This week on the Breadboard: The Emerald Green Overdrive

[HamishR]

I finally got around to trying this. I have already built an EGDM and found it underwhelming but I quite like this one. Amazing how changing a few parts can really change things. But we already knew that, right?

Like most BJF overdrives it's quite restrained sounding; not particularly aggressive. But for the most part the low strings retain a decent amount of crispness and definition. And this one has some lovely mids at either end of the Voice knob.

FWIW I tried it first with a 2N1308 but then tried a MP38. A usual I liked the MP38 better. I always find the 2N1308 sounds a bit thin in comparison. The MP38 was just the first one I tried, HFE around 50. Sounds great!

 

[Chuck D. Bones]

I believe that one of the things that makes Germanium sound so mellow is the lower HFE. The Diamond Peak is all low-HFE Silicon and it would be easy to mistake it for Germanium.

 

[HamishR]

Funny you should say that... I was thinking about trying a 2N3903 in place of the Ge tranny. I've had some success doing that. I have some ancient 2N3903s which vary wildly in very low HFE ranges.

Like Szukalski I'm finding that the more I play and experiment with this pedal the more I'm enjoying it. Although as with most of Bjørn's weird controls I find the Voice knob exasperating because I don't know exactly what it's doing! I like this circuit so much more than the Honey Bee or EGDM.

 

[Chuck D. Bones]

The VOICE knob is a bass control for 90% of its travel and a treble cut at the far CW end.

If you sub Si for Ge in the 2nd stage, plan on increasing R8 to bring the bias back to where it belongs.

 

[HamishR]

That's weird but probably makes sense. The Voice control definitely adds bass to the left and it seems to add a lot very suddenly at the very start of the rotation. It seemed to me that at the clockwise end it was a mids boost but being a treble cut makes sense. I was experimenting and realised that the mids were everywhere after all. And the mids are very good. Present but far from overwhelming.

 

[Chuck D. Bones]

You used A-taper for VOICE, right?

 

[HamishR]

Yup.

 

[Chuck D. Bones]

You could try A25K or even W20K to smooth out the sensitivity at the ends of rotation.

 

[HamishR]

With a different guitar (it sounds amazing with a Les Paul) I can hear the gradation in bass etc a lot better. I feel like I'm channelling my Kiwi friend - this pedal sound better the more you play it. I forgot to try the bright pot mod so will do that shortly. And it's making me want to revisit the EGDM...

 

[HamishR]

Well I have another one of these, this time using a 2N3903 in Q2, HFE around 120. Used a 9K1 resistor for R9 for a collector voltage of 4.8VDC. Sounds great! It's a tiny bit brighter as you might expect which isn't such a bad thing. I tried a 2N3903 HFE around 70 but it was a bit noisy. This is nice and quiet and sounds very similar to the Ge but maybe a tad crisper as mentioned. No more gain or anything really.

Also changed C12 to 4µ7 and it allows for more low end which is lovely! I may dial it back to 2µ2 but I'm not sure - the Voice control seems to handle dialling out excessive bassiness quite well. Speaking of the Voice control I used s C50K pot and switched it around so it works a bit more like a conventional bass control.

I'm enjoying this pedal more and more!

 

[Chuck D. Bones]

You can vary C2 to adjust the brightness up or down. Different transistors will respond differently to C2.

 

[temol]

 

[Chuck D. Bones]

Looks great! Very clean.

 

[HamishR]

I just noticed that in my layouts I have missed R17. So C8, the 22µF from Q2's Emitter goes straight to ground instead of through a 330R resistor. What difference would this make? The OD sounds great as it is. Will it lower the gain?

 

[Chuck D. Bones]

R17 reduces the gain of the 2nd stage. Shorting it out increases the gain and makes it like the EGDM, so of course it sounds great. You can (sort of) compensate for the increased gain by using a lower drive setting. Now what was that you said about this sounding better than the EGDM?

 

[Fingolfen]

Pictures coming soon... well... sort of... but I just got my layout of this one together... I'm totally digging it. It's a bit crunchier overdrive than I was expecting based on some of the comments, but when I paired it with my strat with "black strat" pups and decided to play some Floyd with it... oh YAS!!!! Lovin' it!