Author Topic: Is Bandwidth/memory depth a waste of money in oscilloscopes?  (Read 31912 times)

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Offline Pete FTopic starter

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #75 on: July 03, 2018, 11:08:17 am »
I have no idea why somebody would think working on a stereo audio system requires 4 inputs, that makes no sense.

To measure many components of an audio system you need to look at the difference between input and output voltage, not the difference between input voltage and ground (for example).

eg.  Loudspeakers, the outputs of an amplifier.

That means a single measurement needs two channels.

In a stereo system you might want to look at both channels simultaneously - to make sure they're equal and electrically isolated. That's four channels.

Or you might want to look at the input and output of a crossover circuit simultaneously on screen. That's four channels.


In fact most of my work was done by probing with a single channel, and that put bread on the table for many years without the world spinning off its axis. I've never really had much (or any I can think of) need for more than 2 channels.

Sure, but that doesn't mean you can't do it much better.

I don't mean to be rude, but that is complete and utter crap. My career began in high-end audio, and I was involved in the area both professionally and personally for quite some time. While I went off into other areas of the industry and eventually left the industry professionally, I would sometimes revisit that area very seriously purely for my own interest. I expect that interest to continue to ebb and flow. There is almost never an instance where there is a "need" (to quote you) to monitor both channels in the manner you describe, and if so then by your logic what would you do if presented with a 5.1 or, God forbid, a 7.1 system, look for a 16 channel oscilloscope? Having made my living from this, I can assure you that 2 channels was more than adequate, and any more almost invariably sat there unused. If you want to use 4 channels then that's great, but your claim of it being a requirement is utter nonsense.
 

Offline bd139

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #76 on: July 03, 2018, 11:14:11 am »
If you want to compare the phase relationship of two channels with differential outputs then it’s reasonable. I’ve done that and my requirements are generally noddy in that space.
 

Offline Pete FTopic starter

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #77 on: July 03, 2018, 11:22:20 am »
If you want to compare the phase relationship of two channels with differential outputs then it’s reasonable. I’ve done that and my requirements are generally noddy in that space.

Great, then you best buy a 4 channel oscilloscope. One of those 12 bit ones maybe?  :-DD
 

Offline GeorgeOfTheJungle

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #78 on: July 03, 2018, 11:27:53 am »
I'm currently fixing this Delco and I'm with Pete, you don't need four channels at all.
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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #79 on: July 03, 2018, 11:43:41 am »
I'm currently fixing this Delco and I'm with Pete, you don't need four channels at all.
I'm fairly sure Pete has the skills to fix most anything with a 2 ch scope and he's got enough info from replies to now make a somewhat informed decision.
Good on him for coming aboard and sorting out the bits he was unsure of.
Good luck Pete and give us an update when you've got your head around this new fangled DSO thing you're gunna get.  ;)
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Offline Pete FTopic starter

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #80 on: July 03, 2018, 11:50:54 am »
I had hundreds, maybe even thousands, of units pass across my bench and seriously can't think of a time where I really hankered after 4 channels, even when they were right there in front of me. Maybe if doing development and design work it could be useful, but even then not essential. There's obviously a world of difference between somebody doing this professionally where time is money, and somebody dicking around in their home for a bit of a laugh and a giggle. There is no way I'd want to waste that time, when quickly probing through the circuit with a single channel is almost always all that was required.

Yes but it's a different world now "tautech", and while I can understand those who suggest sticking with an old school CRO, I can see these DSO are just incredible in what they can do. It's probably old news for you blokes, but for somebody like myself I find it absolutely incredible the power that is available at what at the end of the day is such an incredibly cheap price. It's an exciting world now that's for sure.
« Last Edit: July 03, 2018, 11:53:32 am by Pete F »
 
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Offline Specmaster

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #81 on: July 03, 2018, 05:28:58 pm »
I've never actually needed 4 channels but if there was an option of having 4 channels for not a lot more, I'd certainly take that opportunity, I have a 4 channel CRO and have used all 4 at the same time but I could have managed with 2 but 4 does give that flexibility if required.
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Offline rstofer

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #82 on: July 03, 2018, 08:04:09 pm »
Thanks for the previous discussion on Delayed Trigger on the DS1054Z - it works great!  I knew I could shift the trigger point on the screen but I had never needed to shift beyond the left edge.  Today I did and it works well!

Back to the original topic...

