Which oscilloscpe for audio-related DIY?

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Paul Fury 161
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Which oscilloscpe for audio-related DIY?

Post by Paul Fury 161 » Wed Jun 30, 2010 2:41 pm

Hi all,
I'm thinking about picking up a cheap o'scope for audio troubleshooting, mostly for DIY solid state stuff (e.g racking and servicing old pre modules) and possibly my valve amps as well. I see some for under ?50 here in the UK - are these any good? Should I be looking for A/D and some software instead?
Any features/brands to look for or avoid?
Thanks as always for your thoughts....you TOMBers are the best!
Cheers,
Paul
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Post by CurtZHP » Wed Jun 30, 2010 6:31 pm

Anything that goes up to 20-30 MHz should suffice.
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RickvH
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Post by RickvH » Wed Jun 30, 2010 8:42 pm

Personally, for any kind of troubleshooting, I would want to have a dual channel scope, which allows you to look at two signals simultaneously and do various comparisons between the signals. Some of the inexpensive models are only single channel.

I would think that even 1MHz bandwidth would be sufficient for audio work.
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The Scum
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Post by The Scum » Thu Jul 01, 2010 10:30 am

I see some for under ?50 here in the UK - are these any good?
Specifically, which ones? I've seen some decent cheap stuff, and some absolute trash.

We've got a little Owon around the office that can get the job done...but I hoard the Tek TDS2024. We have a little Velleman LCD scope that's handy for field troubleshooting because it's so mobile.

If you looking used, the previous posters both mention valid criteria: 2 channels, and bandwidth in the 20 to 100 MHz range. Tek 465 (with scope-mobile, natch!), anyone?
Should I be looking for A/D and some software instead?
If you mean using a soundcard and fashioning a probe, it'll work in a pinch, but I wouldn't confuse it with real test equipment. Audio converters have some intrinsic hangups that a real scope won't. Usually, the probe includes a big coupling cap, so it's AC coupled...and won't work for DC. The CD accuracy of audio converters isn't particularly great, either. If you get rid of the cap, you risk cooking the ADC stage with out-of-range DC Voltages. Finally, it's bandwidth limited to the audio range. If you're hunting for RFI bugaboos, you'll never see them.

Alternatively, there's a new category of product that's catching on: the USB-oscilloscope. It's a little box that you plug probes into, then plug into a computer, with software that acts like an onscreen scope.

The one I've had any experience with worked OK...the software reminded me a little too much of some plugins: they tried too hard to mimic the hardware, where some liberties in the UI would have made it more usable...onscreen concentric knobs, etc. The biggest hangup is that it was limited to 30V on the input...or 300V with an X10 probe...which still might not be enough for some tube amps.

Elektor has been running some USB-scope reviews recently.

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Post by mrc » Thu Jul 01, 2010 5:45 pm

I picked up a tek 2235 dual/100 that works perfectly for $150 a couple of years ago, with 1 probe, and the guy sold me another new one for $10. Military surplus.

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millzners
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Post by millzners » Wed Jul 07, 2010 4:07 am

I'll echo the idea that you'll need two channels. I wouldn't even consider a scope w/out them, b/c some of the most basic tests you'll be doing are input output comparisons to look for gain, clipping, biasing, etc.

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Post by permanent hearing damage » Wed Jul 07, 2010 9:44 pm

just saw this post and it roused my interest as i'm looking for a scope myself. i just wanted to add that when i was at electrical audio with a friend's band a few months back, albini had the main outs hooked up to a scope as well. i only noticed him looking at it while tinkering with guitar tones/levels. aside from phase, would there be anything else a scope would tell you?

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Post by coopersloan » Fri Jul 30, 2010 11:42 am

10mhz dual trace would be more than adequate for audio.
In audio we're only talking about KHz folks. You're only gonna get into MHz if you're looking at blazing fast digital signals (doubt it)

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Post by The Scum » Fri Jul 30, 2010 12:47 pm

If all you're interested in is looking at audio, 10 MHz will get you there.

If you're looking for something that's a more useful general purpose DIY tool, it's on the very bottom edge of useful, for several reasons:

-One of the most common things we see requests for here is advice on component upgrades - often opamp swapping. The usual caveat is "make sure they're stable," meaning make sure you're not building an RF oscillator with the swap. I've seen stuff scream in the 5 to 20 MHz range...sometimes right on the limit of what my poor ol' B&K scope can discern.It's easy to fix, but only if you can see it.

-If your interests move beyond the audio range, a higher bandwidth scope will be useful - say, building/troubleshooting radios or HAM gear. Or indeed getting into digital stuff. If you're really keen on DIY, there may be an Arduino or DSPic in your future.

-A 10 MHz scope is probably an antique, with it's own maintenance issues. If you're troubleshooting equipment isn't working, how do you troubleshoot it?

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audioboffin
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Post by audioboffin » Mon Aug 02, 2010 9:20 pm

There are plenty of 20 to 40 mHz dual channel CROs out there, and usually not too hard to find on the used market.
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Post by Justin Foley » Thu Aug 05, 2010 10:26 pm

permanent hearing damage wrote:just saw this post and it roused my interest as i'm looking for a scope myself. i just wanted to add that when i was at electrical audio with a friend's band a few months back, albini had the main outs hooked up to a scope as well. i only noticed him looking at it while tinkering with guitar tones/levels. aside from phase, would there be anything else a scope would tell you?
You can set azimuth on a tape machine without a scope, but it's tricky. Once the machine is aligned, it's probably most helpful in visualizing phase effects (as you note).

= Justin

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audioboffin
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Post by audioboffin » Thu Aug 05, 2010 11:43 pm

Once you work with a scope for a while there's lots of stuff it's handy for, and similarly to a spectrum analyser, once you get used to how things "look" when they sound right, can be a valuable diagnostic tool.

Awesome for getting things in phase (multiple mics etc) not just in terms of using a phase switch, but in positioning mics etc as well.
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