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Old 13th December 2009, 04:27 PM   #21
SY is offline SY  United States
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For you again, i am not a developer to answer questions about different stage technics.
Then why did you open a thread for circuitry discussions? Part of discussion is understanding reasons and rationale.
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Old 13th December 2009, 07:22 PM   #22
oshifis is offline oshifis  Hungary
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Old 13th December 2009, 08:51 PM   #23
kevinkr is offline kevinkr  United States
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I think the SRPP has become something of a tube audio design fashion statement, and possibly an irrational one at that.. I used them a lot in some of my older designs, and perhaps (definitely) a bit too widely. To my chagrin I found some real practical downsides to its use including excessively high output impedances with low transconductance high mu triodes like the 12AX7A/ECC83. (Much worse incidentally that a straight CC stage driving a CF in this case.)

About 11 yrs ago I designed a phono stage that used one in the output stage and lost the possibility of a very lucrative distribution agreement because it could not effectively drive the capacitance of the most popular interconnects of the day. It bombed in a critical 3rd party system evaluation for that reason, despite my verbal warning about its inability to drive very capacitive cables.

There are other shortcomings including linearity and noise where it is generally inferior to the mu follower, and a CCS (or resistively) loaded common cathode stage.

It is quite good at driving the specific load impedance for which it was designed and for delivering some appreciable amount of power into a load. It is not a great choice where the primary goal is voltage gain, and the wrong choice in tube type will result in a stage that can't drive even reasonable loads. (Usually the result of needing voltage gain)

I still admit to liking the way the 6SN7 sounds in SRPP configuration, and use it that way in one of my old line stages, I also use it to drive the output stage in my SE amplifier where it works pretty hard, and gives a good account of itself. Certain tubes like the 6021 IMHO sound dreadful and produce bad measurements when used in SRPP. I haven't designed anything using this topology since about 1999..

How about a 5842 with a CCS load, and LED bias, output impedance will be <2K, (or you could configure as a mu-follower using a DN2540 mosfet) gain is high enough that a very small I/V resistor could be used for good dac linearity, and it is extremely low noise.
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Old 13th December 2009, 08:53 PM   #24
SY is offline SY  United States
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How about a 5842 with a CCS load, and LED bias, output impedance will be <2K, (or you could configure as a mu-follower using a DN2540 mosfet) gain is high enough that a very small I/V resistor could be used for good dac linearity, and it is extremely low noise.
Nope, makes way too much sense.
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Old 13th December 2009, 09:42 PM   #25
Cobra2 is offline Cobra2  Norway
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Me too would think the simpler/se stage would be better...but then again, John Broskie/Tubecad gets away using SRPP in a RIAA...

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Old 13th December 2009, 09:54 PM   #26
kevinkr is offline kevinkr  United States
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Originally Posted by Cobra2 View Post
Me too would think the simpler/se stage would be better...but then again, John Broskie/Tubecad gets away using SRPP in a RIAA...

Arne K
I made that mistake once..
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Old 13th December 2009, 09:54 PM   #27
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How about a 5842 with a CCS load, and LED bias, output impedance will be <2K, (or you could configure as a mu-follower using a DN2540 mosfet) gain is high enough that a very small I/V resistor could be used for good dac linearity, and it is extremely low noise.
And then maybe even add the Salas Simplistic Mosfet HV Shunt Regs? That would be a cool pcb.
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Old 13th December 2009, 09:57 PM   #28
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Originally Posted by kevinkr View Post
How about a 5842 with a CCS load, and LED bias, output impedance will be <2K, (or you could configure as a mu-follower using a DN2540 mosfet) gain is high enough that a very small I/V resistor could be used for good dac linearity, and it is extremely low noise.
Good suggestion - a 7119 with a 1:1 transformer is my chosen solution...for now at least

FWIW: Our SRPP experiences are very similar, Kevin.

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Old 13th December 2009, 10:02 PM   #29
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a 7119 with a 1:1 transformer
Is the transformer before or after the 7119?
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Old 13th December 2009, 11:44 PM   #30
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After.

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