good catch on the opamp polarity, i remember that error on the fix it list.
remember, i said " i think it works" did ii know something?
;D
the 470 pf cap was for tone,
without an output transformer to screw things up,this is as close to a "strait wire" amp as you will find.
so the 470 pf was a substitute for a HS 66, which was added later with gusto. 8)
certainly the following signal chain will roll things off, but i was going straight into an OTL headphone amp, into the Sony Pro phones which have this high end thing going on already, oh, and a transformerless SM 57 getting barked into by the dog, can you imagine the eq needed for this signal chain?
(i wanted to hear the incredible detail, in order to appreciate this amp, your support gear has to be as clean or better, or else, ...?)
the transistors have the old tropical fish color codes for matching or id.
i built my DIY valley pre with i believe 3 transistors in parallel instead of 2,
i had four on each side for ultra low noise, but the trade off was not worth it, noise elsewhere, (can you say opamp, or pwr supply?) so why bother. (thanks 2002 vca
)
plus, the matching was greatly simplified going from 4 to 3 pairs.
and the current source trimmed out easier you can get this back and forh zener thing going on, especially if your meter does not have a high input Z.
they were stuck together with thermal pads and grease, better thermal than the epoxy.
i was shocked to find no coupling foil or shaved cases, like the DBX stuff.
this HP vacuum tube meter goes down to 1 mv AC Full Scale. just sits there, even with the cover off.
no shield around the wafer sw or tube or nothing. good for this type of matching.
one of the draw backs of this circuit is no tone control.
certainly , something could be kludged in, but i do not think that would be in the spirit of the original engineers.
did we not have the original engineer post up here, or we had a letter that he had written to one of the forum members? it was uhh....rather....."provacative", yes, that it.
;D
ok, looks like i opted out for some fancy smancy state of the art Burr Brown op amp,
some German stacked film caps, and ran the I/O Langevin style, passing the traces over each other for stability C.
you can see the gray thermal pad, just put a roach clip ocross the pairs, contact cement and Go.
looks like i shaved the current source triples.
optional 1/4 inch output jack so i don't have to F with silly patch bays.
UTC 66 equiv, external pwr supply and we are rockin.