What PP circuit to use for 6SN7 and 2a3? - diyAudio
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Old 12th December 2004, 09:41 AM   #1
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Default What PP circuit to use for 6SN7 and 2a3?

I'd like some ideas please for my next PP amp. The ingrediants I want to use are Sovtek 2a3s and 2C22/7193, which is a 6J5GT equivalent, so basically for a pair, think 6SN7. I guess choices are a) some kind of cascode, SRPP or Mu stage. If so, do I use 2C22 top and bottom or some other combination? There are some 6J5GT values in Morgan Jones' book
b) One diff pair (and a high output preamp)
c) Two diff pairs
d) Direct coupled
e) Transformer coupled (I'm pretty happy with teflon caps.....)
f) Other
Sound quality is the main concern - whatever sounds best.
I mention the 2C22 because so far it's the cleanest most detailed valve I've used for input stages. I have some older valves I haven't used yet if that helps - 76, 56, 37, 27, 26. I also have 6C45 but haven't used that yet, likewise 8532. I have loads more valves if you want to make any other suggestions. I don't mind any kind of overkill on this project, since the idea is to have a reference amp. Smallish room, lowish sound levels, jazz and classical. Two monobloks. Power supply will have damper diodes, a number of chokes and all polypropylene caps. OPTs are Lundahl 6K PP. Andy
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Old 12th December 2004, 10:44 AM   #2
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I agree with your comments about the 2c22 / 7193 having used these in linestages and preamp applications. A cleaner and more detailed 6SN7 really but lets keep that quiet before the prices start going up! If you don't already have curves for the 7193, you can find a datasheet at Gary Kaufman's site - http://www.the-planet.org/ in the linestages section.

When it comes to power amplifiers my ears prefer single ended to push-pull designs. The main differences for me are resolution of low level detail and ability to preserve rhythm and timing. Given the choice, I would prefer a SE 211 over the PP 2A3.
If you prefer the sound of PP, then I would consider using an interstage transformer to do the phase splitting as in my experience, the reduced component count and shorter signal path does improve resolution.
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Old 12th December 2004, 11:09 AM   #3
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Two diff pairs for sure. Current source cathode loads. Direct coupling.

If you use a transformer for a phase splitter, do it right at the input; low level signals are easiest to transform and galvanic isolation is a benefit.
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Old 12th December 2004, 11:16 AM   #4
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I was just looking at Jeremy Epsteins direct coupled SET 2a3 amp with 8532 input. It would be interesting, though would tax my skills a bit, to double this up for PP starting with a diff pair of 8532. Easier not to direct couple - that would be a simple two stage design. A thought..........

http://db.audioasylum.com/cgi/m.mpl?...32&r=&session=
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Old 12th December 2004, 12:47 PM   #5
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Quote:
Originally posted by SY
Two diff pairs for sure. Current source cathode loads. Direct coupling.

If you use a transformer for a phase splitter, do it right at the input; low level signals are easiest to transform and galvanic isolation is a benefit.
That sounds good, with the 8532's in the front end.
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