Ok, I recently got my hands on some schematics for a distortion pedal, but as it is my first one, I have a few questions about the pots.

For the volume and tone pots, I believe they are supposed to be both audio, if not let me know.

My main concern is the internal trim pots for each section. Should they be linear or audio?

Schematic:

I have seen the screen shot of Audio vs. Linear Pots.In linear taper pots, the change in output as you move the pot linearly from center indent to the max in either direction is "linear".Most audio controls are designed around an "optimal" range of effect on the signal, so it helps to have more control around that optimal range and less at the extremes.

i know the difference between them, linear changes the resistance linearally, whereas audio changes the resistance logarithmically (to ensure setting 5 is half as loud as setting 10). Volume is obviously an audio pot, but that wasn't the question. For the tone control and for the internal trim pots (to alter the clipping of each individual section) i need to know if they should be linear or audio taper.

My guess is that tone and bias would be linear, otherwise all the control will be at one end.

 

The others, audio or log law if you want them variable, but it looks like the ones with a "*" setting are meant to be preset trimmers, when you generally don't have a choice - never seen presets in anththing other than linear.

My guess is that tone and bias would be linear, otherwise all the control will be at one end.

 

The others, audio or log law if you want them variable, but it looks like the ones with a "*" setting are meant to be preset trimmers, when you generally don't have a choice - never seen presets in anththing other than linear.

Thanks so much! I'll post when i finally start and finish the thing (i'm strapped for cash atm XP)

I'm guessing bias could be a preset, adjust on a low signal to avoid cutout - if the control trim range is too sharp, then add a 100k resistor to each end - it may work just as well if you leave out the bias trim and the 1M resistor, as the CMOS inverter input should be pulled into the linear range anyway - if it acts as a "noise gate" on quiet signal, then try adding the bias control, or if you want it to noise gate, use the bias control and take it some way off centre.

 

And definitely, try the assymetric setup of 1 and 2 diodes, that should give an extra zing as it shifts from one sided clipping to two sided - or you could try one silicon and one germanium diode.

 

The CMOS IC is a 4049AE in the original - a 4049UB or UBE should be ok, but avoid "BE" CMOS for linear applications, as they require unbufferred.

http://www.key2study.com/elogic.pdf

 

NB. Doesn't matter that the device is referred to as an inverting buffer, what matters is that the particular architecture is "unbufferred", as B or BE CMOS does not work well in linear use.