Thanks. I will look at this as well as other suggestions now...it appears I may have to hide out in the hills for a while...
Leo, don't worry about it. No-one offends more people more often than I, yet they made me a moderator.
Thanks Sy...who knows maybe in the maze of wire, caps, resistors, solder, iron I'll be working with, I'll stumble upon (completely by accident, of course) a dirt cheap 12AX7 tube phono-stage design that actually works like a charm with nothing but upsides and no downsides? I know...I know...I won't hold my breath on that pipe dream.
If you're adament about 12AX7 then look into Jadis' JP200 MC/MM line
preamplifier.That's provided you can reverse engineer it but there are cheap
chinese line stage clones which you could modify to phono use.
Not at all...just being a little cheeky....I think the verdict is in...got some great advice and ideas from many people and as you pointed out time to listen to my inner Zen.
I am still curious as to what SY's P-JFET trick is. With an N-JFET (as below) the fet provides bias (equal to Vgs) for the grid of the first tube, which seems like a neat trick in of itself.
But, that aside, I think you could do a pretty good "tube" phono stage with 12AX7's as the amplifying devices for under ~$200 so long as solid state is allowed. Here's what I'd do.
I left part values as an exercise, but CCSes could all be a single 10M45, and you'd just have to adopt someone else's filter network. Also, you would need a well regulated power supply but that's easy with such a low current draw.
But, that aside, I think you could do a pretty good "tube" phono stage with 12AX7's as the amplifying devices for under ~$200 so long as solid state is allowed. Here's what I'd do.
An externally hosted image should be here but it was not working when we last tested it.
I left part values as an exercise, but CCSes could all be a single 10M45, and you'd just have to adopt someone else's filter network. Also, you would need a well regulated power supply but that's easy with such a low current draw.
You can certainly do that if you can choose the FET/tube appropriately (they will have to be happy at the same bias). A good CCS will have really low current noise, and the looking-in impedance at the cathode/source is pretty low.
NB: We're still not talking about super cheap and easy builds. The power supplies will be numerous and there will have to be some device selection.
NB: We're still not talking about super cheap and easy builds. The power supplies will be numerous and there will have to be some device selection.
Then you could put a MOSFET gyrator of some sort in the anode for good PSRR A solid state sandwich!
You could also bias the upper MOSFET with a CCS in parallel with the triode to raise the effective gm, and if you take the signal from the mosfet's source, increase the driving ability somewhat
So then it becomes a solid state sandwich with some more solid state on the side
A solid state sandwich!You could also bias the upper MOSFET with a CCS in parallel with the triode to raise the effective gm, and if you take the signal from the mosfet's source, increase the driving ability somewhat
So then it becomes a solid state sandwich with some more solid state on the side
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Am I think about this backwards? Wouldn't be the first time.
JFET with the gate at ground will have a source at a negative voltage. That is, assuming that the current through the FET is less than Idss, Vgs for a 2sk170 is something like -1V, which would puts the grid of the 12AX7 at -1V w/r/t/ ground. No? Perhaps I am overestimating the amount of Vgs for most N-FETS? Maybe an IRF610 with Vgs ~-4.5V would be better if -1V bias is not enough. Or a darlington would force the grid to be at -1.2V.
No. A p-jfet works in depletion mode. So the source has to be biased negative with respect to the gate (which is at DC ground). If the grid is grounded and the cathode is negative, that will be a Bad Thing.
No. The source of a depletion mode n-fet will be positive with respect to the gate.
Doug, meet Anatoliy.
No. The source of a depletion mode n-fet will be positive with respect to the gate.
Doug, meet Anatoliy.
Bah, you're right, I am thinking about it backwards
I can't keep all these sand devices straight. OK, I'll redraw with an E-MOSFET. Then it should work ... I think.An externally hosted image should be here but it was not working when we last tested it.
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