Valve / Tube DAC with transformers

[Arno Pf]

With a lot of pleasure I have been using my DIY DAC with I/V transformer and output tube section for years now, BUT I was thinking of rebuilding the DAC with an output transformer output-section in combination with tubes.

Anyone ever made a DAC with an input AND an output transformer?

 

[MarcelvdG]

Yes if you count my S/PDIF input transformer

 

[abraxalito]

Yes if by 'input transformer' you mean one between the DAC and analog stage : Grossly parallel multibit DAC adventures

It doesn't have valves though.

 

[Arno Pf]

Yes if by 'input transformer' you mean one between the DAC and analog stage : Grossly parallel multibit DAC adventures

It doesn't have valves though.

It doesn't have an output transformer I think..

 

[Arno Pf]

Yes if you count my S/PDIF input transformer

So it does have an output transformer? If so, got a topic link of schematic?

 

[abraxalito]

It doesn't have an output transformer I think..

Sure it does - if you look at the picture the output transformers are top right, they're RM10 ferrite cores. They're needed not for impedance transformation (they're 1:1) rather balanced to single-ended conversion.

 

[Arno Pf]

Sure it does - if you look at the picture the output transformers are top right, they're RM10 ferrite cores. They're needed not for impedance transformation (they're 1:1) rather balanced to single-ended conversion.

Got it, Thx!

 

[sumotan]

Don't the ferrites make the sound dry & constrain Richard ? I never have good experience even when using ferrite beats for PS.

Cheers

 

[abraxalito]

Ferrite beads are a rather different application for ferrite than as a transformer core. Probably a quite different mix - optimized for high losses at HF. The sound of the transformer-based DAC is ironically completely the opposite of 'dry'.

 

[sumotan]

Thanks Richard, I use transformers for my dac too but have never experimented with Ferrite types. I don't use it for I/V application anymore as they tend to sound too polite for me on the 1541 dac.

Cheers

 

[abraxalito]

I use ferrite because its easily available, fairly easy to DIY and its cheap. Its far from ideal as its flux limit is very low (as core materials go) but for signal transformers that's not too much of an issue. I'm not using my trafos for I/V (still using a resistor for that) but to enable me to use a much bigger resistor (for line level output directly) but present it to the DAC as a very small one.

 

[sumotan]

Aaaah noted Richard. The i/v resistor type used is very important to sound.

 

[MarcelvdG]

So it does have an output transformer? If so, got a topic link of schematic?

Sure, see:

Valve DAC from Linear Audio volume 13
Linear Audio | your tech audio resource
https://linearaudio.net/sites/linearaudio.net/files/ThevalveDAC_PCB_FPGA_files for web posting.zip
https://linearaudio.net/sites/linearaudio.net/files/additionaldatavalveDACversion2p1.zip

The article costs 2.99 euro, but the design databases can be downloaded for free. Mind you, the fact that I used an input transformer for each S/PDIF input is not documented.