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Author Topic: USB Oscilloscope for Audio Work  (Read 1853 times)

Frank Koenig

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Re: USB Oscilloscope for Audio Work
« Reply #10 on: April 19, 2021, 02:13:03 PM »

For amp testing I really like an old Fluke 123 battery powered handheld......it's isolated and i can't blow it up haha....and it's a handy little bugger.

Good point about having an isolated instrument. If you get a battery-powered scope you can float the scope and not worry about a differential input. Just be sure that it's really floating and be aware that a big amp can put out enough voltage to give you a shock. -F
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Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #11 on: April 19, 2021, 04:35:51 PM »

Thanks much guys for the comments.  The part about some amps floating both outputs could cause real problems with a 4 channel scope.  Maybe I better pick up two 2 channel scopes.  I've been thinking about battery operated for isolation.  On the input side I have a ART DI box that should work ok for just basic level checking and maybe some burst tests for output power.  Driving both channels and monitoring them independently would be fine.

Testing amps today is very different from what I did the past with a Tektronics 555, wire wound ceramic 250W resistors and a Phase Linear 700.  Back then we tested for RMS continuous and assumed 2+ db of headroom.  Today I have 5000W continuous rated amps with a 20A 120V power plug on it.  Yeah it will run on 240V and the pigtail can be changed, but I don't feel it necessary for any continuous power testing at those levels.

At power, planning on burst testing to confirm specs are met and low power level for gain and a look at waveform.

Won't just be testing the amps, DSC's as well to ensure unity is unity and limiter setting levels and such.

I just took a DVM and checked amp outputs, they are all single ended - so a 4ch scope will work ok.  Differential inputs won't be a big deal - probably just do a pick off from the signal generator signal or use isolation balancing transformers.

The Siglent looks to be plenty of scope for this basic testing:  https://www.siglent.eu/product/1139249/siglent-sds1104x-e-100mhz-four-channel-oscilloscope

Now to start looking at Function Generators as well.  :)
« Last Edit: April 19, 2021, 05:01:28 PM by Steve-White »
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Ike Zimbel

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Re: USB Oscilloscope for Audio Work
« Reply #12 on: April 19, 2021, 05:10:25 PM »

Thanks much guys for the comments.  The part about some amps floating both outputs could cause real problems with a 4 channel scope.  Maybe I better pick up two 2 channel scopes.  I've been thinking about battery operated for isolation.  On the input side I have a ART DI box that should work ok for just basic level checking and maybe some burst tests for output power.  Driving both channels and monitoring them independently would be fine.

Testing amps today is very different from what I did the past with a Tektronics 555, wire wound ceramic 250W resistors and a Phase Linear 700.  Back then we tested for RMS continuous and assumed 2+ db of headroom.  Today I have 5000W continuous rated amps with a 20A 120V power plug on it.  Yeah it will run on 240V and the pigtail can be changed, but I don't feel it necessary for any continuous power testing at those levels.

At power, planning on burst testing to confirm specs are met and low power level for gain and a look at waveform.

Won't just be testing the amps, DSC's as well to ensure unity is unity and limiter setting levels and such.

I just took a DVM and checked amp outputs, they are all single ended - so a 4ch scope will work ok.  Differential inputs won't be a big deal - probably just do a pick off from the signal generator signal or use isolation balancing transformers.

The Siglent looks to be plenty of scope for this basic testing:  https://www.siglent.eu/product/1139249/siglent-sds1104x-e-100mhz-four-channel-oscilloscope

Now to start looking at Function Generators as well.  :)
That certainly looks like a step up from my Rigol. It does make me wonder how they can get so many features in there for the price. I'd be very interested to hear your impressions if you go for it.
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~Ike Zimbel~
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Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #13 on: April 19, 2021, 07:44:48 PM »

That certainly looks like a step up from my Rigol. It does make me wonder how they can get so many features in there for the price. I'd be very interested to hear your impressions if you go for it.

I'll let you know Ike.  I picked up some 1000W load resistors, 2 x 16 ohm and 2 x 8 ohm.  Full power burst testing or close, then maybe 1/2 power or lower continuous runs to ensure the cooling system is working as it should.

I picked up about 1/2 the amps used, some B stock, open box, what have you.  Always been one to bench test anyway.  Thinking the Siglent may be worth a try.

Now on to a function generator.  :)
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Mark Wilkinson

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Re: USB Oscilloscope for Audio Work
« Reply #14 on: April 21, 2021, 09:48:59 AM »

I'll let you know Ike.  I picked up some 1000W load resistors, 2 x 16 ohm and 2 x 8 ohm.  Full power burst testing or close, then maybe 1/2 power or lower continuous runs to ensure the cooling system is working as it should.

I picked up about 1/2 the amps used, some B stock, open box, what have you.  Always been one to bench test anyway.  Thinking the Siglent may be worth a try.

Now on to a function generator.  :)

Hey Steve, don't mean to deter you from getting a scope, but since you started out thinking about a USB scope, this might be of interest.

I've been playing with wavelets as a better way to find sub timing, per Pat Brown's neat article https://www.prosoundtraining.com/2019/07/26/signal-aligning-using-wavelets/
At the end of the article, he shows how Arta (a $100 dual-channel FFT) can generate the wavelets and capture them with a little bit of built in digital scope recorder capacity.
It works so well, and is crazy repeatable.  (First screenshot below are wavelets from Arta of a sub (tan) and main (green) time aligned at 100Hz.)

