mixers

At least a simple mixer is essential to provide gain & tone adjustment of microphones; what is required is dependent on application. From the very start we were expecting to be working with bands, so we needed a relatively complex mixer.

I already had an eight input Spirit Folio mixer; these require a power supply of +/-18v. This is derived from the internal power supply of the power amp (+/- 46v) - each rail is very simply dropped down by a large resistor, to avoid the mixer internal regulators being overloaded. The alternative would have been to build or buy a custom +/-18 (or 15v) 12v power supply, at around fifty pounds.

Eight channels is barly enough for bands; I've had to combine microphones into one channel before, and am working on getting a mixer with more channels to use on the system. For simple acoustic acts, or just speeches, four, or even two channels can suffice.

A very few commercial mixers will run from a 12v supply, mainly designed for portable broadcast use, and unlikely to be cost effective to buy. It is also possible to design & build mixer circuits that will run on a single 12v rail; as mixers get bigger the time and effort required to get a useful and reliable result makes it less worth while to build your own.