June 7, 2005

I have a pair of PSB Image 2B speakers that were used with a Rotel RA-02 amp. They are now in a second system, which includes a vintage '70s Technics SA-5170 receiver. I notice that the woofer cones move in and out in a rough manner, especially with hard-bass/beat-driven music and ambient-like music. I also have a computer hooked up to the system, and when playing MP3s this behavior seems to get worse. Also, it goes to extremes when I tune in radio stations. The cone looks like it is ready to jump out of the cabinet. What I find odd is that this is not the case when I have the speakers connected to my new Rotel amp. Q: Can it be the receiver (because of its age) that is causing this? To what degree is it considered normal for a woofer to bounce in and out?

Gianluca DeCapua

A: I consulted Gilbert Yeung, the president and chief designer at Blue Circle Audio, for an appropriate answer. Gilbert has designed many outstanding amplifiers. Because this is happening with the Technics receiver and not the Rotel amp, it definitely seems like something has gone awry with the SA-5170, whether due simply to age or otherwise. In Gilbert's words, it's "time to check it out. Without doing any measurements, it may have over 3 or 4V DC being applied to the woofers, and that is not exactly good." In other words, you could be doing damage to your speakers, so the best thing to do would be to stop using the receiver immediately and get it checked by a qualified technician if you wish to continue using it.

...Doug Schneider