Re: eric clapton mid boost
yes there is a circuit board. its a little smaller than a credit card and needs 9v power.
the boost in claptons guitars is actually two boost circuits. one is an always on 12db clean boost, the other is a 12db adjustable mid boost. its a cool unit with the right setup. i like it best with tweed and marshall plexi type circuits over bf/sf fender circuits but thats just me. i also dont like the tbx tone control so just use a standard 250k/.02 tone circuit