are menus and buttons, sometimes organized in not so intuitive ways. Also getting a waveform on the screen in a pleasant way may take some more time and button pressing, and, at times it may even be impossible to display the correct waveform, as Paul has demonstrated. For me the main reason for starting this topic, is the ease of getting images of signals. For most of the other upsides of digital scopes, I have been able to use scopes at work or at school. However, dragging something like a 15kg amplifier along with me for some screencaptures is something I'd rather not do.

But my original question, what are the minimum parameters for a digital scope, if I mean to use it for audio designs, is still mostly unanswered.
 

Offline KJDS

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Re: A digital scope for audio circuits, what do i need?
« Reply #14 on: June 01, 2013, 03:03:18 pm »
10 bits is enough for audio, unless you're extracting the data and doing a complex analysis to check for distortion and frequency dependent performance. Even then, 10 bits is probably enough and 8 bits usually will do. A reasonable computer screen until recently was 640 by 480, so only 10 bits high. If you're just looking at the waveform on a small screen you'll not see much beyond 8 bits.

I've just checked and the shipping cost of sending a scope from the UK to Estonia is £40.80 so it's not surprising that products are expensive out there.

Offline don.r

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Re: A digital scope for audio circuits, what do i need?
« Reply #15 on: June 01, 2013, 03:11:51 pm »
Bandwidth. You will need more than you think, especially when trying to look for noise. Luckily, many of the cheap Chinese scopes can be hacked for higher bandwidth so you need not spend a lot. A 60Mhz Hantek DSO that sells for about Euro300 can be hacked to 200MHz for instance. I do a little audio work as a hobby and my two most used scopes are old Tek analogue models, 2225 and 2245A. The 2245A is 100MHz and 4 channel, great for seeing how various stages change a signal, and the 2225 has 500uV/div for tracking noise although its limited to 50MHz.
« Last Edit: June 01, 2013, 03:14:07 pm by don.r »
 

Offline ivan747

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A digital scope for audio circuits, what do i need?
« Reply #16 on: June 01, 2013, 04:07:04 pm »
Something to note about the DS2072: it has a 500uV/div setting. That and the persistence display makes it much more useful for audio. With the 500uV setting and a FFT you can analyze the spectrum of the noise in your high gain amps.

Dave has said not many scopes have such a high gain. And it has the function generator you wanted. I'm not sure if it does sweeps, though.

And of course, all what I mentioned except for the FFT is not available in the DS1052E. Dave has a comparison video.
« Last Edit: June 01, 2013, 04:24:29 pm by ivan747 »
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #17 on: June 01, 2013, 05:30:06 pm »
I can not afford to buy a scope very often, so I did some research before I bought one.

How I made my buying decision:

Rigol offers the best performance/quality from all aspects of operation v. price, if you need 4-channels, good for debugging digital circuits. Rigol has thought out fairly well how to ease setup using multiplexed rotating controls with switches,  and choosing switches that provide a nice feel to the push and  a nice feel when turning of knobs, etc.

Owen is the second best in quality and ease of use and limited to 2-chan. Good enough for a fast overview of your audio signals.

The more you pay for either brand, the closer you will get to nice-feeling, easy to use controls and a digital scope that emulates a cheap used analog scope for audio use.

I found the Rigol DS4024 to be the closest thing to best value for both digital and analog use, and having fairly good fidelity of waveform display compared to an analog scope when used within its graticule range of input signals. 4 chans makes digital troubleshooting possible.

If you get the cheapest digital scope model of either brand, you will be able to see what's going in and out of any audio apparatus, with some distortion caused by display limitations and have to deal with some limitations on vertical amp dynamic range, but any digital scope will be so so much better than what you have now.

If you have the bucks for an Agilent, the more expensive low-end models include a function generator as an option, good for testing audio equipment, though I have easily built my own little circuit  using a battery or two in a small box to do generate sines and triangles and squares good enough for audio work. (It doesn't really matter if a sinewave is slightly distorted at the input if you can get the amplifier to match the same waveform at the output. The squarewave and triangle waves are almost perfect.) Two channels are a must to do this and does the trick.

I have watched all the videos on YouTube.com about reviewing scopes, and all reviews have not seemed to find a better use for an oscilloscope than to display sinewaves from a function generator, and they all restrict their reviews to do this than to show any other digital trouble-shooting or for any advanced use or for any other purpose one might imagine to use a very expensive 500MHz scope for.

Watch the YouTube reviews because they show how nice the knobs and buttons are and then go on to show a few other inconsequential things.

Tektronix and Agilent and Rigol have videos that show little somethings about how their scopes work, usually with sinewaves again, are very careful to avoid displaying signals that are distorted by their scopes, of course, in all ways avoiding showing their scopes to reveal limitations and faults .

For use, isn't viewing sinewaves all about what you want a scope to do?

Rigo and Tek and Agilent tech support were friendly and honest and rapid. Rigol support was limited mostly to "that's the way it works, we are working on these problems", and replies direct from Rigol engineers about more technical aspects were very short and in Chinglish.

On the other hand, Tek and Agilent were all too eager to bring by a demo model of my choice and willing to converse in great detail over the phone. I also took a trip to a local technical university and took a look at what they were using in their instructional labs.

