What is this R doing at the fb loop?

Stompboxes circuits published in magazines, books or on DIY electronics websites.

What is this R doing at the fb loop?

Postby Enrulado » 27 Jan 2020, 12:26

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!!!

Image
https://www.dropbox.com/s/s5xzfbsclir1p64/Fender.jpg?dl=0
Enrulado
 
Posts: 3
Joined: 02 Dec 2007, 00:06
Location: Argentina
Has thanked: 2 times
Have thanks: 0 time

Re: What is this R doing at the fb loop?

Postby heaterman » 29 Jan 2020, 15:44

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.
heaterman
 
Posts: 23
Joined: 27 Jul 2017, 09:44
Has thanked: 7 times
Have thanks: 20 times

Re: What is this R doing at the fb loop?

Postby Manfred » 30 Jan 2020, 13:36

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.
FB_Resistor.jpg
You do not have the required permissions to view the files attached to this post.
Manfred
Transistor Tuner
 
Posts: 1023
Joined: 05 Apr 2009, 00:42
Has thanked: 1087 times
Have thanks: 695 times

Re: What is this R doing at the fb loop?

Postby Manfred » 31 Jan 2020, 08:42

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-capacitance-works-in-a-650-mv-lrc-circuit/

For this message the author Manfred has received thanks:
bmxguitarsbmx (08 Feb 2020, 18:07)
Manfred
Transistor Tuner
 
Posts: 1023
Joined: 05 Apr 2009, 00:42
Has thanked: 1087 times
Have thanks: 695 times


Return to DIY Stompbox designs

Who is online

Users browsing this forum: No registered users and 1 guest