I seem to think with this type of connection Manitunc has made introduces the impedance of the tube amps input stage into Dussun loop through the Dussun preamp section. This would seem to be the source of the overload to the Dussun preamp stage.Hi Ed,
Typically tube amps have high input impedances, so its presence most likely does not result in a significant load on the preamp out signals from the Dussun. Even if it did, it would most likely just result in a small effect on sound quality, not an overload that would result in oscillation or shutdown. Depending on the output impedance and other aspects of the design of the circuit that drives the preamp outputs, even a dead short on that point is unlikely to cause those effects (although it would reduce the volume of what is heard to zero or close to it).
What is the point of pre/power RCA jumper threw if you need to use the "Y" cable?The y-adapter allows the tube amp to be connected to the preamp out signals at the same time as the preamp out signals are routed into the power amp section of the Dussun. When the Dussun is the only amp being used, the jumpers that are normally in place (instead of the y-adapters) allow the preamp out signals to be routed into its power amp section.
I did ask Manitunc about the line out RCA's being attenuated from the volume control or if they only feed a constant signal.I would feel pretty certain that the volume at the "line out" jacks is not varied by the volume control, while the volume at the "preamp out" jacks is varied by the volume control. The "line out" jacks are probably the same as what are sometimes referred to as "tape out" jacks.
Best regards,
-- Al