That's how I've come to the conclusion about buying the Rigol DS4024 and not an  Agilent or a Tektronix, or an Owen or some Signalent, or an Instek or Tenna or else getting one of those many who-the-heck-ever-heard-of-this-company models.
« Last Edit: June 01, 2013, 06:24:01 pm by Paul Price »
 

Offline zibadun

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Re: A digital scope for audio circuits, what do i need?
« Reply #18 on: June 01, 2013, 10:45:06 pm »
I'd like to make sure I understand the problem with DSOs.

here are three pictures from Rigol 2072 (using its test output) 

1. Full scale signal
2. Maximum "zoom" on picture 1 (so this not captured in real time)
3. Real time capture with most of the signal off graticule range.

There is a difference between 2 and 3. 
Are you saying waveform #3 is not accurate because the input exceeds screen limits?
Is #2 accurate then?  Or both 2 and 3 are wrong?

I don't have an analog scope anymore to compare. :(


« Last Edit: June 01, 2013, 10:48:03 pm by zibadun »
 

Offline NiHaoMike

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Re: A digital scope for audio circuits, what do i need?
« Reply #19 on: June 02, 2013, 03:28:56 am »
50MHz should be enough for audio work, unless maybe if you're into the digital interfaces or amplifiers with very high carrier frequencies. (With SiC FETs switching faster, that can happen pretty soon.)

For actually digitizing and analyzing audio, an AFE (can be DIYed) and good sound card can work nicely. If you also use an external ADC and an optical link to the PC, you'll also have a very well isolated interface.
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Offline vk6zgo

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Re: A digital scope for audio circuits, what do i need?
« Reply #20 on: June 02, 2013, 04:08:53 am »
In fairness to digital 'scopes,analog instruments do show errors due to overload when the signal is very much greater than the vertical scale.

Some 'scopes have a hardly discernible problem,while for others it is more evident.
The higher grades of instruments are usually better!

To the OP--I wouldn't throw away the old Soviet beast.
If the new one ever dies,you will be glad it is still there to help you fault find! ;D
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #21 on: June 02, 2013, 06:22:07 am »
Zibadum:

Without an intermediate voltage setting view, it is difficult to see any detail of the baseline waveform in the 500mV/div top waveform, and then you jump in view from 500mV/div to 5mV/div. How about one more view at 50mV/div? That would reveal what is really going on.

Having an analog scope would help to resolve this question, but it looks to me like both 5mV/div pictures are severely distorted at the baseline since this is a calibration waveform that should have a clean shape and fast fall time.
There also seems to be a D.C. shift in the baseline, a difference between views two and three at 5mV/div.

However, the calibration signal should be putting out a clean square wave  and the short horiz. voltage excursion on the falling edge, in the middle picture does not match either the top or bottommost view, so it looks very likely distorted.

 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #22 on: June 02, 2013, 06:46:26 am »
I've been looking around and so far the Rigol 2000 series just seems incredible bang for the buck. I'll contact the local retailer who carries some Rigol stuff and see, if I can order through them. Probably have to find a cheap function generator from someone as well, or just build something.
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #23 on: June 02, 2013, 06:49:36 am »
MrsSadMan,

Although you may have had a bad experience with 'THE CARRIER", you must not think your luck will always be bad.

But probes should be no problem.

On ebay you can find sets of 2 or 4 ea.  100mHz 10x/1x probes cheap and I've bought them and they work well, most importantly, they are not likely to be damaged by shipment and the cost of shipment will be much less.

Attached: Here's how I built a small function generator for audio testing from just one chip in small project case, a cheap solution to testing audio equipment.
« Last Edit: June 02, 2013, 07:10:36 am by Paul Price »
 

Offline larry42

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Re: A digital scope for audio circuits, what do i need?
« Reply #24 on: June 02, 2013, 10:19:08 am »
As a sidenote I would like to mention probes.

I'm sick and tired of chinese crap - and when testing tube designs with 500V (e.g EL34) - invest in some reasonable probes.

PMK make 100:1 and 10:1 probe that are high quality and reasonably priced and reliable. I have a pair of PMK PHV1000 1000V CAT II for that purpose.

A differential probe (one of the cheaper 1:20 25MHz units 700V CAT I rated) might also be very useful.

When I did my tube amp work (Mullard 5-20 type amp) I was using an old HP 180A and the 100MHz plugin. Unfortunately I had a dodgy probe and later discovered a dodgy channel in my scope (the wiring to the input hybrid had failed) - which made fault-finding the tube design a bit more difficult!


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Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #25 on: June 07, 2013, 07:27:25 am »
I think that right now the choice is between Rigol and Hameg. Agilent is out of my pricerange, unless I go for the 2000 series but to get the same functionality I'd have to spring for the 3000 series, Tek don't have anything nice in the entrylevel market, GW Instek GDS2000 has some downsides pointed out by Dave.

Other scopes I could get are Tenma(something rebranded by Farnell I think), Lecroy, Uni-T(Again rebranded scopes I think)

Now, I could just go with the Rigol and be done with it, but I am a bit concerned about aftersales suport, should something happen to it. Infact, this is the only reason I am actually considering spending some more money and getting an Agilent, because I know they have a really good service policy here. Also, I understand all the upgrades are software implemented so i could just buy them if the need arises later on? Think it's the same with Rigol?

The Hameg scopes are something I haven't had a chance to really look at, but the basic numbers seem promising.
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #26 on: June 07, 2013, 01:54:24 pm »
Rigol Scopes!

Rigol websites  do not allow you to register yourself so as to login. It doesn't accept  your registration, says it has sent you an email which is never sent.

