low cost ADAU1452 China board...

[torgeirs]

But I could live with frobek's results. But don't see how it is possible without a 1.88 Volt DC out of AD codec. Then 1 volt peak to peak is possible
But the spec sadly says: "Each output pin has a nominal common-mode dc level of 1.5 V and swings ±1.27 V for a 0 dBFS digital input signal." https://www.analog.com/media/en/technical-documentation/data-sheets/ad1938.pdf
So then with digital DC insert on signal, it is possible with 2,77 Volt max. And 0.77 Volt peak to peak for signal into 1612. That is on the limit of enough.
frobek has -6dBFS input on his ADC

 

[torgeirs]

Dmitrij_S had this values​

Post in thread 'low cost ADAU1452 China board...'

2024-08-29 4:09 pm

The power supply voltage for all operational amplifiers is the same 5.05 V. However, bias voltage at the pin 5 for input opamps is a bit lower (1.55V), than that for output opamps (1.77V).

• Dmitrij_S

 

[torgeirs]

For the input with 1612 and 1.55Volt it is a no go

 

[frobek]

But I could live with frobek's results.

I probably didnt mention before but I swapped opamps to OP1662. Measured signal was slightly lowered in DSP to avoid both codec and opamps clipping. Same board, codec supply connected to DSP board USB supply:

 

[torgeirs]

That explains alot. Thank you.

 

[torgeirs]

Back to the cirrus board and removing passives in output filter, for me then.