Looking for a DAC tube output for 1794

[meezger_seep]

Hi,

I have a DAC with two PCM1794 and want to upgrade it with an all tube output (no semi conductors in the signal path). The 1794 has differtial current output.
Does anyone know a schematic for such an output?


BTW: the RAKK DAC kit is no option.

Many thanks in advance

Ralf

 

[dsavitsk]

By nixing the RAKK Kit, do you mean to nix the design, too?

An externally hosted image should be here but it was not working when we last tested it.

I use an output stage very similar to it, but with 6688's and a different CCS design.

 

[meezger_seep]

Hello dsavitsk,

the RAKK kit is no option - I like to use my own layouts and PCBs. But as it is a commercial product I don't expect to get a copy of the schematic (with values).


Do you also use the 1794 and in case you do is there a chance to get a copy of your schematic?

Best wishes

Ralf

 

[dsavitsk]

Do you also use the 1794 and in case you do is there a chance to get a copy of your schematic?

I don't think I have a drawn out version of the schematic, but I can describe it -- here's an old picture of the DAC with only 1 of the 4 inputs connected. It now has USB, RCA, BNC, and Toslink inputs, and a pair of toggles to switch between them.

The digital board is just a basic CD8416 -> ASRC -> PCM1794.

The output stage is as the schematic above. The I/V resistors (4 of them) are 50R Mills. Rk is 80R or so and CCSes run at about 12mA each. OPTs are LL1674's, though lots of different transformers will work fine, and the parafeed caps are 4u. CCS is a cascoded 10M45 design. PS is CLCRC with 5u, 15H, 150u (BG), 220R, 150u (BG) -- power transformer is electra-print.

As I say, tubes are 6688 and rectifier is an EZ81.

Overall, a pretty nice DAC. I listen to it a lot, and unlike my old cd player, I do not find myself picking at its flaws, but just enjoying.