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Old 22nd February 2008, 07:17 AM   #1
Cobra2 is offline Cobra2  Norway
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Question Cathode follower & SRPP q

I have searched...and read different tube-books & articles...getting more confused by the day.
Q. about CF:
I do not understand the plate(anode) reistors role...? (not always there...)

Q. about SRPP; having read the tubecad.com articles about SRPP, it should almost be written off as a line-stage circuit?

Arne K
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Old 22nd February 2008, 10:26 AM   #2
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All I can see a plate resistor doing is increasing the OP impedance of a cathode follower. I can't understand why anyone would do that.

As for SRPP, I've never used one and don't think I'll ever want to.
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Old 22nd February 2008, 11:53 AM   #3
oshifis is online now oshifis  Hungary
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CF: another reason is that the tube does not get the full Vb.
SRPP: most circuits I have seen use a bypass capacitor across the cathode resistor, and this spoils the sound IMHO.
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Old 22nd February 2008, 12:14 PM   #4
Cobra2 is offline Cobra2  Norway
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The "SRPP - kill" article; http://www.tubecad.com/articles_2002...ted/index.html

And bypass cap on CF?? Does not change gain much anyway???

Arne K
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Old 22nd February 2008, 01:15 PM   #5
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Default srpp

Hi.
I have spent the last 5 months building different toplogies from the "simple" circuits like grounded cathode through to the kimmell mu stage and all manner of preamps in between.
And to find that myself and the golden ears of my lady still prefer an srpp line stage.. go figure.
For my phono stage i tried many setups and currently I have a Mu stage in one of 6sl7's and in another I have e80f in triode mode fed by an ixys ccs.. the ixys version to us sounds much more dynamic, detailed and isnt fatiguing. I am going to convert one channell of my sl7 mu stage to an ixys ccs setup to see what gives.
Both these phono stages are hooked up to an srpp 6sn7 which runs 175V on the upper tube which many say isnt enough but having tried various values of b+ I seem to prefer the lower voltages which happily increases tube life and puts less thermal strain on components.
Take a look at this link and read one angle on harmonics and the spectrum of orders of the fundamental. It is interesting to see where srpp is placed
http://www.nutshellhifi.com/library/FindingCG.html
There a lot of serious tube dudes in this forums that have amazing amounts of knowlege. I dont have the nouse or the desire to contradict anyone but rather let your ears decide.
You may find one that suits your music and taste. I think everyone is different in what they hear. The bumble bee apparently is unable to fly or at least thats what I am led to believe based on a story re wing span and weight, but nobody told that to the bumble bee.
I humbly suggest that sometimes theory may not be enough so build the srpp (its probably the simplest circuit I can think of) and build some others and judge for yourself. I will no doubt raise the ire of some in this forum but no matter. I am not having a go at anyone and their preferences.
BTW in some designs that dont deploy some kind of ccs, a plate resistor is a must. Thats how you draw load lines thus predicting some of the more influential behaviours of tubes. Look into it. Bypassing cathodes isnt always necessary either.
I have also tried battery biasing of grids of cathodes and using leds for same. For now I will stay with srpp because for me it works.
If you think reading about tubes will lessen the confusion just remember the concept of "shades of grey".. not too much black and white as I see it
Good travels
Nick
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