Chunk Chunk - No sound

[bgalvao]

Hello I have assembled a PCB of the Chunk chunk Pedal and I have no sound on the out put of the board.
Replacement parts used are the ones suggested in the manual here at madbeans. Used the transistors 2N5457, 2.2M resistor and so on...

So the first thing was to Bias all the 2N5457 to 4.5v on the drains (left most pin if flat face is facing me, correct?) measured against the ground on the board.

The I looked for bridges or bad soldering, soldering looked OK, and I think pots are correctly wired (can attach if you think it will help).

So as it still didn't work my second guess was to build a Beavis board (to rule out wiring) with an audio probe, and look around for the signal.


With the probe I got stuck. I get sound from the Gate of Q1 but no sound from the drain (I should get some sound here, correct?) I get 0V.

Is it a faulty Transistor? I replaced them...still the same... any Ideas?

Is it possible I am killing the transistor by some  problems else where, how can I test the transistor?

Thanks for the help.
Regards,
Bruno


PS. I am new to this building pedal thing although I did have some training in electronics a few years ago...although it is not helping me much . Maybe can point me in the right direction

[jkokura]

If you're getting 0V at the drain of Q1 that means you have a problem with your power. You should be able to bias that transistor to 4.5V. Check T1, C2, R16 and R17 for DC voltage. You should have full power on the 9V side of R16, with a progressively smaller voltage after R16, R17 and then after T1. T1 should give you a variable voltage which you can measure at both Q1 and C2 which connect together at the trimmer.

After that I don't know.

Jacob

[mgwhit]

I'm a bit confused.  You said you biased all of your JFET's to 4.5v, but later you said you got 0v on the drain of Q1.

If you are really getting 0v on Q1 that explains why it is not passing any signal.  If you are able to bias the other JFET's to 4.5v, then it is unlikely that there is a problem in your power section.  More likely a bad trimmer or a bad JFET.  If you socketed your JFET's, make sure they're making good contact (i.e. push down on it or wiggle it while you're testing it).  Or mark the one that is currently in Q1 and swap it with another.  Did you test all of your trimmers before you put them on the board?

If you aren't getting positive voltage on any of your JFET drains, then folllow Jacob's advice and debug farther up in the power section.

I've built the Chunk Chunk with 2n5457's and I like it quite a bit.  I biased my JFET's to 6v as per suggestions here and at guitarpcb.com, but it's really a matter of just getting it where you like the sound.  Not really an issue until you get it fixed, though.  Good luck!

[bgalvao]

Mgwhit you're correct I had them biased had 4.5V on the drains but wrote incorrectly(sorry)...
Just ended doing Jacob's test and found that had bad resistor connection...problem solved it's rockin!! Also one of the 5457's was on off, changed it now all ok!!

Next step box it!

Thanks for the help guys!!!
Regards,
Bruno

[jkokura]

Great Bruno! Thanks for letting us know what happened! Glad I was able to help.

Can't wait to see the boxed pedal!

Jacob

[mgwhit]

Congratulations!  Debugging electronics can be miserable, but it feels great when you finally get it working.

My 2n5457 Chunk Chunk got its first real work out tonight at band practice.  (So far I had only played it at home with a tele through a tweed Princeton!  )  We used it with a two-humbucker PRS through a Dr Z Maz Jr into a 4x12 cab and it sounded fantastic -- Metallica to high-gain alt-rock tones.  I'm under strict orders to bring it back next week.  Definitely does not sound as fizzy as so many of the YouTube Dr Boogie vids do.  Have fun with yours!