What oscilloscope Should I buy first time?

[CodyRepairShop]

Timb,

I thought I would need one to make sure there isn't any clipping and distortion of too much when testing my units after repair and restore because I don't do this kind of work very offtan and wanted to be sure I would not kill my speakers or my av receiver from something stupid i could have done during the restore.

[tggzzz]

I thought I would need one to make sure there isn't any clipping and distortion of too much when testing my units after repair and restore because I don't do this kind of work very offtan and wanted to be sure I would not kill my speakers or my av receiver from something stupid i could have done during the restore.

A scope will show gross clipping and gross slew-rate limited waveforms.
A scope is not the best tool for measuring distortion.
A scope will be good for showing you whether the low voltage power supplies are ripple and noise free.
A scope will be good for tracing signals through a circuit.

If you are budget-limited, then consider a working second-hand analogue scope. Ignore adverts which don't show traces (until you have more experience). Try to see the scope working before purchase (pay for it and take it with you, which avoids shipping costs and damage due to poor packaging). 10 or 20MHZ bandwidth is adequate for audio. Expect to pay $1-1.5/MHz plus shipping.

[bitseeker]

Well it's hard to find a working one without any issues when I look on ebay all I see is for part or not working for anything that is not new.

They're out there, but it takes time (sometimes a lot of time) to get good stuff at good prices on eBay. Be sure to also check Craigslist, local ham fests, garage sales, etc.

As Tim said, not everything marked "parts, not working" is bad. It's less risk/hassle/effort for the seller to label as such. Of course, shopping locally where you can try out the scope, is best. At least connect it to its probe calibration waveform to ensure it shows a proper trace.

[tautech]

If you're going to get an old CRO, be sure you can find service manuals for it and while you're at it get anothe CRO in order to have the necessary tool to fix the original when it's broke. 

Don't ask me how I know this. 

Edit
Oh, and BTW not all CRO's have 400V rated inputs either, be sure to do your homework.

[CodyRepairShop]

If you're going to get an old CRO, be sure you can find service manuals for it and while you're at it get anothe CRO in order to have the necessary tool to fix the original when it's broke. 

Don't ask me how I know this. 

Edit
Oh, and BTW not all CRO's have 400V rated inputs either, be sure to do your homework.

But the biggest issue is how would I connect an Oscilloscope to a av receiver to test it would I connect it to the speaker outputs?

[BMack]

If you're going to get an old CRO, be sure you can find service manuals for it and while you're at it get anothe CRO in order to have the necessary tool to fix the original when it's broke. 

Don't ask me how I know this. 

Edit
Oh, and BTW not all CRO's have 400V rated inputs either, be sure to do your homework.

But the biggest issue is how would I connect an Oscilloscope to a av receiver to test it would I connect it to the speaker outputs?

Yes, you will also need a signal generator.

[CodyRepairShop]

Yes, you will also need a signal generator.
[/quote]

What kind of signal generator would this work? https://www.amazon.com/KKmoon-Precision-Dual-channel-Generator-Arbitrary/dp/B014KT3SVO/ref=sr_1_3?ie=UTF8&qid=1469496631&sr=8-3&keywords=signal+generator

[BMack]

Yes, you will also need a signal generator.

What kind of signal generator would this work? https://www.amazon.com/KKmoon-Precision-Dual-channel-Generator-Arbitrary/dp/B014KT3SVO/ref=sr_1_3?ie=UTF8&qid=1469496631&sr=8-3&keywords=signal+generator
[/quote]

Even though I'm not an older tech, I prefer the older equipment. I didn't even bother looking at the specs(I'm sure others can help recommend a good signal generator brand and model) because I want knobs and simple, quick-to-use interface. This was the first one I found on eBay, I'm sure there are better options but I wanted to show you the difference so you can see why these are easier to use: http://www.ebay.com/itm/Wavetek-VCG-Model-116-Function-Signal-Generator-Works-/142056260568

I have a digital portable scope that I bought because I got a great deal on it but I much prefer the shop's analog scopes, so I may not be the best for recommendations. I'm sure some will laugh at me but I really like the old Heathkit equipment, we have quite a bit at the shop, older than me and they still work perfectly.

