Electra Distortion

[amz-fx]

The famous Electra distortion was never exactly the circuit in one of the MPC modules. A diy builder took the circuit from the Electra MPC5 Power Overdrive module and modified it. He then posted that info to Usenet. I finally found my copy of the post and I am attaching it here.

The famous Electra distortion was never actually used in the Electra guitars! 

From: bew4568@xxxxxxxx.edu (Bruce E.)
Newsgroups: rec.music.makers.builders
Subject: Simple Distortion circuit schematic
Date: 14 May 1994 13:18 CDT
Organization: Texas A&M University OpenVMScluster

Here is a little distortion circuit that I kinda like.  It's very easy to 
build and sounds amazingly like an Ibanez tube screamer.  With the exception 
of the diodes it is the circuit for the Electra Power Overdrive module (the 
one that went inside the guitar--another relic of the '70's).  It's important 
to use Germanium diodes to get the right sound.  The voltage out is .4 volts.  
If you need more power and less distortion use Silicon diodes, for 1.4 volts 
output (you can change the values of the 4.7K and 470 ohm resistors to get 
more distortion if you need.  Just tell your electronics friend that it's an 
emitter follower and you need more gain).  



                            B+= 9v
                            |
                            |
                            /
                            \
                            /  4.7K
                            \
                            /
                    2.3M    |       | |
                   /\/\/\/\-o       | |
                   |        o-------| |--------o-------o---> Out
                   |        /       | |        |       |
                   |    |  /C       | |        |       |
          | |      |    | /                  -----   -----
          | |      |    |/          0.1 mfd   /^\     \./  Both Ge-type
 In >-----| |------o----|  2N3904            -----   -----
          | |        B  |\                     |       |
          | |           | \                    |       |
          0.1 mfd       |  \E                  |---o---|
                            \|                     |
                             |                     |
                             |                ----------
                             |                  -------
                             /                    ---
                             \                     -
                             /
                             \ 470
                             /
                             \
                              |
                              |
                              |
                          ---------
                            -----
                              -
Now for all you electronics types who just said, "Heck, that just hard-clips 
the signal.  It'll sound horrible", you should realize that the gain of the 
transistor is changing with the signal level, and has the effect of rounding 
out the upper lobes of the undistorted wave.  If you don't believe me just put 
it in your PCSPICE program and watch what it does.  I don't claim credit for 
the circuit--the Electra people came up with the amp, and I was just fiddling 
with it and found that this worked well--later on I figured out why.  If you 
want an uninverted signal (if you think there is a difference) take the signal 
off the emitter instead of the collector.  It might not sound the same, 
however.  I didn't test it.

Have fun with it.  Should cost about $10 from Radio Shack components, 
including jacks.

Ask me about it if you really really really need to.

Bruce
bew4568@xxxxxxxx.edu

Best regards, Jack

[amz-fx]

I probably should post the MPC5 schematic too:



regards, Jack

[Ben N]

So it's an NPN boost . Huh.

(Groovy pic, Jack, BTW.)

[Steben]

Does the text really state sounds like tube screamer? 

[duck_arse]

Code Select Expand

Just tell your electronics friend that it's an emitter follower and you need more gain

what would my electronic friend say about this?

[Mark Hammer]

Does the text really state sounds like tube screamer? 

Keep in mind that Bruce E.'s post is WELL before the creation of Youtube and the gazillions of product demos it provided, WELL before the widespread availability of the informational and physical resources we have available to us now (e.g., toner transfer and this forum), WELL before the glut of mostly-redundant-but-juuuuuussssst-a-little-different overdrive "designs" and products out there, and also well before the world went crazy for Tube Screamers and started being picky about TS-808-vs-9-vs-7-vs-10 differences.

I hasten to note that when Thomas Edison was going around to county fairs and charging people for the privilege of recording their voice onto a wax cylinder, reporters of the time said that it was REALLY hard to tell the difference between the recording and their actual voice.  We've gotten a little better at differentiating reality from wax cylinders over the intervening years.

Thanks for that Jack.  Ah, the "good old days", when schematic drawings had to be produced with Courier alphanumeric characters, and almost everything there was to know about pedals and music electronics was found on alt.guitars and rec.music.makers newsgroups.

[aron]

Now we find out LOL!

Along with the LPB-1 and Jack's Fuxx Face, those were my starting projects! I think I still have mine.
Thanks Jack!

