ELECTRA: Modular Powered Circuits - Tube Sound MPC8, AKA the Electra Distortion

Recently the Electra Distortion grabbed my attention again, so as I often do, I went digging for more information on the Electra MPC series guitar effects (modular powered circuits).  

One problem; Electra doesn't appear to have ever made a Distortion module.  Interesting...   

Then I read what we know as the Electra Distortion is really the Tube Sound Module, and it had just been mislabeled as a Distortion by the internet.  OK, that can happen -  basically, take the Power Overdriver and add clipping diodes.

During my search, I found the schematics of the entire MPC range, care of pinkjimmiphoton on Free Stompboxes.  On closer inspection, the Tube Sound is nothing like the Power Overdrive.  So my question is - was the Electra Distortion ever a real thing, or does someone's early mod on a Power Overdrive now have a life of its own?  Was there another version?  

Naturally, I'm not even close to being the first person to have this thought.  It turns out that there were two versions - but neither was ever called a Distortion.

POWER OVERDRIVE MPC5

The power overdrive is actually a clean boost, with low frequencies dropping off around 100hz - they called it an overdrive as the boost was meant to overdrive an amp.  Makes sense.   

TUBE SOUND MPC8 - ALTERNATE VERSION

So after looking at the alternate version of the Distortion / Tube Sound, I'm even more confused than I was when I started writing this.  

I ran the alternate version on LTspice, and nothing really happened - boost yes; anything resembling distortion, no.   I tried high-gain transistors and different diodes, and nothing really happened.  Maybe a tiny little bit of clipping, but it was so small, I'm not sure anyone would notice.  

I did of course try flipping the diodes and resistor after Q2 to ground, and then it looked a lot like one would expect.  Quite similar to the Electra Distortion.  

Below is with the diodes flipped to ground, which is not how the circuit is drawn, but it did get a result.

TUBE SOUND MPC8 AKA THE ELECTRA DISTORTION

So onto the common version.   

I'm still kind of curious about this one, as people say that it's the same as the Overdrive but with diodes, but there's clearly no 120k resistor on the input, or a pot controlling the input level, which in turn reduces the effect of the clipping diodes.

Either way, it’s still a great little circuit.

The trace below compares three options.   

1) the Tube Sound - the Power Overdrive with diodes added.  Includes the 120k resistor on the input and the input level pot

2) the Distortion - as above, but no 120k input resistor or pot at the front

  

3) The classic Distortion - as shown above

As you can see, there are varying levels of clipping occurring, in numerical order as listed above.