Tremulus Lune - build report and troubleshooting noise question

[shoggoth]

This is only my second build, so fair warning on n00b questions.

Built the pedal off the commonsound schematic on perfboard. Sounds fantastic except for some noise (not a tick or pop) when not playing or when the guitar starts to fade out. I used a homemade LDR/LED combo with a Cds from Radioshack, also I dropped the Fine knob and added the Sym instead. Had to troubleshoot two issues: 1st being that I didn't attach pin 8 of the TL072 to the 9v, and the symptoms were gain pot didnt work, and unit wouldnt trem unless depth was at max. 2nd was no sound after connecting pin 8 to 9v - re-soldered a few bogus looking connections and began working.

My questions on how to troubleshoot the noise issue:
A lot posts I have seen mention adding this or that cap across certain connections, but these all seem old. From what I understand the commonsound schematic already includes a lot of the tweaks to reduce ticking sounds. I wouldn't even say the noise is that bad on my pedal - its certainly usable and you cant hear the noise when actively playing notes, but it does bug the hell out of me that it isnt silent. As a point of reference, when I turn the Depth all the way down, I can still hear slight noise to the beat of the LFO.

So, given that the commonsound schem has these improvements, are there any additional resistor/cap additions someone could recommend?

Also, I read that you should decouple the connections to the power and ground between the audio circuit and LFO circuit.... does the commonsound schem already do this? If not... well, could someone explain to me how to do that? It seems it may decouple the power connections but not the grounds?

[shoggoth]

This is the schematic link: http://commonsound.org/tremulus/tremulusscheme.pdf

[GibsonGM]

Hi Shog:

To further 'decouple' the LFO from the power supply, you could try adding a 100R resistor in series with the power supply to that opamp, and just after that resistor, you place a cap to ground (the bigger the better, 100u certainly, and try to keep leads as short as humanly possible).     That sort of 'buffers' the power supply, so it isn't dragged down by the demand placed on it by the LFO's cycling rate.

Now, that said - that 100u cap at the voltage regulator should be doing this.   Sometimes, LFO/LDR type circuits simply make some noise; some light ticking, or white noise.   You could get pretty fancy by bypassing in a few places with pF value caps to try to eliminate this, or just accept it for what it is ) 

Also check your wiring runs....are they short, only cross at right angles, and don't pass near/over the LFO section?    Are your power wires kept away from signal wires?   All grounds going back to one place on the board, as directly as possible?   These things can be quite important!   You could shield any wiring runs, too, which might help (using shielded wire, with only one end of the shield connected to ground). 

If you have room on the board, I'd say go for the 100R/cap deal, and see how it works out!  If you have wiring runs, try 'chopsticking' them to see if moving them around affects the tick....it really might!  Noise pulses couple into signal wiring very easily... 

[shoggoth]

Gibson - thanks for the advice, perfect explanations for my limited experience/knowledge! This is also great general info for future builds.

When laying out the circuits, I did separate the audio and LFO as much as possible. However, having almost no experience with schem to perf layouts I probably have longer-than-needed wiring runs everywhere (serious rats nest), so that probably contributes to the issue. I have some other ideas on how to change the layout from your advice. It may take awhile but I'll update after I make the tweaks.