MADBEAN: Kraken

The Madbean Kraken is basically a Mu-Tron Micro V with attack and decay controls, but the rest remains the same.  

MADBEAN KRAKEN - VERO LAYOUT

RUNOFFGROOVE: Nurse Quacky (EHX Dr Q)

This one seems to have many parents - I was not really sure what to tag it as.  It started life as an Electro-Harmonix Dr Q, which ended up as a Jack Orman Dr Quack and then at some stage Mark Hammer mods have appeared, and more changes bought it to Nurse Quacky by Runoffgroove.   Hopefully I have all that in the right order.

RUNOFFGROOVE NURSE QUACKY / MODDED EHX DR Q - VERO LAYOUT

MUSITRONICS: Mu-Tron III

I've already built the Micro V, and it's a really cool-sounding envelope filter, so I thought I might try the Musitronics Mu-Tron III.  It's generally regarded as THE envelope filter of its day.  As much as I love a bit of fuzz, I really do enjoy sitting in a groove with an envelope filter running....  

Note read comments below - currently unverified. 

MUSITRONICS MU-TRON III - VERO LAYOUT

Same again, but bigger...   bit more room on the board.

Recommend that you check it against the schematic below if you plan to build this before I do.  I'll post photos etc once I have it made, or at least a progress report from the bench.   

The placement of the trimmer is a bit clumsy, but I think I will test some values and hopefully replace it with a standard resistor.  The trimmer is R23 on the schematic - see note re value.

Once (if ever) working, I'll need a suitable funky enclosure to fully release the seventies vibe.

ON THE BENCH

Seems to be partially working, but it's not fully wired up with all the switches etc yet.  I used the larger layout for this.

The homemade vactrol is working, although white heatshrink still lets light through.   Needs to be blacked out more - the case should take care of that, but it's not helpful trying test it like this.

It’s being very tricky to dial in, which may be the homemade vactrol, and/or the size of the trimmer on the LED.   Seems to have a very small spot where it works, but even then, the sweep is not great.    

Apparently, these are notoriously difficult to get going properly - maybe a Micro V is a better idea if you consider trying this.  

Suggested mods/notes to self to address issues 

1) bigger trim pot.  220k

2) change 180k resistor to 500k trimmer 

So still a work in progress - UNVERIFIED.

MUSITRONICS MU-TRON III - SCHEMATIC

Note that the schematic above shows where to place an external control input for the envelope filter.

The strange part labeled O805 is a single LED with dual LDRs.  It is not available to buy, so your options are make your own with LDRs and an LED, or try a couple of single optoisolators and see how that works.  

Google "R.G. Keen Neutron Filter" for more details on options.  

MUSITRONICS MU-TRON III vs EHX Q-TRON

As it happens the EHX Q-Tron is a direct progression of the Mutron III, albeit appearing over twenty years later.  They share a lot in common in terms of topology - perhaps due to the fact that they were both designed by Mike Beigel of Musitronics fame.

MUSITRONICS: Mu-Tron Micro V

The Musitronics Mu-Tron Micro V is a cool old auto-wah / envelope filter from the seventies - I feel I need to be wearing a valour tracksuit, possibly with a half-unzipped jacket exposing generous chest hair with a gold dangler to really play this properly.  Maybe a moustache too...   

I've used a LM13700 instead of the near impossible to find CA3080 (real ones that is).  In the thread on DIY Stompboxes there's a reference to changing the 1M resistor on the collector of Q2 to 470k / 500k for a better sweep (I have not tested this yet).

If you're interested in how envelope filters work and have some spare time to read and wrap your head around this, here's an excellent reference by Mark Hammer.

MU-TRON MICRO V  - VERO LAYOUT

This one is verified.  Note the two sides of the LM13700 are tied together.  I'm yet to test them being split.  In the thread, they say that it just sounds a bit sweeter with both sides running together, so I'll probably leave it that way.

It did take some filing to make it fit, but I did manage to fit it in a smaller than planned enclosure.

ORIGINAL SCHEMATIC 

VIDEO DEMO