[tggzzz]

If you're going to get an old CRO, be sure you can find service manuals for it and while you're at it get anothe CRO in order to have the necessary tool to fix the original when it's broke. 

In this case my attitude would be that a working 10/20MHz scope should be so cheap that if it breaks you can just get another. Or buy two.

The OP will, one way or another, pay to get experience. There's an argument that the first experiments should be fast and cheap so that the OP can work out what they really need without wasting too much time/money.

Oh, and BTW not all CRO's have 400V rated inputs either, be sure to do your homework.

And check the probes, especially if higher frequency signals are present.

[Fungus]

That would be a great idea I will think about it, but what would be a good handheld would you know of around my price range?

You'll regret purchasing any "handheld" for $200.

The Siglent mentioned earlier would do the job but it's the minimum you should consider. As pointed out: the memory is quite small (still bigger then most old analog 'scopes though). You might also be able to find a Rigol DS1052E if you shop around. This is a lot 'scope for a teeny bit more money. Still over $300 though.

An old analog 'scope will work for audio. If you can get one for $50 then it's an option ... but I have no idea where all the people who say "get one for $50" live. They certainly don't sell $50 'scopes around here. I wouldn't pay more then $50 for one though. They're all old and likely to die at any moment (although repairing them might be good practice for your line of work). As noted by other people: You need a signal generator to provide an input to the amplifier while you're looking at the output.

As for safety: If you're going to go anywhere near mains equipment then get a decent, fixed x10 probe. Don't use a probe with a little "x1" switch on mains equipment - it's too easy to move the switch accidentally (or for somebody else to move it).

nb. You hardly ever need the "x1" position on a scope probe so you won't constantly be swapping probes or anything like that. "x1" is for very special cases (I don't think I've ever used mine in the "x1" position, go figure).

A x10 probe divides the incoming voltage by 10, ie. If you have a 100V input the 'scope will only see 10V. Most 'scopes can handle a few hundred volts on their inputs so it's safe to look at hundreds of volts with a x10 probe.

Remember: The ground clip on scope probes is connected to real ground. You can't go clipping it wherever you like or you'll short-circuit things to ground. Only use the ground clip on isolated circuits (usually everything after the power supply). If in doubt don't use the ground clip, switch the 'scope to "AC" mode instead. Ground clips are usually detachable so they don't accidentally touch things when you're poking around inside power supplies.

[Fungus]

A x10 probe divides the incoming voltage by 10...

Does anybody know why they aren't called "divide by 10" probes? 

[timb]

Timb,

I thought I would need one to make sure there isn't any clipping and distortion of too much when testing my units after repair and restore because I don't do this kind of work very offtan and wanted to be sure I would not kill my speakers or my av receiver from something stupid i could have done during the restore.

You could really do all this with a USB sound card. There's software that will let you use one as an oscilloscope. There's also software to turn one into a distortion analyzer, plus a signal generator!

You'll need to create some attenuators to bring the voltage from the speaker outputs on your amp to a level safe for the USB sound card, but that's not hard and can be done with nothing more than a few resistors.

[Fungus]

Timb,

I thought I would need one to make sure there isn't any clipping and distortion of too much when testing my units after repair and restore because I don't do this kind of work very offtan and wanted to be sure I would not kill my speakers or my av receiver from something stupid i could have done during the restore.

You could really do all this with a USB sound card. There's software that will let you use one as an oscilloscope. There's also software to turn one into a distortion analyzer, plus a signal generator!

You'll need to create some attenuators to bring the voltage from the speaker outputs on your amp to a level safe for the USB sound card, but that's not hard and can be done with nothing more than a few resistors.

If it's only for looking at amplifier outputs then yes, you do it with a PC and $10 of components (plus a bit of time and knowledge).

OTOH owning an oscilloscope opens lots of doors to other things.

[tautech]

A x10 probe divides the incoming voltage by 10...

Does anybody know why they aren't called "divide by 10" probes? 

Work in reverse:
Scope input rating x 10. 

