Big Muff Pi White Noise LOUD Background, Possible Causes?

[killerkev]

This is a Ram's Head with PnP trannies in it.   A very loud white noise background hum comming from it.  Voltages from all four trannies look typical for a muff.  Seems to show itself in the second stage and of course more  in the third stage etc...Possible causes?

[R.G.]

Most to least likely:

- bad solder joint
- self oscillation at RF
- RF pickup
way, way down the list is:
- overcooked transistor, bum resistor or cap, cracked component lead

Retouch all the solder joints and clean flux off the board with alcohol.

Hmm... it just struck me, you said "PNP". You didn't make a PNP Muff with negative ground, did you?

[killerkev]

No, the battery leads are hooked up properly, positive to ground, negative to power source.  The noise does sound like radio frequency since you mentioned it.  I'll go and hit each and every solder joint and clean up the board and report back.  What would make the pedal self oscilate?

[killerkev]

Well, I've retouched every solder joint, traced each trace, and retouch all off board points. Cleaned up as much as the left over flux as possible with rubbing alcohol.  Plugged it in and no good.  I do get the effect but when your not playing it this Loud white noise is blaring through.  Any suggestions?

[R.G.]

Try a ceramic cap from V+ to ground. Do you have a decoupling electro cap from V+ to ground?

[killerkev]

I put a 47 uf electro between the power to ground and no change.  I also put a 100 pf from the effect input to ground, I've read somewhere that this could help reduce RF. But in the end, still no change. When you say V+ your refering to the power right? This pedal only takes a 9 volt battery and there is no port for a power adapter.

After probing the circuit, you can start to hear some noise (little) after Q2 collector.  The noise is very loud after the third transistor's collector.  Now here is something that may be of interest.  After probing I noticed that the noise was very loud on the last transistor's emitter where all the other Q's emitters were silent.  does this shed some light?

[killerkev]

After comparing this "noisy" muff to another ram's head, I found that using an audio probe doesn't help shed any light. They both give the same "noise" when probing so i guess what I said in the last post doesn't offer any help.  Any other suggestions before I have to start swapping out components?

[theehman]

I'd guess you've got a noisy transistor somewhere.  Start with replacing Q1 and work on down the line.

[killerkev]

Tried it with no success, still this loud white noise in the background.  I started swapping out capacitors, diodes, and a few resistors around the second stage but no change   I'm really not looking forward to changing every component! What would really suck is if I did that and the noise was still there! Could there be something with it being PnP?  I've never experienced this noise with othere PnP muffs before but I scratching my head here.  Help!

[theehman]

If you don't want to lift transistors, lift one leg of the cap or resistor between each stage.  You could also cut the trace w/ an exacto and solder back over it.  Eventually you'll find the noisy stage.

[killerkev]

Well, like I said before it's difficuilt to pinpoint the source of the problem with an audio probe. I have a healthy ram's head here that I'm comparing it to. The both seem to sound alike as I probe around each stage of both pedals. Of course when I clip on to the output jack of each the PnP is riddled with white noise.