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.

An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.

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.