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previous: Joe Fuzz R.G.: Thanks for the analysis. Jus... -- 9/9/1999 1:36 AM view thread

Re:Minibooster Operation

9/9/1999 3:06 AM
R.G.
Re:Minibooster Operation
quote:
" Just so I'm perfectly clear on this: you're saying that the circuit is ON all of the time? In other words, there is a constant DC current draw even with the AC input at GND and that this DC current could be as high as 15 mA. Correct?"
 
 
Yep. As long as you put a voltage supply on the drain of the top JFET, this thing will run at close to Idss for the JFET. Some JFETs have low Idss, in the units of milliamps, but some are fairly high. Depends entirely on the type number and specific device.  
 
 
 
It's *not* a push-pull circuit, even thought it might look like it. It's a linear, class A amplifier. The top JFET is just an active current source.  
 
 
 
quote:
"Maybe I was slipping down the JFET curve -- in a "linear" fashion. If that makes any sense."
 
 
 
 
It makes a lot of sense - that's exactly what was happening. The two devices stayed balanced, but were moving into their triode region, I'd guess, so the tone changed.  
 
 
 
You could go find low Vgs-off JFETs. These things have a lower Vth and so they would stay in channel saturation (hence out of triode mode) to lower voltages than higher Vgs types. 2N5485 would be a good place to start.

 
Replies:
Joe Fuzz q{The two devices stayed balanced, ... -- 9/9/1999 5:51 AM