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

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#845
Yes, 10 pcs. I meant that I can`t see which resistors on schematic are 180R and witch are 510R.
In my understanding of balancing all the 4 resistors should be equal when gain is 1. So I cant get the math of 5 180R and 5 510R to add up?
I measured 7/8 and found the same 18 dB CMRR.
But maybe I have missed out something?
 
#846
Regarding the LPF. Here are my measurements of frequency responce
No LPF
LPF low gain
LPF high gain
1743094505043.png
 
#847
Here is a LPF low gain stepped response. -20dB to 0dB. 4,5V setting on DAC. Last half dB is DAC clipping.
On this setup the smallest total distortion is at about -5.6 dB.
But it changes rapidly with level!
dBr y axis, dBFS on outputas x axis

1743094925976.png

Another measurement zooming 2 dB with longer FFT and
dBFS y axis, dBFS on input as x axis
1743095694405.png

FFT at -5,6dBFS in.
Really low distortion measurements, indeed!
1743095293609.png
 
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#850
torgeirs said:
Yes, 10 pcs. I meant that I can`t see which resistors on schematic are 180R and witch are 510R.
In my understanding of balancing all the 4 resistors should be equal when gain is 1. So I cant get the math of 5 180R and 5 510R to add up?
I measured 7/8 and found the same 18 dB CMRR.
But maybe I have missed out something?
Click to expand...
the simplified diagram shows all 10pcs as 510, in a real device one pair uses 180(positive input).
 
#853
torgeirs, I measured CMRR for Lch bal2unbal stage and got 53.21db@1kHz. The first layout was 9039S Lout+ to Lin+ of the Lch bal2unbal stage, 9039S Lout- to Lin- of the Lch bal2unbal stage, next to the ADCiso(-2.47dbfs). The second layout has both Lin+ and Lin- of the Lch bal2unbal stage tied to the Lout+ of the 9039S, ADC shows -61.68dbfs. As you can see, my result is about 58 times better than your 18db 😉


2025-03-28_22-40-18.jpg


2025-03-28_22-39-18.jpg
 
#854
But are the balancing legs 160R and 590R or all 160 or all 590?
Mixed R should be 18 dB
Unmixed R should be 60 dB

But, i really struggel to understand with no schematic and real values.

But my card functions because of good CMRR on LPF. So don’t need the CMRR on the unbal input.
Just switched the plugs so I know my messurement dont lie
 
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#855
One switch open at the time. Same stimulus signal on L and R. R not inverted
10 open -19,50 dB
9 open -27,32 dB
8 open -19,52 dB
7 open -27,34 dB

7 and 9 open. Virtual balanced input. -92,8 dB
8 and 10 open. Virtual balanced input. -91,25 dB
9 and 10 open. Virtual balanced input. -33,00 dB
9 and 10 open. Virtual balanced input. R stimulus inverted -21,56 dB
 
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