Fuzz Pedals with Germanium Diodes Inside

Chuck D. Bones

Chuck D. Bones

Circuit Wizard
What are your favorites?

I've got a pile of Ge diodes and I'm looking for something good to build with them.

Related question: anyone have a schematic for the Keeley Red Dirt Overdrive? I've read that it's based on a TS, but I want to know what Mr. Keeley did with it.
 
Yup, good choice! I've already got one!

Cleese as French Knight.jpg

At the moment, I'm leaning toward a Crystal Drive with D9B's in place of the BAT48's.
 
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Chuck D. Bones said:
Related question: anyone have a schematic for the Keeley Red Dirt Overdrive? I've read that it's based on a TS, but I want to know what Mr. Keeley did with it.
Click to expand...

I have the schematic for the Mini somewhere... I'll have to find it.

It's a TS with the usual Keeley mods and a JFET input buffer, if I recall correctly.
 
Tone Bender MK3 and others like it: Buzzaround, Dizzytone.
For Muffs, the Fuzz War and Pharaoh. Fender Blender if you want to try another octave fuzz.
Two op amp drives I like are the MXR Dist+ and Riot. I want to try the Univox Square Wave.
Then there's the Nugget Fuzz here.
 
Are Ge diodes as sensitive to temperature as Ge transistors are? As I live in Australia I'm reluctant to use Ge in anything which I may rely on for gigs. I love my Ge fuzzes (the Marshall Supafuzz is a fave) but worry about weird shit happening when I don't need it to.
 
Yes and no. What happens with Ge transistors is the leakage rises rapidly with temperature, upsetting the bias. Ge diode leakage will go up with temperature, and Vf will go down. Depending on the circuit this may or may not cause a problem. A hard clipper, like the Distortion+, is not sensitive to diode leakage and changes in Vf only affect the volume a little bit. I just ran a quick & dirty experiment on my Crystal Drive. It has been running on the bench for a few hours, so it's at thermal equilibrium. I adjusted the output to 3.00Vp-p with a 500Hz sinewave input. Then I put my finger on the three D2E diodes. In less than a minute, the output dropped to 2.88Vp-p. Not a huge change, less than 0.4dB. The circuit impedance is low enough that diode leakage is not an issue.

On the other hand, circuits with Ge diodes in the feedback loop, like the Cornish NG-2, may not fare so well at elevated temperature.

Update: later on I pulled out the heat gun and warmed the diodes up a little more; got a -3.5dB volume drop. Noticeable, but not a show-stopper.
 
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I should add that for now, I've scratched my germanium itch. The Crystal Drive is a nice low-gain distortion pedal, very smooth. Not sure whether I'm satisfied with the TONE control. I'll put something in Build Reports this weekend, after I get the labels on it. Thanks for the recommendations!
 
Can you tell us a circuit where you are satisfied with the tone control? :LOL: I imagine that if I knew what you know I wouldn't ever be satisfied.

(edit) Just looked at the schematic and can see why you're not impressed. I might have a look at building that one - do you think the BAT48s are an essential part of the sound or is that why you went with Ge?
 
LoL. Here's what I built (so far). I didn't want it to load the pickups, so I rescaled VR1, C2 & R3. It still loads the pickups when DRIVE is dimed, but is better behaved at lower DRIVE settings. Clipping diodes were changed from Schottky to Germanium for softer clipping. C5 did nothing at 100pF. 1nF shaves of a tiny bit of the top end. The TONE pot used to changed the volume and tone when turned, now it only changes the tone. I might increase C6 some more, undecided at the moment. Scaled up R7 & R8 so they don't load the tone network as much. Seemed a bit silly to me to use a high-gain transistor for Q2 and then make R7 & R8 so small, so I scaled them up and biased Q2 a little hotter.

Q1 and the diodes make all of the distortion and are responsible for the sound, so yes, Ge and Schottky will sound different.

Update: I corrected the diode part number on the schematic.

EQD Chrysalis [Crystal Drive] cb mod v1.5 sch.png
 
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I suspect that with my vast (not) knowledge of electronics my point of "good enough" comes earlier than yours.
 
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