I am looking at the PP version of the single valve spud amp. Perhaps with a small 10k a-a. Or perhaps teh Z565's I have on my shelf. Do the valve stage as a common cathode diff amp with a CCS as the cathode load. 25:1 turns ratio if I run from the 16R tap( and a 10k A-a ). I figure I'll need soome fraction of a volt, perhaps a whole volt RMS output. More like a half I suspect...

So, a pair of 12A4, the 12B4 with mu=20 and I'll have less than unity gain to the output. the active linestage will be able to feed it noooo problem. It will be absolutely class A, and might even work with 12B4's. Either will plug right in, the CCS will set the op point.

Seems like nothing I have seen to date anyway...
regards,
Douglas

You got a set of Grados, didn't you? I find the headphone amp I built from Mapletree Audio works very well with these low impedence phones. The Ear+ design sound very close to what you described, but without the CCS. Schematics can be found in the website. I call it my personal parafeed SET amp.

Interested in hear your thoughts on the design.

Gar.

• Mapletree Audio (scroll down to Ear+ Purist)

Anyway, MtA looks quite neat. I do think that the lower impedance of the Grado cans ought to be driven w/TX coupling. I am examining the RK34 for a linestage valve. It looks like ~2W is available with 250V and 10k a-a. More than enough power I think. Put a CCS under the cathodes and Class A is insured. Now to find out if these things are matched section-section. This would be a voltage gain of ~1/2 and would be the PP eauivalent of the 'Spud Amp' One twin element valve per channel and the PS. Probably get another Heyboer 8039. The amp will consume less than 80 mA in total.

My general MoO has been to step out with my own design, and THEN do some more research if the design does not show any promise. The traditional methods will no doubt yeild traditional results. I am seeking more. Now to find a proper 10k:32 OPTx. Perhaps the low power will allow me to ratio a 10k a-a into 20k by running the Grado's on the 16R tap.

regards,
Douglas