Earthquaker Devices Dirt Transmitter - Verified

[anders]

This thing just got traced by Storyboardist at Effects Layouts. He also posted a cool video about the process how to trace the pedal.
Schematic and video HERE

It looks like a tweaked fuzz face with a bias knob and a BMP style tone control. My 2N1711 transistor meassure about 150 Hfe so I think other low gain NPN silicon might work like PN2222 or MPSA06.

*Edit* Now verified
*Edit2* Changed orientation of 4,7uF cap

[storyboardist]

You work fast! I was just about to post the vero I drew up, but your's is smaller and looks better. haha I'll stick to perf and pcbs. :D

Input cap is backwards on your layout. It seems counter intuitive compared to pretty much every other silicon/npn fuzz face, but on the DT I traced the negative side of the 4.7uF goes to the base of Q1.

[anders]

Wow, thanks! And thank you for tracing it and post a schematic. It's been on my list for a couple years, almost bought it once just to trace it.
Keep em coming!

[Sphere80]

I just built your layout, Anders.  I'm using MPSA06's till I get the stock values.  And thank you too, Storyboardist, I saw your post this morning. What a great presentation.

[anders]

Thanks again for verifying Alex.
Just finished this one myself and I love it. It's worth getting the stocktransistors IMHO since they sounded best to my ears. They are pretty cheap and up for grabs at most DIY vendors.

Metal can 2N2222 and MPSA06 sounded good too as well as 2N1308 germaniums.

[music6000]

Storyboardist points out that the 4.7uf Negative side of Electrolytic should be at the Base of Q1.
Should the Layout be updated.

[Travis]

The orientation of that cap is technically correct as is but maybe EQD installed it backwards on accident or maybe they’re all like that

[anders]

Thanks for the catch, I'll update the layout. Just desoldered and tried the cap the other way around and it sounds exactly the same.

[tracer03]

Just built this, and it's really noisy. Checked all the grounds, etc. - is this expected?

[anders]

No, I don't have noise issues in mine. You could try to flip the input 4,7uF cap the "correct" way around (positive leg to base of Q1). I've had some noise issues in other circuits where the elctrolyctics was soldered the wrong way around.

[tracer03]

anders wrote

No, I don't have noise issues in mine. You could try to flip the input 4,7uF cap the "correct" way around (positive leg to base of Q1). I've had some noise issues in other circuits where the elctrolyctics was soldered the wrong way around.

I'll give that a shot and let you know how that works - thanks.

[tracer03]

Finally got back around to this one - must have been a loose ground on my test rig, because I tested again, and didn't seem as noisy. Once it got boxed, it's just fine.

One thing I *did* notice is that the 'Dirt' pot seems to work in reverse: CW is 'less' and CCW is 'more'. I wired it exactly per the original layout (where the positive side of 4.7 uF cap connects to base of Q1). Do you think that reversing the cap (negative side to base of Q1) will correct this? Or could I reverse/change the Dirt pot wiring to get the correct behavior?

EDIT: swapped the cap around and verified that the Dirt pot was wired correctly (again). Still works the same - CCW, more dirt - CW less.

[tracer03]

Bumping - I have now quadruple-checked the pot wiring, and it's correct to the layout. I still get less dirt when the pot is fully clockwise, and more when it's Fully CCW. Anyone else have this issue?

[anders]

Sorry for the late reply...I blame the holiday season.
Ok, I opened up mine and and it is wired as per layout and it has more gain when turned clockwise.
Have you checked the values of the 1M and 4,7K resistors? And input goes to lug 3? Otherwise than that I really don't know...have you tried an another pot?

[tracer03]

anders wrote

Sorry for the late reply...I blame the holiday season.
Ok, I opened up mine and and it is wired as per layout and it has more gain when turned clockwise.
Have you checked the values of the 1M and 4,7K resistors? And input goes to lug 3? Otherwise than that I really don't know...have you tried an another pot?

I double-checked the resistor values - spot on.
Pot is wired correctly, and I tested it before assembly, so...I'm gonna swap it out for another pot as a last resort. I also have a 2nd build almost completed, so I'll see what happens there.

[GrooveChampion]

Dont have 2N1711's, so I am going to try the lowest Hfe 2n3904's I could find, which is 190-ish Hfe

[GrooveChampion]

Works with my 190 HFE 2N3904's, sound like a better Woolly Mammoth.