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
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
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.
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?
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.
Is it like this?

Source>Dussun In>Speaker Cables>Low Module
Dussin Line Out>Nobis Amp In>Speaker Cables>High Module
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.
Do your speakers instruction manual talk about bi-amp configurations? Not all speakers with dual binding posts and jumpers can be bi-amped only bi-wired. Don't try to bi-amp until you get more info from PSB.
The more I read your post It seems like you may be getting a feedback from having your tube amp connected to your integrated amp. How close is the tube amp to the integrated on your audio rack?
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.
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.
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
why not just go with preamp out of the Dussan to the tube amp's in puts?
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'll give 8:3 Al is right.
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.

Is this a recommended connection for the Dussun-"Y" cables?
What is the point of pre/power RCA jumper threw if you need to use the "Y" cable?

I would think the correct connection is to use a male to male jumper across the pre/power RCA's and connect the tube amp to the line out RCA's. My speculation is that this would allow the line out RCA connections to attenuate the tube amp he wants to connect to the mid/high section on the PSB

All the speaker connections are correct. Also his PSB speakers are bi-amp capable.

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 was waiting to hear back before I made this recommendation

No manual was a available from the website so all this is trouble shooting for him.

Ed
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
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

Ed
Thanks Al I got it now. I had to look at the picture again of the Dussun
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
Yes, the line out bypasses the preamp volume control. That is why I dont use it for this purpose.

Almarg, you get it. 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. The manual for the Golds definitely provides for biwire and bi amping the speakers just by removing the jumper between the speaker connectors and running the cable from each amp to each pair of connectors. But I will try the multimeter this weekend and see what I can see.
thanks.
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
Almarg's choice seems to want to get rid of the risk, of having these two amps outputs, that may be tied together in the speaker some way. If this is happening, it could be a recipe for disaster. Checking with the meter should answer that easy enough.

Another possibility I'm thinking, is mechanical feedback. This would be similar to a guitar, or a microphone picking up the vibration from the speakers, and causing that feedback. The same happens with records. I've had this problem over the years (all size rooms) with vinyl. If the speakers are close enough to the speakers, the record will get the vibration. The result, feedback. I remember this happening is a big Disco, and it sounded like that large building was going to fall apart, until they turned the volume down.

So, the OP has a lot more bass now (higher power solid state), and most likely less treble and midrange (low powered tube), with this new mis-matched level combination. If you don't hear enough highs and mids, you turn it up, and also receive more bass. This is a possibility that I'm thinking might be happening. Try a CD at your risk, to see if this is the problem.

Then another possibility. I'm assuming both of these amps are using feedback. This is taken off at the speaker output area. This output is signal is then fed back into the front end (input area) of an amp.

If either of these amps is doing something a little strange (odd), it may handle that (odd signal) in its own feedback loop, and play fine by itself.

Now if one of these amps is doing something a little odd itself, and that odd signal (that doesn't bother the amp with it) is being fed right back to its input tied right to the RCA area. And, bonding this amp with a different one may give that little odd (feedback) signal to the other amp, that its (RCA) inputs are tied to.

So, if this is happening, that little odd signal in the one amp (that doesn't mind it), can be driving the other crazy, so to speak. And, these two amps may not ever work together, if one these amps is wired this way, and being the problem.
If the speakers are close enough to the speakers, the record will get the vibration.
Correction for my second paragraph. It should say, if the speakers are close enough to the record, the record will get the vibration. Sorry.
If we had a diagram for all of the things involved, it would be a lot easier for a hypothesis, that may solve the problem.
I dont know how to post a diagram, but its pretty simple. From the preamp out on the SS amp I have a y connector with two male and one female ends. One male goes in the preamp out jack, the other male goes in the amp in jack and the female connector takes an interconnect cable which runs to the tube amp for that channel.

Speaker connections run from the SS amp to the woofer connection and from the tube amp to the mid/hi connection. The jumper between the two is removed. This is the way the PSB manual shows it should be hooked up, and the only way that makes sense.

I will try to reconnect it all again this weekend and see if the problem repeats.
Manitunc, sorry for not being clear. I meant the manufacturers diagrams for the amps and speaker. You made your connection part clear.
http://www.dussun.com/english/v6.html

here is the dussun website that shows the rear of the unit and the connections
Manitunc, hopefully you check the speakers out first, like Almarg suggested. He catches stuff the rest of us overlook. It's cheap insurance to do it first. I'm worried that the protection in the amp may not work 100% of the time, if it is something like the speakers causing it. If it is mechanical feedback, that may not be as risky, like something in the speakers, that may be still tying the two amps outputs together. Whatever caused it the first time, is most likely there yet. Your original wiring looks right.
I guess the amp's protection kicking in has me worried. The amp running out of that much power just doesn't seem right. So something wrong must be happening.
Check the Y-connector(swap back-fourth) see if problem goes do a different amp.