Balanced Soundcard Interface for Power Amplifier Distortion Measurement - Page 3 - diyAudio
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Old 29th June 2012, 03:08 PM   #21
Pano is offline Pano  United States
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Default M-Audio vs HP 8903B

Here is a little test of my M-Audio Fast-Track Pro USB soundcard vs an HP 8903B distortion analyzer. In the plot below, the green is the M-Audio looped back into itself and the orange trace is the signal from the HP. The M-Audio looks just slightly cleaner.

The 8903B does detect some HF noise coming out of the M-Audio, about 3mV worth. I'll have to check that on the o'scope. If I use the 80Khz low pass filter on the HP, then the THD+N results approximately agree between it and what the computer tells me.

It a nice look at an inexpensive way to measure. Running at 96Khz sampling rate is similar. The advatage of the HP is that it measures up to 100Khz, but the M-Audio and computer show you the actual harmonics and noise floor
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Old 29th June 2012, 03:43 PM   #22
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The high frequency noise from the M-Audio board is due to the dither and noise shaping of the DAC. The biggest drawback of the M-Audio board is the limited number of harmonics of 20kHz that can be measured. OTOH, CCIF and SMTPE tests can be used to measure high frequency distortion products without the need for higher sampling rates.
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Old 29th June 2012, 04:14 PM   #23
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Yep, would like to be able to see out to 100Khz, but that's not happening with this card. Some of the M-Audio cards can see up to about 80Khz when using the 192Khz sampling rate.

The noise may well be dither, or something else. It's there whether there is a tone running or not. The HP says:
3.3mV full bandwidth
0.33mV 80Khz BW
0.027mV 30Khz BW
0.0095mV A weighted 80Khz BW
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Old 29th June 2012, 04:28 PM   #24
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I see noise also, increasing above about 40kHz, even without a test signal. That is why I believe it is dither and noise shaping, which is always active, even without signal.
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Old 29th June 2012, 04:58 PM   #25
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Cool, thanks.

I'll look at it on the O'scope when I get home.
So far, I'm pretty impressed with the results.
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Old 11th February 2013, 01:34 PM   #26
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I'm looking for a good soundcard for $120. I was looking at the Xonar D1. I need something with at least 110db SNR and 192KHz samplerate. My current soundcard is an on-board STAC9227 which actually is not too bad, except for very noisy output.

Are there any new soundcards on the market in this range? The Creative SBX sounds interesting, but Creative does not have a good track record...

I suppose I could keep buying cards and returning them until I found something suitable? Whatever it is needs to be compatible with Linux.

Where can I find measurements of the cards in question?
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Old 11th February 2013, 02:07 PM   #27
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I have been happy with the M-Audio Audiophile-192. It is available for around $100 and it works well with Linux.

Quote:
Originally Posted by keantoken View Post
I'm looking for a good soundcard for $120. I was looking at the Xonar D1. I need something with at least 110db SNR and 192KHz samplerate. My current soundcard is an on-board STAC9227 which actually is not too bad, except for very noisy output.

Are there any new soundcards on the market in this range? The Creative SBX sounds interesting, but Creative does not have a good track record...

I suppose I could keep buying cards and returning them until I found something suitable? Whatever it is needs to be compatible with Linux.

Where can I find measurements of the cards in question?
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Old 16th November 2013, 07:01 PM   #28
lhquam is offline lhquam  United States
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I recently zapped my M-Audio Audiophile-192 due to an accidental short circuit while testing a preamplifier card. I decided it was time to build an interface with over voltage protection. AA batteries and diodes limit the range of the soundcard input and inputs and outputs to about +/- 3.6V. Eight-pin dip plugs with resistors provide current limiting and customizable attenuators. Loopback measurements look fine. Here it is:
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File Type: jpg soundcard-interface-asc.jpg (195.4 KB, 195 views)
File Type: jpg soundcard-interface-pcb.jpg (100.6 KB, 189 views)
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Old 21st November 2013, 01:25 AM   #29
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I'm not sure how the circuit works with a balanced circuit, as a balanced circuit has no direct reference to ground. The XLR connector pin #1 is chassis not circuit ground.
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Old 11th December 2013, 10:38 AM   #30
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Will the clamping diodes only work with batteries ?

Best regards
Arthur.
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