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Old 12th May 2010, 11:07 PM   #1
Stee is offline Stee  Italy
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Default the Reversal SRPP

my last project is a SRPP tube preamplifier
with a special input and output buffer:
cathode follower with a current source
that is to have a compensation of "triode tone mark"
in other word appear technically unnecessary but "magic for music"
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Last edited by Stee; 12th May 2010 at 11:24 PM.
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Old 12th May 2010, 11:13 PM   #2
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Hi,
I see a circuit with an input and an output cathode folllower, with a SRPP gain stage between.

I see no point in having either cathode follower, the input one is not needed to drive a pot and a SRPP input, and the output Z of the SRPP should be low enough to drive a cable without the extra CF.

Why add them? KISS is my key principle, and a CF (even with a CCS load) still is not 100% transparent.

Regards, Allen
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Old 13th May 2010, 12:34 AM   #3
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V1a, V2b and V3b can be replaced with resistors.

Tim
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Old 13th May 2010, 01:12 AM   #4
kevinkr is offline kevinkr  United States
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I have to agree with Allen.. It seems needlessly complex which can't IMHO help the sound. Simpler is usually better.
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Old 13th May 2010, 06:47 PM   #5
Stee is offline Stee  Italy
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Default Simpler is usually better

of course
but I think the success of the SRPP is just replacing the anode resistor load with a triode:
an active load is good for the cathode in terms of sound
it is true that the principle of character's compensation is not measurable
but your ear will notice a more realistic scene
just because works another identical unit in opposition of phase
a too modern concept for designers more orthodox
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Old 13th May 2010, 07:04 PM   #6
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I have no argument with your use of the SRPP topology as a gain stage, but cannot see why you need a CF buffer before it AND after it. Pointless IMO.

Regards, Allen
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Old 14th May 2010, 05:12 AM   #7
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Input cathode follower: do not need. Ditch it.

Output CF: use a proper CCS tail load, either cascoded, discrete BJTs, a CCS IC, or if you insist on a "no sand" solution, a high g(m) pentode CCS. Triodes are horrible as CCSs.
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Old 14th May 2010, 07:31 AM   #8
Arnulf is offline Arnulf  Europe
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Stee, how does this thing sound with 150V B+ ?
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Old 14th May 2010, 10:12 AM   #9
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Quote:
Originally Posted by Miles Prower View Post
Input cathode follower: do not need. Ditch it<<

Agreed.

>>Output CF: use a proper CCS tail load, either cascoded, discrete BJTs, a CCS IC, or if you insist on a "no sand" solution, a high g(m) pentode CCS. Triodes are horrible as CCSs.
Miles, why does he even need an output CF? A well designed SRPP's purpose is to act as a active load AND a "CF" with a low OPZ.

But if you want to do a really sonically transparent CF, I believe you need to use my SLCF, which can be seen as the last section of my FVP-5A schematic, linked here:

http://www.vacuumstate.com/index.tpl...271.4389191557

Regards, Allen
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Old 14th May 2010, 01:21 PM   #10
316a is offline 316a  England
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I can't see how this thing can work . Look at the grid arrangement on the input stage V2A .

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