Asus Essence STX issue

blmn

Member
2001-02-01 2:43 am
.
Hi,
I´m using an Asus Essence STX for audio measurements, with Virtins MI.

The problem is while the left channel shows excellent residual values in loopback (0,0001% THD, 0,0003% THD+noise and -110dB SNR at -6dBFS), the right channel shows much worse ones (0,0011%, 0,0012% and -104dB).

The problem is in the right line out.

I changed the ICs at the output (swappable) and the caps in the signal path, with no success.

Someone had in the past some problem like this one?

Regards,
 
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1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
Usually those numbers suggest that the left is in software loopback and not going through the dac and ADC. Try swapping cables so l goes to r and just opening the l link to confirm the hardware is passing signal as intended.

I have not seen a DAC ADC doing that well but there is always a first time.
 
Actually software loopback would show significantly better performance than either of those figures and when used at 48kHz the STX can manage 0.0003% performance. The 0.0001% without noise included seems exceptional for the silicon used but it's within the ballpark.

The other channel is the problem. But first you need to find out if it's the DAC or ADC side of things that's at fault. So take the ADC channel you know to exhibit 0.0003% performance and try it with both left and right DAC outputs. If the performance is 0.0003% for both channels then you've got an under performing ADC input.

If it's one of the DAC outputs that's at fault try using the headphone outputs, rather than the line outs, and see if that fixes the problem.
 

blmn

Member
2001-02-01 2:43 am
.
Tks!

Actually I know that the problem is in the line front out (RCA), because when I swap the line outs the problem change in the input of the analyser.

After all there is a major suspect on it: the right side of the DAC, a PCM1792A smd chip.

I´ll buy one piece (15 bucks at Mouser) and I´ll try to replace it. SMD sucks!

The headphone out uses a TPA6120A2 power amp, and shows 0,001% THD. It might be a good test because the THD must rise to 0,002%+ in case of defective DAC.

Regards,
 

blmn

Member
2001-02-01 2:43 am
.
Usually those numbers suggest that the left is in software loopback and not going through the dac and ADC. Try swapping cables so l goes to r and just opening the l link to confirm the hardware is passing signal as intended.

I have not seen a DAC ADC doing that well but there is always a first time.

Tks Demian!

I´ve have it done, and checked it many times. Swapping the outputs moves the distortion to the other input and disconnecting the cable shows no signal in the spectrum analyzer.

The values in the left side, in loopback, are impressive, but not because the ADC/DAC and output operational amps (LM4562/LME49990 etc). The input operational amps are NE5532 and similars in SMD versions.

Stereophile tested it with an AP SYS2722 and the results were very good.

My numbers were achieved at -6dBFS, the best level regarding THD. At -0.95dBFS, THD rises to 0,0003% similar to the Stereophile´s one.

Regards,
 

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