Quote from: teemuk on February 20, 2008, 07:50:20 AM
If I would use the circuits in that kind of parallel arrangement I would likely put some kind of a rotary switch to that setup and I would also try to switch at both output and input sides of the pre circuit just to eliminate noise (few hi-gain circuit in parallel may contribute a lot of hiss). If you do not "drop out" the "unused" circuits with some switching arrangement you need to consider the total impedance of all preamp final stages that are connected in parallel: Most of them have a resistor that ties the output to ground reference, when you parallel few of these the total resistance may end up being substantially low, there's a good chance that some of the circuits cannot handle it and at at least it will effect the coupling/cut off frequency. The thing may need mixing resistors or buffers. I'm quite certain that you can't just parallel the circuits and get away with it without any modifications.
Another issue is how wise this paralleling even is in practice. I mean, do you really need all those preamps or could you just work out an arrangement where you remove all the "unnecessary" parts and devise a couple of ways to make the circuits share the parts that are common to all. For example, quite a many of ROG circuits (and their variants) have almost identical attenuating volume and gain control arrangements, the final low-pass filter stage is similar in most circuits, most of them use FET gain stages where only differences are practically the values of gain and coupling capacitance/cut off frequency. These can easily be made switchable and controllable, which allows voicing one basic circuit with many alternative ways. Many ROG circuits also substitute a proper tonestack circuit with some simplified arrangement.
i tried to point out it was a very basic idea, so you would indeed need a way to mute the "off" preamps that i didn't deem necessary to outline my idea
but i do like your idea of using common parts