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In Reply to: RE: I'm starting to get a picture different than I thought it was posted by Tre' on May 28, 2017 at 10:34:20
"I believe the tube provides gain."
It does, but so would a FET in that position. You know, it's only a small step from believing that a MOSFET used as a follower or CCS won't affect sonics to replacing all the tubes in the circuit with solid state. When a group consists of individuals who will readily argue which resistor, capacitor, diode, fuse or wire type sounds best, I think this is extremely hypocritical. Not referring to you, just the forum in general.
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Buy Chinese. Bury freedom.
Follow Ups:
I see the sonics being affected more by a FET as a follower than as a CCS.
One more question. Is the output impedance value of the FET follower affected by the plate resistance of the tube below it?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The more important question ought to be, 'what about SS sounds so different'? Their input capacitance varies depending on the voltage across them for one. But that does not seem to be of any interest; 'SS is bad', or some such and then complete dismissal...LOL
Tubes are not without significant limitations, which when crossed leave them sounding like crap. I suspect combinations that take advantage of the strengths are much more capable than either alone.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
The Rp of the tube has almost no effect when it's driving a MOSFET follower. Nearly all the AC signal current to the load is supplied by the MOSFET. That's what sets the output impedance.
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Buy Chinese. Bury freedom.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
This exercise gave me a chance to review the current paths for these various configurations. I had forgotten that signal current in the cathode follower flows through the power supply. That means it's important to have a good quality cap in the last position, and to be sure the cap's full potential isn't degraded by semiconductors or poor quality components upstream. Maybe this is another reason some CFs have an unpleasant sound. A common cathode stage with a CCS or anode choke wouldn't be vulnerable to this.
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Buy Chinese. Bury freedom.
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