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Old 31st October 2006, 10:53 AM   #101
ingrast is offline ingrast  Uruguay
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Quote:
Originally posted by kambule
Rodolf,

Interested to see the active LPF clean up some residuals if the sound card output.

Do you mind to post the schematic of the active filter circuit ??

thanks in advance.

kb
I do not have the original schematic files since it is a very old design (over 15 year back), so attached is a new one on LtSpice and simulation.

The actual circuit measured in the previous post includes a couple of modifications:

1. Devices are 3 parts from a OPA4134, and the spare one is connected as inverting unity gain buffer at (Out).

2. Resistors R1 and R2 are 10 turn 5K potentiometers.


Care should be taken as usual with grounding, power supply decoupling etc.

Rodolfo
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Old 31st October 2006, 10:57 AM   #102
ingrast is offline ingrast  Uruguay
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Default Re: Waveterminal 192L performance

Quote:
Originally posted by ashok
Here is the FFT of a Waveterminal 192L sound card. Card OUTPUT to card INPUT.
44.1Khz/16bit/32.7Ksamples/Hanning/ 1volt
Not sure what the input impedance is. Probably 10 K ohms.

Obviously a much better sound card Ashok

Rodolfo
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Old 31st October 2006, 12:33 PM   #103
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Ashok --
while it's nice to have the fundamental displayed it's more useful to just show the spurs -- build a passive twin-t notch filter, measure the insertion loss, then measure the magnitude of the spurs.
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Old 31st October 2006, 03:11 PM   #104
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Quote:
........measure the magnitude of the spurs.....
Yes that would be nice if I had the notch filter .
I was actually going to put up another FFT with a bandpass filtered signal with the same card. I couldn't because I can't locate the dual opamp ( AD826) 9v battery run circuit board.

I will find it soon and put up the FFT for comparison. IIRC it measured lower than 0.001 % with the filter. Could have been about 0.0003% or so and also with a slightly cleaner looking noise floor .
About measuring the amplitude of the spurs. The software has markers that can measure it directly as seen on the FFT.
I like to avoid as much labour as possible ! Another filter board....



Cheers.
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Old 31st October 2006, 10:56 PM   #105
kambule is offline kambule  Hong Kong
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apart from using standalone audio spectrum analyzer,
which pc software recommended for audio measurement.

Freeware is best.

My belief is an external usb soundcard (box) is better than internal one.....considering the pc switching power supply noise. However, seeing the FFT of waveterminal soundcard, I change my mind. Any comment please ??


thanks
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Old 1st November 2006, 12:04 AM   #106
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Quote:
Originally posted by kambule
Freeware is best.
Is that a statement of fact, or merely your opinion.
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Old 1st November 2006, 04:03 AM   #107
jcx is online now jcx  United States
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just starting to play with the iPod shuffle I bought this week to test a 12 bit adc with - the shuffle output goes as low as you want - I've put 1 Hz sq, tri in r,l channels of a 16-bit 48K .wav file (created .wav in LtSpice bv source .wave cmd, load into iTunes>Shuffle) - no output coupling cap - no droop, just a few % gain loss when driving into 32 Ohms

for sine distortion I looked at a 800 Hz sine + dither .wav played back thru Shuffle into esi Juli@ soundcard set for 24 bit 192K gives -93 dB 2nd, -99 dB 3rd harmonics (10 sec record to reach below the noise)

refurb 1st gen iPod Shuffles are <US$40
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Old 1st November 2006, 08:58 AM   #108
MikeB is offline MikeB  Germany
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I use internal pci-soundcard with very good results.
The trick is to not use full scale signals and avoid the internal resampler of the soundcard.
This way i got perfectly clean fft plots, no harmonics visible. (below noise floor)

The signal source was goldwave, using the expression evaluator you can generate any testsignal you want. (Don't forget to manually add dithering) Playback was 24bit,48khz.
FFT plot also 48khz, 32768 window size, blackman, averaging = 10.
The soundcard is M-audio delta 24b96.

With this setup i can perfectly measure amp output, clearly seeing only harmonics created by the amp.

Attached is fft of cable loop back, output to input, no extra hardware.
Here is rmaa plot.

Mike
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Old 1st November 2006, 09:12 PM   #109
kambule is offline kambule  Hong Kong
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jackinnj,

excuse for my poor english. I dont mean the performance, I only mean I am a poor guy....for freeware I dont need to pay.


MikeB,

Do you mean the generator is from : www.goldwave.com ?
How about the FFT program, which one you use ??

I think I still prefer external USB soundcard(box) because I am going to use portable computer.


thanks everybody.
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Old 1st November 2006, 10:22 PM   #110
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Quote:
Originally posted by kambule
jackinnj,

excuse for my poor english. I dont mean the performance, I only mean I am a poor guy....for freeware I dont need to pay.
It was my fault, I was in a cranky mood yesterday evening.
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