Emerson Custom Guitars E-M Drive.  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.

Re: Emerson Custom Guitars E-M Drive.

Postby soggybag » 17 Aug 2013, 05:02

Looks like this is, essentially, an SHO variation, with the crackle free gain control. Might be good to add an LED from S to G to protect the MosFET.
soggybag
Solder Soldier
 
Posts: 240
Joined: 08 Aug 2007, 00:29
Location: San Francisco
Has thanked: 17 times
Have thanks: 7 times

Re: Emerson Custom Guitars E-M Drive.

Postby geiristudio » 17 Aug 2013, 14:22

rugeb wrote:
geiristudio wrote:I've got the original unit......


In the original unit: what transistor is used?


I'll have a look later today. I popped it open once before and it's covered with glue. It's clear glue though. I'll see if I can make it out.
geiristudio
Breadboard Brother
 
Posts: 127
Joined: 02 Jun 2011, 16:40
Has thanked: 3 times
Have thanks: 21 times

Re: Emerson Custom Guitars E-M Drive.

Postby geiristudio » 17 Aug 2013, 22:37

I had a look inside my EM-Drive and there's A LOT more glue than in the original photo at the beginning of this thread. Also the transistor was covered with black nail polish.

It's an MPSA18. I couldn't take a photo because my iPhone can't get the text to show. But yes, it's an MPSA18. There you go!

For this message the author geiristudio has received thanks: 3
IvIark (06 Jan 2014, 02:12), modman (28 Aug 2015, 03:41), rugeb (17 Aug 2013, 23:23)
geiristudio
Breadboard Brother
 
Posts: 127
Joined: 02 Jun 2011, 16:40
Has thanked: 3 times
Have thanks: 21 times

Re: Emerson Custom Guitars E-M Drive.

Postby Roast7 » 05 Jan 2014, 23:30

my "Em-Drive"
Image

I'm still in testing, I use it to boost volume but I need more volume ...

I tested an old 2N4401 and has given sound
The sound without the effect is more bass than with the pedal on.

Tested a 2N4401 and 2N3904
2N4401 - More bass than the 2N3904 and has more gain
2N3904 - Clean and balanced (with little gain compared to 2N4401)
Roast7
Breadboard Brother
 
Posts: 64
Joined: 18 Jul 2012, 14:07
Has thanked: 1 time
Have thanks: 8 times

Re: Emerson Custom Guitars E-M Drive.

Postby vandermann » 08 Jan 2014, 13:36

Hey Guys!

Any factory EM - DRIVE owner could please post the transistor voltages!?

Many Thanks!!

Cheers, Vanderson
User avatar
vandermann
 
Posts: 11
Joined: 18 Nov 2009, 13:56
Has thanked: 0 time
Have thanks: 21 times

Re: Emerson Custom Guitars E-M Drive.

Postby commathe » 09 Jan 2014, 03:04

Those look like really, really nice pots. Does anyone know which brand?
commathe
Breadboard Brother
 
Posts: 97
Joined: 01 Jul 2013, 23:31
Has thanked: 6 times
Have thanks: 8 times

Re: Emerson Custom Guitars E-M Drive.

Postby mdtc » 09 Jan 2014, 05:15

Thanks for all the posts on this pedal. I'm about to embark upon it as my first "from scratch" build. I see there are plenty of opinions on which transistor to use. I've ordered the MPSA18, although it sounds like it's worth experimenting :-)
mdtc
 
Posts: 1
Joined: 31 Dec 2013, 23:15
Has thanked: 0 time
Have thanks: 0 time

Re: Emerson Custom Guitars E-M Drive.

Postby tiagojoy » 22 Jul 2014, 18:52

tiagojoy
 
Posts: 17
Joined: 21 May 2010, 01:21
Has thanked: 0 time
Have thanks: 9 times

Re: Emerson Custom Guitars E-M Drive.

Postby jonnyxjuturna » 07 Aug 2014, 12:49

Would a 5.1k work in place of the 4.7k? Much sound difference?

Trying to use components that I already have. So I can either use a 5.1k carbon comp. Or I could use 2 2.4k carbon films in series. Thoughts?
jonnyxjuturna
 
Posts: 24
Joined: 30 Jul 2008, 03:38
Has thanked: 0 time
Have thanks: 0 time

Re: Emerson Custom Guitars E-M Drive.

