Twin Reverb 65 hiss (tremolo related)

[goldenGeek]

I just scored a Twin Reverb (AB763) from around 2012 with a few minor issues. It was mostly tube related but there seems to be some hiss related to the tremolo. Even if I pull all pre amp tubes (only leaving in the PI tube) there is quite a bit of hiss (kind of mid heavy hiss) introduced when you turn ut the intensity. Looking at the old AB763 schematics I can only see the roach and the intensity potentiometer present that can make this hiss. But upon opening the amp there is no roach installed, instead there's an extra PCB wired to the four pads where the OP1-component should be with lots of tiny components (digital tremolo?). Does anybody have experience with this board? Is it possible to replace the board with a roach?

[sluckey]

I'm not familiar with that. Does it look like a factory job? I have a TRRI from around 2006. It has a roach.

[goldenGeek]

Yes it looks like it’s factory, the board says fender and tremolo. There is also a psu board way over by the power transformer that’s feedeing this board.

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[sluckey]

Wow! That's a radical change from the simple AB763 circuit. Are you sure it's an AB763? Got a schematic?

[goldenGeek]

Wow! That's a radical change from the simple AB763 circuit. Are you sure it's an AB763? Got a schematic?

The tube layout sticker in the cabinet says AB763, the previous owner bought it new around 2012. The main PCB says Fender 1999-2009.. I found some post online about this "digital" tremolo on some European Fender amps, and I'm in Europe so... I don't know, the PCB clearly outline the placement for the roach. is there some voltages at the roach bulb end around that I can double check against?

[sluckey]

It's a Fender Twin Reverb PR186. I found some info online but no schematics. I only looked a few minutes. You can probably find voltage info by looking at some real Fender Twin Reverb AB763 schematics.

[goldenGeek]

It's a Fender Twin Reverb PR186. I found some info online but no schematics. I only looked a few minutes. You can probably find voltage info by looking at some real Fender Twin Reverb AB763 schematics.

Thanks, when I googled that model number I found this thread that might help me further (haven't read it yet, but someone else linked to it for conversion to the normal optocoupler) https://music-electronics-forum.com/for ... sue?t=5756

[goldenGeek]

So I read the thread over at music-electronics and I managed to remove not just one but two PCBs and replace it with a single LDR.. The amp is not hissing any more when the intensity is turned up. There was some other colors on the cables in my amp than in the link (if someone else is reading this in the future), but it was fairly easy to understand. There was two brown leads coming from the transformer and they connected to the yellow and orange lead going to the main PCB.

Now I’m off to do some more mods I found on the same forum for even more noise reduction

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