Fuzzdog Moo-Tron Help

[FormulaFourteen]

Hi guys,

I just finished building a Fuzzdog Moo-Tron (its a Mutron III, but based on the Madbean Nautilus / NaughtyFish). I used Vactrols. The build doc is here:

https://pedalparts.co.uk/docs/MooTron.pdf

It has the worst kind of problem --- a "sort of working but sort of not" problem.

The issue seems to be the two toggle switches (one for the Drive/Up-Down sweep which Fuzzdog labels Hi-Lo) and the other for the Range settings (which the original Mutron called Low and High).

The pedal approximately works as expected with the Range toggle 'up' (I don't know if this is 'Low' or 'High') but with the toggle in the 'down' position depending on the settings elsewhere I get either no filter effect, or noise/whining, or an extremely quiet and weak filter effect accompanied by noise.

The Hi-Lo (drive) toggle also doesn't seem to operate correctly. One of the settings is a lot noisier than the other.

One other symptom is that as my playing signal decays it sounds like the filter is opening and closing rapidly as the volume lowers.

I have absolutely no idea how to go about debugging this. I've built dozens of pedals now and this is the first one that has required debugging.

Anyone got any tips? I'm feeling pretty depressed about this one

 

[Feral Feline]

You're off to a good start, posting pics.

Pics of both sides of the board are even more helpful, so circuit's removal from the enclosure would be necessary.


SOP is ...

• clean all flux off, because next is...
• visual inspection, look for cold solder-joints/cracks/dull-looking solder and reflow as required;
• ensure all values of components are correct. Watch out for resistors that can read both ways, ex 10k (Brown Black Black Red Brown) vs 120Ω (Brown Red Black Black Brown);
• try replacing op-amps etc (transistors if socketed) with known-good components or at least re-seat them;
• audio-probe the circuit to see where exactly in the signal path the problem insinuates itself;
• ... there's a trouble-shooting FAQ somewhere, here 'tis thanks to BuddytheReow ...

 

[FormulaFourteen]

Thanks.

I'll take it out the enclosure, clean with IPA (need to get some) and come back with some pics...

 

[Diynot]

Envelope filters can be very setting dependent especially when flipping from an up to down filter. What works in one will get you little in the other. Also, make sure you are setting the sweep knob to ab noon since that affects the response of the vactrols. Other than that, make sure your switches are truly connected to the board I know with the rotary switches there is very little of the switch to solder in and a couple of those look pretty empty.

 

[Diynot]

I just ran through some settings on my recently completed Moo-tron and I can confirm that there is some decay flutter in mine as well, but I think that is just inherent behavior for some EFs. I know my Procrastinator does this too. Try putting a compressor in front of the moo-tron. I did compare against my Snow White Auto-wah which doesn’t display it as much, but it’s not really a fair comparison since it is an OTA based EF. As far as the toggles mine still operates about the same in either direction. I do notice a good amount of noise if the peak and gain are set high and toggle is in the high position. All this to just sort of give you a baseline of what might just be native and what might actually be an issue.

 

[FormulaFourteen]

Thanks!!

Honestly that's super helpful.

What would be really good is if you could give me some knob settings where the effect is pretty obvious regardless of toggle settings - so that I have somewhere known good to start with my debugging.

(also, have you managed to work out which settings of the toggles correspond to which settings of the original mutron?)

 

[Diynot]

Had a minute to record an unapologetically shitty demo…..enjoy?

Telecaster bridge pup into Epiphone Pathfinder. Moo-tron, then SWAH, then BassBalls, then finally the Slow Gear. You can catch some decay flutter even on the SWAH, again, a compressor in front can mitigate some of that.

 

[FormulaFourteen]

Thanks!

Hopefully will get onto the debugging this weekend...

 

[Diynot]

Def do your value checks, reflow solder joints even if you think they don’t need it, and get some continuity checks on those switches. I know it might not be a popular way of doing things since it requires a rather large washer, but for those alpha 3pdt rotaries I actually drill the hole to match the last ring around the shaft. you have to do a little surgery to remove the little lock tab but the extra wiggle room is Indispensible