Rigol websites does not post any scope firmware updates to firmware, does not even mention anything about updates, and  even though they are available, you have to call tech support and beg to get one that is undocumented as to fixes,  nor is any tech support available except by email on the website. You can contact them by phone and they were honestly trying to be helpful from that way of communication. Only tech support info on website is a list of discontinued scope models.

I requested a firmware update, hoping it would solve some scope problems, but got first an update for their DG waveform generator, then after calling again, got a DS4000 series firmware update with incorrect instructions on how to enter the firmware update mode, I had to discover how to do this myself. The firmware did not solve my use problems with the scope, fixed somethings unknown and made some other situations of use more difficult than the original firmware.

Agilent, on the other hand called me back about questions before purchase and a service engineer talked with me for almost an hour in a phone call abut their scopes, even offered to bring any model by for a test drive. Same experience with Tektronix

Never the less, I didn't send the scope back for a refund because for the very high memory and the price it still was the best economical solution for me, even though this scope has a fair share of anomalous behaviors, especially with slower sweep speed displays, trying to capture a single-sweep, quirky way of shifting triggering modes, some very slow sweep settings are unusable and to save a single 70-mega sample CSV waveform image data to a USB stick takes over 2 and 1/2 hours that locks up the scope from being used for any other purpose...and this is a $3000 US priced model, not a cheaper hobbyist model.
« Last Edit: June 07, 2013, 02:10:59 pm by Paul Price »
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #27 on: June 07, 2013, 03:34:03 pm »
Rigol websites  do not allow you to register yourself so as to login. It doesn't accept  your registration, says it has sent you an email which is never sent.

I haven't had any problems registering at the Rigol site in order to download documents.

Quote
Rigol websites does not post any scope firmware updates to firmware, does not even mention anything about updates, and  even though they are available, you have to call tech support and beg to get one that is undocumented as to fixes,  nor is any tech support available except by email on the website. You can contact them by phone and they were honestly trying to be helpful from that way of communication.

Unfortunately, it's been well-known for awhile that Rigol does not distribute FW very well via the normal internet channels. OTOH, I haven't had a bit of trouble getting the latest FW - or reporting bugs to Rigol - via my dealer, the one who sold me the DSO. Why wouldn't you contact your dealer about FW upgrades?

Quote
...especially with slower sweep speed displays, trying to capture a single-sweep, quirky way of shifting triggering modes, some very slow sweep settings are unusable...

As reported elsewhere, this 'quirky' behavior has to do with the way the Rigol handles intensity grading/persistence. At <= 100ms/div, the Rigol is capturing full screens of data so that they can be combined into the intensity/persistence map (impossible to do when 'rolling'). Whether you like this behavior or not is a question of preference, but there's nothing especially strange about it.

Quote
...and to save a single 70-mega sample CSV waveform image data to a USB stick takes over 2 and 1/2 hours that locks up the scope from being used for any other purpose...

I think something must be wrong with your scope. It takes me 4.25 minutes to save a 14MPt CSV file on the DS2000 - 5x that would be 21.25 minutes. BTW, if I had the desire to save 70MPt CSV files often, I would just write a small utility to convert the sample data to ASCII CSV format myself at the PC - which is fairly simple - and would save oodles of time later.
« Last Edit: June 07, 2013, 03:35:40 pm by marmad »
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #28 on: June 07, 2013, 05:00:56 pm »
Marmed:  I have repeatedly, over several efforts over several weeks attempted to get a log in registration. Always fails.

Has anyone on eevblog  managed to get a log in registration on their website?

If so, did it logging in give you any other information about their scopes?

Rigol does not following  the convention of posting updates, so the effect is to make the a firmware download a secret and difficult.  That is not tech support, that is simply red tape.

I contacted Rigol engineer about the USB problem and they said that slow USB save was normal.
A friend of mine who bought the same scope wrote an email about the same problem to a Rigol design enginee. The engineer  who wrote back said below about the slow USB save:
-------------------------------------------------------------------------

thanks for your email.
 
You are right. But our previous idea of product definition is that mainly
function of scope is analysis instead of data transfer, speed etc..
 
of course, if it can support fast speed, that is the best.
 
So far, I don't know if we release similar product with USB3.0 interface.

 
 
Mit freundlichen Grüßen/With best regards
 
James Zhu
Rigol Technologies EU GmbH
Lindberghstraße 4
82178 Puchheim
+49 (0)89 - 8941895-21
Cell:+491752239450
E-Mail: zhuguangyuan@rigol.com
Skype:  zhuguangyuan78
------------------------------------------------------------------------------------------------

I requested videos of scope operation from Tektronix and Agilent, which they promptly sent. The Agilent scope at about the same level of price showed much better display update performance and roll range. The Rigol surprises me with display updates that are history and jump back and forth at speeds between 100mS/div and 5mS div, with the effect less noticeable towards the fastest sweep rates.
« Last Edit: June 07, 2013, 05:11:25 pm by Paul Price »
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #29 on: June 07, 2013, 05:22:08 pm »
Rigol does not following  the convention of posting updates, so the effect is to make the a firmware download a secret and difficult.

Again, I'm not sure why you don't just contact your dealer for new FW? My dealer in the Czech Republic will always get the latest FW to me.

Quote
I contacted Rigol engineer about the USB problem and they said that slow USB save was normal.

2.5 hours is not normal - unless you were joking (I quoted my speeds to you). Every DSO I've tried has been using low-speed USB, so they've allways been a bit slow - but nothing like 2.5 hours for ~800MB (the CSV files are approximately 11 * sample length).

