EM Drive

[stevewire]

I picked up the layout at Guitar FX Layouts.  A friend of mine has an Emerson Custom EM Drive.  After researching it a bit online and watching a few demos on YouTube my inertested was piqued.  I had bought a few Russian paper-in-oils caps to build my EggHead OD, so I had those on hand ready for this project.  And after I saw the parts count I knew I had to give this a try.  



The drill is press is new to me and this was a learning experience.  I wish I had spaced the knobs slightly closer together and not so far near the top of the enclosure.



Directly from the Guitar FX Layouts, the 2N5088 didn't not work out for me.  It sounded like a low gain fuzz. With this transistor the gain knob did not work as expected.  I looked through my very sparse collection of transistors and search the internet for a similar pinout.  I found a 2N3904 and this did the trick.  Suddenly the tones and controlability fit the description and matched the demos.



I am still playing around with it.  I just finished last night.  I've had it going head to head with my King of Klones, Timmy and Morning Glory.  Started running it at 12 volts and like that even better than 9 volts.  Curious about 15v or 18v.  As of so far it is pretty cool.

[hoodoo]

Looks great mate, nice shade of blue, and you just saved yourself a pile o' cash for very few components

[lincolnic]

The rest of the circuit is hiding in those giant green shells, right?

I kid. Nice build!

[televisiondown]

Very nice looking build! I've been eyeing up that layout, too I'll probably try it out with regular caps first, but where did you pick up the paper-in-oil caps?

[stevewire]

televisiondown,
I originally bought four Russian paper-in-oil caps on ebay for my Egg Head build.  I tried three different 2N5088s and they all sounded the same.  Make sure you have a few alternatives around for when you are disappointed with the 2N5088s.  I do recommend the 2N3904, but let me know if you find something that works nicely.

I should add that it stacks well with my King of Klones, Timmy and Morning Glory as well. It's in that low gain transparent class, but they all seem to have their own EQ and texture.

I am already planning out a 1590A version of this with some Wima MKP2 box caps.  I am curious if the high end of the EQ might turn out a little differently.

[televisiondown]

Very cool...thanks for the tips! I'll have to check eBay now. Those big green caps just look so good.

[stevewire]

televisiondown,
Watch for the 100v or 250v.  I can't recall which I bought.  I'll have to look again.  If you are trying to keep the size down, you aren't going to be happy with a 630v or 1000v caps.

[Roctopus]

wow this is great! i'v been working on one myself and i really appreciate the insight. you rock!

[stevewire]

I added a 1M pulldown resistor at the input.  It needed it.  This is for anyone of you that is considering building one of these.

[televisiondown]

Built this on vero today and threw it into my test rig. Yeah, the 2n5088 wasn't that great. I had a 2n2222 and I think it sounds really good. Much better low end. The boost is very clean and there's some good dirt at the end of the gain pot. I have to look around and see if I have a 2n3904. With it socketed, I can at the very least keep it as a transistor tester hehe.. But it really is a great boost/clean drive.

Btw I didn't get any PIO caps. I just used some box caps I had on hand. I'll have to try the pull down resistor, too.

[stevewire]

Hey Televisiondown,
Awesome that you got it together.  I have a friend that just built one.  He also stated that the 2N5088 didn't work for him.  I'd like to compare a 2N2222 with the 2N3904 to see what works best for me.  Thank you for that information.  I understand the nature of the circuit as a boost, but I would say with the 2N3904 it really is a low gain drive.  I compare it a lot against my King of Klones, Morning Glory and Timmy.   I am also glad that I socketed the transistor, which I always do anyways. 

Please post if you get the chance to compare the 2N3904 with the 2N2222.

[midwayfair]

Really, the EM Drive would work correctly with basically every transistor you put in it if they had designed it with proper biasing. Gus over on DIYSB made an improved version that doesn't require sifting through a bunch of different transistors to get exactly the right gain for a working build:

http://www.diystompboxes.com/smfforum/index.php?topic=103688.0

It's kind of sad to me to see such an electronically poor design become a popular beginner build ... there are dozens of more common projects that are guaranteed to work right out of the gate and there's nothing about the sound of the Em Drive that can't be achieved while still making it sound the same.

Next time I can rant about charging $150 for the thing. I mean, that's almost admirably balsy. 

[televisiondown]

Ok, I tried the 2n3904 and I liked it more than the 2n5088 but not as much as the 2n2222. Mostly it's the way it breaks up with the gain up and the way it sounds when it's clean boosted.

I agree, Jon, it's not worth the price tag for such a simple circuit. But, for 10 minutes of soldering and the fun of playing guitar for longer than the build time...I couldn't resist