The Fulltone GT-500 Pedal- A Gain and EQ stacker's dream:

Fulltone GT-500 Distortion Booster DescriptionThe Fulltone GT500 Pedal offers discrete circuitry (no Op-amps) F.E.T Hi-Gain Distortion and discrete F.E.T Overdrive / Booster IN ONE BOX. You could think of the GT500 channels as 2 separate pedals in one box...or think of them as stages to be linked together for endless combinations. The GT-500 Hi-Gain side has Volume, Distortion knobs, Bass, Mid, and Highs minipots. The GT-500 Booster Side has Volume, Overdrive knobs, Bass and Highs minipots.(these new hi-Q sealed minipots don't break BTW) 

Hard clipped distortion (the way most pedals achieve distortion) at one point in a circuit can be cool, but stage after stage of FET (GT-500) is very real, very amplike, has ridiculous amounts of sustain even at low volume, does the great chunky low string rhythm stuff and cleans up incredibly well when you turn down the guitar's volume.

What's special about the EQ?

The GT-500 has a discrete Inductor-Driven Midrange circuit....never been done in a pedal before. Yes there's wah wah inductor inside the pedal that gives the Midrange control its ability to drastically increase or decrease the entire Low Mid, Mid, and Hi-Mid frequencies, to comical proportions. All this is done without any opamps because all of the active 3 Band EQ's I've tried are horrible, killing all harmonics, all excitement, and sounding as sterile as the "EQ" in a Digital Recording Program. 100% discrete matched FET's ;)

This Mid control mixed with a strong Bass and Treble control help give the GT500 the ability to dial in more variations than a simple tone control, which can only roll off the Highs.

What's this Series/Parallel switch?

Series/Parallel switch allows for a nice range of tones: In "Series Mode" the signal path is FET Distortion w/ 3 band EQ--->FET Boost with 2 Band EQ. In "Parallel Mode" the signals travel side-by-side allowing infinite Blends of Distortion and Clean, or Distortion and Overdrive/Boost.... and when the two EQ sections enter into the equation, there are more chances to create a uniquely voiced tone. Most who have tried to offer this Parallel feature on a pedal don't realize that you can throw the signal out-of-phase.....not an issue here.