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So, got a Rivera Knucklehead 55 that the reverb would squeal on both channels after it was hot.
I could duplicate the problem by turning the FX loop on/off quickly with the footswitch.
The switch contact debounce would cause a pulse through the reverb opamp and start the oscillation.
Only with the footswitch, rear panel switch didn't generate enough of a noise pulse.
Put a snubber on the loop footswitch and put it back together.
A couple hours later it was squealing on it's own, same exact oscillation.
Seems to be coming from rear loop board, changing loop from either channel or both changes pitch of the oscillation.
Remove reverb send or return cables kills the noise, turning loop on kills the noise.
I scoped the hell out of the many low voltage power supplies and switching circuits, but could find nothing strange.
Will try different tank/cables later today, didn't think they were the cause since switching the loop on/off initially would start the oscillation.
This schematic is for the Venus 5, it looks to be about the same and is the cleanest of all the Rivera schems I could find.
They use the same topology for reverb & loop and switching it seems for a bunch of their amps.rivera_venus_5_sch (1).pdf
I could duplicate the problem by turning the FX loop on/off quickly with the footswitch.
The switch contact debounce would cause a pulse through the reverb opamp and start the oscillation.
Only with the footswitch, rear panel switch didn't generate enough of a noise pulse.
Put a snubber on the loop footswitch and put it back together.
A couple hours later it was squealing on it's own, same exact oscillation.
Seems to be coming from rear loop board, changing loop from either channel or both changes pitch of the oscillation.
Remove reverb send or return cables kills the noise, turning loop on kills the noise.
I scoped the hell out of the many low voltage power supplies and switching circuits, but could find nothing strange.
Will try different tank/cables later today, didn't think they were the cause since switching the loop on/off initially would start the oscillation.
This schematic is for the Venus 5, it looks to be about the same and is the cleanest of all the Rivera schems I could find.
They use the same topology for reverb & loop and switching it seems for a bunch of their amps.rivera_venus_5_sch (1).pdf
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