 

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #83 on: July 03, 2018, 10:15:12 pm »
Hey Pete. When you have a new scope it might be worth wandering over to this tread and looking at what Vince did to repair his 2215:
https://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/
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Offline Pete FTopic starter

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #84 on: July 03, 2018, 11:02:42 pm »
Hey Pete. When you have a new scope it might be worth wandering over to this tread and looking at what Vince did to repair his 2215:
https://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/

Cheers for that mate, I'll read through that while having my breakfast; coffee and Australian Manuka honey  :P

The SDS1202X-E is currently nil stock, so I'll poke around and see if I can find one elsewhere, otherwise buy a Hantek DSO5202BM if I can't find the Siglent. This is precisely the sort of thing that pisses me off about the Australian retail scene. Distributers get exclusive rights to a brand and can then do pretty much what they like (including the good ol' "Australian Premium").

On a positive note, I did buy one of Dave's multimeters last night. I never looked at why mine started going a bit flaky, and don't much care. Once a piece of test or measurement equipment starts to do something other than it should I have no confidence in it and unless that problem can be sorted with 100% confidence it's gone. Multimeters aren't that expensive in the grand scheme of things and mine is old in any case. I was going to buy a Fluke (and still may) but Dave's 225 will be perfect for now.
 

Online tautech

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #85 on: July 03, 2018, 11:16:01 pm »
Hey Pete. When you have a new scope it might be worth wandering over to this tread and looking at what Vince did to repair his 2215:
https://www.eevblog.com/forum/repair/tektronix-2215-scope-repair/

Cheers for that mate, I'll read through that while having my breakfast; coffee and Australian Manuka honey :P
The jury's still out on that so  :P back at ya !  :box:

Quote
The SDS1202X-E is currently nil stock, so I'll poke around and see if I can find one elsewhere, otherwise buy a Hantek DSO5202BM if I can't find the Siglent. This is precisely the sort of thing that pisses me off about the Australian retail scene. Distributers get exclusive rights to a brand and can then do pretty much what they like (including the good ol' "Australian Premium").
Really ? I went through to checkout and there was no indication that was so.
https://www.triotest.com.au/store/siglent-oscilloscopes/1248-siglent-sds1202x-e-digital-oscilloscope-200mhz-2-channel-1gss-with-serial-decode.html
Probably pay to give Trio a bell.

Quote
On a positive note, I did buy one of Dave's multimeters last night. I never looked at why mine started going a bit flaky, and don't much care. Once a piece of test or measurement equipment starts to do something other than it should I have no confidence in it and unless that problem can be sorted with 100% confidence it's gone. Multimeters aren't that expensive in the grand scheme of things and mine is old in any case. I was going to buy a Fluke (and still may) but Dave's 225 will be perfect for now.
:-+
« Last Edit: July 03, 2018, 11:19:35 pm by tautech »
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Offline Pete FTopic starter

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #86 on: July 04, 2018, 12:02:33 am »
I did contact them and that's what they said. Another couple of weeks ... apparently. The issue is they're already later than they were supposed to be, so who's to say they won't be later still? Go through their ebay store and you'll see their note.
 

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #87 on: July 04, 2018, 12:35:58 am »
I did contact them and that's what they said. Another couple of weeks ... apparently. The issue is they're already later than they were supposed to be, so who's to say they won't be later still? Go through their ebay store and you'll see their note.
Quite simply it's due to production pressures that stem from recent demand on a range of Siglent products.
I've got SDS1202X-E and I'm waiting too, but for other models.
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Offline David Hess

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #88 on: July 04, 2018, 12:41:21 am »
I guess the DS1000Z is an exception then but I find it hard to understand why it can't do it because it is so simple to implement.

I wonder the same thing every time it comes up.

So it seems the DS1054Z can do delayed triggering.

No, the trigger delay function can sort of replace trigger after delay which is useful in its own way but it is not the same thing as "runs after" delayed trigger.

I think I start to understand where the confusion is coming from. David Hess is looking for (delayed) B-trigger. This effectively means having 2 different time bases (time/div).

Oddly enough there were some weird analog oscilloscopes which provided a delayed A sweep.  The 2215 being replaced by Pete F has a delayed B sweep but the 2213, which is its lessor brother, has a delayed A sweep which is what simple DSOs should be providing because as you point out, it is so simple.  It was pretty complicated for the 2213 though so I do not understand what market Tektronix was thinking of.  Maybe it was a way for them to distinguish the 22xx series from earlier oscilloscopes although they dropped this function in the later single timebase 2225 and the single timebase 22xx DSOs never had it.