[CodyRepairShop]

Ok so I was thinking about getting me a  High Voltage Probe one that is like 100x probe but since I don't know how much power a 10x and a 100x is rated in volts since my av receivers and amps each receiver is plugged into the wall is 120 volts AC @ 60hz and most of my av receiver units are rated 100 watts per channel but I have a amplifier that is rated 300 watts into 4 ohms and 200 watts into 8 ohms all my receiver when @ the 100 watt that's at 8 ohms. I will have to buy me dummy loads and those probes maybe and the signal generator since this one https://www.amazon.com/Rigol-DS1054Z-Digital-Oscilloscopes-Bandwidth/dp/B012938E76/ref=sr_1_1?ie=UTF8&qid=1469545654&sr=8-1&keywords=oscilloscope  Does not have a built in signal generator so I am thinking of getting me this signal generator  https://www.amazon.com/KKmoon-Precision-Dual-channel-Generator-Arbitrary/dp/B014KT3SVO/ref=sr_1_2?ie=UTF8&qid=1469545952&sr=8-2&keywords=25+Mhz+signal+generator     since I don't have money growing on trees I don't do this kind of work all the time.

[idpromnut]

Ok so I was thinking about getting me a  High Voltage Probe one that is like 100x probe but since I don't know how much power a 10x and a 100x is rated in volts since my av receivers and amps each receiver is plugged into the wall is 120 volts AC @ 60hz and most of my av receiver units are rated 100 watts per channel but I have a amplifier that is rated 300 watts into 4 ohms and 200 watts into 8 ohms all my receiver when @ the 100 watt that's at 8 ohms.

Let's have a quick look then; you'll recall both:

V = I * R
P = V * I

from which you can derive:

V = sqrt(P * R)

So if we look at the example of a 200W into 8 ohms, you get sqrt( 200 * 8 ) = 40V.  This is easily handled by most scopes + probes, but if you want to be safe, a x10 probe will be perfectly fine with this. Note that it is the voltage that is important when looking at an oscilloscope probe's rating, as you will not be passing much (hardly any) current through it (unless you are probing incorrectly and short out the ground clip, for example).

[nctnico]

Nowadays you can buy lots of cheap DDS signal generators (like the one from the Amazon link) and I think they are great for general purpose use. The output level, frequency, etc are controlled digitally which is a major improvement over the old style generators. I wouldn't go for an oscilloscope with a build-in generator because the cheap DDS signal generators offer much more bang for your buck.

[Fungus]

I wouldn't go for an oscilloscope with a build-in generator because the cheap DDS signal generators offer much more bang for your buck.

Yep.

You save a bit of bench space but the difference in price simply isn't worth it.

[bitseeker]

You could really do all this with a USB sound card. There's software that will let you use one as an oscilloscope. There's also software to turn one into a distortion analyzer, plus a signal generator!

You'll need to create some attenuators to bring the voltage from the speaker outputs on your amp to a level safe for the USB sound card, but that's not hard and can be done with nothing more than a few resistors.

I'm with Tim regarding using your computer's audio output for your signal generator. There's a variety of programs available for generating tones. Alternatively, you can use an old MP3 player, outdated smartphone, etc. to play audio tones that you create on your PC.

I'd be a little more wary about using the computer's audio input as an oscilloscope right now, since you're new to scopes, unless you're using it with a very inexpensive computer that is OK to fry (only accidentally, of course).

[nctnico]

I'm not a fan of the computer & soundcard approach. Software is often cumbersome to use and a soundcard may have sound effects enabled which screw up the frequency response completely. I'd go for the dedicated generator and oscilloscope approach.

[David Hess]

Ok so I was thinking about getting me a  High Voltage Probe one that is like 100x probe but since I don't know how much power a 10x and a 100x is rated in volts since my av receivers and amps each receiver is plugged into the wall is 120 volts AC @ 60hz and most of my av receiver units are rated 100 watts per channel but I have a amplifier that is rated 300 watts into 4 ohms and 200 watts into 8 ohms all my receiver when @ the 100 watt that's at 8 ohms.

Damage from overload of the oscilloscope will not be a problem with audio amplifier output signals unless you are working with 100s to 1000s of watts or more (into 8 ohms) but a x1 probe will only allow 5 volts/div which will not be enough.  x10 probes will allow 50 volts/div which is plenty to watch a full power output.

