Thanks for the info, jdiamantis!
That's interesting. I wasn't aware of that.
So maybe I should build all my other FET-as-VCR-applications with
BF245C instead of A,B types (FET-based Phasers, whatever.)
I wonder why the 1176 has used a FET with rather low Vgsoff then?
As I said, the info I got called for something like 2.x Volts. (Can
anybody confirm this?)
[quote author="jdiamantis"]jhaible said,
"Why does a higher vgsoff mean less distortion ??
I see that the wrong Vgsoff (too high or too low) would f**k up the whole threshold and loop gain settings, but I wasn't aware that higher Vgsoff would also give a wider linear range in VC resistor mode. Is this really true?"
In checking the following document, under "distortion causes", we find:
http://www.vishay.com/docs/70598/70598.pdf
"Where large signal-handling capability and minimum
distortion are system requirements, the feedback neutralization
technique for VCRs is an important tool in achieving
either or both ends.
It has also been shown that FETs with high pinch-off voltage
require larger drain-to-source voltages to produce
drain current saturation. Therefore, FETs with high
VGS(off) will have a larger dynamic range in terms of applied
signal amplitude, while maintaining a linear resistance.
It is advantageous to select FETs with high VGS(off)
compatible with the desired rDS value if large signal levels
are to be encountered."
By large signals, this means reasonable and usable signals in a compressor/limiter. The value you chose, -2.0V is about minimum for good results. Anything lower and you could run into noise/distortion issues.
In designing and building several FET limiters, FETS with higher Vgsoff were more linear, and produced lower distortion for equivalent audio input. I have recently received some dual FET's with Vgsoff of -11Volts! It will be interesting to see how these test vs. other types I've used.[/quote]