I never cared much about the B trigger function until I started working with switching power supplies.  (1) Set the A trigger to trigger off of the switching waveform, delay to reverse recovery, and then set the B trigger to trigger off of the reverse recovery waveform which would otherwise be difficult to pick out.  Now you can view the reverse recovery in real time at any time/div with no jitter.

I remember long ago before I understood trigger after delay cobbling together a little circuit to select the rectifier recovery so I could trigger on just it.

(1) Also mildly useful to track down power line "buzz" in linear power supplies used for audio applications.  Check the reverse recovery of the slow power line rectifier diodes just after the peak of the power line cycle.  Place a 220 picofarad capacitor directly across each rectifier diode to fix.

"Where this becomes a problem, and this was discussed on these forums more than a year ago, is things like measuring jitter in a 1 pulse per second GPS signal.  20M points over 1 second is only 20MS/s yielding 50 nanosecond resolution which is worse than the jitter of many GPS 1 PPS signals."

Ok I do have to ask, out of curiosity, why would you be measuring the jitter of a GPS signal? Many years ago my apprentice built a master clock oscillator for our workshop and we used the Omega signal as the phase master to drive the local clock. However I'm interested in why you'd be measuring that GPS jitter outside of navigation needs.

The time acolytes have great interest in measuring jitter of the 1 pulse per second timing output available from GPS receivers.  This signal is almost always synchronous to the GPS receiver clock which is asynchronous to GPS time itself producing jitter equal to the clock period.  This jitter limits precision of a GPS disciplined oscillator over medium timescales unless it is corrected.

Quote
I have no idea why somebody would think working on a stereo audio system requires 4 inputs, that makes no sense. In fact most of my work was done by probing with a single channel, and that put bread on the table for many years without the world spinning off its axis. I've never really had much (or any I can think of) need for more than 2 channels.

I might want 4 channels so I could use them in pairs to make 2 differential measurements without expensive differential probes.  Otherwise 2 channels (and an external trigger input) are plenty for almost all applications.

4 channels are also needed to fully decode SPI although as I recall, one of the recent budget DSOs can do it using 2 channels with the external trigger input as a 3rd channel.

Quote
While "more is better" in terms of bandwidth, I'm sometimes concerned that at the bottom end of the market (ie where I'm looking) models may be pushed beyond their real practical limits in order to provide better specs. In other words, a series of oscilloscopes, say 50, 100, 200 MHz. While the 200 MHz 'scope may indeed meet the -3db spec for its front end, the rest of the machine may not really be a 200 MHz oscilloscope and is just pushed up there because it looks good on paper. I don't know if that's a fact, but is definitely a concern.

Probing also becomes more difficult above 100 MHz and 200 MHz is as high as it is reasonable to still use a ground lead and that is marginal.  For an analog oscilloscope, high bandwidth has another benefit; high bandwidth analog oscilloscopes use higher acceleration voltages producing brighter and sharper displays.  For instance a Tektronix 350 MHz 485 with a CRT acceleration of 21 kilovolts has a better display (albeit smaller) than a 100 MHz 22xx series with a CRT acceleration of 14 kilovolts.

There is a use however for a high bandwidth oscilloscope in audio applications; it is very handy for detecting spurious oscillations or "snivets".  I wish there was some way to link a video here without embedding it but as Emperor Joseph II would say, "Well, there it is."


 

Online tautech

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #89 on: July 04, 2018, 01:08:49 am »
I never cared much about the B trigger function until I started working with switching power supplies.  (1) Set the A trigger to trigger off of the switching waveform, delay to reverse recovery, and then set the B trigger to trigger off of the reverse recovery waveform which would otherwise be difficult to pick out.  Now you can view the reverse recovery in real time at any time/div with no jitter.

I remember long ago before I understood trigger after delay cobbling together a little circuit to select the rectifier recovery so I could trigger on just it.

(1) Also mildly useful to track down power line "buzz" in linear power supplies used for audio applications.  Check the reverse recovery of the slow power line rectifier diodes just after the peak of the power line cycle.  Place a 220 picofarad capacitor directly across each rectifier diode to fix.
Not at all hard with a DSO with a Zoom mode.
Trigger on whatever you like at a slow timebase setting and then Pan to the area of interest in the Zoom'ed window and at whatever timebase setting you want/need.

It's just done different but the result is still the same.

Much like in the 2nd screenshot in reply #60 from rf-loop.

