Help me understand the Ugly Face

[soggybag]

I have built a these and I like the sound. This has to be one of the all time great "destroy your tone" effects. Total sonic mayhem. My hat's off to Tim Escobedo for thinking this up.

I've redrawn Tim's schematic and added part numbers for ease of discussion. I took the liberty of adding the ROG additions of the two .001 caps on input and output of my drawing. I've also drawn an internal diagram of the 555 from Forest M. Mims III Engineer's Mini-Notebook 555 Timer IC Circuits.



Over all it doesn't look that complex. But it presents an odd use of the 555. Though, it's probably one of the most popular chips of all time, the 555 sees little use for guitar effects.

The 386 is set up as a basic preamp stage. The 555 seems to be set up in the basic Astable circuit. But, there are a few things that I don't get.

First the what shuts off the oscillator when you are not playing. The Threshold control seems to have something to do with this.

Second, the audio output is very strange. From what I can tell it looks like the output is held high at 9V! And then drops to 0V when 555 oscillates. That is pin 7, Discharges to ground as the internal flipflop changes state.

I'm guessing it's C5, R4, R5 and the LDR that set the frequency. From experimentation there doesn't seem to be a great change when changing C5 for a larger value. My guess is that this has something to do with the way pin 4, Reset is being used.

One problem with the Ugly Face is the out put. Which is ridiculously high. I never have the Volume above 25%. I'd like to change this. I experimented with a few things. I tried powering the 555 from a 5V reg. I though I'd need to make some change to the other parts. But this was not the case. Everything worked the same with any further modification. The volume however stayed about the same.

[Seljer]

to fix the volume thing add another voltage divider before the volume control


no idea about why it sounds like it does