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In Reply to: BJTs as CFs posted by SomeJoe on April 13, 2007 at 20:51:58:
Dude,
BJTs, FETs, and pentodes are themselves constant current devices. You model them using the Norton equivalent circuit, which is a current source.CCS loading pentodes, FETs, and BJTs is a BAD idea, as "head butting" occurs. However, you can choke load the constant current active devices.
Why a BJT, when it's EASY to DC couple an enhancement MOSFET to a triode's plate?
Follow Ups:
> > Why a BJT, when it's EASY to DC couple an enhancement MOSFET to a triode's plate? < <Been there, but didn't like the sound. The dynamic was there but it sounded a bit too harsh. That's why i wanted to try BJTs, preferrably a model desgned for audio, with a mosfet CCS in the emitter. But, while at it, i might just go with a 6SN7.
There's little doubt about a CCS loaded 6SN7 CF sounding GOOD.The IRFBC20 might change your mind about FETs. Also, the coupling cap. from FET to load could have contributed to harshness.
As stated previously, CCS loading is pretty much reserved for vacuum triodes. 2 constant current entities connected to each other will fight.
Eli D.
Hello Eli,I must admit, i said that i tried a mosfet DC coupled to the driver stage but that ain't exactly true. What i did was, a cap-coupled mosfet source follower, resistor loaded, DC coupled to the output stage . Maybe DC coupling to the output stage might have produced different results.
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