« Last Edit: July 04, 2018, 01:11:40 am by tautech »
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Offline David Hess

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #90 on: July 04, 2018, 01:22:08 am »
I never cared much about the B trigger function until I started working with switching power supplies.  (1) Set the A trigger to trigger off of the switching waveform, delay to reverse recovery, and then set the B trigger to trigger off of the reverse recovery waveform which would otherwise be difficult to pick out.  Now you can view the reverse recovery in real time at any time/div with no jitter.

I remember long ago before I understood trigger after delay cobbling together a little circuit to select the rectifier recovery so I could trigger on just it.

Not at all hard with a DSO with a Zoom mode.
Trigger on whatever you like at a slow timebase setting and then Pan to the area of interest in the Zoom'ed window and at whatever timebase setting you want/need.

It's just done different but the result is still the same.

Oh, I have done it that way with DSOs and most analog oscilloscopes can do that without delayed sweep as well.  Some analog oscilloscopes like the 2225 even have extra functions to do it this way without a delay function.  The difference is that if you use trigger after delay, all jitter between the switching waveform and recovery is removed.
 

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #91 on: July 04, 2018, 01:30:06 am »
I never cared much about the B trigger function until I started working with switching power supplies.  (1) Set the A trigger to trigger off of the switching waveform, delay to reverse recovery, and then set the B trigger to trigger off of the reverse recovery waveform which would otherwise be difficult to pick out.  Now you can view the reverse recovery in real time at any time/div with no jitter.

I remember long ago before I understood trigger after delay cobbling together a little circuit to select the rectifier recovery so I could trigger on just it.

Not at all hard with a DSO with a Zoom mode.
Trigger on whatever you like at a slow timebase setting and then Pan to the area of interest in the Zoom'ed window and at whatever timebase setting you want/need.

It's just done different but the result is still the same.

Oh, I have done it that way with DSOs and most analog oscilloscopes can do that without delayed sweep as well.  Some analog oscilloscopes like the 2225 even have extra functions to do it this way without a delay function.  The difference is that if you use trigger after delay, all jitter between the switching waveform and recovery is removed.
The point is I mentioned 'like' and I'm sorry I wasn't entirely clear ......meaning there'd be no need to use any Trigger delay. None !
You'd have 1/2 the display with the pre-trigger record and the other 1/2 with the post-trigger and it's all available by panning within the Zoom'ed window.
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Online CatalinaWOW

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #92 on: July 04, 2018, 02:34:06 am »
I'll try not to add confusion here.

There is only one reason I can think of for lots of bandwidth when doing the kind of work you describe.  I have on a couple of occasions found problems in audio gear that were the result of RF oscillations which then upset bias points, caused heating or even failure of transistors and the like.  Things like this are easier to find and correct when you can see the birdies.  Whether this is common enough for you to invest in is hard to say.  As I said I have run into in a small number of cases.  But I don't do that much so it might be a single digit percentage.  Whether you care about this is up to you.

For straight audio work, multiple channels aren't too useful, but as newer receivers often have lots of logic for switching inputs/audio presets/speaker protection/etc. I have found the ability to watch multiple signals at once useful.  This surrounding logic has been the source of failure more often than the straight audio chain in my experience. 

Something no one has mentioned (except for disparaging remarks about some ones disfavored brand) is user interface.  All DSOs I have used are really different in this area from classic analog scopes as they try to pile lots of functions onto the number of knobs they can cram onto a front panel.  UIs are a very personal thing and it would be worth quite a bit of effort to find local dealers or owners of equipment you are thinking of to see how you deal with it.  I can't really say that one or another is bad, but will say that I find some more congenial to me than others.   The ones I find congenial are not necessarily the ones that are popular with others.

Finally, for the limited amount of use you are projecting you might actually find one of the USB scopes appealing.  Again, I have no specific recommendations, but many of them have plenty of bandwidth for audio work and the small size is appealing.  No matter how large your lab, the instruments you can use at once are limited by the length of your arms and small instruments rule in this area.  If you will already have a laptop or PC in your mix
 

Offline Pete FTopic starter

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #93 on: July 04, 2018, 03:15:22 am »
The time acolytes have great interest in measuring jitter of the 1 pulse per second timing output available from GPS receivers.  This signal is almost always synchronous to the GPS receiver clock which is asynchronous to GPS time itself producing jitter equal to the clock period.  This jitter limits precision of a GPS disciplined oscillator over medium timescales unless it is corrected.

