White Noise - Very loaud in backgound of effect

[killerkev]

Howdy!
Looking for some suggestion here.....I've build two Big Muff Pi's, One is a Triangle style and one a Ram's Head. I basically copied the traces from the original which are available on the net and etched the boards. In the end, the Ram's Head sound good but the triangle has this unbearable white noise coming from it. Of course the Ram's has some white noise but nothing like the other one. I compared them together by A/B them with the guitar volume down all the way. The triangle is unbearably loud white noise. I changed transistors, nothing changed. I took out the electrolytic caps and replaced with film, still no good.

What is a common cause for white noise in a situatio like this?

[killerkev]

Schematic is on this link at the bottom of the page:

http://www.singlecoil.com/triangle/triangle.html

Transistor voltages are:
Q1                 Q2                  Q3                  Q4
E- 0.01            E- 0.03            E- 0.03           E- 1.11
B- 0.65            B- 0.64            B- 0.63           B- 1.70
C- 5.67            C- 4.17           C- 3.89           C- 5.26

[killerkev]

The schematic I am following with component values closely follows this link below:

http://www.kitrae.net/music/Images_Secret_Music_Page/KITS%20V1%2066-11%20SCHEMATIC.jpg

I does omit the ceramic cap in the first stage (C10,. 500 pf), I'll try putting one in there to see if it quiets down.

Still looking and hoping for suggestions!

[gritz]

Hmmm... that cap will reduce the gain quite considerably above the middle frequencies, but you say the hiss is "unbearable". Are you powering it from a battery, or a wallwart? If you're using a mains power supply try hooking up a battery to see if that makes a difference.

Does the hiss reduce considerably when the sustain is turned down to minimum? If so then the cap will make a difference (although it does seem to be a tad big, but I'm not a muff guru...).

Let us know how it goes.

[killerkev]

I had powered it with a battery. Yes, the noise increases as you turn up the sustain also the volume pot which I guess would be expected. The effect sounds good but the white noise in the backgound is way loud.

[R.G.]

My order of suspicion on this one is
1. Cold solder joint. Reflow/solder every solder joint with some fresh rosin-core solder til they are all smooth and shiny, not grainy or dull.

2. If that does not fix it, I would suspect ultrasonic/RF oscillation. Check wiring, check grounding, and if there is no power supply bypassing on the board, put on a 22uF to 100uF/25V electro cap with a 0.1uF *ceramic* cap in parallel across +9V to ground.

3. If the two aspirins don't help, call back. It is possible that you got one of the very rare bad resistors or caps, but this is incredibly unlikely compared to the two above.

[killerkev]

Thanks for the suggestion R.G. will try it out tomorrow evening. One thing I didn't mention was that I made two of each - the triangle and Ram's head. Both Ram's head work fine yet BOTH triangles are plagued with the same horrible white noise. Maybe I have a problem with this particular board? Just throwing things out there, possibly the traces may have a problem? Etched too thin? No solid? Could this be a cause? Just brainstorming....

[R.G.]

The schemo looks to be blissfully barren of decoupling.  While board etching can cause many problems, I don't think that's what's happening here.

I'd still go with the same diagnosis and recommendations.

[killerkev]

OK R. G.
I hit every joint on the board, switch, pots and jacks. All shinny joints. Put a 47uf electro with the ceramic suggested in parallel from power to ground. I await tomorrow to test. Can't do it tonight since the kids are a sleep! Looking forward to report.

Since you mentioned decoupling,  on the schematic, C3, the electro between the tone pot and Q4, shows the positive side of the electro facing the tone pot. Measuring the voltage on each side of this cap shows that the voltage will vary on the side of the cap pointing to the tone pot when adjusting the pot, ranging from 0.5 to 3.2v while the othe side stays somewhat constant, depending on how fast the tone pot is adjusted, at 1.6v. Will have to listen when adjusting the tone pot to see if there is any reduction in noise. I did change his electro cap to a non polorized film cap with no difference though.....

[killerkev]

Forgot to add... Thanks much for your suggestions! Much appreciated!

[killerkev]

Well, A big Bummer. The touching up of solder joints did not work along with the caps from 9V to ground. Still loud crazy white noise