I will have to buy me dummy loads and those probes maybe and the signal generator since this one

Dummy loads are not difficult to make.

I agree about an analog oscilloscope.  Since you are in the US, it should be relatively easy to find a working one or maybe you have an electronics friend who can help you restore one to working order.  You should be able to find something for $50 or less unless you are deep in a rural area.

[CodyRepairShop]

How many watts in in that 50 volt since I can't figure out the amps part to convert volts to watts I don't know?

[timb]

You could really do all this with a USB sound card. There's software that will let you use one as an oscilloscope. There's also software to turn one into a distortion analyzer, plus a signal generator!

You'll need to create some attenuators to bring the voltage from the speaker outputs on your amp to a level safe for the USB sound card, but that's not hard and can be done with nothing more than a few resistors.

I'm with Tim regarding using your computer's audio output for your signal generator. There's a variety of programs available for generating tones. Alternatively, you can use an old MP3 player, outdated smartphone, etc. to play audio tones that you create on your PC.

I'd be a little more wary about using the computer's audio input as an oscilloscope right now, since you're new to scopes, unless you're using it with a very inexpensive computer that is OK to fry (only accidentally, of course).

In my original post I recommended a USB isolator to protect the computer. They're fairly inexpensive and will galvanicly (or capacitivly) isolate the computer from the sound card.

Most of the inexpensive ones use an ADI chip that's good to at least 1kV; the more expensive ones use an LT chip which isolates to a higher voltage, but that would be overkill in this case. (The LT chips are pretty awesome though; they actually etch the isolation transformers into the substrate of the chip!)

The other approach would be to hook the sound card to a Raspberry Pi and use some remote USB port software. Basically you install the driver on the Pi and then on your Windows/OS X box; it actually adds a "Virtual" USB root interface. Then, when you plug a USB device into the Pi, all the data is transferred over Ethernet to your PC and enumeration happens there.

It's pretty slick and actually works fairly well. I'm not sure how well it would work for a device sensitive to latency like a sound card... But on the other hand I've seen it work with webcams, so maybe it would be OK? I might give it a try this evening, just to see... (I actually ran all my USB test equipment this way; that is I plug them into my Pi and can access them from any PC/Mac on my LAN.)

As to the OP and an analog scope, I'm not sure how much that will help him... Sure, he can see clipping, but he can't really do distortion measurements (at least in any meaningful way). Plus there's no FFT...

For the $50 + shipping price of an analog scope, he could buy a USB sound device, isolator *and* a multimeter!

That would serve him well enough to learn with, while he saves up for a digital scope.

[CodyRepairShop]

You could really do all this with a USB sound card. There's software that will let you use one as an oscilloscope. There's also software to turn one into a distortion analyzer, plus a signal generator!

You'll need to create some attenuators to bring the voltage from the speaker outputs on your amp to a level safe for the USB sound card, but that's not hard and can be done with nothing more than a few resistors.

I'm with Tim regarding using your computer's audio output for your signal generator. There's a variety of programs available for generating tones. Alternatively, you can use an old MP3 player, outdated smartphone, etc. to play audio tones that you create on your PC.

I'd be a little more wary about using the computer's audio input as an oscilloscope right now, since you're new to scopes, unless you're using it with a very inexpensive computer that is OK to fry (only accidentally, of course).

In my original post I recommended a USB isolator to protect the computer. They're fairly inexpensive and will galvanicly (or capacitivly) isolate the computer from the sound card.

Most of the inexpensive ones use an ADI chip that's good to at least 1kV; the more expensive ones use an LT chip which isolates to a higher voltage, but that would be overkill in this case. (The LT chips are pretty awesome though; they actually etch the isolation transformers into the substrate of the chip!)

The other approach would be to hook the sound card to a Raspberry Pi and use some remote USB port software. Basically you install the driver on the Pi and then on your Windows/OS X box; it actually adds a "Virtual" USB root interface. Then, when you plug a USB device into the Pi, all the data is transferred over Ethernet to your PC and enumeration happens there.

