can transistors become microphonic?

[G.G.]

hi guys,
I built up a fuzz face recently with some MP38A's and I'm trying to track down some michrophonic behavior when the pedal is on. I first noticed it when I accidentally bumped the pedal with my foot and it made a really loud popping noise. So I started tapping around on it, the jacks, DC jack, stompswitch, enclosure, etc., thinking it might be a bad solder joint or something but wasn't able to isolate where the issue is. I can get the popping sound by tapping pretty much anything on the outside of the pedal. I suppose it could be a cold solder joint somewhere but was wondering if it's possible for transistors to be microphonic? Any ideas?

[midwayfair]

Possible but rare. Ceramic caps more often.

Reflow your solder joints. Especially if your transistor is in a socket.

[Ralfg]

I had a similar thing happen to me once. The problem for me was that the ground connections on the jack were loose. Once I reflowed those the problem went away. I was quite confused because no matter where I tapped it would make a popping noise. Crazy it was the jack!

[WormBoy]

Faulty grounding could indeed cause noisy behavior, at least when it is noise just by touching a supposedly grounded part. If you can hear tapping on the enclosure through the amp, but not a soft touch with the fingers, it would appear to be a microphonic component.

I recently had a faulty ground connection in a guitar; it relied on grounding through the pickguard shielding, but apparently that was not such a good idea. After time, the connection became poorer and the guitar became noisy to my touch (in a different manner than I intended  ).

[G.G.]

good call on reflowing the solder joints, that seems to have fixed the issue. I think it was a dodgy solder joint on the DC jack, and a couple lugs on the stomp switch that looked kind of crusty.

thanks for the suggestions!

[brianq41369]

Any good Hfe on those transistors? I had a good bit of leakiness on a lot of 50 last year. readings all over the place.Mine were pretty noisy?  a smallish capacitor across base & collector usually quiets those noisy ones somewhat? But in your case it really does sound like a dodgy ground connection.


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