Author Topic: NPN Boost: Loud hum when plugged in, but no signal when activated  (Read 4493 times)

graylensman

I've just built the NPN beginner's project, and (naturally) have a big problem. When I plug in my guitar, all i get is a loud hum - no obvious signal from guitar (i.e., no music when played). When I click the switch, I get no sound at all. But hey, the LED lights up!

Pulled out the multimeter and hit some connections. Here are the values for Q1:
C = 8.85
B = 1.13
E = .08

I'm using an 2N222 transistor, plugged into a makeshift socket. I'm certain the leads are in the right place. I made no substitutions. I haven't yet put the circuit into an enclosure. I examined my solder joints, and I didn't see any unwanted bridges, or cold joints. One oddity: before I connected the LED, I had bypass in the circuit, though no functionality when active.

Thanks to everyone who can lend a hand!

graylensman

Re: NPN Boost: Loud hum when plugged in, but no signal when activated
« Reply #1 on: March 31, 2013, 11:33:16 AM »
okay- well, solved this problem on my own. after a good night's sleep and a morning run, i discovered a few joints that had not been properly soldered (at the switch, and on the output jack). i repaired those, and now i have guitar signal on the bypass, and actually signal when i hit the switch. however, there is a loud pop when the switch is activated, and i get no noticeable change to the signal when the boost is engaged.

time to figure out that problem...

Thecomedian

Re: NPN Boost: Loud hum when plugged in, but no signal when activated
« Reply #2 on: March 31, 2013, 07:33:39 PM »
If you hear the same kind of pop when you have amp gain up to mid level and guitar volume on high, then you're just hearing the normal pop that comes from power being switched on and low resistance. This is normal in such a case, and turning down all knobs of gain or volume before turning things on can defeat that. I think someone, or google, can tell you how to get rid of the "power pop" that comes from switching a pedal on. I don't know that off hand.

As for the booster, is sounds like it might be already in the circuit, and the switch for it is redundant.
If I can solve the problem for someone else, I've learned valuable skill and information that pays me back for helping someone else.