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Use dual channel scope to measure amplifier gain?

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Use dual channel scope to measure amplifier gain?

Postby ariaaudio » Fri Jan 14, 2011 1:44 am

Can a dual-channel oscilloscope, such as the 3206, be used to measure an audio amplifier's voltage gain? With a sine wave signal connected to the amplifier's input and the 'scope's channel A input, and with the scope's channel B input connected to the amplifier's output, we have all the data necessary to calculate the gain. It can be done by hand, of course, but I wonder if there is a way to have the Picoscope software do the (simple) math?
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Re: Use dual channel scope to measure amplifier gain?

Postby ziko » Fri Jan 14, 2011 4:49 pm

I am not fully up to speed for calculating audio amplifier gain, but are you looking at the output signal divided by the input signal?

There is no measurement to do this.

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Re: Use dual channel scope to measure amplifier gain?

Postby ariaaudio » Fri Jan 14, 2011 5:11 pm

Yes, that is accurate. (rms output signal) / (rms input signal).

Also useful would be 20 * log(output/input) for gain in dB.

Not a worry -- it is easy to do by hand. Thank you for your response. 8)
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Re: Use dual channel scope to measure amplifier gain?

Postby ziko » Tue Jan 18, 2011 5:16 pm

Ah ok just like what I was thinking standard calculation. Yeah the issue is we don't do measurements across two channels.
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Re: Use dual channel scope to measure amplifier gain?

Postby ziko » Thu Jan 27, 2011 1:54 pm

Actually you may be able to do this on second thoughts, (or more like one of my colleagues found a way to do this! :D)

You can do a maths channel 20*log(abs(A/B) then do a measurement on channel 3 for DC average.

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Re: Use dual channel scope to measure amplifier gain?

Postby ariaaudio » Thu Jan 27, 2011 6:50 pm

Cool.

Okay, I created the maths channel, but how do I : "do a measurement on channel 3 for DC average"?

Measurements > Add Measurement only offers channels A or B.
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Re: Use dual channel scope to measure amplifier gain?

Postby ariaaudio » Mon Jan 31, 2011 9:42 pm

Bump
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Re: Use dual channel scope to measure amplifier gain?

Postby ziko » Thu Feb 03, 2011 3:45 pm

I assume Bump is ok?
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Re: Use dual channel scope to measure amplifier gain?

Postby ariaaudio » Thu Feb 03, 2011 4:20 pm

"Bump" is sometimes used on forums to bring an old, unanswered thread up to the top, in case it has been overlooked or forgotten. It is "bumped" to the top.

My question is how do I : "do a measurement on channel 3 for DC average"?

Measurements > Add Measurement only offers channels A or B.

Thank you for your help.
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Re: Use dual channel scope to measure amplifier gain?

Postby ziko » Thu Feb 03, 2011 8:59 pm

Ah that makes sense! Yeah sorry I didn't get back sooner I was looking into this to see if has something to do with different versions of software by my attention got diverted somehow!

I have both 6.49.92 and 6.5.54 and under measurements I can add the maths channel, please see attached image.

What version of the software are you running?
Attachments
ChMathsDCAv.JPG
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Re: Use dual channel scope to measure amplifier gain?

Postby ariaaudio » Fri Feb 04, 2011 7:51 pm

Thank you. If I had been smart enough to first turn on the Maths Channel then I would have been able to select it.

Anyway, the idea works.

Gain.JPG
Screen shot


Many thanks for helping!
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