NOS TDA1541 + D1 I/V & output stage

[abraxalito]

The internal CCS of the 1543 is a 'pull-up' source, to the +ve supply. The digitally controlled current source (DAC) sinks current to 0V. In a D1 configuration the pull-down is what's needed, no requirement for a pull-up source as the 'pull-up' function is effectively provided by the common-gate MOSFET as long as its biassed above the maximum 'pull-down' current from the DAC. To keep the FET in its linear region for all possible DAC output currents it needs some extra 'pull-down' from an external CCS, that's Q2/Q3 on your schematic in post #218. Adding the 1543's internal CCS into the mix just means you'll need to increase the Q2/Q3 current to compensate and that'll just generate more noise.

 

[FYC]

Thanks for the explanation. Will drop the idea of using the bias current.

 

[abraxalito]

I'd work on getting the +30V supply as clean as possible or alternatively change the configuration to a folded cascode (with I/V resistor to 0V) so as to improve the PSRR on the +ve supply. Adding more 1543s in parallel would also improve the SNR overall.

 

[michaelbehrendt]

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[michaelbehrendt]

I have this with pcm1704, the Sound is very good.

 

[ggetzoff]

I use Salas’ Ultrabib for the 28v floating in my D3 (Ryanj design) TDA1541 dac build. I run it in simultaneous mode and to my ears it’s significantly more musical than any DS dacs that I’ve built or bought. For 5v digital I use his reflektor D.

So, yes, PSU quality makes a big difference.