[antonis]

Code Select Expand

Just tell your electronics friend that it's an emitter follower and you need more gain

what would my electronic friend say about this?

The last thing one could see is an Emitter follower..

[BubbaFet]

Did you see this video about the elusive Electra Distortion?
It features Josh Scott (JHS), David Barber (Barber Electronic), Jamie Stillman (EarthQuaker Devices), Nick Greer (Greer Amps) ?

https://www.youtube.com/watch?v=LWig2L2mvjI

[Rob Strand]

The 2.3M on that schematic is an error.

This thread discusses the schematic errors and variants.
https://www.diystompboxes.com/smfforum/index.php?topic=124041.0

I also gave some biasing examples of different transistors.

In short: 2.3M should be 2.2M and transistor gain probably around 220 (yellow dot).

[Ben N]

Did you see this video about the elusive Electra Distortion?
It features Josh Scott (JHS), David Barber (Barber Electronic), Jamie Stillman (EarthQuaker Devices), Nick Greer (Greer Amps) ?

https://www.youtube.com/watch?v=LWig2L2mvjI

A lot of Josh Scott blabbing on and on about nothing.

[Phend]

Does 2.2 vs 2.3 M make a difference in sound or operation?

[amz-fx]

Does 2.2 vs 2.3 M make a difference in sound or operation?

It's not going to make much difference. It is within the 5% tolerance of a even a good resistor. It is a typo in the ascii schematic as can be seen from the MPC Power Booster schematic that I included.

I thought it would be interesting to see the original  post from 1994 that started the whole Electra distortion circuit method.

I believe that the MPC Pot in the schematic of post #2 is the volume control in the guitar and not part of  the module.

Best regards, Jack

[Steben]

Does the text really state sounds like tube screamer? 

Keep in mind that Bruce E.'s post is WELL before the creation of Youtube and the gazillions of product demos it provided, WELL before the widespread availability of the informational and physical resources we have available to us now (e.g., toner transfer and this forum), WELL before the glut of mostly-redundant-but-juuuuuussssst-a-little-different overdrive "designs" and products out there, and also well before the world went crazy for Tube Screamers and started being picky about TS-808-vs-9-vs-7-vs-10 differences.

I hasten to note that when Thomas Edison was going around to county fairs and charging people for the privilege of recording their voice onto a wax cylinder, reporters of the time said that it was REALLY hard to tell the difference between the recording and their actual voice.  We've gotten a little better at differentiating reality from wax cylinders over the intervening years.

Thanks for that Jack.  Ah, the "good old days", when schematic drawings had to be produced with Courier alphanumeric characters, and almost everything there was to know about pedals and music electronics was found on alt.guitars and rec.music.makers newsgroups.

Allright. We will note this as "adds drive just as things like that tube screamer does"

[Rob Strand]

It's not going to make much difference. It is within the 5% tolerance of a even a good resistor. It is a typo in the ascii schematic as can be seen from the MPC Power Booster schematic that I included.

It's just a wrong value outright.  Besides 2.3M is not a standard value.

[Phend]

Nor is a 50uF electro cap, but I have seen it often on schematics.

[GibsonGM]

I've seen 50u caps, only a few times - in vintage equipment.  Mouser still sells them!

[pacealot]

You could easily buy "weird" non-E24-value caps, especially electrolytics (and especially especially axials), like the aforementioned 50µFs (and 2.5µF, and 4µF, and 80µF, and 0.006µF, and...), for decades after the E24 standard was put in place. (You can still buy most of those values, but now they're prohibitively expensive and probably thoroughly unnecessary for their role in the circuit.) But you still can't buy a 2.3M resistor!

[amz-fx]

But you still can't buy a 2.3M resistor!

It might be that Bruce looked at an almost 20 year old module and saw what he thought were red-orange-green bands that actually were red-red-green!  Or since the original Usenet post was probably done in DOS, and editing text was such a pain when doing an ascii schematic, it was just a typo. Either way, 2.2M is the correct value according to the MPC5 schematic in the second post. Since he seems to have built the circuit, he probably used a readily available 2.2M resistor, and it is just a typo.

Best regards, Jack

[Mark Hammer]

But you still can't buy a 2.3M resistor!

Ah, but you CAN.  They're just cleverly disguised as 2M2 5% resistors! That means you have to "hand select" for them.