gain knob crackle - rrrrrrr!

[burningwater]

Hi yall, new member here. A friend of mine and fellow DIY enthusiast just turned me onto the site. I've built afew effects for myself over the years and think its a blast whenever I can find the time to make something new. I just made my first circuit by taking parts of different overdrives and slapping them together on one board. There is a buffer, transistor boost and opamp side for more gain. Sound good but definitely needs some tweaking to be useable. One thing that's bugging me is that the gain on the boost side makes a lot of noise when I adjust the pot.  I guess because there is dc current across the leads? I guess like the zvex sho cirucit - crackle OK thing? Anyone know of a way to compensate for this. I know it can be done - probably by isolating the pots current, but it beyond my scope of knowledge - any suggestions?

[KerryF]

If you post a schematic maybe we can help 

[markm]

This seems to be quite the topic of discussion lately.
Read the crackle post here and it will explain most of what you're looking for.
http://www.diystompboxes.com/smfforum/index.php?topic=48984.0
Hope this helps.
BTW.....Welcome 

[zachary vex]

heh.  8^)

[any]

I envey your crackle knob.... 

[burningwater]

Thanks, some good suggestions in that link.
Heres another problem -  I essentially put a boost and an overdrive in one box, both wired to the same 9v supply. when they are both on they dont sound as good as they should - like it would to use a separate boost and overdrive with separate power. So I guess my options could be
a: use 2 9v batteries - one to power each circuit- which I really would rather not do
b: use an 18v transformer
c: add a voltage pump circuit to bring the power up to 18v

the problem with b and c is if Im only using one side - say the boost, the 18v may be too much for that circuit.

Is there a way to have an 18v supply but isolate 9v to each circuit separately?

[petemoore]

I essentially put a boost and an overdrive in one box, both wired to the same 9v supply. when they are both on they dont sound as good as they should - like it would to use a separate boost and overdrive with separate power.
  Sounds like you've re-tested it enough to be certain they don't sound as good...and separating/using same PS's being the only thing changed..but also sounds odd because we've been using common rails to supply multiple stages or circuits...All my 8 circuits now have DC jacks only, so, for me, testing this would be a matter of building up a bunch of battery clip to DC Jack adapters, I have enough 9v batteries here...
  Not to battle your finding, but I'm not certain. Maybe we've not noticed or this condition only happens under specific circumstances [like which particular circuits etc..].
  So I guess my options could be
a: use 2 9v batteries - one to power each circuit- which I really would rather not do
  Have you tried a ~100 ohm resistor and 'BFC' ..100uf or so capacitor to filter the supply a bit to each stage or circuit? this has been known to 'iron out' <'flat DC' supplies.
b: use an 18v transformer
c: add a voltage pump circuit to bring the power up to 18v
  the problem with b and c is if Im only using one side - say the boost, the 18v may be too much for that circuit.
  Is there a way to have an 18v supply but isolate 9v to each circuit separately?
  MAX1044 provides ~17.2vdc from a 9V supply [or +/- 9V], then to drop voltage from there you could use an LM317 regulator, this would require a medium sized board...kinda bulky, and would pull a bit more current.
  I would first persue isolating the problem by trying filtering or other preferred method to see if same/same performance conditions using 1, or multiple batteries can be had, starting with a 100ohm resistors between Batt+ and circuit V+'s, followed by a large value caps across the rails...of course those caps will 'add up' ...probably best to wait and see if someone else has more detailed math and such on this subject.

[Ge_Whiz]

If you post a schematic maybe we can help 

See above - read carefully.

[burningwater]

me can read good, no post schem because no have scheme - just  slapped it together

Imagine taking a fulltone fat boost or some similar boost and a TS circuit without the buffers and putting them in one box, then using one 9v to power both with a common ground. I have the switching set up so I can insert either or both parts of the circuit into the signal. Thats basically what I did.

Ive seen some pedals like this like the jekyll and hyde / burris boostiest etc etc

Thanks for the suggestions pete, its a bit above my head though and I dont get how filtering the power supply will regulate it so each side gets the required voltage to sound good.