Quote
I requested videos of scope operation from Tektronix and Agilent, which they promptly sent. The Agilent scope at about the same level of price showed much better display update performance and roll range. The Rigol surprises me with display updates that are history and jump back and forth at speeds between 100mS/div and 5mS div, with the effect less noticeable towards the fastest sweep rates.

I can't attest to exactly how those DSOs are handling low time base settings, but slow time bases mean slow display updating on every DSO. The Rigol has 14 divisions, so that means for example,  that @100ms/div, it will do one screen update every ~1.4 seconds - while the Agilent 2000 X-Series (with 10 divs) will do one screen update every ~1 second.
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #30 on: June 07, 2013, 05:29:20 pm »
I was not joking about the 2.5 hours to save a 700mega point CSV file to a USB 2.0 memory stick.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #31 on: June 07, 2013, 05:36:48 pm »
I was not joking about the 2.5 hours to save a 700mega point CSV file to a USB 2.0 memory stick.

Ok - I will test myself with 56MPts CSV file right now (4/5ths the size of your file) and post the speed.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #32 on: June 08, 2013, 10:07:34 am »
I was not joking about the 2.5 hours to save a 700mega point CSV file to a USB 2.0 memory stick.
Yes, I see what you mean - trying to save massive CSV files to USB stick is unusably slow. When  I reached 1 hour while trying to save 56MPts as CSV, I broke out of the routine.

Well, I'm working on a new version of my RUU software with enhanced file capabilities (since they fixed the transferring bugs in the newest DS2000 FW). It works with DS4000s - and the next version will allow you to create and save CSV files from the PC using the raw sample data transferred from the DSO, so it will be MUCH faster for getting big CSV files of the waveform. I hope to have it ready in the next couple of weeks.
« Last Edit: June 08, 2013, 11:46:41 am by marmad »
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #33 on: June 08, 2013, 12:13:42 pm »
Well, it seems i have my choice narrowed down to Rigol D2000 series, Hameg HMO series or Agilent 3000
Rigol:
+
by far the best bang for the buck, doesn't seem to be lacking in any area
-
Doesn't have a local retailer and thus, no local suport.
Agilent:
+
Everything is upgradeable, so I could go for a lower spec model for now and upgrade as needed.
Performacwe wise should be similar to the Rigol
-
Cost, even without the upgrades
Hameg:
Somewhere between the Rigol and Agilent in almost all aspects, but has a low waveforms per second figure. Watching the review videos on youtube didn't leave me as impressed as the Rigol review by Dave

if you can add something to this list to help me decide, please do so.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #34 on: June 08, 2013, 01:08:49 pm »
Rigol:
-
Doesn't have a local retailer and thus, no local suport.
I live in NL and bought my Rigol from EEVBlog member Drieg - his real name is Petr Šmíd (smidp321@gmail.com) - and he runs Silcon Electronics in the Czech Republic (and is the Rigol distributor there). That's almost as far away from me as it is from you  ;) But he's really a great person - and he may be able to offer you a good deal. He also has fantastic after-sales support.

Quote
Agilent:
+
Everything is upgradeable, so I could go for a lower spec model for now and upgrade as needed.
Yeah, but the price of those upgrades is pretty steep. BTW, did you know people are starting to hack the Rigol?
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #35 on: June 10, 2013, 04:54:48 am »
Something that just occurred to me. Modern scopes require proper wiring, mainly a PE connection. This is something that I don't have. I guess that sort of limits my choices to the Fluke scopemeters or an USB scope....
 

Offline ddavidebor

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A digital scope for audio circuits, what do i need?
« Reply #36 on: June 10, 2013, 05:21:01 am »
No, to the scopemeter only.

Even for pc scope is required, or your entire pc will become at an hight voltage.


In my opinion is better to spend money to do the pe instead of buy a scope
Safety first
Davide Bortolami,
Fermium LTD
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #37 on: June 10, 2013, 10:47:16 am »
If a PE connection means having a three wire ground system, you don't need to stress yourself about that.
You don't need a PE connection to use an oscilloscope no more than you would using a radio or a PC on anything else in your house that plugs in. And if you did have a PE, you just don't connect an oscilloscope probe ground directly to any AC mains circuit. If you did connect your scope with a PE connection, you would damage the oscilloscope probe, likely your oscilloscope also, and you could possibly electrocute yourself if you touched the circuit and the oscilloscope ground connection at the same time while trying to connect the scope to a live AC circuit.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #38 on: June 10, 2013, 11:06:35 am »
You don't need a PE connection to use an oscilloscope no more than you would using a radio or a PC on anything else in your house that plugs in.

You absolutely do for DSOs. It's dangerous in a couple ways if you don't.
From a Tektronix document on the subject:

