Emerson EM-Drive Clone

[Roctopus]

Hey gang! Been a while since I posted anything on here. I just finished a clone of the Emerson EM-Drive based on the vero from Guitar FX Layouts and a retail version of the EM-Drive as a comparison. I had issues with the Guitar FX Layouts version, particularly the 2M resistor that was connected to 9v and the Base of the transistor. It always sounded spit-farty and gross. So, with some help from a friend, I ended up connecting one side of the 2M resistor to the Collector and the other side to the Base of the transistor and it worked so much better. I'm not sure why I couldn't get it to work the FX way. Maybe someone can shed some light to that for me. I also added a 1M pull-down resistor to the circuit and I'm still trying out different transistors.

Happy building friends!
Roctopus

[rullywowr]

Perhpas it's possible that the transistor was a NPN or PNP and was reversed?  Or lack of black goop on the PCB (just kidding!)  Nice job, btw.  How do you like the sound? 

[Roctopus]

Perhpas it's possible that the transistor was a NPN or PNP and was reversed?  Or lack of black goop on the PCB (just kidding!)  Nice job, btw.  How do you like the sound? 

That could be the case. I like the goop theory though too The sound is good. It's a great clean boost and mild overdrive.

[wolfingsworth]

For a production pedal, the Emerson version isn't all that clean on the inside. I like yours better 

[stevewire]

Hey Roctopus,
Give a 2N2222 or a 2N3904 a try.  As you know from my build report that 2N5088 did not work well.  And if you read through the Guitar FX Layouts comments, some others did not have success with the 2N5088.

For a brief moment I saw inside my friend's production EM Drive.  His was not gooped.  But I also did not take the time to actually see what the transistor was.  As of now the 2N3904 is doing quite well by me.  televisiondown has stated that he prefers the 2N2222 even more so.  There is nothing that I changed about the 2M resistor in the layout.

All the internet sources I have read seem to feel that lower gain transistors work better.  Possibly Emerson tests a big batch of 2N5088 for just the right gains? Or I have a feeling that the Guitar FX Layout might have the wrong transistor listed.  As far as I can tell they are being consistent with the two resistor values.

There is a three page thread on freestompboxes.org about the EM Drive.

I wish, before I had drilled my enclosure, that I had planned to use CTS full size pots.

[Roctopus]

Stevewire,

Thanks so much for the info. Radio Shack has a 2n3904 NPN locally so I'm gonna run and grab it and report back. I believe the CTS pots I got are the same as in my retail version.

http://www.allparts.uk.com/online-shop/vintage-amp-parts/electronic-components/potentiometers-for-amps/potentiometer-cts-250kl-intensitytreble-control-p-15773.html

Roctopus

[stevewire]

Oh yes.  There are a few different sources that I use for CTS pots.  I've redone the wiring, pickups and electronics in all my guitars.  In fact I'll pay a little extra for some spot on 550k and 280ks.  I drilled my enclosure before thinking out the measurement for the full sized pots.  So instead of scraping the enclosure and putting the project on hold I used 9mm Alpha pots that I had on hand.

My friend that is working on an EM Drive tried a 2N3904 and said he felt it sounded better than the 2N5088, but he is having issues with low volume.  Mine is louder than my King of Klones build.  No problem there.

[Roctopus]

So I ended up getting a 2n3904 transistor and put it in another EM-Drive clone I had that was made per Guitar FX Layouts specs with the 2M resistor going to 9v and the other side to the Base of the transistor and it sounded good. Still not as loud or gainy as the original but it indeed proves a lower gain transistor works best for that vero design. I also plan on trying the 2n2222 to see if that beefs things up a bit.

All in all after testing my first build (with the 2M to C and B of the 2n5088), my second build (with the 2M to 9v and B of the 2n3904), and finally an original EM-Drive, I have to say that I feel like my first build sounded better and closest to the original. Perhaps I'll make a few demo videos and y'all can be the judge.

Happy Building!
Roctopus

[dawntreader]

Hey Roctopus,

Is this how you have your Em Drive wired after you adjusted the tagboard layout?

[Roctopus]

Hey Roctopus,

Is this how you have your Em Drive wired after you adjusted the tagboard layout?

Not quite. I have one side of the 2M resistor going to C of the Transistor and the other side going to B.

[dawntreader]

I see. I wired up the tagboard version and didn't get any sound. We're you able to get a functioning sound using the original vero layout with the 2M going to 9V?

[Roctopus]

I see. I wired up the tagboard version and didn't get any sound. We're you able to get a functioning sound using the original vero layout with the 2M going to 9V?

Yes I was but I had to use a lower gain transistor like the 2N3904 or a 2n2222.

[irmcdermott]

The folks over at FSB looked at the original and saw the transistor used was a MPSA18... if that helps.

[jewbacca]

Hey, Rocktopus - how did you wire up your switch? I built this today but cannot get my switching to work, for some reason. Thanks!

[Roctopus]

Hey, Rocktopus - how did you wire up your switch? I built this today but cannot get my switching to work, for some reason. Thanks!

I wired up the pedal in this thread as close to the stock version I had at home. However, I'v recently have been experiencing a popping when engaging the footswitch. My guess is that I might need an additional pull-down resistor on the output as well. Either way, I have build another EM-Drive clone and wired it according to Madbean's wiring diagram and it works great! My suggestion is to wire it his way and be safe