It's pretty slick and actually works fairly well. I'm not sure how well it would work for a device sensitive to latency like a sound card... But on the other hand I've seen it work with webcams, so maybe it would be OK? I might give it a try this evening, just to see... (I actually ran all my USB test equipment this way; that is I plug them into my Pi and can access them from any PC/Mac on my LAN.)

As to the OP and an analog scope, I'm not sure how much that will help him... Sure, he can see clipping, but he can't really do distortion measurements (at least in any meaningful way). Plus there's no FFT...

For the $50 + shipping price of an analog scope, he could buy a USB sound device, isolator *and* a multimeter!

That would serve him well enough to learn with, while he saves up for a digital scope.

I'm not doing anything with my computer it's only a year old and not going to use it for something with this audio stuff not trying to be mean or anything just I don't want to use my computer for any of this stuff.

[timb]

You could really do all this with a USB sound card. There's software that will let you use one as an oscilloscope. There's also software to turn one into a distortion analyzer, plus a signal generator!

You'll need to create some attenuators to bring the voltage from the speaker outputs on your amp to a level safe for the USB sound card, but that's not hard and can be done with nothing more than a few resistors.

I'm with Tim regarding using your computer's audio output for your signal generator. There's a variety of programs available for generating tones. Alternatively, you can use an old MP3 player, outdated smartphone, etc. to play audio tones that you create on your PC.

I'd be a little more wary about using the computer's audio input as an oscilloscope right now, since you're new to scopes, unless you're using it with a very inexpensive computer that is OK to fry (only accidentally, of course).

In my original post I recommended a USB isolator to protect the computer. They're fairly inexpensive and will galvanicly (or capacitivly) isolate the computer from the sound card.

Most of the inexpensive ones use an ADI chip that's good to at least 1kV; the more expensive ones use an LT chip which isolates to a higher voltage, but that would be overkill in this case. (The LT chips are pretty awesome though; they actually etch the isolation transformers into the substrate of the chip!)

The other approach would be to hook the sound card to a Raspberry Pi and use some remote USB port software. Basically you install the driver on the Pi and then on your Windows/OS X box; it actually adds a "Virtual" USB root interface. Then, when you plug a USB device into the Pi, all the data is transferred over Ethernet to your PC and enumeration happens there.

It's pretty slick and actually works fairly well. I'm not sure how well it would work for a device sensitive to latency like a sound card... But on the other hand I've seen it work with webcams, so maybe it would be OK? I might give it a try this evening, just to see... (I actually ran all my USB test equipment this way; that is I plug them into my Pi and can access them from any PC/Mac on my LAN.)

As to the OP and an analog scope, I'm not sure how much that will help him... Sure, he can see clipping, but he can't really do distortion measurements (at least in any meaningful way). Plus there's no FFT...

For the $50 + shipping price of an analog scope, he could buy a USB sound device, isolator *and* a multimeter!

That would serve him well enough to learn with, while he saves up for a digital scope.

I'm not doing anything with my computer it's only a year old and not going to use it for something with this audio stuff not trying to be mean or anything just I don't want to use my computer for any of this stuff.

That's not a realistic option, sorry.

Keep in mind that professionals who design and repair audio gear almost always use a PC with some sort of external interface (be it an Audio Precision System One, or even a $70 Behringer UM2 USB Audio Interface+TrueRTA software).

In the end, to really do what you want, you're going to need to use your PC. You'll obviously need a scope as well, and I didn't mean to imply you didn't.

That's why I recommended starting out with just the PC, as you can get some software to turn the USB audio interface into a scope as well. However, if you're not comfortable with the idea of making your own attenuators and such, then by all means just get a cheap analog scope! Like someone else said, having a real scope can open up doors to other areas of electronics.

The analog scope will show you clipping in various parts of your amps, and you can use it to get a rough idea of the noise floor, but you won't get any sort of precise numbers out of it.

If you want to actually see your THD or THD+N %, or measure actual frequency response, you basically have two options:

1) Buy thousands of dollars worth of vintage test gear (spectrum analyzers, distortion analyzers, etc.)

Or

2) Use your PC and a 24/192 USB Sound Card, plus an analog or digital oscilloscope.