“Floating” a ground referenced oscilloscope is the technique of defeating the oscilloscope’s protective grounding system – disconnecting “signal common” from earth, either by defeating the grounding system or using an isolation transformer. This allows accessible parts of the instrument such as chassis, cabinet, and connectors to assume the potential of the probe ground lead connection point. This is dangerous, not only from the standpoint of elevated voltages present on the oscilloscope (a shock hazard to the operator), but also due to cumulative stresses on the oscilloscope’s power transformer insulation. This stress may not cause immediate failure, but may lead to future dangerous failures (a shock and fire hazard), even after returning the oscilloscope to properly grounded operation! Not only is floating a ground-referenced oscilloscope dangerous, but the measurements are often inaccurate. This results from the total capacitance of the oscilloscope chassis being directly connected to the circuit under test at the point where the common lead is connected. At higher frequencies, severing the ground may not even break the ground loop as the line-powered instrument exhibits a large parasitic capacitance when floated above earth ground.' Etc.
« Last Edit: June 10, 2013, 11:08:25 am by marmad »
 

alm

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Re: A digital scope for audio circuits, what do i need?
« Reply #39 on: June 10, 2013, 12:08:28 pm »
If a PE connection means having a three wire ground system, you don't need to stress yourself about that.
You don't need a PE connection to use an oscilloscope no more than you would using a radio or a PC on anything else in your house that plugs in. And if you did have a PE, you just don't connect an oscilloscope probe ground directly to any AC mains circuit. If you did connect your scope with a PE connection, you would damage the oscilloscope probe, likely your oscilloscope also, and you could possibly electrocute yourself if you touched the circuit and the oscilloscope ground connection at the same time while trying to connect the scope to a live AC circuit.

IEC recognizes (among others) class I and class II protection classes for appliances. Class II requires double insulation (eg. larger clearance/creapage) to make it extremely unlikely that a single fault will bring the user into contact with mains. Class I does not require this, because any conductive surfaces (like the metal case) is connected to PE, and shorting mains to PE should either trip the GFCI or (if it's a dead short) blow the fuse. At no point will the case become elevated to dangerous potentials above PE. If you remove the PE connection, a single loose wire touching the case can elevate it to mains potential. Unless the floor or your shoes/chair are a very good insulator, this will result in you acting as a current carrying conductor. So no, a PC or radio with three-prong plug without PE is not safe. Just because most countries consider it too expensive to go around and rewire all old buildings does not make it safe.

A scope is even worse. You don't generally connect your radio to random circuits, but you do clip your scope to unknown DUTs that may have faults. For example, some old Fluke bench DMMs with battery option carry mains all the way to the charging circuit. The unknown DUT (not grounded either) may also have a loose wire touching against the chassis. You can easily accidentally clip the ground lead to this. People make mistakes, and sometimes this mistake destroys a piece of equipment like a scope probe. Getting electrocuted because of a mistake is quite harsh, however.
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #40 on: June 10, 2013, 12:51:03 pm »
In many countries of Europe three wire AC plugs are not used at all, and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time. Instead of PE connections GFI Ground Fault Interrupters are used for safety and work very well. 

I repeat: It is deadly dangerous to ground an oscilloscope to an earth ground, both for you and the scope.  If you touch a live AC mains circuit and the scope with another part of your body you will suffer a serious shock that would likely not occur if a two wire connection was used.

Whenever using a scope or a refrigerator, it must be used with caution if you think you might connect somehow directly to the AC mains.
In all situations, this means don't work on equipment barefoot on a wet cement floor, don't use the scope in the shower or swimming pool, you don't play with an oscilloscope outside in the rain. Don't work on electrical equipment with wet clothes or shoes. Don't sit on metal benches or chairs while working on equipment or high voltages,  don't work on any electronic equipment naked or barefoot. Always try a single hand, a one-handed approach when working with mains connected equipment or with any high voltages. Above all, don't ground yourself to a PE connected piece of equipment with one hand and touch any other equipment with the other you are not sure about.

This is just common sense.

Secondly, ground loops between PE connected grounds can damage the circuit you are working on or cause you to experience mild shocks.  Even though PE connected devices should eliminate this problem, difference in ground resistance and generated currents from separate AC mains outlets connected equipment, even in the same room can create small voltage, but high-AC current connections. These low voltages with high  currents can blow out USB and printers etc, and you might even a low-voltage spark when connecting these grounds.

Connecting yourself between PE grounded equipment and equipment with faults or AC mains circuits might give you possibly fatal shocks that would not happened if the test equipment you are using ware using two wire AC connections and (and it helps if you have it) GFI.

If there is any suspicion that a piece of equipment could be damaged and presenting an AD mains hazard, this can be quickly checked with an AC handheld voltmeter. If you are getting high voltage readings to an earth ground, you should not connect your scope to it until you've repaired the trouble.

In most instances, these types of AC mains faults do not exist, to be sure you can always check with a multimeter before you risk connecting yourself to any equipment with your hands.

When repairmen work on high-voltage main lines, they deliberately isolate themselves and any other metal around them from an earth ground, or else they could be killed.  How do you think it is possible for repair technicians to work on 500000 VAC lines if they didn't isolate themselves completely from AC grounds.



« Last Edit: June 10, 2013, 01:25:38 pm by Paul Price »
 

Offline Harvs

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Re: A digital scope for audio circuits, what do i need?
« Reply #41 on: June 10, 2013, 01:09:52 pm »
In many countries of Europe three wire AC plugs are not used at all, and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time. Instead of PE connections GFI Ground Fault Interrupters are used for safety and work very well. 

I'm not sure if we're talking about the same thing, but we've just been through ground disconnection in another thread.
https://www.eevblog.com/forum/testgear/first-impressions-and-review-of-the-rigol-ds2072-ds2000-series-dso/1230/

The reality is, if you don't have a ground connection on the DS2000, you will have half the mains potential on the BNC grounds.

Are you talking about something else?
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #42 on: June 10, 2013, 01:12:10 pm »
I repeat: It is deadly dangerous to ground an oscilloscope to an earth ground, both for you and the scope.  If you touch a live AC mains circuit and the scope with another part of your body you will suffer a serious shock that would not occur if a two wire connection was used.

