Just revisited an EM-Drive I built a while ago while trying out low/medium/sparkly drives. It worked ok first go, but really sounded like a fart inside a jam jar full of bees. I'd used some random tranny I'd had lying around so once I got some 2n5088 I figured I'd try it according to spec.
After replacing the tranny, it didn't work. I checked the vero layout and found a resistor in the wrong spot - Odd, it worked previously. So I replaced that resistor with one closer to the value (under rather than over) in the proper position resoldered, checked, double checked, looked at voltages (looked low) and touched up the solder joins again.
It still didn't work, so I grabbed my exacto knife and started running it down between the strips like a 15 year old virgin who'd been promised paradise if he could get it working. I re cut the two breaks in the strips with my drill bit and retried it.
It finally worked. It still sounds like a bad flubby fuzz, although it's a lot better than before, but it's still not going to get boxed. I'll be going with a Wampler Cranked AC for that side of the box instead (The English Gent was just a bit messy with the outboard wiring, but sounds very similar).
Here's the culprit:
(http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/Emerson/Em-Drive-with-trimmer.png)
Fresh battery?
There is someone in the huge thread of comments on tagboard that mentions connecting one of the resistors to the collector of the tranny instead of the base. I don't remember which one but I do remember doing it and it made the pedal sound much better.
That's where I had the resistor originally, but when I couldn't get it going I reverted back to the original vero layout thinking I'd messed up someplace (while still knowing I'd done the resistor-between-collector-and-base thing for some reason). I might shift that resistor back and see what happens, but I'm playing through high output humbuckers and it doesn't like those a great deal apparently.
I flipped the tranny on the one my daughter built. and it sounded amazing. A few other people on tagboard mentioned it.
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Yes, it's possible, and Emerson messed it up.
The Em Drive is probably the worst 5-component effect for a beginner to pick. The biasing method is pointlessly terrible. It looks simple, but it relies on a very tiny portion of transistors actually working throughout the entire gain range, and it sounds awful in the upper part of the gain range anyway. There are probably hundreds of simple effects that will do the same thing it does (boost) better, starting with the LPB-1.
If you can't get it working when connecting the resistor to the collector, then start looking for problems.
Also, photos and voltages help. The collector volt will change based on the gain pot setting.
+1
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Quote from: midwayfair on April 27, 2016, 06:09:12 PM
The biasing method is pointlessly terrible. It looks simple, but it relies on a very tiny portion of transistors actually working throughout the entire gain range, and it sounds awful in the upper part of the gain range anyway.
I had never heard of the pedal before but when I saw the layout I just thought "WTF is this". Thanks for confirming :)
I'm guessing that this pedal is really only going to work if you audition transistors until you find one that happens to work.
I was literally waiting for Jon to comment on this.. he LOVES this circuit. lol
I agree 100% with him on this one.
Cody
So there was an episode of the short lived Sarah Silverman show where Brian Posehn's character (I believe) finds a jam jar he saved a fart in that he had forgoten about. Funny ep. ;D. No bees though!
Quote from: selfdestroyer on April 27, 2016, 08:59:29 PM
I was literally waiting for Jon to comment on this.. he LOVES this circuit. lol
I agree 100% with him on this one.
Cody
I had kinda been waiting for Jon to chime in as well.
My friend has one (as in the Emerson one) and it doesn't sound bad. Of course when he told me how expensive it was I went home and built one with the cheapest parts I had on hand. Mine sounds fine too. I use it sometimes, but I've never built another boost. I have a feeling once I build the Jack Orman mosfet boost pcb I got that the Em-Drive will come of the board. I've been eyeing a SHO as well.
Wasn't that I couldn't get it working, it just sounds like arse: even after a tranny swap, a resistor move, a tranny rotate, with and without a buffer in front.
I have never before actually binned a project (usually they get put in the box of fail for part recycling where possible), but I desoldered the pots and jacks, and turfed the whole vero in the bin.
Oops, right, I meant "work" in the sense of "act as a mild distortion/boost", sorry.
It's not an overly impressive drive anyway.
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