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What is this R doing at the fb loop?
Posted: 27 Jan 2020, 11:26
by Enrulado
I know it may be fairly simple, but i'm having some trouble figuring it out ... why is
R23 there?
I guess it's a compression thing, but not for sure.
It's the schematic of a SS Fender Amp ... nice cleans but awful (really, disgusting) distortion channel.
Thanks!!!
https://www.dropbox.com/s/s5xzfbsclir1p ... r.jpg?dl=0
Re: What is this R doing at the fb loop?
Posted: 29 Jan 2020, 14:44
by heaterman
hey!
Not shure, but i guess R23 is bypassing some signal around D3 and D4, so not all of the signal is going through D3 and D4, which means that they clip less.
Re: What is this R doing at the fb loop?
Posted: 30 Jan 2020, 12:36
by Manfred
Compared to a common diode, an LED has a significantly higher junction capacitance.
So my guess is that this junction capacitance in series with the 220k resistor will reduce the gain at higher frequencies as long as the LED and diode voltages remain below their threshold voltage.
If I am right, this would be a very tricky circuit design.
Re: What is this R doing at the fb loop?
Posted: 31 Jan 2020, 07:42
by Manfred
In this essay a diagram is shown with the curve of the capacity as a function of the voltage across the LED:
https://www.edn.com/an-leds-intrinsic-c ... c-circuit/