Fetzer/Ruby Motorboating Problem

[Erich F]

I’ve searched the archives and still have not found a solution. I need some help. I’m not sure I’ve got a handle on the concept.

I added the Fetzer to a Ruby amp that I had perfed. I installed a switch to select between the normal Ruby buffer and the Fetzer. It works great with the normal buffer but I get a motorboating sound in the Fetzer mode. The mottorboating is worst when the FET is accurately biased. I’ve supplied power and ground to the Fetzer by tapping into the rails on the Ruby. I’m using a 9V battery (more like 8.6V actually)

I have increased the power supply filter on the Fetzer by paralleling a 220UF cap with the 22Uf cap, and this slowed the motorboating down a lot but the clicking is still there. I also reversed the input pins 2 and 3 on the LM386, but to no effect.

Is there something else I should try? Thanks in advance for any suggestions.

[PB Wilson]

My Ruby amp motorboats when the battery is low. It seems to pick up speed as the last bit of life is drained from the 9V. A quick swap with a fresh one may fix your problem. I hope it's that easy.

[Erich F]

I'll certainly try that when I get home tonight. It's odd that it only happens when I switch in the Fetzer and not with the normal buffer. I suppose that now that I'm providing power to both modules, the current draw would be greater. Thanks for the advice.