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July 1, 2009

Question of the Month: System shuts down at half volume.

Q. I have a Yamaha PianoCraft-E810 Micro Component System that uses its original manufacturer’s speakers. Its specifications are: 55W+55W Minimum RMS output power per channel (6 ohms, 1 kHz, 0.1% THD). My problem is that the system plays well, but as soon as I try to raise the volume (not even reaching the halfway mark of the volume dial), it cuts out and automatically switches off. Do you have any clue as to what the problem could be? – A.M

A. There are three possibilities: An intermittent speaker-wire short circuit; overheating because of improper ventilation; or overdriving the amplifier. Of these three, I’m almost certain you have an intermittent short circuit in the speaker wire connections either at the amplifier or where the wires connect to each speaker. Even a single strand of copper wire would cause the system to short and go into protection mode, shutting down to avoid damage. It could be the bass vibrations from the speakers cause a strand of wire to touch the opposite connection as you raise the volume. Check those connections very carefully to ensure there are no stray strands protruding. Try wiggling the speaker wires while your system is playing to see if it will trigger the shutdown. (By the way, I just fixed a friend’s Sony system in Toronto that was doing exactly the same thing. It turned out to be a bad speaker wire connection that shorted out as he raised the volume.)

Do you have adequate ventilation (6 inches or more) above the amplifier section? Almost all amplifiers produce more heat as you raise the volume level, and most have thermal monitoring to shut down the system if the output transistors become too hot. It may be overheating and shutting down until it cools.

The other possibility (unlikely) is that the “taper” on the volume control is very short, so that even at half volume the full output of the amplifier is being fed to the speakers, and clipping or distorting. This would also cause a shutdown. On many of these micro-component shelf systems, the volume control “opens up” to full output really quickly so that when it’s demonstrated in a store, the “louder” system is the big seller. Since your amplifier has ample output of 55 watts per channel, I doubt that’s the problem but if it’s not a short circuit or a heat issue, then you might be pushing the system beyond its capabilities in a large room.

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