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Cosmos APU a notch+LNA $70 to outperform APx555b for $30,000

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#381
APU residual THD+N@1kHz is -135db(also simulated value for the same reason).
2022-07-04_16-21-37.jpg
 
#382
Fair enough. You're pushing the limits at that point.

Besides, at what point does it matter with regard to audio reproduction?

It's fun to see how well you measure things, but being able to measure the diameter of a pizza to within a micron may not be really important in the world of pizza.
 
#384
CG said:
Fair enough. You're pushing the limits at that point.

Besides, at what point does it matter with regard to audio reproduction?

It's fun to see how well you measure things, but being able to measure the diameter of a pizza to within a micron may not be really important in the world of pizza.
Click to expand...
To his credit, IVX has said more than once (at least for his DAC) that audio can be perfectly served with equipment of lesser specifications
Such good numbers are intended for measuring gear.
George
 
#385
I have quite big ears and my hearing was better than 90% of people around me(24kHz at 25 years old). I never heard the difference in the cable directions, or original vs burned copies of CDs, and I won't lie kinda "Oh, yeah, I can hear the difference for sure". I remember one funny case when I wasn't able to hear a cable direction difference but noticed that one screw-fixed grill at the speaker system wasn't screwed down well. So, I can't notice the difference ESS vs AKM DAC for instance, if both are accurately implemented. Of course, my PowerDAC has an audible difference but this is an extremely unusual DAC indeed, a digital PWM modulator + LVC logic array as an output stage + LC demodulation filters.
 
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#394
IVX said:
remember that Cosmos ADC/APU/Scaler have limited ability to withstand input DC
Click to expand...
It's ok I have dc blocker + manual attenuation with INA1651 buffer for measuring large signals. I want automated attenuation as well, that's why I'm asking for rms-to-dc implementation since AD737 is expensive haha.

Sanity checking my setup... the results are consistent, though not sure where the high-ish H3 comes from (is it really from DAC or from APU).
I'm satisfied 🙂 now I need a better DAC lol.

DO100 -> Motu UL MK5 (no signal)
1697464866382.png


DO100 -> Motu UL MK5 (~4Vrms, 0dbfs = 12Vrms)
1697464914474.png


DO100 -> Motu UL MK5 (on +2dB Mic input)

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DO100-> Cosmos APU 1kHz notch (0db) -> Motu UL MK5 (Without CAL file)
1697465023798.png


DO100-> Cosmos APU 1kHz notch (6db) -> Motu UL MK5 (Without CAL file)
1697465063887.png


DO100-> Cosmos APU -> Motu UL MK5 (With CAL file)
1697465155938.png


DO100-> Cosmos APU -> Motu UL MK5 (With CAL file)
1697465362700.png


Same but with the other DAC channel
1697465529660.png


DO100 -> Cosmos APU -> Motu UL MK5 (on +12dB Mic input)

1697465638155.png
 
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#395
I did a backread, I suspect that the APU adds about 10dB on H3 out of the box (literally received it yesterday), preamp section is good and doesn't add H3. I will order some OPA1612 and try to change the opamps inside on the notch section.
 
#397
I've tried the following: compared XLR and RCA outs, RCA L + inverted R used as balanced out (usually it should produce better graphs compared to XLR outs with my DAC), run both DO100 balanced outs simultaneously, run the measurements on my windows laptop, feed the signals on APU preamp section, also checked Archimago's DO100 measurements with the APU. The H3 only goes up substantially (compared to other harmonics) when being fed on the notch section, not sure though how much dB. Nothing much to do other than waiting for the opamps (around 2 weeks)
 
#400
Yes, SMSL DO100 DAC, either the DAC that I received has a subpar performance, or the Cosmos APU with me is. Based on ASR's review and Archimago's review, DO100's H3 shouldn't veer away much higher compared to other harmonics. Unfortunately, I don't have a generator here that has an ultra-low THD like Victor's osc, so it's only my speculation for now unless I try to change the APU's opamps to confirm.

Notice that my measurements are almost similar with Archimago's, except for the huge H3.

DO100 ASR's
1697560313929.png


DO100 Archimago's
SMSL DO100 DAC - THD+N - RCA and XLR.png



Most if not all of Archimago's DO100 measurements have an H3 that is always better than -132dB.
Sample below has an H3 not much worse than other harmonics.
1697561677864.png


I can't get H3 better than -126 to 127dB. Other harmonics are superb.
My measurement below.
1697561241718.png
 
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