Author Topic: What is this cap doing here anyway?  (Read 2063 times)

armdnrdy

What is this cap doing here anyway?
« on: May 01, 2015, 09:55:18 PM »
I threw this in the Foxx phaser thread but....it rolled down the line unnoticed....so...I'll try again.

I have a question about the voltage divider coming out of the LFO. (R21, R25, C12)

What exactly is C12 doing? and is the value critical?

The answer to question #1 probably answers question #2.  icon_wink


I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)

Digital Larry

Re: What is this cap doing here anyway?
« Reply #1 on: May 01, 2015, 10:14:28 PM »
Off the top of my head, it AC couples the resistor divider so that the LFO output signal amplitude is halved (compared to the op-amps output pin) without shifting its DC point.
Digital Larry
DSP tinkerer and former transistor twister

armdnrdy

Re: What is this cap doing here anyway?
« Reply #2 on: May 01, 2015, 10:28:53 PM »
Ahh...Thanks for that Larry!

That makes sense!

I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)

PRR

Re: What is this cap doing here anyway?
« Reply #3 on: May 01, 2015, 10:56:02 PM »
> the LFO output signal amplitude is halved

Right; but 0.47u+100K is 3.5Hz. This suggests the voltage is cut-down for the faster speeds, but maybe not for the lowest speed.
  • SUPPORTER

armdnrdy

Re: What is this cap doing here anyway?
« Reply #4 on: May 01, 2015, 11:25:29 PM »
Thanks for that Paul.

The schematic is from the model 1482 Phasing Pedal that Foxx made for Sears but...I'm working with gut shots (no trace side images) of the Foxx Foot Phaser Studio model 7. There isn't a mylar cap anywhere in the vicinity of the area in question.

There are a few electros in the area that I cannot identify the value of.

Can a polarized cap be used for C12?
I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)

Fender3D

Re: What is this cap doing here anyway?
« Reply #5 on: May 02, 2015, 07:15:22 AM »
+1 on what Paul said,
it works as C13 in M117 or C20 in MicroFlanger...
In these circuits cap is polarized because of the higher value, but you may use whatever you want..
"NOT FLAMMABLE" is not a challenge

anotherjim

Re: What is this cap doing here anyway?
« Reply #6 on: May 02, 2015, 08:15:34 AM »
You can get .47u electrolytic, so yes, it could be one of the polarized ones you can see.

I think it makes a lot of sense with pedal control to automatically cut modulation depth as speed increases.
Croeso i Diystompboxes.

There is no aspect of human endeavour that cannot be improved with cheese.

armdnrdy

Re: What is this cap doing here anyway?
« Reply #7 on: May 02, 2015, 09:28:23 AM »
Thank you for the replies Federico and Jim.

Before I posted the question, I looked around the net. The only thing I came up with (Zobel network) had nothing to do with this application.


I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)