This is one of the more recent Sola Sound MK1.5 Tone Benders built by David Main.
THE DIRTY HIPPIE MOD - OC75 ONLY
This has two additions to the regular circuit. A 10n cap to ground on the input and a 47k bias resistor on the base of Q1 to help stabilise the circuit when it's a bit warmer. Some Goldies have the resistor hidden under the circuit board, but no 10n cap. Reference by Mr Main here. MK1.5s without this mod have been referred to as the 'bear fart' MK1.5 because of the biasing issues. reference here
The 47k resistor on the base of Q1 certainly makes a difference - the tone is the same, it just adds some extra beef. Where I live in Australia it's substantially warmer than England, so this mod is very handy. How much warmer? It's winter at the moment, and it's 22 degrees celsius, not a cloud in the sky.
The OC84 version does not need this mod.
SOLA SOUND "GOLDIE" TONE BENDER MK1.5
Nice! The cap from ground to input shouldn't change anything soundwise, while the 47k resistors might be variable depending on the transistors, right? One could also use a trimpot here, right?
ReplyDeleteOr am I missing something?
Sure - trimmer would be fine, or breadboard and try some different values. I never got around to testing different caps today. Might just be a radio frequency thing.
ReplyDeleteSounded pretty good on the breadboard. Need lowish leakage OC75s with decent gain from my limited experience. Low leakage by OC75 standards anyway.
I can hear some high end loss with 10n from input to ground but it's minimal and it does tame the hiss. I never pick up radio stations with Germanium transistors but I always do with Silicon.
ReplyDeleteI have a 1.5 on a breadboard with low gain GC116Ds - Q1 hFE 59 leakage 303uA, Q2 hFE 85 leakage 596. Sounds as expected, brighter than a Fuzz Face with the same cleanup and not noisy. Not enough gain for me however.
I always use 1k instead of 470r and C1k instead of B1k for Fuzz.
1k and reverse log is a good combo.
DeleteMine wasn’t working well with anything low gain for Q1. Might just be the OC75s that I’m using - have not tested with other transistors (yet).
Had some nice Velcro lead tones happening, and thick chords.
The cap from input to ground it's just to take away some highs, in the explanation from DAM he uses always as an example the MKII, I think that any cap from 4,7nf to 15nf can be good enough to start!
ReplyDelete10n sounds fine to me. I thought it might be 10n based on the MKII values. But the cap in to photos didn’t look the same as the 10n output cap. Whatever the value, it’s sounding very nice.
Delete