Quiet Please

In January I bought a guitar and a small practice amp. As I noted back then the amp has lots of effects which saves me buying an array of pedals. It has one problem though: it is very loud. And by that I don't mean that it goes to 11, but that it goes from zero to hero already around 2: below is too quiet, above too high, and the optimal setting in the middle is too hard to find.

There's simply not enough (usable) dynamic range. I could turn down the input volume from my guitar, but that changes the sound unfavourably (I get lower signal-to-noise ratio, and many of the effects rely on high input level to work satisfactorily).

To solve the problem I measured the resistance through the speaker to 6.2 Ohms, hooked a 57.4 Ohm resistor in series with it (for a total of 63.6 Ohms) and a 8.2 Ohm resistor in parallel with that. Substituting 63.6 and 8.2 for R1 and R2 in 1/R1 + 1/R2 = 1/R, the formula for calculating the combined resistance in a parallel circuit, and solving for R gives a combined resistance of about 7.3—close enough for my purposes.

The result? Most of the output from the amp now bypass the actual speaker, shunted off into a resistor where it is converted to heat rather than sound; the volume dial has a much greater effective range, making it much easier to adjust to a sensible level; and my neighbours are much happier.

Posted 2 March 2007 Copyright © Stig Brautaset