27-PP2A3-S245 (pic)

MagneQuest/Peerless Forum

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While direct-coupling a PP output has to be one of the worst things for global warming, it does produce a couple watts of interesting sound. The above is my shopworn circuit, now with a SE 27 directly-coupled to a "compact" or long-tailed-pair PP2A3, and then a nickel S245. The second 27 has a grounded grid and an adjustable current set resistor in its C4S and a separate 1.8K cathode bias resistor. The circuit has also worked well now with 6N1P, 6C45s and 6SN7.
I've tried joining the cathodes of the first "stage", but so far have prefered the separate cathode bias and resulting SE circuit. This may change if I ever get a proper CCS in that mix.
The 27 and its 4.5 mA of plate current make for a kind of wimpy driver, but do take the amp one step closer to using a grid choke and no attenuator in the input. For the moment I'm using the primary of a B7 as a grid choke, which I think gives a hint of what the real item will offer.
A key to the low noise and great sound is the adjustable C4S. Maybe when DC offset is nulled, PSU noise rejection is at its greatest? With other inputs, the noise has dipped to a stable 0.4mV, which is as low as my DVM will go.
A direct-coupled phono stage set up this way might be interesting. Grid choke, SE pentode (maybe Gary Pimm's 6BN11 idea, here), 6SN7, and a 5Kct:500 linestage OPT. The input would have to be a pentode, so as to apply Gary's current-balance regulator in the output.
That's the latest... --keto

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Topic - 27-PP2A3-S245 (pic) - keto 08:10:11 05/15/04 (2)

27-PP45 - keto 21:11:42 05/17/04 (1)

update... - keto 19:11:46 05/29/04 (0)

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