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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
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almarg
9,670 posts
 
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
hifihvn
943 posts
 
There is also the possibility having mechanical feedback if your playing vinyl, and the record is getting vibrated from the sound. This would sound like what you describe. This could be happening now due to level mismatch that wasn't there before, at the right frequency that can be louder, and now vibrating the record. If it increased with volume, and decreased as you turned it down, then this may be happening.
maineiac
649 posts
 
Do you have one set of speaker cables going from the dussun to the bass module of your speakers and another set of speaker cables going from your nobis to the mid/hi module?
manitunc OP
795 posts
 
yes, one set from Dussun to low, one set from Nobis to mid/hi. I was playing a vinyl record on an Oracle Delphi V which has never had an issue with feedback, so I dont think that was the problem.
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