Hi all,
I'm building an external tone/vol stack (aka the Insect - it's got six feet and is a pain in the bum) for a Leak Stereo 20 valve amp I restored some time ago. At the moment the amp is connected only to a tuner, via a
20k dual pot to act as a volume control since niether the amp nor the tuner have their own vol/tone controls. The Insect has four inputs, so I can connect other separates to it at some point in the future.I decided it would be funky to use logic switching between inputs using those little clicky buttons (of which I have a lot of reclaimed ones) and led indicators, for the 4 inputs. I designed a circuit to handle the analogue side using an npn transistor in common-base mode connected to each input. Each channel (ie, left & right) having 4 tranistors, and each group of 4 sharing a collector load and output coupling capacitor. My existing 20k pot could then be used as a load resistor, and function as the volume control. The bases of the transistors are then connected to the switching logic. On paper, it seems like a reasonable circuit, giving an output better suited to feed the amp's 1M-ohm input, via a baxandall circuit, than if I did similar using a common emitter arrangement.
Then I discovered the 4066 analogue switch, of which I have 2 in my very limited junk box - just the right number. Now the question is, considering it is supposed to be a hi-fi controller, would I be better to use these, or the bi-polar circuit I have designed? Given I have no means, apart from my own hearing, of testing the result (and I'm not an audiophile), and if I were to use the 4066's, they would still need some kind of impedance matching. Or should I just abandon the idea and use a 4 way switch.....?
Thanks in advance, Monster