DEMO Wishing y’all a Mürry Christmas (and a Happy New Ear!)- Modded MuTron III envelope filter (and a christmasy bonus)

This post contains an audio or video demo

Bricksnbeatles

Member known well
Build Rating
5.00 star(s)
A few years back I ordered a few Moo-Tron boards from FuzzDog in the UK, but a lack of ideas for graphics left me holding off on building them for a long time.

Not too long ago, I finally came up with with an idea, so I put together a few designs and had a few forum members “vote” on their favorite. I had the winning design made up into faceplates by Spencer over at @amplifyfun , and after finishing up a long and busy semester just over a week ago, I was finally able to get back to the workbench, and on Wednesday I whipped this up. The other one will have to wait until after the new year (and might get some additional mods) since I’m all out of caps in the single-digit nF range and my last charge pump chip is coming to NJ with me today to fix a busted charge pump in a relative’s pedal.

The pedal is called the μ-Wahhh! in homage to the recurring sound in the late 60s/early 70s era of the Mothers of Invention (most notably on Weasels Ripped My Flesh, which is my favorite Zappa release) wherein “Moo-ahhhh!” is aggressively shouted. As you may know, μ is the Greek lowercase letter “Mu”, which points towards the Mu-tronics/Mutron DNA of the pedal, while the “Wahhh!” part is because it’s an envelope filter/auto-wah. The dash in μ-Wahhh! Is the Zappa moustache insignia, since it’s of course a Zappa themed pedal, and Frank was an occasional user of the Mu-tron III envelope filter, even if he’s better known for his use of the Mu-Tron Bi-Phase and the Maestro SF/H /Oberheim VCF. At the bottom is a quote from Lowell George’s iconic “German-boy” monologue in the opening track of Weasel’s Ripped My Flesh. Red anodized hardware all around, but it’s a bummer that not all of it matches in shade. The other one will be all green hardware.

The circuit FuzzDog has designed this board around already includes some of the Madbean naughty-fish mods, but I’ve incorporated additional mods by, first off, increasing the range of the Sweep control, and secondly, setting the rotary switch to have 4 stops, rather than the circuit’s intended three, and numbering some unused pins of the switch to give a fourth secret notch-filter mod. The notch filter is absurdly subtle with a clean signal, but if you put something with strong harmonic content into it, like a fuzzes out guitar or a fat monosynth, it gets pretty wild and super fun. The vactrols are Xvive VTL5C3s that I bought back in highschool, and were tested to match them into pairs for matching off-resistances and response times.

It filters, and boy does it filter good!



Demo forthcoming— didn’t have time to record one before Christmas!

Recorded a quick demo of it– Not my greatest, but whatever lol. Here's the breakdown of the settings on the demo:
  • Rhythm (Left): High-Pass; Hi; Up; Vol- 11:30; Gain- 9:30; Sweep- 4:30; Peak- 2:00
  • Rhythm (Right): Band-Pass; Lo; Down; Vol- 3:00; Gain- 11:30; Sweep- 11:30; Peak- 2:30
  • Lead 1 (Clean; first 32 bars): Low-Pass; Lo; Down; Vol- 5:00: Gain- 11:00; Sweep- 10:00; Peak- 5:00
  • Lead 2 (Dimed Silicon Fuzz Face into µ-WAHHH!; last 32 bars + fade out): Notch; Lo; Down; Vol- 12:00; Gain- 11:30; Sweep- 1:00; Peak- 3:30


Now, for the bonus:

During the semester I made a latex mold of my ears for a sculpture project I did. I wound up with some of the plaster casts breaking partially when removing them from the mold due to the thinness of the material and the steep undercuts requiring them to be removed at a fairly unusual angle. What did I do with these spare broken ears? Make Mike Tyson ornaments of course!
Merry Chrithmath, to you and yourth!

