This week on the Breadboard: The Emerald Green Overdrive

Chuck D. Bones

Chuck D. Bones

Circuit Wizard
This schematic is based on info I received here and I'm 95% confident it's correct. The EGOD is basically an EGDM with the biasing and gain tweaked a bit on each stage. This is the "as traced" schematic, again based on info I received here. It has one more part than the EGDM. I leave it as an excercise to the reader to figure out which part. I breadboarded it per this schematic and ended up making two mods. I changed VR2 to W20K for a better feel on the VOICE knob and changed Q1 & Q3 to J112 because a) they are still in production, and b) we get a little more high-freq gain in the first stage which translates to more range in the VOICE control. It's a mild OD. The DRIVE knob ranges from almost clean to a smooth grind. The circuit will accommodate almost any NPN Ge tranny. Highly recommended.

BJFE Emerald Green Overdrive.png

Green knob: VOLUME; Green knob: TREBLE; Green knob: VOICE; Green knob: DRIVE

EGOD breadbboard 03.jpg
 
cooder said:
Fork ready as above? Looks yummy.
Click to expand...
With the inclusion of the mods I mentioned above. Bias tweaking will be req'd of course. When VOICE is W-taper, one can orient it either way. As shown in the schematic, CCW is max BASS. I actually built the breadboard the other way.

NB: The EGDM can be built on an EGOD board by replacing the one extra part with a jumper.
 
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Chuck D. Bones said:
With the inclusion of the mods I mentioned above. Bias tweaking will be req'd of course. When VOICE is W-taper, one can orient it either way. As shown, CCW is max BASS.

NB: The EGDM can be built on an EGOD board by replacing the one extra part with a jumper.
Click to expand...
Well yes very much the same almost begs the question if putting the extra C8 / 22uF on a switch? Some component values are different to the EGDM schematic you posted in that thread too.
I do love my version of EGDM. How different does this sound?
 
I have not A/B'ed them. The addition of R17 reduces the gain and distortion in the 2nd stage. I would not bother with a pot. You could put a switch across R17, but I expect that you're going to find one setting you like and keep it there. The are some component value differences between the two circuits, but I think the biggest difference sonically is down to R17.

Because the circuits are so similar, there is a lot of overlap in the tones between the EGDM & the EGOD. If you're diming the DRIVE on the EGDM, then the EGOD will probably not satisfy you. If you're looking for a dirty boost, then the EGOD may well be the preferred choice. Might be interesting to stack them, kinda like the KoT. Hmmmmm. :unsure:

BTW, the schematic indicates C12 is electrolytic. I used film on the breadboard. The three 22uF caps are all aluminum electrolytic. I connected C5 to GND instead of Vcc... same difference. I subbed 15K for the 14.7K resistors. Close enough for pedals. :cool:
 
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Well, this was underwhelming to begin with but the more I play the more I really appreciate it. (It doesn't help that my tube head is out of action and I'm using a amp sim).

Really nice (under)drive. A boost in front and it's like an amp, and stacks quite well. I owe Dave another round of drinks (or at least some PCBs).

Also, highly recommended.
 
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