Sorry, I'll take the expertise and recommendations of companies that have been building oscilloscopes for decades.

BTW, most DSOs have switched-mode power supplies, which means noise reduction caps between the mains and ground - so if you power up your DS4000 without a ground connection, you will have 110-120VACrms on the chassis and BNC jacks.

Someone just posted over in the Rigol thread about getting a shock when they were running the DS2000 without a ground connection.
 

Offline ddavidebor

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A digital scope for audio circuits, what do i need?
« Reply #43 on: June 10, 2013, 07:04:30 pm »
In many countries of Europe three wire AC plugs are not used at all, and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time. Instead of PE connections GFI Ground Fault Interrupters are used for safety and work very well. 

I'm not sure if we're talking about the same thing, but we've just been through ground disconnection in another thread.
https://www.eevblog.com/forum/testgear/first-impressions-and-review-of-the-rigol-ds2072-ds2000-series-dso/1230/

The reality is, if you don't have a ground connection on the DS2000, you will have half the mains potential on the BNC grounds.

Are you talking about something else?

Well, more dangerous is that if you probe a 14.000v crt power line with the ground clip, all the damn piece of metal of your scope will become 14000v
Davide Bortolami,
Fermium LTD
 

Offline ddavidebor

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A digital scope for audio circuits, what do i need?
« Reply #44 on: June 10, 2013, 07:07:08 pm »
Ah and paul, please shut up.

It's a public forum, full of engineer and full of idiots and morons.

Leave the natural selection to darwin.

Some idiot can kill themself reading you.
Davide Bortolami,
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Offline c4757p

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Re: A digital scope for audio circuits, what do i need?
« Reply #45 on: June 10, 2013, 07:12:14 pm »
14.000v crt power line

This is why I never use delimiters inside a number like that! It took me a second to process what CRT would run on 14V and require five-digit precision!
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #46 on: June 10, 2013, 07:19:38 pm »
Probably going to go for a USB scope and use it with a laptop. I know the proper choice would be to fix the wiring problems but I can't do this safely and will be moving once I finish school anyway.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #47 on: June 10, 2013, 07:56:26 pm »
In many countries of Europe three wire AC plugs are not used at all, and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time.

BTW, PC's use switched-mode supplies as well - and will also have 90-120VAC present on the metal case if you hook them up without a ground wire. I found that out the hard way when the ground line connecting my PC became accidentally disconnected once.

Probably going to go for a USB scope and use it with a laptop. I know the proper choice would be to fix the wiring problems but I can't do this safely and will be moving once I finish school anyway.

Another alternative is a battery-powered DSO or handheld. They can usually safely measure 30V to 600V - depending on whether they're double-insulated.
 

alm

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Re: A digital scope for audio circuits, what do i need?
« Reply #48 on: June 10, 2013, 10:35:04 pm »
Battery powered scopes without isolated channels, especially those with metal BNC connectors, scare me. If I'm going to clip probes to a DUT involving mains, then I want any exposed metal connected to these probes solidly bonded to earth, since I'm likely connected to earth somehow.

I fail to see how using a PC-based scope connected to a laptop improves safety: apart from the BNC connectors and USB connectors on the scope, the connectors on the laptop will also become live when clipping the ground lead to the wrong circuit node. Keep in mind that features, bang per buck and usability of USB scopes is usually way inferior to bench scopes.

Note also that if you're into low power stuff, eg. an Arduino powered from a USB connector, a bench power supply, or a small plug pack, then it's quite hard to receive a shock from it, and I wouldn't be too worried about grounding a scope. It's good practice to ensure a good ground connection, and I would consider it critical when working on anything involving high energy circuits like mains, but it's not like a 5 V / 500 mA USB supply is going to electrocute you. Of course if the case is connected (via caps) to mains, like apparently on the Rigol DS2000 series, then it's a good idea to have a ground connection. The caps should be small enough so the shock is not dangerous (otherwise Rigol screwed up), but some electronics can get unhappy when receiving 120 V on their inputs.
 

Offline Harvs

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Re: A digital scope for audio circuits, what do i need?
« Reply #49 on: June 10, 2013, 11:11:19 pm »
Of course if the case is connected (via caps) to mains, like apparently on the Rigol DS2000 series, then it's a good idea to have a ground connection. The caps should be small enough so the shock is not dangerous (otherwise Rigol screwed up), but some electronics can get unhappy when receiving 120 V on their inputs.

Just checked the DS1000 and it's the same as well.  DS2000 has 4.7nf from L-G and N-G, the DS1000 has 2.0nf.  My PC psu has 10nf.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #50 on: June 11, 2013, 12:09:24 am »
Battery powered scopes without isolated channels, especially those with metal BNC connectors, scare me. If I'm going to clip probes to a DUT involving mains, then I want any exposed metal connected to these probes solidly bonded to earth, since I'm likely connected to earth somehow.

But it seems a bit as if you're mixing two different things: the safety of test equipment - and the safety practices of the operator.

I have a workshop filled with dangerous equipment: band saw, table saw, radial arm saw, etc. The machinery itself is designed to be as safe as possible - but there all kinds of things that operators could do with the machinery that would be unsafe.

Battery powered scopes without isolated channels are designed to be used floating with CAUTION to 30Vrms max - and if there's any doubt whether more than 30Vrms is present or not, the DSO should be grounded and floating measurements shouldn't be attempted. In other words, I wouldn't go probing in an unknown DUT with it until I had done some thorough checking.
 

