Curing hiss: Fender Custom Vibrolux Reverb

[Dave Curtis, dB AudioTech]

This is a '95. PCB (PITA) that has had all resistors in the signal path (and a few others) changed to metal film. I've added a feedback loop (the PCB was set up for it and swapped the PI tube for a 12AT7, but the owner would like it as quiet as possible and it still has a bit of hiss, although it's reduced considerably.

Any thoughts?

[martin manning]

http://www.tdpri.com/forum/amp-centr...-vibrolux.html

Scroll down to post #17 for some relevant info.

MPM

[Dave Curtis, dB AudioTech]

Thanks! It seems I've seen this before somewhere...

[overlook1977]

Here is a demo of my CVR after I had it modded. It's quiet and sounds great now.

Fender Custom Vibrolux Reverb with Mark Moyer Mods - YouTube

[clyde1]

No hum, no hiss. I was unable to do the Mark Moyer mods with the feedback loop because for whatever reason, there was a nasty parasitic on both channels. Tonestacks are AB763, no tapped pots and I lowered the gain to clean up the amp at the customer's request. I think it sounds a lot better than orginally designed.

[Chuck H]

That's a lot of work. Almost certainly improved the ground scheme. If you swap the OT primary leads the amp won't oscillate when you employ NFB.

[clyde1]

Funny you should say that Chuck. I did swap the secondaries and got the dreaded positive feedback howl. My thinking was if that didn't change the polarity then swapping the primaries would result in the same scenario, plus they were buried under the heater wires and my referencing resistors. Laziness I guess. There was a problem with the board that I couldn't trace so we decided to hand-wire, always the better option.