Today's tech tip revolves around the age-old issue of lighting dimmers inducing buzz into audio equipment. Anyone who has ever played a gig at the hotel ballroom has probably fought this at one time or another, but it's really frustrating when it happens in your own studio. We had one reader who claimed to have moved his lighting and audio to different circuits on different legs of the electrical service to no avail.

There are several problems that cause this, and usually when it becomes noticeable it's because more than one of them are active. The variables are the quality and type of lighting dimmers, the amount of lighting being dimmed (is it one 100 watt bulb or 20 kilowatts of ballroom lighting?), the nature of the electrical wiring, and the nature and quality of the audio wiring.

Lighting dimmers that use big, inductive coils can cause hum to be induced in audio equipment just by being in close proximity. Dimmers that use potentiometers or solid-state circuits (as many inexpensive home dimmers do) will cause hash noise and other garbage to be induced. In both cases the induction often occurs through the electrical wiring. Basically, they feed a bunch of garbage back up the AC line (and ground line) and it finds its way into your gear. Similarly, however, they radiate electromagnetic energy through the air, which means your poor guitar is going to pick it up. Without getting into an entire electrician's course on lighting circuits, suffice it to say that the quality of the dimmer and the way in which they are wired is an important variable.

If lighting dimmers put enough garbage into the air and back on to the electrical lines you may be stuck with some of it getting into your audio, but there are some precautions you can take to better your chances. Make absolutely sure you have no ground loops. A ground loop acts as a big antenna for electromagnetic radiation so your best bet is to not have an antenna. A power conditioner with isolated outlets will also help, both in preventing ground loops and in preventing general garbage on the AC line from getting to your delicate audio equipment. Balanced wiring (both audio and electrical) will better be able to prevent problems than unbalanced wiring.

If you solve enough of these problems you should be able to bring the noise under control. If you can't - and sometimes you just can't - we suggest not dimming the lights. It's not a perfect world folks.