Hi-Fi Pre-Amplifier with Bass Treble Tone Control Circuit

The preamp featured is very straightforward to make on the PCB, and has an innovative tone defeat function. Rather than completely disable the tone controls, they are massively de-sensitised, and when "defeated" have a maximum range as shown in below. This can be increased if desired, so you can have two tone control settings, one with the normal 10dB boost and cut, and the other with a very subtle 3dB boost and cut - this will be enough (surprisingly) for very minor adjustments such as you might need for day-to-day listening.


Otherwise, the design is fairly conventional, with the main advantage over other designs being that there are almost no wires to run. Source switching is done any way you like - I suggest a rotary switch at the rear of the enclosure, and an extension shaft to bring the shaft to the front. This results in the minimum of wiring, and reduces crosstalk from other active inputs.

As you can see, the PCB is very compact. The volume pot is actually spaced a little further apart than the others to allow a larger knob, since this is the most commonly used control in any preamp. The use of 16mm pots makes for a small and neat layout, and makes it very easy to include the preamp with a power amp, making a complete integrated amplifier system.

Note that the Rev-A board is slightly different from the Rev - circuitry shown here. The differences are not great, but you do need the info in the secure site to see where the various parts are located.