I built this system from a new kit decades ago, and it's been pretty much one of the best audio values of my life... still enjoy it very much, and currently being fed by an Adcom GFP-565 pre and a Hafler XL-280 amp. I just noticed a strange anomaly, and wondered if anyone had any insight.
For those not familiar with the system, it utilizes a single down-firing dual voice coil sub driver housed in an "aperiodically" damped enclosure (oversimplified, a sealed box with a designed amount of leakage). The sub's XO is fed by both channels of the amp. Each channel goes though a low pass filter and on to each of the two voice coils, and through a high pass filter and onward to each of the two satellites. In each satellite, that signal is then fed directly to the mid-woofer and through a high pass filter to the tweeter.
Here's the anomaly. I have the satellites set up as expected w/ respect to the listening position, and the subwoofer is towards the left corner of the room, about a foot away from the left wall and about three feet from the back wall. While listening to a mono signal, I noticed that the image did not seem to be centered, with the right channel appearing stronger than the right. With the mono switch engaged on my pre and manipulating the balance control, what was happening was that the subwoofer's output was greatly reduced when the balance control was set full left, but full strength full right, giving the right satellite speaker the "appearance" of being stronger. Up close, both satellites sounded identical as one would expect. Laying on the ground next to the sub with a finger lightly touching the driver verified the difference in strength between responses to left and right channel feeds.
Is this to be expected? How does a DVC driver deal with a stereo and therefore possibly different signal, compared to how it deals with a mono signal from two different feeds?
Even stranger... about 20 minutes after turning the system on, this issue seems to have disappeared and the response is now equal. Will have to see if this is repeatable every time I turn on the system after being unused for a while.
What could cause this? It's been decades since I built these speakers, and I can't recall exactly what the XO looks like and the manuals I have don't include schematics... just very generic pictorials showing locations of components. It LOOKS like each voice coil is fed by a series coil with a shunt cap or resistor to ground. I built the Hafler XL-280 amp even earlier... probably late 80s?.. and it's never hiccuped and always worked beautifully. Any ideas? We had been away for a few weeks and the system has probably been powered off for about a month until today. Would it be normal for a solid state amp to take some time to stabilize? One or more caps in the XO or amp on the way out? Coils are either good or bad, no?
Any ideas much appreciated! Thanks in advance. Is Mike Dzurko still here or around? I spoke with him about ten years ago... good guy and very knowledgeable.
