Biamping Dunlavy SC-V

Dazzdax: I can't tell you what's going on, but you have obviously changed the impedance that the preamp sees. That is, you're dividing the signal between two amps rather than just feeding one. This lowers the impedance that the preamp sees by 50%, effectively cutting it in half. This in turn will draw twice as much current from the output stage of the preamp, which could account for yet another reason that the system sounds loaded down or bass heavy. Most preamps are horribly under-designed in terms of their output stage, hence designers trying to keep the input impedance of the amp up. Your system is now making your preamp work twice as hard and it may not like it at all.

The way that you are splitting the signal also creates different nodes in terms of voltage to current distribution within the cabling itself. This too could be a factor in why things sound differently than they did with just one amp per speaker. Optimally, the signal should have been separated at the preamp. Not only does this introduce less line loss by increasing the surface area, the amps also receive the benefit of better electrical separation from one another.

By splitting the signal closer to the amps, the potential for crosstalk from one amp to another is drastically increased. Given that most all amps suffer from their output stage modulating their input stage to some degree, the woofer amp may be modulating what the tweeter amp sees. Using separate interconnects all the way back to the preamp would have provided better isolation between the amps with the longer pathway acting as a buffer.

You've got a lot of variables going on here with the electronics in the system, not so much with the speakers. While it is possible that the speakers have an internal wiring problem inside of them as Tom suggests, you would literally have to pull the speakers apart and make a diagram of the crossover network. While Dunlavy was a good engineer, that doesn't mean that some knucklehead in production couldn't have made a mistake.

As a side note, we ran into this with my Father's Legacy speakers a while back. Sometime during construction of the crossover of these speakers, one leg of the midrange circuit was tied to the woofer circuit. Given that my Dad had never bi-amped these speakers ( only bi-wired them ), this wouldn't have created a problem since the entire circuit was all driven by the same amp anyhow. Having said that, had he tried to bi-amp the speakers, this simple mistake in production could have severely damaged both of the amps. That's because the mis-wired midrange would have electrically tied the two channels of the individual woofer and tweeter amps together. Sean
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PS... For as much money as some of you guys are spending on gear, you really need to find a technically competent dealer to work with. Buying and assembling a few components to work together and produce sound is completely different than building a complex audio system at the cutting edge of music reproduction. From what i've seen though, this might be more difficult than i've thought.

Most of the high priced dealers are either lacking in technical chops and / or more interested in profit margins than anything else. Keeping the customers on the equipment carousel i.e. "flavour of the month club", whether on purpose or due to lack of technical understanding, surely isn't going to hurt their income levels. That is, until the customer has had enough and either gives up entirely or learns to do for themselves.

Once you learn to do for yourselves and can understand basic electronics, it makes it much easier to cut through the marketing hype and snake oil. This is why i encourage folks to learn on their own, but at the same ti me, it is also why finding and supporting a good dealer is important to the survival of high end audio. Without them, we have no visible means of entry into this hobby to the general public.

You can unscrew the rear terminal panel and the entire crossover will slide out a tract..In this way you could diagram and inspect the crossover..These babies are ripe for component crossover upgrades..What a suprise lurking..Tom

Tom brought something up to me privately that i'm hoping all of us didn't forget to address. It is so simple that it is easy to overlook as we tend to take this kind of matter for granted. That is, the jumpers that connect the woofer section to the high frequency section should have been removed. If that wasn't taken care of, i would highly recommend doing so pronto : ) Sean
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Thanks both of you Sean and Tom. You have been tremendously helpful. You are very knowledgable Sean, you must have a technical background I suppose.
Well, the Acoustic Reality has an 8 kOhm input impedance, which is low. An Accuphase representative stated that that wouldn't be a problem with the C-290V preamp I am currently using. But when splitting the signal at the end of the interconnect the amp's input impedance is going to be... 4 kOhms, which is very low indeed. How can I raise the input impedance of the amp? Would be using two pairs of interconnects a solution? The preamp has two pairs of outputs. I've been told though that the preamp actually splits the signal that goes to the amps, instead of driving the two outputs actively. So it will also "see" halved input impedance.

Dazzdax: Now we are getting somewhere. 4K is too low for most preamps and will result in the exact problem that you've described i.e. bloated bass response and trunctuated treble output.

My Dad ran into the same problem in his system several years ago. The dealer had set him up trying to drive a 5K Ohm amp with a preamp that had a higher output impedance. The sonics sounded bad, but much of that was also a speaker based problem. In effect, his whole system sounded bad, so you couldn't really point the finger at any one given thing. In this regards, you might be a lot luckier : )

The simplest solution here is to install series resistors either at the output of the preamp or inside each of the amps. While this will attenuate some of the signal fed into the amps, it should solve much of the tonal balance problems that you're experiencing.

The key here is to find a value that is low enough not to eat up too much signal while being high enough to remove the current drain from the preamp. If you were happy with the tonal balance of the system using one amp per speaker and simply wanted better but equivalent performance, installing 8 K resistors in series with the input of each amp or output of the preamp would put you back appr where you started at.

Personally, i would install the resistors in the amp as that keeps the signal level higher through the interconnects. This is beneficial in more ways than one. Secondly, i would probably use resistors in the 12K region, as this would bring the total load up to appr 10K or so when running both amps in parallel. Even if you chose to run one amp per speaker, the input impedance would be 20K, which is still quite reasonable and easier on the preamp. You should also keep in mind that different brands and types of resistors have different sonic attributes, so you may have to pick and choose your poison there too.

You might want to discuss this with the dealer / manufacturer at Acoustic Reality and see what they suggest. Hope this helps and solves your problems. Sean
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