Morula Build

[Radamus]

Hello.

I just completed my very own Morula. The Link: http://www.aronnelson.com/gallery/main.php/v/Richard-Boop-RLBJR65/album107/Morula_Schematic.gif.html

The circuit does what it's supposed to and it comes up with some very cool sounds. I have run into the problem though of some excessive LFO thumping. The morula has little use for me if I can't use it fast, and the thumping gets louder as the rate gets faster.

I read where nordine explained that changing the 100k R4 to 1M would get rid of a lot of the thumping. Unfortunately, on my build it did not and it also changed the sound of the auto wah and made it throatier and less pleasant. I also tried a 1k resistor in place of R4 thinking it might work the opposite. 1k sounds about the same as 100k. The thumping might be a little bit louder.

Is there any way we can filter out the LFO thumping earlier in the circuit? Anyone have any ideas? I want to make this pedal work with those faster rates.

Thanks
Conrad

[Lurco]

do you have a large electrolytic from Vcc to Vss? or at least any cap across the rails?

[Radamus]

I do not. I built the schematic exactly. How big is big? I could probably spare a 10uf, and I might have a couple 100uf available. You think it's the power supply? Well, I'll give it a shot tomorrow and see if it helps.

Thanks

[Lurco]

100uF should work fine. An additional 100n right at the IC powerpins might even improve things.

[Radamus]

I added a 100uf cap from 9v to ground and it did not help at all. I also replaced R4 with a 1M again to see if that would help. That still changes the tone of the unit, and shuts the LED off, but the pounding stayed constant through all of those changes. I even tried it with my 12v regulated supply, which helped things a little bit, but not a whole lot. It's frustrating, because I can hear the potential of the unit.

I don't think I can fit the 100n between the power pins. As it is, I connected the + end of the electro to where 9v connects to everything, and the - end to where ground connects to pin 3. There's a jumper from pin 3 to pin 8 (or whichever is ground) which connects to the rest of the grounds. It's perfboarded.

Any other thoughts? I think the issue is in isolation here, but this schematic is a little beyond me.

Thanks for the help.

[Radamus]

I audio probed my build hoping that I could understand it a little better and maybe find the source of the thumping, but I did neither. I found that the 100k resistor as R4 really gives the best tonal sound, to my ears. How do people usually get the LFO ticking out of their builds? Also, if someone could briefly explain how this works, that would be awesome.

Not working on this anymore tonight.