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Problem with bi amping speakers

I tried to biamp my PSB Stratus Golds tonight using a Dussun V6i 150 watt SS integrated amp for the woofers and a Nobis Contigore 40 watt tube amp for the mids/highs. The contigore is similar to a Dynaco ST70. I used the preamp out on the Dussun and ran one cable to the preamp in on the Dussun and the other cable to the Nobis. Took the jumpers off the speakers and connected both amps to the respective terminals using the 8 ohm output on the Nobis.

When I turned on the amps, they both worked well for about a minute. Then I heard what sounded like feedback from a guitar amp, then ok, then feedback again, then the Dussun amp tripped. the Nobis kept playing. The feedback sound lasted for about 2 seconds each time.

Took it back apart, and both the Dussun and Nobis work fine alone. So what about my connections would cause this problem. I use a 2 male phono to a single female phono. One male end goes in the preamp out on the Dussun, the other male goes in the preamp in on the dussun, and an interconnect goes into the female end of the connector. There is one of these for each channel.

So, what am I doing wrong?
manitunc
marakanetz's avatar
marakanetz
5,473 posts
 
Your set-up as I understand is missing description about Y-connectors that should connect Dussun's poweramp section to Dussun's preamp and than to Nobis.
If you did not follow it than certainly your Dussun will have loud guitar-amp feedback.
Another my guess(assuming that Y-connector is present) is that load impedance of disconnected woofer is too low that causes the amp to oscillate.
manitunc OP
795 posts
 
The PSB Golds are set up for biamping and there are instructions for hookup in the manual which I followed.

The tube amp was sitting on the floor for this test, and the integrated was about 5 feet off the floor, directly above.

I used a y connector, two males to one female. The male ends pluged into the preamp out and power amp in on each channel and the female connector was attached to an interconnect running to the tube amp's input.

The PSB woofer does go down to 2 ohms at about 100hz, but I use the same Dussun integrated normally with these speakers without a problem. I was just trying to add the tube amp for the mid/hi to see how it worked, and maybe sweeten the sound.
apachef1
164 posts
 
I went to the Dussun website to see the amp you have. I'm not sure I understand the "Y" phono connections you are using? The website had very good photos of the rear of your Dussun so I will ask you a few ?

I did see an "line out" on the back next to all the RCA inputs, Is this attenuated from the volume control or does it provide a constant signal say for a tape deck?

I'm not sure I really understand the use of the amp in preamp out RCA connections where I think you are using the "Y" phono connections?

Ed
cerrot's avatar
cerrot
1,700 posts
 
why not just go with preamp out of the Dussan to the tube amp's in puts?
almarg's avatar
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almarg
9,670 posts
 
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
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