Tremolo footswitch problem

[cgharrison]

I've got an Ampeg J20 jet, and I recently decided to convert it from a brownface Deluxe type (the J20 is very close to the 6G3 circuit) to a 5G9 Tremolux. All is well, except when I try to use the tremolo footswitch. Every time I plug into the footswitch jack, I hear a loud motorboat/jackhammer sound that gets even louder when I hit the footswitch. I can't really tell if the louder sound comes with the tremolo engaged or off - the noise is too loud. I've gone over every solder, replaced the trem caps, and double checked all my wire runs. Any brilliant ideas as to where the problem might be coming from?

Here are some links to schematics/layouts:

J20
http://www.prowessamplifiers.com/schematics/images/J20_Schem_w_transformer2.pdf
http://www.ampeg.com/products/diamondblueguitar/j20/images/wiring_LG.jpg

5G9
http://www.davidsonamp.com/sf/images/tremolux5g9.gif
http://www.thevintagesound.com/ffg/schem/tremolux_5g9_layout.gif

6G3
http://www.thevintagesound.com/ffg/schem/deluxe_6g3_schem.gif
http://www.thevintagesound.com/ffg/schem/deluxe_6g3_layout.gif

Thanks!

 

[Ht @ Clipper Amps]

Does the tremolo work properly when you bypass the footswitch? In other words, see if you can get the tremolo working without using the footswitch. This would give you a good starting point.

 

[Silent Sound]

It'd be hard to tell without actually hearing the sound your describing, but whenever I've had a motorboating sound in one of my amps it was due to a failed capacitor somewhere. This may not be true in your case, but I've come across this a few times myself and each time I traced it down to a failed capacitor. In any case, I'd check the other components first, as they're easier to test with a VOM than a capacitor.

I would take HT's advice and see if the problem lies in the tremolo circuit or the footswitch for the tremolo circuit first. Get an idea of where the problem is coming from. Then work your way from there. Electronics troubleshooting is all about eliminating possibilities. Sometimes to know what's not working, you have to know everything that is working.

 

[BassHog]

Does your jack for the Trem have a very good ground connection? How about the ground wire in the footswitch cable/plug. I have had this problem in one of my old Sunn amps and it ended up being that the trem footswitch jack made it's ground connection mechanically using the jack bolts to hold the ground tab to the chassis. These bolts had loosened over time and oxidation had formed between the chassis and the jack, causing there to be no ground connection.

 

[Keyser Soze]

What specific changes did you make (if any) to the original trem circuit?

Does the trem work when the FS jack is empty?

 

[cgharrison]

Thanks for the responses guys.

The trem circuit works perfectly without the footswitch. The second I plug in the foot switch, I get a jackhammer sort of sound. The only change I've made is dropping the value of the 1m resistor coming off of the right leg of the depth pot.

I've tried swapping out the three trem caps, and the 2 input caps, with no improvement.

I'm thinking my next step is to swap out the rest of the caps. Any chance it could be a filter cap or grounding issue?