Yes I know what jitter is, it's an issue with all oscillators. But the question was how many people are ACTUALLY doing these sort of measurements where they are "time stamping" signals from ADCs and the jitter from the GPS reference is a real issue. This was in fact the claim made.

"Very precise time distribution is one of the applications to measure jitter on 1PPS outputs. There are lots of applications for this. For example having several A/D converters 10km apart and be able to timestamp their samples with less than a nanosecond uncertainty."

Unless the person happens to be the lead at the Large Hadron Collider I'll be polite and say that I find the assertion that jitter errors in the above scenario are a real life problem "difficult to believe" ;)

I'm taking a look at the 2215 in between about a billion other things and have to laugh at the irony. The fault would be a perfect opportunity for a DSO as the PSU is starting but then blowing the fuse. I'd love to capture that start up. I'd like a DSO to repair an oscilloscope that I'm replacing with a DSO so I can then throw out the repaired oscilloscope. Something is definitely wrong with that picture  :-DD
 

Offline Fungus

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #94 on: July 04, 2018, 09:36:08 am »
I have no idea why somebody would think working on a stereo audio system requires 4 inputs, that makes no sense.

To measure many components of an audio system you need to look at the difference between input and output voltage, not the difference between input voltage and ground (for example).

eg.  Loudspeakers, the outputs of an amplifier.

That means a single measurement needs two channels.

In a stereo system you might want to look at both channels simultaneously - to make sure they're equal and electrically isolated. That's four channels.

Or you might want to look at the input and output of a crossover circuit simultaneously on screen. That's four channels.

Sure, but that doesn't mean you can't do it much better.

I don't mean to be rude, but...
 If you want to use 4 channels then that's great, but your claim of it being a requirement is utter nonsense.

I'm fairly certain I said "might", not "need" when referring to four channels.

The only time I said "need" was when referring to two-channel, differential measurements. Loudspeakers, etc., are inherently differential devices. A differential measurement is the only way to measure the signal correctly when you get to that point in the circuit.

If you're doing it differently then I'm going to be blunt: You can do it better.
 
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Offline GeorgeOfTheJungle

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #95 on: July 04, 2018, 09:41:02 am »
The only time I said "need" was when referring to two-channel, differential measurements. Loudspeakers, etc., are inherently differential devices. A differential measurement is the only way to measure the signal correctly when you get to that point in the circuit.

In that Delco in the picture, above, the loudspeakers' - are connected to earth/chassis.
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Offline Fungus

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #96 on: July 04, 2018, 09:43:16 am »
The only time I said "need" was when referring to two-channel, differential measurements. Loudspeakers, etc., are inherently differential devices. A differential measurement is the only way to measure the signal correctly when you get to that point in the circuit.

In that Delco in the picture, above, the loudspeakers' - are connected to earth/chassis.

Fair enough, but I don't think I've every seen even the most rabid audiophool grounding the negative terminal of his loudspeakers.

("it's to avoid ground loops!")
 

Offline GeorgeOfTheJungle

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #97 on: July 04, 2018, 09:45:50 am »
Actually, the sound of that Delco is quite good!
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Offline bd139

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #98 on: July 04, 2018, 10:01:14 am »
Fungus is right. This is pretty much EE 101 really. Being blunt there too.

Most basic/classic hifi amps have ground referenced output. That’s only because there is a reasonable voltage headroom and dual supply available due to the transformer sitting there. Car audio amps, studio stuff, anything above class C, not necessarily. Also sources. Think balanced line (XLR etc).  Things are heading rapidly in this direction because of supply voltage limitations and signal integrity requirements.

How do you pull a differential signal off a balanced line or output? Math (A-B). Bye bye both channels on your scope. You can’t look at them independently as the common mode signal is present which might have more noise than signal on it. Good luck with that one.

So if you’re debugging single ended to differential amp or the other way round, which is something I tend to have to do occasionally, you need at least three channels or two scopes. Plus sync off your signal source. Four channels takes up a hell of a lot less bench space than two scopes.

I’d rather have a four channel scope these days. Less head scratching. Time is money or time away from something else so screw it and go four channels. 

Hell even fixing my old 475 analogue scope was pleasurable using a 4 channel scope to debug the trace unblanking and amplifiers (also differential output!)
 

Offline Fungus

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Re: Is Bandwidth/memory depth a waste of money in oscilloscopes?
« Reply #99 on: July 04, 2018, 10:02:30 am »
Actually, the sound of that Delco is quite good!

Should I be using half-inch copper pipe to ground my loudspeakers or is 8-guage wire good enough?

 


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