Problem with bi amping speakers

What am I doing wrong?

Good question. Nothing that is immediately obvious to me.

If you have a multimeter available, what I would suggest for starters is that you disconnect the speaker cables from the speakers, and with the jumpers removed verify that no continuity is present between the + terminals of the lows and the mid/hi's, AND that no continuity is present between the - terminals of the lows and the mid/hi's.

Also, does the Dussun by any chance have speaker outputs that are balanced, so that the negative output terminal has a signal present on it, rather than being connected to ground? If you are not sure, and you have a multimeter, see if continuity exists between the negative speaker output terminals of the amp and the ground sleeve of any of its rca input connectors (while nothing is connected to the amp).

I assume, btw, that when you referred to "preamp in" on the Dussun you meant to say "power amp in." Also, as you probably realize, if the gain of the Nobis does not closely match that of the Dussun, or cannot be made to match via a gain adjustment provision if it includes one, a tonal imbalance will result.

Regards,
-- Al

Guys, the Dussun normally has a jumper connecting the rca output jack of its preamp section to the rca input jack of its power amp section, for each channel. What Manitunc has done is to replace that jumper with a y-adapter. That maintains the connection that is normally provided between those jacks by the jumper, while also allowing the inputs of the other amp to be connected to the preamp out signals. All of that is correct.

My guess, assuming that no shorts were introduced by any of the cables or connections, and despite the fact that the speaker supposedly can be biamped, is that the low frequency and mid/hi frequency parts of the crossover are not completely separate, and a path between the outputs of the two amps somehow exists through the speaker. Which is why I suggested the multimeter measurements in my earlier post.

Regards,
-- Al

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

Let me ask you this, if the jumpers are removed this disconnects the integrateds amplifier power output so hence the need for the "Y" cable

Yes. If no jumper and no y-cable were present, no signal would be going into the power amp section of the Dussun. Presumably the purpose of having a removable jumper between preamp out and power amp in is to allow the Dussun to be used just as a power amp, in conjunction with a separate preamp or other front-end component.

Best regards,
-- Al

12-21-11: Manitunc
So, if everything is hooked up as I say with no shorts, then you say the only cause of my problem could be a connection between the woofer and the mid/high in my PSB Golds.

More precisely, it's the only one I can think of :-)

Best regards,
-- Al