|Author:||mhelyar86 (registered user: 1025 posts )|
|Date:||Fri, Jun 08th, 2012 @ 09:30 ( . )|
Looking at this schematic [link] I can't see why that would be a particularly good pedal. It's simply a common source MOSFET biased by 2x10Meg resistors, Input impedance being set by the 2 ressitors essentially being in parallel as far as AC is concerned. So you've got big resistors, which means lots of resistor hiss. There's a high input impedance, which I hear increases the risk of more general noise/radio pickup etc. and which would provide little benefit over the standard 1Meg input impedance of a valve circuit. There's no gate stopper so there's a risk of high frequency oscillation and it's at risk from ESD (PN junction overvoltage protection diodes provide little ESD protection as they won't turn on fast enough). You'd be better off with a common emitter bipolar junction transistor, but what would be better than that is just about every other booster/overdrive pedal that has come since the Rangemaster...
As for valve boosters, there are plenty of examples on the net and I'd suggest using one of those rather than designing from scratch. At low voltages, valves can be a bit hit-and-miss, so there's extra complication involved in the design. That's the way I'd go if I wanted a "distortion" pedal (i.e. one which produces its own distortion) rather than a booster pedal to overdrive an amp. Even before they clip though, valves produce some nice harmonic distortion, and you can set your pedal just enough to colour the sound without clipping too hard.
If you just want a very clean booster to overdrive a valve amp though, this is as far as you need look: [link]
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