OA47 Germanium diodes and their uses

Some like 'em and some don't, but I bet everyone has at least a couple — Analog Delay, Digital Delay, Reverb, Chorus, Flanger, Phaser, Tube Overdrive, Transistor Overdrive, Fuzz, Octave Fuzz, Tremolo, Vibrato, Compressor and the list goes on!

OA47 Germanium diodes and their uses

Postby ThisLifeILead on Fri Jun 13, 2014 5:55 pm

Hi Everyone,

I came across a wicked pair of late 50's early 60's British Germanium diodes: OA47's. from what i understand they are british 1N34's. similar forward voltages. 0.3-0.35v. They were pulled from a very old Conductivity meter we were throwing away in the lab. It had top quality components in it for its time. including a mullard 12AT7 and 12AX7.
anyways, ive been doing some research on diode clipping mods in pedals and i instantly was reminded of the diodes i have kept stashed away. i have a boss SD-1 just sitting there and was thinking of replacing the clipping diodes with these wicked old diodes.

Schematic :http://www.hobby-hour.com/electronics/s/sd1-super-overdrive.php

Looks like D4, D5 and D6 are my assymetrical clipping diodes. i was thinking of replacing the pair D5 and D6 with the OA47's. or just setting up a symmetrical soft clipping with one original 1S2473 diode and one OA47.

Is this a waste of the diodes? i know they arent worth much but i feel like they could be used better then in a boss pedal.

any ideas or suggestions? :jam: :old:
"Great spirits often encounter violent opposition from mediocre minds" - A.Einstein
ThisLifeILead
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Re: OA47 Germanium diodes and their uses

Postby ThisLifeILead on Thu Jun 19, 2014 7:07 pm

Update for those interested or future readers:
This pedal is similar to a tube screamer but sounds nothing like it. The TS uses symmetrical clipping. The SD-1 uses asymetrical clipping. when i engage my TS-808 reissue its soft and subtle. The stock SD-1 is harsh and dull to my ears when engaged.

I replaced D5 and D6 with the OA47 germanium diodes and replaced the treble bleed cap C6 (0.01ufd) for a 330pf.

C6 is a big cap and is shunting too much. using a sub box i determine to my ears and setup a 330pf is perfect. actually 33pf-1000pf was the best range.

With both diodes swapped the output was noticeably lower but very round and mellow sounding. Not a bad thing but lacked some punch. Had to dime the gain and volume to get the punch i was after but still sounded nothing like the stock pedal. So i swapped back in one of the original clipping diodes and found a sleeper inside this mass produced pedal.
Its mellow, its more dynamic and its easy to listen to. It sounds alot more like an overdriven amp with that little bit of fuzz attached to the sound. Id thought i would share my experience and encourange anyone to try it who has this pedal and doesnt use it. rock on :jam: :cheers:
"Great spirits often encounter violent opposition from mediocre minds" - A.Einstein
ThisLifeILead
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Posts: 582
Joined: Fri Feb 12, 2010 6:15 pm
Location: frozen prairies


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