Tube-I-zator SRPP DAC I/V-Stage circuit discussions

[dvb-projekt]

Hi to all,

Because of the big success of the I/V SRPP Tube Stage in my finished 4x TDA-1541A DAC,
i am planning a PCB Group Buy for those who want to have a optical and technical perfect solution.

Because i am no technical guru who could answer Tube circuit details,
i would like to open this new thread to discuss questions arround this SRPP-Stage.




The values of the resistors in the SRPP Stage are for use with a 6N2P Tube but could be changed for other tubes.



Best regards,
dvb-projekt

[Bas Horneman]

The schematic is a bit hard to read like this. But the first thing I noticed is the small value grid leak (R5/R7)? Should be 100k or larger. And I would add a grid leak to the output as well.

[dvb-projekt]

Originally Posted by Bas Horneman

The schematic is a bit hard to read like this. But the first thing I noticed is the small value grid leak (R5/R7)? Should be 100k or larger. And I would add a grid leak to the output as well.

Hi Bas,

i forgot to write that the 28R are the I/V value for my 4xTDA1541 DAC...

Surely this resistor value depends on the DAC you will use (Tolerance +10/-50%):

1x TDA1541A: 90R ; AD185x: 500R ; PCM 56/58: 500R
2x TDA1541A: 60R ; AD1862: 500R ; PCM 63: 100R
4x TDA1541A: 28R ; AD1864: 250R ; PCM 170x: 100R ; 2x PCM170X: 55R

[Bas Horneman]

i forgot to write that the 28R are the I/V value for my 4xTDA1541 DAC...

Ofcourse! Duh. Forgot that that is your I/V resistor.

[revintage]

Why the light load on the 1541? Normally we see ca 30ohm/dac to avoid distortion.

And why SRPP? Even Broskie who have talked so much about this circuit dumped it years ago. At these very low signal-levels it might not be noted but PP makes uneven harmonics be dominant and the circuit is also load-sensitive.

But as you have found it well-sounding, go for it!

[dvb-projekt]

Originally Posted by revintage

Why the light load on the 1541? Normally we see ca 30ohm/dac to avoid distortion.

And why SRPP? Even Broskie who have talked so much about this circuit dumped it years ago. At these very low signal-levels it might not be noted but PP makes uneven harmonics be dominant and the circuit is also load-sensitive.

But as you have found it well-sounding, go for it!

Hi Lars,

as a simple Tube-Buffer-Stage with only a few needed parts instead of a normal SS Buffer-Stage and the resultant advantages , it runs like hell in my DAC.
I had absolute no problems at all and the circuit is well proven as a great upgrade to standard Output-Stages in CDP´s and DAC´s.

I absolute agree that you could make many various stages at this point, but i opened this thread to discuss questions around this SRPP-Stage.

Best regards,
Oliver

[revintage]

Hey Oliver,
Can absolutely understand that you find tubes superior against SS.

Just curious , have you tried lower I/V resistors? 100ohm is where you get unacceptable distortion, 90ohm seems to close. But of course you get higher output level.

[dvb-projekt]

I for myself not, because of 4 TDA´s.
Get it as indication value.

[revintage]

i forgot to write that the 28R are the I/V value for my 4xTDA1541 DAC...

If that is for four parallelled 1541´s it means 112ohm/DAC. Far above what is said to give gross distortion. Typo? If 28ohm is for each DAC it is close to what is commonly seen. Also checked the Lamp-guy and he recommends 60-80ohm/DAC.

[dvb-projekt]

With the 28R resistor it is hard on the edge, yes. But it works well

But that´s why i started the thread, to talk about things in the circuit.

Every opinion is welcome.