Blue Colander GT420 MK1 [schematic]
Posted: 22 Jun 2023, 08:31
Hello, here's Juliusz from BCS. I thought I'll share some schematics of my discontinued pedals for anyone fancy diy.
Here is GT420 MK1 model (current MK2 version is completely different circuit-wise). It's a LM386 based distortion with a fat silicon Rangemaster in front. What was neat in this particular pedal was hitting 386 not with a boosted signal, but feeding it with already dirty and compressed signal. This caused a rich, powerful distortion with reduced typical farting-out sizzly sound of simply smashed 386. Dual gain pot is crucial for this circuit and provides a wide range of available distortion. I included Rangemaster-based booster instead any other type, because it brings a favourable colour instead of sheer volume, what works great for the whole design (especially in 'dark' mode). EQ section was carefully tuned for a variety of interesting tones with only muff-style tone knob and a shape switch, but of course there is much room for experiments.
Type of 386 chip doesn't matter, nor exact transistor model. Hfe for rangemaster was circa 180 and for distortion input stage 330-350. I also recommend to add 1k trimmer between 386 pin 1 and 10uf cap to possibly reduce high gain range a bit.
And here's demo:
https://www.youtube.com/watch?v=yNANdmXP1WI
Here is GT420 MK1 model (current MK2 version is completely different circuit-wise). It's a LM386 based distortion with a fat silicon Rangemaster in front. What was neat in this particular pedal was hitting 386 not with a boosted signal, but feeding it with already dirty and compressed signal. This caused a rich, powerful distortion with reduced typical farting-out sizzly sound of simply smashed 386. Dual gain pot is crucial for this circuit and provides a wide range of available distortion. I included Rangemaster-based booster instead any other type, because it brings a favourable colour instead of sheer volume, what works great for the whole design (especially in 'dark' mode). EQ section was carefully tuned for a variety of interesting tones with only muff-style tone knob and a shape switch, but of course there is much room for experiments.
Type of 386 chip doesn't matter, nor exact transistor model. Hfe for rangemaster was circa 180 and for distortion input stage 330-350. I also recommend to add 1k trimmer between 386 pin 1 and 10uf cap to possibly reduce high gain range a bit.
And here's demo:
https://www.youtube.com/watch?v=yNANdmXP1WI