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Old 11th November 2004, 05:59 PM   #1
PMA is offline PMA  Europe
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Default New distortion measurement method for audio amplifiers

After having performed a large number of spectral measurements based on single-tone spectral analysis I have decided to try more complex input signal. The reason is that there is not much correlation between single-tone spectral analysis results and listening preferences during listening tests. This is especially truth for low distortion components (THD of 0.001% order) where audible differences still exist.

First results are shown at

http://web.telecom.cz/macura/fmanalysis/freqdist.html

Your comments and suggestions would be appreciated.
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Old 11th November 2004, 06:22 PM   #2
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Looks good.

In your opinion, would it be acceptable to play this signal from a 16 bit audio source such as .wav file or CD, then analyse the amp output? I can borrow a spectrum analyser, but not a modulating signal generator.
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Old 11th November 2004, 06:30 PM   #3
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Quote:
Originally posted by richie00boy
Looks good.

In your opinion, would it be acceptable to play this signal from a 16 bit audio source such as .wav file or CD, then analyse the amp output? I can borrow a spectrum analyser, but not a modulating signal generator.
The input signal is generated exactly the same way you are describing - by Cool Edit SW. It is better to use a PC, as CD brings new components above 22.05 kHz (already tested).
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Old 11th November 2004, 06:46 PM   #4
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To really go overboard - why not sample a one millisecond pink noise and send this through an amp and sample what comes out the other end. With digital methods it should be easy to identify all distoriton products.
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Old 11th November 2004, 07:15 PM   #5
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I have Cooledit so that's good. How would using a PC be different to a CD? Doesn't the PC have a steep filter at 22.05kHz just like a CD player?
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Old 11th November 2004, 07:19 PM   #6
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By now I have always measured new components above audio band on CD output, when trying 13+14kHz. Please have a look at:

http://web.telecom.cz/macura/cdspectrum.html
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Old 11th November 2004, 07:25 PM   #7
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Default Error correction amp toppology

PMA:

Though off topic, looking at your error correction amplifier topology, I wonder whether this has been treated before.

I was about to start a thread based on a similar hybrid topology only not error correcting like yours, but with a 20 dB gain output buffer.

Being rather new to the audio amplifier speciality, I assume the approach is not original either, but have not seen it more widely mentioned. I mean, moderate gain low distortion output stage driven by high performance audio OpAmp, and mild global NFB.

Simulation results with LTSpice and stock library elements are promising.

Rodolfo
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Old 11th November 2004, 07:40 PM   #8
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Default High precision method of evaluating distortion

Put a non reactive, non inductive, 8 ohms load in both channel output.

From the positive output use 100 ohms in series with some good speaker

Increase the audio volume till you perceive some distortion.....measure the peak voltage in your scope and you will discover the maximum power, undistorted, the amplifier can produce for human ears.

Very simple and stupid..... perceptual measurement based on reality.

hehe, Pavel, i will not go to the place you are thinking now to send me... and i did not like that story that only one way ticket...without return Pavel!?

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Old 11th November 2004, 07:54 PM   #9
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Default Re: Error correction amp toppology

Quote:
Originally posted by ingrast
PMA:

Though off topic, looking at your error correction amplifier topology, I wonder whether this has been treated before.


Rodolfo
Yes, it was discussed here:

http://www.diyaudio.com/forums/showt...442#post469442

Pavel
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Old 11th November 2004, 08:06 PM   #10
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Pavel,

Those results you showed are quite dramatic. I gather that the 20W Class-A has global feedback and the erroro correction one hasn't?

Is there any correlation to listening test differences to this? Independent, blind testing of course, not by you.

Jan Didden
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