change speakers or amp
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You can insert a pair of Rothwell attenuators between the pre-amp and amp. Technically this does not reduce the gain of the pre-amp, but it does attenuate the signal that is input into the amp. Effectively it is the same result. It will require the volume control of the pre-amp to be set to a higher level to generate the same output volume at the speaker.
Contact Audio Research as they may have a "resistor kit" to reduce the gain. The ARC LS5 MK III's gain could be changed between the nominal 12db and the higher 18db value with a pack of resistors. These easily replaced the existing ones on the PC board. And the cost was just a few $$ and a half hour of time. I suspect many ARC preamps could be changed this way so give them a call. If such a simple circuit change can be done, and you are not good with a soldering iron, any competent electronic technician should be able to do this for you.
08-11-08: FordmodConsider yourself lucky to be dealing with a company that's willing to share this info so you can do it yourself. When I asked AES if it was possible to reduce the gain of my AE-3 DJH, they quoted $125 and no mention of the final gain. It was like pulling teeth to get vague details. I've asked repeatedly if their modification would be attenuation resistors or a change to the original circuit. No reply to that question. How's that for a company that built their reputation on kit building?! AR, on the other hand, has never been a kit company, and yet, look at how accommodating they are.
Your situation occurs far too often in a lot of companies. I have never liked this, and I truely do the same as AR did for me, for anyone calling on my business. It boils down to the corporate culture, and typically comes from the top down.
I get what I want out of life by helping others get what they want.
Very impressed with your results from AR. When I was looking for a new amp recently I was impressed with Bryston and Mcintosh, not only for the physical qualities of their products but for their practices. Bryston publishes the schematic for their amps on their web site. Mcintosh will sell you a full set of schematics and a parts list as a service manual for what amounts to little more than the cost of printing. I thus had a chance to study the schematics and make a more informed decision. I ended up with a Mcintosh but I also thought the Bryston amps were well designed and a nice quality product. It certainly says something for the company when they make the technical aspects of their equipment readily available. I prefer solid state equipment but if I ever decide to add a tube amp or preamp, your experience with AR will certainly give me a starting bias in favor of AR. There is no better advertisment. Glad I stopped to read this thread, one of the few times that I actually learned something of value from reading a thread.
Balance on my LS7 seems to be off, wonder if it can be adjusted easily .
One would assume that you've swapped interconnects to see if the imbalance stays in the same preamp channel? You changed speakers, and could have issues with them or their different polar response from your previous speakers interacting with acoustical asymmetries to shift the image.
Tubes might be something to look at. Gain varies between different tubes and even the two halves of a dual triode like a 12AX/AU/AT7. Usually not bad enough to be noticeable though.
Tracking between the two halves of a stereo potentiometer can be bad too.