 
Last edited:
Post updated to include the demo. Linking it here too:


  • Rhythm (Left): High-Pass; Hi; Up; Vol- 11:30; Gain- 9:30; Sweep- 4:30; Peak- 2:00
  • Rhythm (Right): Band-Pass; Lo; Down; Vol- 3:00; Gain- 11:30; Sweep- 11:30; Peak- 2:30
  • Lead 1 (Clean; first 32 bars): Low-Pass; Lo; Down; Vol- 5:00: Gain- 11:00; Sweep- 10:00; Peak- 5:00
  • Lead 2 (Dimed Silicon Fuzz Face into µ-WAHHH!; last 32 bars + fade out): Notch; Lo; Down; Vol- 12:00; Gain- 11:30; Sweep-
 
I've got one of these on the bench right now. Wanting to try your notch mod out before I box it. Can't quite make out the values of the resistors you used, wondering if you wouldn't mind sharing the info
 
I've got one of these on the bench right now. Wanting to try your notch mod out before I box it. Can't quite make out the values of the resistors you used, wondering if you wouldn't mind sharing the info
I think it was 10k for both, but I consulted Chuck about it and he said it wouldn’t change anything as long as the value is the same. I initially had 3k6 for both I think, but those were 1/4w so they didn’t fit as well. The notch mod is incredibly subtle like I said, unless you’re feeding it a signal with an absurd amount of harmonic content like a heavy fuzz or a multi-oscillator synth. You could do different values to change the blend of high and low pass (and thus the character of the notch), so you might also like playing around with something like a 6k8 on the low pass and 10k on the high pass for a slightly more prominent effect. I liked the evenly matched values for this one since it’ll be going on my bass board and will be fed by a Brassmaster or a Moog Minitaur any time I’m in the notch mode, but the twin of this one that I'm building for my guitar setup will be set up to significantly favor the low pass (the value I liked for the notch on guitar when I was testing were 2k7 and 8k2, but I’ll do more testing and some blind-audition recordings to decide when I’m actually putting the second one together).
 
I think it was 10k for both, but I consulted Chuck about it and he said it wouldn’t change anything as long as the value is the same. I initially had 3k6 for both I think, but those were 1/4w so they didn’t fit as well. The notch mod is incredibly subtle like I said, unless you’re feeding it a signal with an absurd amount of harmonic content like a heavy fuzz or a multi-oscillator synth. You could do different values to change the blend of high and low pass (and thus the character of the notch), so you might also like playing around with something like a 6k8 on the low pass and 10k on the high pass for a slightly more prominent effect. I liked the evenly matched values for this one since it’ll be going on my bass board and will be fed by a Brassmaster or a Moog Minitaur any time I’m in the notch mode, but the twin of this one that I'm building for my guitar setup will be set up to significantly favor the low pass (the value I liked for the notch on guitar when I was testing were 2k7 and 8k2, but I’ll do more testing and some blind-audition recordings to decide when I’m actually putting the second one together).
Awesome, thanks!

Perhaps I'll make one a fixed resistor, and use a pot for the other. I plan on using this just after a couple octave boxes and ring mods, so there shouldn't be an issue with lack of harmonics 🤪
I've got a couple tweaks on mine already- 1n5817s for the peak detector, and a VTL5C1 in the second vactrol spot being the biggest changes(considering making the vactrols switchable, but not sure I want to commit four of them this project yet)
I'll detail the rest in my build report. As is, it will be replacing the FX25 on my board, though.
 
Awesome, thanks!

Perhaps I'll make one a fixed resistor, and use a pot for the other. I plan on using this just after a couple octave boxes and ring mods, so there shouldn't be an issue with lack of harmonics 🤪
The pot is *sorta* what I have planned for the other one, but I won’t spoil the surprise ;)
I've got a couple tweaks on mine already- 1n5817s for the peak detector, and a VTL5C1 in the second vactrol spot being the biggest changes(considering making the vactrols switchable, but not sure I want to commit four of them this project yet)
I'll detail the rest in my build report. As is, it will be replacing the FX25 on my board, though.
Looking forward to hearing what differences those mods make. Have you thought about socketing both the diode and vactrols?
 
The pot is *sorta* what I have planned for the other one, but I won’t spoil the surprise ;)

Looking forward to hearing what differences those mods make. Have you thought about socketing both the diode and vactrols?

The diodes and a couple minor tweaks to the gain of the first stage give me a much wider range on the Gain pot. I'm finding it hard to describe the difference in response with the 5C1s, but it's definitely worth a try. If I can find my 5c9s, I'll try those as well

As for sockets -
received_1802507456783043.jpeg
 
This has moved to the top of my pile. Were you guys able to fit it easily into a 1590BB?
No problem at all. Only slight issue was the height difference between the pots and the rotary. Just put a lag bolt washer between the enclosure and each pot to get them closer to the the same pin height as the rotary switch
 
Back
Top