GT420 MkII preamp distortion / overdrive
by Blue Colander
Here it is, the all-new GT420 MkII for 2022. The idea of GT420 series is simple: bring sonic resemblance of a big tube amp abused, but with all available features it has much more to offer. It's distortion character is fat and raw, not super-high high-gain, but it’s 'grainy' and untempered texture makes it appear really heavy in vintage flavour. With it's wide sensitivity range and sweet clean tones GT420 is great for tight riffing at warm overdrive settings, as a fat all-around booster, clangy&grinding drive, or even an EQ / preamp for preceding pedals and driving FX loop return, but it’s best purpose is to turn any existing amp into a true doom machine.
New MkII version is a discrete JFET preamp topology circuit with internal voltage doubler to provide serious power and headroom with a standard 9V power supply. BASS & TREBLE knobs provide effective, straightforward tone and distortion-shaping control (via classic James tone stack), while BASS & TREBLE 'cut' toggles let form overall voice and distortion character in other parts of the circuit, to access even further sonic explorations.
Heart of GT420 is it's complex gain path. Drive knob shapes overall sound throughout it's range - low drive settings favour bright tones with great clarity, while cranking knob smoothens and fattens up distortion. This feature, combined with each of three sensitivity modes provide numerous distinctive setups. High sens mode brings a smooth and dense high-gain amp feel. Middle sens mode presents wider dirt range from edge of breakup to robust distortion, with lots of 'grain' and natural growl. Low sens mode allows to reach crystal clean sounds for good amount of boost.
This device can get REALLY loud and it's reasonable start your first ride with volume knob at zero. So, careful with that axe.
BASS / TREBLE - pre-distortion EQ (turn counterclockwise to cut, turn clockwise to boost)
DRIVE - gain control
VOLUME - master volume control (pedal can get extremely loud!)
BASS cut - alters distortion attack and overall low-end content (bottom position is flat, middle position is moderate cut, top position is heavy cut)
TREBLE cut - filters out post-distortion treble (bottom position is flat, middle position is gentle cut, top position is heavy cut)
DRIVE sens (sensitivity) - changes gain range and distortion character (bottom position is low, middle position is medium, top position is high sensitivity)
No battery operation possible with this pedal. Use isolated, regulated, negative center power supply at 9V only - running it at higher voltage may cause damage and void warranty.