Offline vk6zgo

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Re: A digital scope for audio circuits, what do i need?
« Reply #51 on: June 11, 2013, 08:02:46 am »
In many countries of Europe three wire AC plugs are not used at all, and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time. Instead of PE connections GFI Ground Fault Interrupters are used for safety and work very well. 

I repeat: It is deadly dangerous to ground an oscilloscope to an earth ground, both for you and the scope.  If you touch a live AC mains circuit and the scope with another part of your body you will suffer a serious shock that would likely not occur if a two wire connection was used.

Whenever using a scope or a refrigerator, it must be used with caution if you think you might connect somehow directly to the AC mains.
In all situations, this means don't work on equipment barefoot on a wet cement floor, don't use the scope in the shower or swimming pool, you don't play with an oscilloscope outside in the rain. Don't work on electrical equipment with wet clothes or shoes. Don't sit on metal benches or chairs while working on equipment or high voltages,  don't work on any electronic equipment naked or barefoot. Always try a single hand, a one-handed approach when working with mains connected equipment or with any high voltages. Above all, don't ground yourself to a PE connected piece of equipment with one hand and touch any other equipment with the other you are not sure about.

This is just common sense.

Secondly, ground loops between PE connected grounds can damage the circuit you are working on or cause you to experience mild shocks.  Even though PE connected devices should eliminate this problem, difference in ground resistance and generated currents from separate AC mains outlets connected equipment, even in the same room can create small voltage, but high-AC current connections. These low voltages with high  currents can blow out USB and printers etc, and you might even a low-voltage spark when connecting these grounds.

Connecting yourself between PE grounded equipment and equipment with faults or AC mains circuits might give you possibly fatal shocks that would not happened if the test equipment you are using ware using two wire AC connections and (and it helps if you have it) GFI.

If there is any suspicion that a piece of equipment could be damaged and presenting an AD mains hazard, this can be quickly checked with an AC handheld voltmeter. If you are getting high voltage readings to an earth ground, you should not connect your scope to it until you've repaired the trouble.

In most instances, these types of AC mains faults do not exist, to be sure you can always check with a multimeter before you risk connecting yourself to any equipment with your hands.

When repairmen work on high-voltage main lines, they deliberately isolate themselves and any other metal around them from an earth ground, or else they could be killed.  How do you think it is possible for repair technicians to work on 500000 VAC lines if they didn't isolate themselves completely from AC grounds.

Paul,the lack of an Earth pin on the mains socket (General Purpose Outlet,or GPO in OZ-talk),does not in any way imply that the Mains supply to your house is balanced with respect to Earth.

It simply means that there is no connection from the GPO back to where the Neutral line is earthed at the point of entry("Fusebox" in Oz-talk).

As it is,you will still be able to measure the full Mains potential between the Active line & any earthed object (water pipes,etc).

Non earthed GPOs were ,& are still,to some extent,used in the USA,but they make no mistake about the fact that if you get  connected between Active & an earthed object,you will suffer an electric shock.

Having an earthed instrument protects you against the case where the body of the 'scope becomes connected to the Active line,either due to an internal fault,or connecting the probe incorrectly to a Mains line.

This is a far more likely scenario than touching an Active line while also touching an earthed instrument body.
You will get a (less severe) shock anyway, in the latter case,whether you are actually touching an earth or not,as your shoes,etc,are not perfect insulators.

I have never seen the adverse results you attribute to a  system where the Earth connection is present at the GPO.

All of the above said,thousands of Americans & Europeans have used Oscilloscopes operated from 
non-earthed GPOs to fault-find Electronic equipment,because they know what they are doing & don't do silly things.
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #52 on: June 11, 2013, 08:26:26 am »
As it stands I will have to limit my measurements to around 24 volts. I could use either the Rigol(or any other scope that has a SMPS with similar filters) that has 115V on the chassis when not connected to anything or with a scope that doesn't have that. I know that both the USB scopes and the handhelds are a different thing to use. Getting a 2 channel Fluke scopemeter is out of my pricerange. Something like a Picoscope 5000 series has got a high vertical resolution and could thus be useful after I get a real scope down the line.
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #53 on: June 11, 2013, 01:13:37 pm »
As it stands I will have to limit my measurements to around 24 volts. I could use either the Rigol(or any other scope that has a SMPS with similar filters) that has 115V on the chassis when not connected to anything or with a scope that doesn't have that. I know that both the USB scopes and the handhelds are a different thing to use. Getting a 2 channel Fluke scopemeter is out of my pricerange. Something like a Picoscope 5000 series has got a high vertical resolution and could thus be useful after I get a real scope down the line.
The point is, even with USB scopes (which have metal BNC connectors tied together and back to laptop GND), you will have to be very careful when probing devices running off the mains (in case of unexpected faults).

OTOH, if you get a handheld with isolated channels (such as this Hantek or this Owon), you can safely probe any circuitry running off the mains. And it could also still be useful down the line as a portable.
 

