Monkbam Pro Audio Marketing Blog

I just fixed one of these amps that I had purchased a month or so back and wanted to share some of the experience. (I do this for fun, remember. I’m not a guy who is going to tell you how to build circuits better). The amp was a exact remake of the AB763 circuit (well, as close as is currently feasible) in a reissue Deluxe Reverb chassis. It was laid out on the traditional fiberboard and looked no different than a real DR from the 60’s, except for new components.

This is the second amp I’ve worked on that had a blown or screwed up reverb transformer. This amp had 2 known problems: the vibrato had a click to it and the reverb was incredibly noisy and just messed up sounding. But it mostly worked and only sometimes would be unusable or intermittent. I thought these issues would be grounding-related or use of wrong components, since it was a new build of a AB763 circuit. That assumption turned out to be wrong.

The vibrato was the first to be fixed – it just needed a new photoresistor thing. That’s it. No secret there. I’ve seen them go bad before, but rarely.

The reverb took me longer. The ground was intermittent when checked with an multimeter, but when I fixed it, the problem didn’t go away. So next, I replaced the Mercury Magnetics reverb transformer with a Mojotone one and while things were slightly better and the intermittent wank stopped, it didn’t solve the noise problem. I bet the previous owner had operated the amp without the tank plugged in and as I understand it, this is bad for the reverb transformer.

I finally noticed that if I picked up the footswitch off the ground, the noise would stop. Specifically, it was a shielding problem I’ve never run into on a Fender amp before.The bottom of these footswitches just have a rubber cover and the switches and wires themselves are exposed when that cover is removed. I covered the bottom of the footswitch with copper foil (the kind you get from StewMac for guitar electronics) and the problem was finally solved. No more noisy verb!

Even though this has never happened in all of the other Fender amps I have, it happened to this Deluxe Reverb. The guy I bought it from said that the boutique amp maker and some other techs weren’t able to solve the problem, so yeah me. But really – the problem was worse on a concrete floor as opposed to a second level wood floor, so it’s possible they didn’t hear the problem in the right environment. Either way, I added this simple shielded footswitch trick to my own knowledge through trial and error.