Are Srpp's Any Good (please Help)

[soundbadger]

hello
me again,,,
i want a driver stage for kt88 and was thinking of using both sections of an e88cc the first section as common cathode, then the output from this going in to the grid of the second section which would be run as a cathode follower.

but then i saw this e88cc srpp schematic and thought id ask about it.

i have heard srpp may not sound that good, could someone explain the pros and cons of srpp, and tell me if it would be suitable for use in a high quality hi-fi amp .

also if someone could explain how to calculate the total gain and output resistance of an srpp it would be really usefull.

cheers
soundbadger

[Alastair E]

There is nothing wrong with the SRPP....Preferable to the straight common-cathode IMO...

But--As with many things in life, its quite a personal thing.....

If I was to do summit similar I would probably go for a Mu Stage, followed by maybe a cathode-follower to the KT88....

They say that the Mu stage goes some way nearer to the 'perfect' CCS for the lower gain stage....I like the sound, but some prefer the SRPP for its simplicity, although the Mu stage only has a couple of extra parts and appears 'similar'

[SY]

It depends on the application. For swinging large voltages into reactive loads, they are excellent. For normal sorts of voltage amplification, their linearity is inferior to a simple common cathode stage. This, of course, has not prevented its use in totally inappropriate applications because of the fascination it holds for hobbyists. For driving KT88, the swing requirements are pretty nominal, so SRPP would not be optimum. The badger's recommendation is a better one and, frankly, a plain vanilla 6SN7 with a 50k plate load and a 450V supply will give outstanding results with much lower parts count and complication.

The basics and the trade-offs of SRPP are discussed in "Valve Amplifiers," 3rd edition.

edit: I meant Alastair's, not sb's suggestion. Too early in the morning.

[Gordy]

There is also a lot of stuff (pros and cons) about SRPP over at tubecad.com

[18thell]

From my point of view,SRPP had been using by Luxman products, but no more on the market today, due to the sound reproduction is " too hard " and not that much Audiophile likes it. From the HI-Fi review mag. suggested " Williamson " sounds much better. take 12ax7 for front pre. and phase splitter, 12bh7 for after phase driver, then push a pair of kt88. This combination is employed by amp. manufacturer like fisher, Scott, Radford, H,J, Leak----.

[soundbadger]

i did a bit of reading of valve amps 3rd and decided i think id be beter of with a mu folower.
however after reading some articles here on diy audio it seems that using a pentode as the constant current source / cf would yeild much better results.


ive attached the formula for voltage gain of a mu follower. could someone explain, which tubes do the values for this formula come from.

[Alastair E]

Check out this from Allan Kimmel --

http://www7.taosnet.com/f10/mustage.html

Its a description of exactly how to work out the circuit values, as well as the pro's and cons of various 'active-loaded' triode stages. It examines the SRPP, the Triode Mu, Pentode Mu and if you're not allergic to silicon,
it describes a MOSFET active load....