This attenuator box can be built in about as long as it takes to read this post. I count 5 parts, and that includes the case. What’s an attenuator box? Read on.
Most valve amps need to be run loud to get a good tone out of them, which often makes it difficult when performing in intimate settings, playing late at night or if you have picky neighbours. An attenuator is an electronics device that reduces the amplitude of a signal without appreciably distorting its waveform – perfect for getting that cranked amp sound, at a lower, more manageable volume level.
Learn more about making a DIY: Attenuator Box for your amp
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Pretty cool project. I may have to try this myself – since I happen to have a dozen or so Rheostats like this just sitting around.
The L-Pad is one way to attenuate the volume and is often used in 70V installed systems, but as you attenuate, the load on the amplifier falls off and, as the author said, becomes more “lifeless” – Just like turning down the volume knob. The wire wound rheostat is capable of absorbing a few watts of power.
The professional boxes, such as the Hot Plate, dump the power into a dummy load (with a big heat sink) so the load stays on the amp.
You could use a wire wound rheostat like shown, and sweep the input between the output (speaker) and and internal dummy resistor. Get a power resistor to match the impedance of the speaker, and attach it with some thermal adhesive to a big honkin’ heat sink. Those higher power amps put out a lot of juice, and will toast the dummy load resistor.