Offline Tepe

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Re: A digital scope for audio circuits, what do i need?
« Reply #54 on: June 11, 2013, 10:25:58 pm »
In many countries of Europe three wire AC plugs are not used at all
Until a decade ago I had never had any in the various places I have lived - now I have a couple of outlets with PE in the kitchen and nowhere else.

and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time. Instead of PE connections GFI Ground Fault Interrupters are used for safety and work very well. 
Have had one for like 40 years now.
ceterum censeo systemd-inem esse delendam
 

Offline marmad

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Re: A digital scope for audio circuits, what do i need?
« Reply #55 on: June 11, 2013, 10:38:23 pm »
In many countries of Europe three wire AC plugs are not used at all
Until a decade ago I had never had any in the various places I have lived - now I have a couple of outlets with PE in the kitchen and nowhere else.

and people use oscilloscopes and every other type of appliances form PC's to vacuum cleaners to any other imaginable type of devices all the time. Instead of PE connections GFI Ground Fault Interrupters are used for safety and work very well. 
Have had one for like 40 years now.

Yes, this seems to be common in some parts of Europe. It just means that it's likely that if you have devices with SMPS' (PC, modern DSO, etc) you have ~110VAC present on the metal case (or any metal connected to it). Not necessarily a major problem - but it can be an unpleasant one some times.
 

Offline nctnico

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Re: A digital scope for audio circuits, what do i need?
« Reply #56 on: June 12, 2013, 01:00:40 am »
Yes, this seems to be common in some parts of Europe. It just means that it's likely that if you have devices with SMPS' (PC, modern DSO, etc) you have ~110VAC present on the metal case (or any metal connected to it). Not necessarily a major problem - but it can be an unpleasant one some times.
Actually it sucks pretty bad because when you connect two devices you can have 230V at input pins. Lots of stuff gets wrecked that way.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Paul Price

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Re: A digital scope for audio circuits, what do i need?
« Reply #57 on: June 12, 2013, 02:46:44 am »

When people are talking about voltage potentials between well-functioning electronic equipment, such as oscilloscopes and PC computers, for instance, they are frightened because  they can measure a high voltage with a sensitive multimeter. There can be a considerable voltage between their respective chassis. However, this small, too small to cause any injury, somewhere in the high micro-amps, but it sometimes it can cause a mild electrical shock that should be considered more unpleasant rather than dangerous. If there were any dangerous AC current, the GFI would instantly kick open the AC circuit in the room.

When using my digital  and analog oscilloscopes, voltmeters and the likes under these situations, (which I have been doing for over 25 years doing electronic design and repair work.), I always connect the ground connection of the oscilloscope or other test instrument first to the D.U.T.  This means that the probe tip of the oscilloscope or signal generator, etc. is at the same ground potential before I connect a signal or a meter or an oscilloscope probe and can do no harm to the D.U.T.

I am not a lone maniac who chooses to work in this way, hundreds of other technicians in service shops in this tiny country operate in this very same way.

In fact, almost every house in this country has 2-wire AC plugs and people connect things together all the time without any injuries to themselves or their equipment, thanks to GFI. Once in a while people bring in equipment that they have burned out an USB port  because of connecting equipment where there are power ground loops. I always remind people to unplug at least one of the devices when connecting USB. But even different AC grounded circuits in the same room can have a nasty low-voltage AC but with a high-current that can also damage equipment and cause a tickle.

I haven't had any damage to any equipment that I've serviced, nor to myself, nor to the oscilloscopes and other test equipment in my work area.  I have been occasionally been tickled a bit by the bite of this inter-chassis AC  potential.

Before I plug anything in that I might be asked to repair or modify, I always make visual check of the equipment for rust or corrosion or other water damage or just check if the equipment shows any dampness, water drops, etc.  If I am unsure of the equipment, I use a DVM to check the AC power cord for resistance to the chassis ground before plugging it in. That is just common sense.  Electronics is about working with electricity and can be dangerous, so caution must be a thing to  learn and practice. I am not against grounding equipment if it is something like an electric washing machine, a refrigerator or a high-powered circular saw that is not double-insulated.

On the other hand, having a grounded oscilloscope on my workbench could put me in great danger. It could allow me to get a serious shock from some other piece of equipment that has a AC mains short to the chassis if I am touching the metal ground of the scope and the chassis of some piece of defective or unsafe equipment. I wouldn't be in danger if the oscilloscope was ungrounded.

In servicing thousands of devices, I can recall only two or three that ever had a AC mains short to ground. These few items could have been really dangerous, but a visual inspection and a DVM resistance check revealed the danger of the problem before I even turned them on. One was a miswired 3-wire AC EU-style line cord the other was due to someone trying to repair the item and connecting one side of the AC line to the chassis.

I have checked by oscilloscope and other equipment with an AC ammeter and after years of use, I can detect no breakdown and AC line leakage after been used in this way.  From tear downs of the power supplies of many pieces of equipment, and of my test equipment, I can always see that there are 1 or two 1000VAC to 2000VAC rated small valued capacitors (about .001 or less usually) connecting the hot AC mains circuits to the chassis grounds and with these capacitors, there is very, very little chance that these capacitors would break down by connecting their chassis to other equipment. I have never seen this happen. In fact the worst case stress on the power supply capacitor to ground is the normal operation of these capacitors since they are  connecting on side of the 240V AC line to the 3-rd wire ground to while they are serving their purpose to lower RFI from the switching power supply.
« Last Edit: June 12, 2013, 03:02:13 am by Paul Price »
 

Offline MrSadman

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Re: A digital scope for audio circuits, what do i need?
« Reply #58 on: June 13, 2013, 08:32:30 am »
Neither the Hantek or Owon are avaialble in Estonia. From cheaper brands there are Tenma and Uni-T, also 2 models from Digimess. I could go for the Agilent U1602B but the higher priced Agilent and Fluke devices just seem expensive.
 


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