Postby Nocentelli » 07 Aug 2014, 13:07

I'd just use the 5k1, you'll have a slightly higher maximum gain available. Different transistors will have a larger impact on the sound, worth trying out a few different types, any npn Si should work.
mmolteratx wrote:absolutely zero commercial use allowed. If I find anyone selling these, I'll fly to your house and kick you in the nads. And you may or may not find yourself in trouble.
User avatar
Nocentelli
Tube Twister
 
Posts: 2016
Joined: 09 Apr 2009, 08:06
Location: Leeds, UK
Has thanked: 765 times
Have thanks: 761 times

Re: Emerson Custom Guitars E-M Drive.

Postby jonnyxjuturna » 07 Aug 2014, 14:03

On a similar note I currently have two 1megs in series to get that 2 meg resistance. But I could substitute in a 2.4meg in that spot. I guess same question. Is that going to negatively impact the sound. I am using a bs170 as previously suggested in this thread for my transistor
jonnyxjuturna
 
Posts: 24
Joined: 30 Jul 2008, 03:38
Has thanked: 0 time
Have thanks: 0 time

Re: Emerson Custom Guitars E-M Drive.

Postby Nocentelli » 09 Aug 2014, 20:19

jonnyxjuturna wrote:On a similar note I currently have two 1megs in series to get that 2 meg resistance. But I could substitute in a 2.4meg in that spot


Most people only have 2M2, and would stick that in: It's only 10% higher, some resistors are up to 5% higher with tolerance, another 10% is unlikely to make that much difference.

jonnyxjuturna wrote:I am using a bs170 as previously suggested in this thread for my transistor


:hmmm: BS170 is a mosfet, but the original circuit uses a BJT - a bipolar junction transistor. Any medium gain npn BJT (e.g. 2N5088/9, MPSA18, 2N3904, BC547/8/9, 2N4401, BC108/9 etc...) will probably sound similar to the original.

The mosfet on the other hand might work, but it's not guaranteed. Mosfets usually have similar value resistors from drain (collector) to +9v as they have from source (emitter) to ground, and they usually have a half supply bias voltage applied to the gate (base): Have a look at the AMZ mosfet booster, zvex super hard-on, or catalinbread chili picoso to see an equivalent single stage booster using a BS170. I'd imagine a mosfet in this circuit would sound different to the original EM drive, and I would try any BJT first.

The key point here is that the design is pretty simplistic: Grounded emitter amplifiers are running at full tilt, and are not that stable, different transistors with different characteristics will behave quite differently e.g. resulting in splatty fuzz if you're unlucky. A "better" design (e.g. with an emitter resistor, and some base biasing - look at the EHX LPB-1) would be less reliant on the *right* transistor to get a good sound, but you may well be lucky and get a nice sound you like with what you've got.
mmolteratx wrote:absolutely zero commercial use allowed. If I find anyone selling these, I'll fly to your house and kick you in the nads. And you may or may not find yourself in trouble.
User avatar
Nocentelli
Tube Twister
 
Posts: 2016
Joined: 09 Apr 2009, 08:06
Location: Leeds, UK
Has thanked: 765 times
Have thanks: 761 times

Re: Emerson Custom Guitars E-M Drive.

Postby MrSparkle666 » 15 Sep 2014, 11:49

Glad someone figured out the right transistor for this circuit. The 2n5088 noted in the layout is definitely NOT appropriate here. It has far too much gain. I did some quick spice simulations, and with a 2n5088 the amplifier is biased just above ground and basically producing lots of hard asymmetrically clipping on the low end. Not good. The transistor gain is of critical importance in this circuit if you want it to function properly at all.

The problem with these grounded emitter circuits is that they are basically DC biased by the transistors gain. Since the gain of BJTs varies so much, the bias of the circuit can be drastically affected by the choice of transistor or even somewhat by ambient temperature. The performance is also greatly affected by pickup impedance. As Nocentelli pointed out, it's a highly unstable configuration. That's fine for an unwieldy fuzz pedal, but it's a piss poor design for a so-called "transparent" overdrive. The pedal could sound different on Tuesday than it did last Friday, and there will be even more variation from pedal to pedal. And even if it does sound good at low settings, once the gain knob is cranked this thing is always going to be a splatty fart factory in the low end, like a blown speaker, not amp-like at all. You can hear this clearly in some of the youtube demos of the EM-Drive, and it matches exactly what I'm seeing in the spice simulation.