Ok, this thread and the mention of REW having a scope made me take a look to see if REW could also do the wavelet thingy. Well... does it even better.
Second screenshot is a microphone capture of a 100Hz wavelet generated by REW and captured by its Scope.  It's a neat little scope, cursors and all!

Anyway, I'm realizing I'd rather use REW or Arta with their built in signal generators designed specifically for audio, than my Rigol Arb Function generator.
And with a scope as decent as REW's, as easy to use, and for basically no more than checking out limiting/clipping/distortion in the audio spectrum....well, i'm wondering how much i really need a hardware scope.
I guess the only thing i've measured that would still need a real scope, is how fast amp limiters kick in, using a scope's Roll Mode.....
But even there i'm beginning to wonder...2cents of fwiw
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Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #15 on: April 21, 2021, 02:59:44 PM »

^^^ Mark, I appreciate your input.  My simple response is ALL OF THE ABOVE.

I need it all, as I'll be doing everything mentioned.  Bench testing amps on dummy loads, a stand alone 4ch scope will lend itself well to that.  Run 'em up, make sure cooling fans work and such.  Run some sine wave at lower power continuous levels, check cooling fans function and some burst testing.  Not looking for an amp dyno.  :)  Just to be able to week out problems.

Function generator or Laptop for the source.  Laptop may be the best solution, not sure there yet.  But yeah, some of the testing will be utilizing a microphone and there the laptop applications are how it's best done.

Will likely pick up a function generator and have both available there as well.  Have a couple of Behringer USB IO's  and a Scarlet as well.

Rather than overthink things, which by the way I'm good at - pick up mid line stuff so I can have the variety of options and see what my preferences end up being.
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Ike Zimbel

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Re: USB Oscilloscope for Audio Work
« Reply #16 on: April 22, 2021, 04:50:58 PM »

^^^ Mark, I appreciate your input.  My simple response is ALL OF THE ABOVE.

I need it all, as I'll be doing everything mentioned.  Bench testing amps on dummy loads, a stand alone 4ch scope will lend itself well to that.  Run 'em up, make sure cooling fans work and such.  Run some sine wave at lower power continuous levels, check cooling fans function and some burst testing.  Not looking for an amp dyno.  :)  Just to be able to week out problems.

Function generator or Laptop for the source.  Laptop may be the best solution, not sure there yet.  But yeah, some of the testing will be utilizing a microphone and there the laptop applications are how it's best done.

Will likely pick up a function generator and have both available there as well.  Have a couple of Behringer USB IO's  and a Scarlet as well.

Rather than overthink things, which by the way I'm good at - pick up mid line stuff so I can have the variety of options and see what my preferences end up being.
This post on parameters to look at when choosing a scope popped up in my inbox today http://www.saelig.com/news/newsletters/saelig-042221-newsletter.pdf I do not have any affiliation with this company, but I have purchased from them in the past and was satisfied with the transactions. Just FYI.
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~Ike Zimbel~
Wireless frequency coordination specialist and educator.
Manufacturer's Representative (Canada)
Radio Active Designs
Pro Audio equipment repair and upgrades.
~416-720-0887~
ca.linkedin.com/pub/ike-zimbel/48/aa1/266

Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #17 on: April 26, 2021, 01:06:31 PM »

Having deviated from the original concept of a USB interface with software.

I ordered:

* Siglent SDS1104X-E  4 ch LCD Oscilloscope

* Siglent Technologies SDG1032X Arbitrary Function Generator

Have two 1000W 8 ohm resistors and two 1000W 16 Ohm resistors.  Ordered two more 8 ohm, will build up a dual 4 ohm 2000W/ch dummy load.

* 1/4" Aluminum plate, fans, heat sink ordered.  Not planning on any torture testing, but want the load to remain on the cooler side to maintain consistency and just not fry anything as amps will be run up to test cooling.
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Mark Wilkinson

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Re: USB Oscilloscope for Audio Work
« Reply #18 on: April 27, 2021, 12:32:29 PM »

Cool Steve, nice gear, enjoy.

You have better testing resistors than my cheap butt would spring for......I just have water heater elements in a bucket of water
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Steve-White

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Re: USB Oscilloscope for Audio Work
« Reply #19 on: April 27, 2021, 02:26:33 PM »

Thank's Mark.  Definitely didn't start with this type of gear.

Here's a picture of the first audio load I used, built it in the early 80's - 2 of the new 1000W 8 ohm resistors (other two are ordered) sit atop the old 240W Heathkit.  It sported 4 x 60W wire wound resistors and would get quite warm running up a Phase Linear 700.  Today's amps would incinerate it in seconds.

I talked to a technical rep at Crown this morning for general testing regimen do's and don'ts - good conversation.  Learned a few things that I've never done in the past when testing amps.  When and how to use sine wave continuous testing, and 1/8 power and 1/4 power 12db crest pink noise testing, burst testing.  He suggested looking at the power and thermal tables for monitoring power draw on the amp.  To really determine overall health and confirm that an amp is working and healthy would be to monitor the current draw of the amp during testing, in addition to output, signal quality, heat, etc.

But, not on a 240W Heathkit dummy load - time to retire that one.

I'll post some pictures of the new dummy load when it's completed - not sure if that's anything of use as most guys are running powered stuff these days.
« Last Edit: April 27, 2021, 03:36:42 PM by Steve-White »
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Re: USB Oscilloscope for Audio Work
« Reply #19 on: April 27, 2021, 02:26:33 PM »


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