Valve Amp with soild state front end

[Johan Potgieter]

SY,

No fine then. I was too lazy to calculate! I will compare this some time with my transistor job. Thanks.


Ilimzn,

Ray was commenting on the contents of that article that was quoted - not necessarily to do with our subject.

Regarding the non-linearities you mention, one normally tries to keep their effects out of the audio band. In that way you can get some < [0.1 - 0.05]% non-linear distortion out of a transistor front-end with good design and some local feedback. You will be hard put to get that with tubes. But since one can have inaudible distortion with both technologies, the question does arise, why the extra bother with tube power supplies etc. For me it will be a consideration of convenience, not really a substantial difference in performance.

[ray_moth]

Sy,

I was thinking of both noise and microphony. (Anyway, enough from me on this. As Johan says, we should probably stay on topic - or start a new thread!)

[ray_moth]

Sy,

I was thinking of both noise and microphony. (Anyway, enough from me on this - as Johan says, we should probably stay on topic.)

[DJNUBZ]

So I am reviving this thread because I started thinking about using a semisouth jfet to drive a 300b. That is a bit cost prohibitive for me to experiment with personally but I am curious if there are any amps people have personally built that have a SS front end and tube output? If so how did it sound? If not, do you think this can be done while being directly coupled to the output tube? I like the idea of having no caps, or only one cap in the audio signal path.

[Miles Prower]

Originally Posted by DJNUBZ

So I am reviving this thread because I started thinking about using a semisouth jfet to drive a 300b. That is a bit cost prohibitive for me to experiment with personally but I am curious if there are any amps people have personally built that have a SS front end and tube output?

You can drive a 300B with a more common power MOSFET as a source follower. If you're talking about those new SiC JFETs, you'd do much better to use them as the finals, with a hollow state front end. Also, these SiC JFETs need to operate at higher than usual voltages to keep the device capacitance from going squirrelly. (Attached) Otherwise, it looks like these are very linear if you get the voltage up, and the current down. (The other problem is excessive gate current if you operate at high drain currents.)

If so how did it sound? If not, do you think this can be done while being directly coupled to the output tube? I like the idea of having no caps, or only one cap in the audio signal path.

SS up front, with VTs on the back end is more for guitar amps: high, solid state gain up front, maybe some DSP, and the hollow state back end for the desirable, hollow state, distortion and crunch.

For music reproduction, I would prefer hollow state up front, and a couple of power MOSFETs (or those SiC JFETs, if they ever become something other than unobtanium for anyone who's not in the market to buy hundreds at a time, that is) on the back end.