This week on the Breadboard: The Emerald Green Overdrive

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!
 
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.
 
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.
 
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...
 
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!
 
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?
 
brian cranstor -fuck.gif

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?
 
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!
 
Just revisiting this one because a friend has asked about a "dirty boost with a Voxy kinda chime". It's been a while and I didn't have one handy so I drew up a new Vero layout. I tried a few MP38s in Q2 but they all seemed a bit too woolly sounding, compressed and not very inspiring. My friend is a hard hitter, plays a Jazzmaster with a P90 in the bridge and mainly plays chords. He plays some quite complex chords with gain and likes to hear all the notes, so the Ge transistors didn't seem right. I just happen to have a few 2N3565 transistors which are possibly the coolest looking transistors ever (very important) so I tried a few of those. I tried one with an HFE of 101, one at 150 and one at 265. The higher HFE had more headroom and less crunch. The 101HFE sounds killer! I used the 10nF bright cap because it sounds a bit dull at lower gain settings and the lower HFE 2N3565 sounds to me like the closest to a Vox. Actually this particular transistor sounds great in this circuit!

FWIW the 2N5952s are biased at around 6V on Q1 and about 6.3 on Q3. I ended up with a B25K Voice pot because the A50K had a terrible range in my pedal and I don't have any W20Ks. The B25K sounds pretty good. But I still don't like BJF tone controls!
 
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Do you like the TREBLE control?

A25K might work better for the VOICE pot.

I used 2N1308, they have higher HFE than MP38A (>100 vs 60-ish) and more bandwidth for more top end. Si will not bias correctly with the resistors values on the schematic. What's the voltage on Q2-C? Should be around 6V.
 
I have 5.74V on the collector of Q2. The treble control needs to be quite high to sound good. It's not a bright sounding circuit as it is. It has plenty of mids which is fine and decent low end.

With the A50K Voice pot all the low end was right at the bottom of rotation CCW - I wired it stock. As soon as the pot was turned away from fully CCW the low end reduced suddenly. The bright cap works well to improve the overall sound of the pedal.

The 2N3565 ends a punchier, crisper sound which for my pedal it seems to need. The 250HFE example turned it into a boost more than an OD and the breakup wasn't as smooth. The 101HFE is smoother and crunchier.

I have a few 2N1308s but I have never got on with them. They always sound bright and thin for Ge to me. I guess it couldn't hurt to try some.
 
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