Big Muff Rams Head white noise problem

[oliphaunt]

I just built 2 Ram's Head Muffs on GGG circuit boards.  They both have some white noise in the signal but one is quite tolerable, in the other the noise is very loud.   The effect works and the distortion sounds great on both circuits, I just have the noise issue with one of them.  Voltages are basically the same on the transistors on the two units.  My audio probe shows no noise at the collector of Q1, then some noise at Q2 and lots at Q3 and 4.  Should I replace Q2 or is there something else I shold look at first?

(BTW, I have built the Rams Head on my breadboards multiple times and now on 2 circuit boards.  The voltage on Q1 is consistently around 7 volts, way outside of the normal spec for a Muff, but it appears this is normal for a RH?)

[R.G.]

If you built them from the same kinds of parts, you probably have a noisy transistor in the noisy one.

If it were me, I'd replace the transistors in the noisy one with 2N5088s. While you're at it, put a reverse biased silicon diode, like a 1N4148 across the base emitters of the transistors. This has no effect on operation, but makes it impossible for any circuit condition to reverse-break the base-emitter. Reverse breaking a base-emitter *permanently* increases the noise of the transistor in normal operation, as I noted in "When Good Opamps go Bad" at GEO.

[oliphaunt]

Thanks RG. 

The culprit turned out to be a noisey Q1, a NOS 2N5133.  I socketed Q1 and Q2 and tried a variety of transistors.  I  breadboard tested about 6 of the 8 5133s I had, but I should have tried them all.  I settled on the 2N5133 as my transistor of choice from my breadboarding experiments, but I had not tried some low gain 2N2369A I have laying around.  They sound almost as good so I put one of those in there for now.  I am definitely finding I prefer warmer, low gain tranistors compared to the higher gain 2N5088 and 89 in the RH Muff.

[R.G.]

One man's fish is another man's poisson.

Enjoy!