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Old 10th December 2009, 07:38 AM   #1
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Exclamation Tube-I-zator SRPP DAC I/V-Stage circuit discussions

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.

Click the image to open in full size.


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
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Last edited by dvb projekt; 10th December 2009 at 07:58 AM. Reason: additional text
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Old 10th December 2009, 08:44 AM   #2
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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.

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Old 10th December 2009, 09:33 AM   #3
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Quote:
Originally Posted by Bas Horneman View Post
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
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Old 10th December 2009, 09:51 AM   #4
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Quote:
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.
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Old 10th December 2009, 10:38 AM   #5
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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!
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Old 10th December 2009, 11:33 AM   #6
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Quote:
Originally Posted by revintage View Post
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 CDPs and DACs.

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
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Old 10th December 2009, 11:43 AM   #7
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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.
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Old 10th December 2009, 01:07 PM   #8
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I for myself not, because of 4 TDA´s.
Get it as indication value.
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Old 10th December 2009, 03:14 PM   #9
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Quote:
i forgot to write that the 28R are the I/V value for my 4xTDA1541 DAC...
If that is for four parallelled 1541s 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.
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Old 10th December 2009, 05:16 PM   #10
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With the 28R resistor it is hard on the edge, yes. But it works well

But thats why i started the thread, to talk about things in the circuit.

Every opinion is welcome.
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