audio-talk

IslandPink wrote: ↑Sat Jun 17, 2017 12:12 pm Yes I didn't spend any time measuring my phono, just measured parts and as you say, things like D3a's are tight tolerance. When I looked at values for pentode-driven first stage I remember that 3k or 4k anode load looked very feasible - so the output impedance wouldn't be that high . I think the D3a triode at 13ma as I have now, is over 2k Zout. Pentode did look good . Will be using something like that with the new LCR phono ( currently a top-plate and a big of bits ) although now the Gm amp idea from JC has come along and this opens up the possibility of a SUT-less MC input at the front end.

I should have said the pentode has a high ra so the stage output Z is dominated by the load R. Unlike the triode, I suspect the overall output Z won't drift about with age as much as the triode would where the anode load is only slightly higher than ra, typically twice. I use 4k7 as my anode R. Great thing with the pentode is within reason, you can have any anode R

JCs ideas as always blow my mind. If you can get them stable, I'm sure it would be great. I just don't understand them too well, if at all.

And there's also shunt EQ that a pentode can do as well - no series R. Food for thought?

One day I hope to do an LCR (finances permitting) and I suspect that's the end of the road.

cheers,

Stephen

If you aren't driving anything worse then say 100k into the next amp you can run under 1uF , for instance 0.68 or 0.82uF , in which case you can use film/foils like the Mundorf ZN ( oh, did I ever mention I'm fond of MUndorf ZN's ? ) instead of metallised film.

Thanks Mark, ZNs are a definite improvement on gone off Jupiters.

Cheers

Richard

Thanks - glad to be of service !
And agreed on the value , I use 0.68u on the output of mine as I typically drive 100k on the power amp.