MORLEY PRO SERIES WAH ...Crackle? on breadboard!..

[deadastronaut]

hi guys,

just breaded this wah, but it crackles when i whack my guitar (humbuckers) .. hmmmm..

its all working apart from that...hmmmm.....excuse my ignorance but whats that symbol mean on the 1M input....9v  v/2 ?..... ....i just stuck a 1M there anyway....just thought it might have something to do with
why its crackly...like sort of misbiased or something...

oh yeah i used 16v electro's instead of 50v's....

http://www.morleypedals.com/pwa-iies.pdf

[slacker]

The point marked as V/2 should be half the supply, so 4.5 volts. I would connect the top of R32 to pin 3 of the opamp, the voltage divider made out of R3 and R4 make that roughly 4.5 volts. It's possible that point is supposed to be marked V/2.

[deadastronaut]

cheers ian...

righto...so they didnt draw the voltage divider on there then...

i'll give it a go....i knew there was wasnt something right with it....thanks again man!..


edit: so the 1M isnt the usual pull down then?...hmmmm...

edit: nope!.....still crackles..tried another opamp..same!....checked all board...weird!..

its working, but it crackles still when hit hard!!!!...hmmmm

[Govmnt_Lacky]

Hey Rob,

Something smells fishy with this.... 

It almost appears that the scheme you linked is only a PARTIAL schematic. If you look at the parts list on the bottom left, it lists L1, L2, L3, and an LDR1 that is NOT on the schematic.

I could be wrong however, it looks like you need to find another piece of the puzzle perhaps...

[slacker]

I'd try and figure out where the crackle is coming from, shouldn't be the first stage that's just a buffer, but you can test that by listening to the signal at the point marked BYPASS.
If the crackle is coming from the second stage then try making the 390k resistor smaller, that will reduce the gain which might stop it distorting.
Also measure the voltage at pin3 of the opamp and make sure you've got about 5 volts there.

[Earthscum]

I have a stack of these schems from about a year ago. I came to the conclusion that they are just hack-togethers because the pedals are all fairly close. Take the Vol/Wah pedal, copy just the Wah section, and that's how Morley did it, in a nutshell. I just think that the schem wasn't looked over before being just thrown up.

I have boarded a couple of these... easy to do, and kinda fun. My guitarist has one that needed some loving. The only times I've ever got crackling is because I was putting voltage across a pot. BUT, in one case I had an LDR that acted like a microphonic tube, only in that circuit. I put others in, and it quit, but that one LDR always crackled. I think it's the same LDR I used in my Toe Jam Wah, and it has no problems, actually jammed with it for a 4-hour session yesterday, not a single crackle. For some reason, that LDR would freak out in an op amp circuit.

[deadastronaut]

@gov lacky...hmmm you may be right!..

@ian. cheers i'll take a few measurements and try it...

@earth, yeah ive tried a few others that worked fine...pretty good wahs...

i'll give this a few more go's, if no joy i'll try another that i know works for sure!...just thought i'd try a different inductorless one for a change..and mess with the range etc...

cheers guys.

[Earthscum]

You may try a small cap to ground right after the 39k resistor (maybe 1n-330p?).

[deadastronaut]

aha....changed the ldr...all ok now!...so you were right!...never had that prob with ldr's before!....

i also put a 100k vol pot on the out....and took out the b10k and resistors...the output on this is really loud...

much better...really clean wah now!...now to mess with the range/depth of it...cheers guys!...