My First Working FX Design

[slajeune]

Hi Paul,

if you lower your volume going into the LM386, does the gating / oscillating go away?  If so, maybe you have to lower the input into the LM386.

Thanks,
Stephane.

[Paul Marossy]

Changing the setting on the trimpot to the LM386 section does have an effect on it. I think that I just had it set too high.

[Ansil]

nice man

[slajeune]

Hi Paul,

glad you found the problem!  Nice sound by the way!  Looks to be another great pedal!  Seeing the schematic, the tone control is a simple low pass filter.  Therefore (from my very limited knowlegde) when the tone control is all the way to the treble side, no signal is actually sent to ground (or very little) and therefore, you have a maximum amount of output going out of the tone control.  At least, this is how I understand it.  That's what led me to think about your trim pot!

Cheers,
Stephane.

[Paul Marossy]

Thanks guys.

The 10K trimpot at the input of the LM386 section is there kind of because that part of the circuit is an after-thought and wasn't part of my original design. But, come to think of it, it's probably a good idea to keep it. That way, whatever kind of preamp tube you pop in there, you could adjust the output level to compensate for the lower mu preamp tubes, like a 12AU7 or 12AT7. Life has some happy accidents...