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Tone Tips from the Road: Light Bulb Gear

Tone Tips from the Road: Light Bulb Gear

Can you control the tone, feel, and sag of your amp ... with a light bulb?

“Turn your amp down!” We’ve all heard this from lead singers and soundmen (and neighbors) countless times. As guitarists, it’s really not our fault—the problem is that many amps simply sound best when they are cranked up. We all have that sweet spot on our amplifiers where the tone is perfectly thick and warm, but that sweet spot usually resides at a volume level that is too loud for most stages. So, how do you get that magic tone at low volumes? Simply use some sort of power attenuator, like a THD Hot Plate or Bad Cat’s The Leash. In my quest to find a different way to cut volume, I tried turning to the common household light bulb.

Whenever a piece of my electronic gear breaks, I have my guy Brett Clark fix it. Clark has 16 US patents to his name for fiber optics, electronics, LED (Light Emitting Diode), and speaker products. He also has a pedal company called Distopia that specializes in oddball and unique effects. Brett and I were having an “experimentation day” and decided to check out this old and tattered contraption that looked like an extension cord with a light bulb socket soldered into the middle of the cord. This device was supposed to act as a power attenuator, with the volume being dictated by the wattage rating of the bulb. Since the socket wasn’t working, Brett grabbed a lamp and rigged the zip cord into the lamp to replace the broken component on the original apparatus.

Not quite understanding the science behind how the device functioned, I asked Clark to explain. I learned that the light bulb’s load is always changing due to the fluctuating temperature and brightness of the bulb. The bulb is in series with the speaker, so as the bulb absorbs power and its impedance increases, it decreases the amount of power that goes to the speaker. When a light bulb is cold, it only provides 1/10 to 1/15 the amount of resistance as it does when hot. On a 40-watt bulb, for instance, a light bulb measures 26 Ω cold, but it will be over 300 Ω when lit up correctly. Brett and I tried different bulbs with different wattage ratings and found that each bulb changed the tone, feel, and sag of the amp.

We began our experiment with an 11-watt bulb. It reminded me of the guitar tone on “Wild Thing” from the Live at Winterland album by the Jimi Hendrix Experience—it was very compressed and low volume. Using a 100-watt bulb with the 100-watt head was interesting because the volume was still lowered and compression was present in the tone once again. But the 100-watt bulb didn’t compress the attack like the 11-watt bulb did—it instead compressed only the bloom of the notes and added an unbelievable amount of sustain. Not only did the light bulb experiment provide interesting tones, it also entertained us with a bonus light show. The light bulb’s brightness increased when I hit the strings with more force, but when I wasn’t playing, the bulb was completely dark.

Through the experimentation process, I remembered that my old Morley Tel-Ray wah used a light bulb to make the pedal function. A Tel-Ray wah uses a light bulb and an LDR (Light Dependent Resistor) to take the place of the potentiometer that you’ll find in most modern wahs. A big advantage of the light bulb and the LDR is that you don’t have to deal with a pot getting scratchy and noisy over time. The disadvantage is that the light bulb burns out occasionally, so if you acquire one of these wahs, be sure to track down some extra bulbs for backup. A Tel-Ray wah has an enormous sweep and is great for handling frequencies from baritones, 6-string basses, and even keyboards. Musicians often use terms that relate to light, like dark and bright, to describe how certain tones sound, and this language is certainly appropriate when discussing the sounds of a Tel-Ray. Darker tones provided from the wah in the heel position means that the LDR is not receiving very much light, and brighter tones in the toe position means that the LDR is receiving a lot of light.

I’d be interested to see more companies investigate the tonal possibilities that can be achieved using light bulbs. Guitar players are always looking for the next new piece of gear and new ways to get great tones.