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JFET Audio preamp, diode set constant drain-source voltage, why not with BJT's?

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Many JFET buffer stages I see have a diode or some other circuit that keeps the JFET source-drain voltage constant, I presume this is done for increased linearity right?
But why isn't it done for BJT buffers? I've never seen an emitter follower set up like that.

Here's a couple circuits like that:

The closest thing I've found is the Radford preamp. But it's very much NOT the same, as you can see.

JFETs are not that ideal as BJTs. The drain voltage has more effect and often also the thermal offset drift is larger. A variable voltage causes a change in temperature and this way some extra error (though to a large part linear and mainly low frequency).

As part of chips a constant collector - emitter voltage is still used with super beta transistors, as these usually have too low a maximum voltage. There are few discrete ones too and these would in many cases need a similar bootstrapping of the collector side too.

The Circuit shown as the Radford preamp is the classic Sizlaky stage - not directly related.

Anyway most modern circuits now use OP-amps and feedback - the open loop buffers are a bit outdated in the audio range.

One thing for sure, that m.buffer circuit is a current limiter safety circuit, not a voltage stabilizer circuit.


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