The 32 OD Pure Germanium Overdrive pedal - design and build in words and pictures
Posted: Wed Mar 31, 2021 12:35 am
NO WARRANTIES OF ANY SORT ABOUT THIS DESIGN ARE MADE.
NO SUPPORT IS AVAILABLE.
IF YOU CHOOSE TO USE THE DESIGN OR ANY OF THE CONCEPTS YOU DO SO AT YOUR OWN RISK.
THIS DESIGN IS COPYRIGHT AND MAY NOT BE USED FOR COMMERCIAL GAIN.
==========================
G'day!
So, another OD pedal. And the world doesn't need yet another OD pedal. So why do it?
I have an innate desire to not see electronics "go to waste". That's why I buy and repair any old dead pedals or other music gear that I find - to rescue them and get them back into circulation.
Stay with me - I'm going somewhere with this story.
When I built the first fuzz pedals 10 years ago I found that Russian surplus germaniums sometimes had the right gain for Q1 in a fuzz (about hfe = 75, low leakage), and they sound pretty good. In any batch of 1,000 PNP Germanium transistors between 20 and 50 transistors had the right gain.
So I'd buy the damn things in lots of 1,000 and test every one. And be left with about 950 that weren't any use for a fuzz.
The first time I did this I threw the 950 transistors away. And that just felt like a total waste. Most of them weren't bad, they just didn't have high enough gain for the fuzz circuit.
When I bought the batch of 1,000 a couple of years ago to build the Fuzz Architect pedals I didn't throw out the 950 unsuitable transistors. I couldn't bring myself to waste them.
The 950 transistors sort into buckets like this:
- About 300 have a gain between 60 and 75 and good leakage numbers. Not enough for a fuzz, but not bad.
- About 200 are bad. Failed under test (no gain, super low gain, runaway gain, super high leakage) - they can be thrown away
- About 450 have low gain, but also low leakage and are generally OK, but useless as amplifiers.
The question became "what can I do with them"?
Back in the DingoTone days one of my favorite designs was the BSD. I like germanium. But the BSD uses a silicon transistor as the input buffer and an opamp as the gain stage. The germanium is in a pair of NOS diodes used for very light clipping/shaping.
So I started thinking about an all-germanium overdrive. And that thinking has taken about 2 years of fiddling... I wanted to do something simple, but toneful, and preferably something that isn't "common".
The first real foray came in June 2019 with this thread: viewtopic.php?f=13&t=315&hilit=geode
But the approach I was trying to take didn't produce the pedal I wanted. Or, indeed, any pedal. It simply didn't work because I had the engineering wrong. So things just sat until I had a bit of a brain-fart a couple of months ago.
And this time it worked. A pure germanium overdrive, using five (5) of the germanium transistors per pedal.
NO SUPPORT IS AVAILABLE.
IF YOU CHOOSE TO USE THE DESIGN OR ANY OF THE CONCEPTS YOU DO SO AT YOUR OWN RISK.
THIS DESIGN IS COPYRIGHT AND MAY NOT BE USED FOR COMMERCIAL GAIN.
==========================
G'day!
So, another OD pedal. And the world doesn't need yet another OD pedal. So why do it?
I have an innate desire to not see electronics "go to waste". That's why I buy and repair any old dead pedals or other music gear that I find - to rescue them and get them back into circulation.
Stay with me - I'm going somewhere with this story.
When I built the first fuzz pedals 10 years ago I found that Russian surplus germaniums sometimes had the right gain for Q1 in a fuzz (about hfe = 75, low leakage), and they sound pretty good. In any batch of 1,000 PNP Germanium transistors between 20 and 50 transistors had the right gain.
So I'd buy the damn things in lots of 1,000 and test every one. And be left with about 950 that weren't any use for a fuzz.
The first time I did this I threw the 950 transistors away. And that just felt like a total waste. Most of them weren't bad, they just didn't have high enough gain for the fuzz circuit.
When I bought the batch of 1,000 a couple of years ago to build the Fuzz Architect pedals I didn't throw out the 950 unsuitable transistors. I couldn't bring myself to waste them.
The 950 transistors sort into buckets like this:
- About 300 have a gain between 60 and 75 and good leakage numbers. Not enough for a fuzz, but not bad.
- About 200 are bad. Failed under test (no gain, super low gain, runaway gain, super high leakage) - they can be thrown away
- About 450 have low gain, but also low leakage and are generally OK, but useless as amplifiers.
The question became "what can I do with them"?
Back in the DingoTone days one of my favorite designs was the BSD. I like germanium. But the BSD uses a silicon transistor as the input buffer and an opamp as the gain stage. The germanium is in a pair of NOS diodes used for very light clipping/shaping.
So I started thinking about an all-germanium overdrive. And that thinking has taken about 2 years of fiddling... I wanted to do something simple, but toneful, and preferably something that isn't "common".
The first real foray came in June 2019 with this thread: viewtopic.php?f=13&t=315&hilit=geode
But the approach I was trying to take didn't produce the pedal I wanted. Or, indeed, any pedal. It simply didn't work because I had the engineering wrong. So things just sat until I had a bit of a brain-fart a couple of months ago.
And this time it worked. A pure germanium overdrive, using five (5) of the germanium transistors per pedal.