I don't think this circuit has much value other than as a passing curiosity. I can't believe that some people think this pedal is some kind of holy grail of "transparent" overdrive.
MrSparkle666
Breadboard Brother
 
Posts: 50
Joined: 19 Apr 2009, 00:04
Has thanked: 0 time
Have thanks: 1 time

Re: Emerson Custom Guitars E-M Drive.

Postby newly » 01 Dec 2014, 08:14

any idea which page confirmed the transistor type? MPSA18 is like bursting my speaker....
newly
Breadboard Brother
 
Posts: 71
Joined: 31 Oct 2009, 10:55
Has thanked: 3 times
Have thanks: 2 times

Re: Emerson Custom Guitars E-M Drive.

Postby jay42 » 21 May 2015, 01:36

I was unaware of this pedal until a few days ago. After looking into it, I did a test on my BYOC Tri-Boost. If you short the 360 ohm emitter resistor in the LPB2 section, it sounds pretty much like the demos. I already had an MPSA18 in it...must have been out of 2N5088's that day....can't recall. Kind of surprising. I thought it would gate badly. It rolls off some high end, but that's not necessarily a bad thing in this case. It's subtle.
jay42
 
Posts: 32
Joined: 06 Aug 2010, 01:36
Has thanked: 0 time
Have thanks: 6 times

Re: Emerson Custom Guitars E-M Drive.

Postby mildew » 27 Aug 2015, 07:35

I tried putting my stripboard Em drive after my vox847 wah for a boost but the wah does not "wah" when output to the em drive.

I assume its the same as the "wah output to fuzz pedal stops wah working" problem, but dont know enough to be sure...

Ideas anyone?
mildew
 
Posts: 35
Joined: 01 Jan 2015, 01:50
Has thanked: 2 times
Have thanks: 1 time

Re: Emerson Custom Guitars E-M Drive.

Postby mildew » 27 Aug 2015, 08:46

done some interwebbing and it seems that the common emitter of the em drive gives it a super low input impedance, buggering up the wah before it, just like a fuzz face.

The aim was to put the em drive inside the wah as an output booster.

im still unsure about this issue, so if anybody who knows this stuff can confirm...
mildew
 
Posts: 35
Joined: 01 Jan 2015, 01:50
Has thanked: 2 times
Have thanks: 1 time

Re: Emerson Custom Guitars E-M Drive.

Postby induction » 27 Aug 2015, 09:18

mildew wrote:The aim was to put the em drive inside the wah as an output booster.

The EM drive is a particularly bad choice for that application. Why not use a different booster with a higher input impedance? There are plenty of op-amp or jfet boosts that will work fine.
induction
Resistor Ronker
 
Posts: 269
Joined: 07 Feb 2012, 21:47
Has thanked: 59 times
Have thanks: 130 times

Re: Emerson Custom Guitars E-M Drive.

Postby mildew » 27 Aug 2015, 09:56

ive got a SHO kit in the mail. would this be better for the output of the wah?
mildew
 
Posts: 35
Joined: 01 Jan 2015, 01:50
Has thanked: 2 times
Have thanks: 1 time

Re: Emerson Custom Guitars E-M Drive.

Postby induction » 27 Aug 2015, 11:30

The SHO has a very high input impedance. It should work fine. It adds some grit at higher settings, so it depends whether you like the coloration and how much boost you want. The AMZ mosfet booster is very similar, but has less dirt. The MXR Micro-amp is another louder-but-not dirtier type of boost that would work ok. Almost anything would be better than most of the single BJT boosters out there, especially the grounded emitter ones.

For this message the author induction has received thanks:
mildew (29 Aug 2015, 11:35)
induction
Resistor Ronker
 
Posts: 269
Joined: 07 Feb 2012, 21:47
Has thanked: 59 times
Have thanks: 130 times

PreviousNext

Return to Boutique Stompboxes dissected...

Who is online

Users browsing this forum: andlord, USMarine75 and 5 guests