Is This Preamp Okay?

[Jay]

What do you think of the attached preamp circuit? I usually don't like active preamps but mosfet amps tend to need them, and this circuit is from a commercial amp with build quality that I like to keep.

I know there may be many better solid state preamps in this forum. But I'm not looking for the best, just a "very good" one LOL. I want to know how this circuit may COMPARE with the "best" out there. Oh, I'm aware that you may ask for more detail about this circuit, but I believe that the experienced guy will "know" the quality from looking at the topology.

I'm using this preamp with the following amps:
Stochino ultra fast amp,
Mooly's amplifier,
JLH Mosfet 80W,
Bora's Sigma,
Goldmund Mimesis 3,

From your answers, I will decide if I better sell this preamp

Thanks

[lineup]

It looks like a very good preamp.
Complete and no shortcut in design.

[Jay]

Thanks Lineup. I'm happy to know that

[Jay]

Well, what can I say? I hate to believe in my intuition (based on limited experience and other people opinions) that this preamp (as well as many other preamps) will not gonna work for my "ultimate" system.

If I sell the preamp I will probably get $150-200. If I use the casing for another preamp/buffer circuit, what will I do with the internal components??

My negative feelings towards preamps prevented me from even building the Blowtorch

[Ken Newton]

An interesting design, what with it's J-FET buffered bipolar input stage. Not an excessive amount of open-loop gain (for a feedback based transistor circuit) either. Perhaps, the main thing limiting it's sound quality may be that 100uF electrolytic output coupling capacitor, CL47. Before selling, you might try replacing it with a decent quality film cap. Unless your power-amp has an unusually low input resistance, line-stages usually don't need more than about 10uF of output coupling cap., and often, only a few microfarads will do.

[aparatusonitus]

Originally Posted by Jay

Well, what can I say? I hate to believe in my intuition (based on limited experience and other people opinions) that this preamp (as well as many other preamps) will not gonna work for my "ultimate" system.

Of course it ain't gonna work...it has to many transistors/fets/buffers in it.

Originally Posted by Jay

If I sell the preamp I will probably get $150-200. If I use the casing for another preamp/buffer circuit, what will I do with the internal components??

Use them to build something fare more simpler...like asymmetrical folded cascode/discrete AD797 with J-fet input.

Originally Posted by Jay

My negative feelings towards preamps prevented me from even building the Blowtorch

Then go for S&B TVC as I have

[Jay]

Thanks Ken.
I'm not even familiar with the used FET (M47F) and the bipolar (C2259). Currently (and temporarily) I use Black Gate N for the output cap. Of course pure film cap will be too big for 100uF. But if later I found it has potential, why not?

I'm planning to experiment with active speaker system later on, so I felt that I cannot try too many candidates for the preamp. Later the preamp will drive PLLXO and many kinds of active circuits (discrete opamps).

Yes sure Aparatusonitus,
I think you are right about it too complex I will check your preamp soon (never heard of it). Hopefully it is better than Aikido Chatode Follower in my system. Or may be the preamp designed by VladimirK.

[Jay]

So TVC is Transformer Volume Control. But no thanks I don't want to invest so much money for improvement that I know not so critical. But I read that LDR is even better than TVC? I have very high quality ummm optocouplers (?) around.

The original idea/reason of having an active preamp is because many mosfet amplifiers really need them (such as the JLH 80W). Of course it would be a good idea to select mosfet amp that has suitably high input impedance (such as Mooly's amp).

My preference goes to a buffer with adjustable minimal gain, coupled with "perfect" power supply. Power supply is actually the key element here.

[stratus46]

It's just a little odd to have a bias pot in a preamp though.

G²

[Ken Newton]

Black Gate 'N' type bipolar E-lytics make excellent signal coupling caps. I utilize 4.7uF NX myself as an input coupling cap. on an diy amplifier project. The transparency is amazing, far better than I was getting with 10uF metalized film ClarityCaps.