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E1DA Cosmos APU - Teardown and personal thoughts and measurements

thin bLue

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thin bLue

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hm, what about the knob gain control, just replace that for your switches? o_O
Knob with gain(range) selecter will be smart solutions.
->Wide range with No extremely sensitive knob

Topping's Headphone Amps are great examples!
 

oal

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Nice review. If you sell the Scaler, I will definitely buy it! Having said that, it would have been nice if the APU's 1kHz/10kHz notch switch were 1kHz/No-notch switch. I do not use 10kHz notch, however, the No-notch option will be useful for various measurements such as J-Test, multi-tone signal, etc. The APU can be used as an input buffer for the ADC. My primary issue with Cosmos ADC is low impedance, gain control is only secondly.
 
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pma

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My primary issue with Cosmos ADC is low impedance, gain control is only secondly.
Exactly. The race for lowest noise pushed the designers to offer low input impedance ADCs and preamps (Topping …). However, it is not practical at all. Cosmos ADC would need a high impedance, low noise input buffer (FET). This would be a real challenge for the designer. Anyone can use the low impedance BJT opamp. A good anti-alias input filter would be good as well.
 
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Music1969

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@IVX

I have APU plus Cosmos ADC

With 34dB gain setting, I am getting 14V out of the APU preamp output.

Obviously this is too high for Cosmos ADC (10V max input)

What are my options for gain matching? Prefer not to use digital volume control of the DAC because I lose a lot of SINAD dB's this method.

How is everyone tackling this issue ?

I have a DAC with output impednace 2000 ohm that I am trying to measure - obviously not suitable with Cosmos ADC's low input impedance.

APU has 47k ohm input impedance which is great for measuring my DAC
 

VintageFlanker

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With 34dB gain setting, I am getting 14V out of the APU preamp output.

Obviously this is too high for Cosmos ADC (10V max input)

What are my options for gain matching? Prefer not to use digital volume control of the DAC because I lose a lot of SINAD dB's this method.

How is everyone tackling this issue ?
This is 100% normal.

60/34dB Gain are supposed to work with either -60dBFS or -34dBFS signals, in intend to measure SNR/DR (not SINAD). That way, you bypass the Noise from the ADC itself.

 

Music1969

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This is 100% normal.

60/34dB Gain are supposed to work with either -60dBFS or -34dBFS signals, in intend to measure SNR/DR (not SINAD). That way, you bypass the Noise from the ADC itself.

Noted thanks.

Confusingly Archimago uses SINAD (he highlights THD+N) to calculate DR

Topping%20D10B%20-%20APU+ADC%20-60dB%20DR.png
 

Music1969

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Here is output of my SMSL SP400 headphone output (combination with SMSL D-6 DAC).

APU + ADC

I'm pretty happy with this out of headphone amp

I did the custom 1kHz notch compensation curve following Archimago method


1682075007091.png
 

Ra1zel

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