Need help with guitar pedal noise mod

[AMelbye]

Hi, I have this great sounding wha pedal (snarling dogs whine-o). the problem is it's too noisy. I guess all pedals have a bit of hiss, but i'd like to get rid of it, at least to some degree.

I'd like to find the noisy components and replace them, rather than just replacing everything, so I've borrowed a neutrik A2-D, which is a great peace of gear that does pretty much anything you'd want it to. It does a load of stuff, including THD measurement, oscilloscope, freq response analysis using sine wave sweeps etc.
Now how do I do this? where do I start?

I have taken some pictures, and will link to them as soon as I've uploaded them to somewhere...

Now there are three transistors in there. they are:
2x C9014 - C021
1x K30A - Y OH

I assume they are junk. how do I determine suitable replacements?

[AMelbye]

[bipedal]

Yeah, wahs in particular can be among the noisiest pedals.

Can't offer any help on how to use the A2-D to diagnose things, but replacing the resistors with metal film equivalents might help a little bit - less thermal noise.

Notice any difference when running a battery vs. wall wart power?

[AMelbye]

ok, I'll look into changing the resistors. I have however seen loads of gear using these 'regular' resistors, so I'm sure that's not the main source of the problem

There isn't any audible difference between using battery and wall-wart. I don't have a battery around at the moment, so I can't measure the difference, but the noise level measured by the A2-D is -89dBq (unweighted) with the pedal swithced off, vs -54dBq with the unit switched on. that's 35dB of additional noise, which I think is an awful lot.

To compare, my sansamp (which is considered to be a noisy distortion pedal, barely anyone uses it without a gate) sits at -60dBq with all the settings flat (just about enough gain for playing some serious metal) -55dBq with the gain all the way up (more gain than you'll ever need)

There's a data sheet for the C9014 here: http://www.futurlec.com/Transistors/C9014.shtml

for tje K30A this was the closest I could find: http://www.alldatasheet.com/datasheet-p ... 30ATM.html

[okgb]

yeah , the wah being a hi gain boost filter with a narrow bandwidth ,
one might expect some noise from the boost , if this one more than others
then you'd think it the design and not so much the components .

I think if you can find the schematic , some of the more knowledable here
can help more , does it work any better with a buffer or booster used
ahead of the wah ?

I suppose you can look for low noise equivalents for the transisters

[AMelbye]

yeh, low noise equivialents would be great, if I knew how to pick the right ones.

There's no scematic available for the unit, but I guess I could draw one up myself if I get the time for it...

I realize that changing components may alter the sound as well as getting rid of the noise, but I'm absolutely willing to give it a try, since the pedal is fairly useless in its current state...

[gutsofgold]

In my limited experience carbon film resistors are just as quiet as metal film. I would start with getting some information on any transistors in the circuit and looking up the modern (if its an older tranny), low-noise equivalent. Those caps are fairly high quality so no worries there.

[AMelbye]

how do I decide on suitable replacement transistors? What features do I look for? which specs need to stay the same?

I'm not sure if I have managed to properly identify one of the transistors. is there a way of measuring its specs?





placing a buffer ahead of the pedal doesn't make much difference