weird-ass mastodon issue

[Anonymous]

hey kids,

so i built one of these mastodon fuzz boards up for a bud. so far, nothing but nightmares with it.
its doing some very weird stuff. it PASSES signal… sorta…

but only if…. well, let me describe it.
bypass works fine. so the switching and jacks are good. led part too. all fine.

tested continuity from p2p everywhere. everything seems to be fine… switch, wires between board and switch etc.

if i disconnect the wire to the input of the pcb, and touch it with my fingertip, the circuit passes signal, and all knobs work as expected. voltages, tho a little funky, are close enough for rock and roll, and vary somewhat depending on knob positions.

anyways… if i connect the wire back to the footswitch, it no longer passes signal. at all. disconnect the switch, passes signal fine. until
ya wire your guitar directly to the input wire from the jack, bypassing the switch. then same thing. dead quiet, no signal.

so i hooked up my signal generator, and applied signal and hit it with my audio probe. suddenly its passing signal again. wtf? all the way thru the circuit. disconnect, reconnect the jack, boom, dead again. i triple checked the jacks, cuz even after 1000+ builds, mistakes happen. all wires have continuity, no wires backward <ie going to ground instead of signal hot>… very freeking weird.

so i reflowed the entire board, sucking out the old solder and using fresh to ensure good joints. rough on the board, but everything shows continuity where it should. got it working. was like… cool. call it a day.

plug it in before shipping to my bud, and its fucking dead again. wtf? so began the debug process again. i had socketed the q’s, and when it was working, soldered them in cuz sockets suck and always fail eventually. have done this hundreds of times over the decades. so i removed the sockets and soldered in q’s, installed fresh sockets <hint: if ya buy machined 6 pin sockets, they work great for q’s, just cut ’em in half… tend to be much tighter than the ubiquitous SIP’s everyone uses> and tried again. everything remained identical to the previous issues. will pass signal if i touch the input wire directly, but not if its referenced to ground in any way, or if the jack/switch is connected.
wtf? this one’s got me kinda stumped…
any ideas? its possible i smoked the board i suppose, but then it shouldn’t be passing signal at all. the bypass part of the circuit is obviously working. the CIRCUIT is working… sorta… but not right.

somebody buy the old pink madman a clue?
thanks
PjP

gonna have a crack at it again today, but if this continues, screw it, i’m gonna just build it on vero so i can wash my hands of it.

[Big O]

I not one of the experts on the board, but I will give it a try.  Hopefully I am following what you are trying to state as the problem.

First, is the input to board wire from the footswitch soldered to the input pad/eyelet marked with a “T” and the same for the output wire from the board to the footswitch?

Second, could you have a bad footswitch?

I, too, am befuddled that you are having problems as you are one of the true guru builders on the net, especially with vero.  We are quite honored to have you visit the board!

[Anonymous]

I’ll venture a SWAG at this (scientific wild ass guess).

 if i connect the wire back to the footswitch, it no longer passes signal. at all. disconnect the switch, passes signal fine.  Possible defective switch?

wire your guitar directly to the input wire from the jack, bypassing the switch. then same thing. dead quiet, no signal.  Was the guitar ground connected directly to the board?

I feel your pain, PJP.

[Barry]

Wassup Jimi!!

I have to agree that whenever some weird shit like that chaps my ass it is usually some unexpected off-board item that is giving me a fit that really should not be.

[Anonymous]

hey brothers,

yeah, it’s a true pissah, as we say up here in the great new blighty.

i traced it all again. same exact thing. finally said screw it, built the whole damn thing on veroboard.

all new parts, other than the pots, which i tested before using.  new transistors, from a DIFFERENT batch in the q drawer.

hook it all up again, having retested the footswitching/bypass/jacks and confirmed that i have true bypass thru the pedal. used the same box, same power jack, and led circuit, since it is all working.

same dang thing. this one is doing EXACTLY what the pcb did. if i disconnect the input wire, which was also changed when i rebuilt it.. and touch it… loud honk. if i touch the casing of the pedal, no sound at all. that’s not right either, and a phenomenon i did notice on the pcb build and forgot to mention.

so somewhere, something is dumping something to ground i guess. i mean, the jacks and switch are gonna work or they’re not. rebuilt with all new parts other than the pots and getting the same result seems to me like its gotta be one of the pots, but i meter’d them for value, and swept between both outer lugs and the wiper to make sure they were good. i mean, they were brand new, outta the parts bag! lol

this is maddening. so i guess next step is replacing the pots. i suspect its gonna continue. the ONLY thing i didn’t check out, tho, come to think of it, is the led circuit, wired to pins 1 and 3 of row b on a standard 3pdt like i normally would. if this were shorted internally, perhaps its allowing the signal to get shunted to ground thru the diode?

i’m a-gonna try replacing the footswitch and see if that makes it stop. something seems to be majorly weird here, and the game’s afoot to debug this one. i like a challenge as much as the next guy, but to throw a second build in the bin? SACRILEGE!

will check back, with voltages. i used IvIark’s verified vero with the gtrpcb values for stuff, so the odds of it being either your board or his being bad are now getting pretty minimized.
stay tuned, and thanks for the support!
pink

[Anonymous]

hey ray,

yeah, actually i star ground everything to the input jack, so the guitar is connected directly to ground thru the jacks, enclosure, and board. marginally thru the pots, too, i suppose.

big o – love the handle..

yeah, i am beginning to think switch too. its gotta be a passive at this point.

 

i’ll try and remember to get some voltages, too. tried 5088’s and 404’s

updated update…
replaced all 4 pots. no change. completely rewired circuit, no change. bypassed switch completely. no change. replaced jacks. you guessed it… no change.
different q’s. no change. 5088’s as a sub. same deal. no change.
same circumstance had been happening… disconnect the wire leading to the board input, boom, it would buzz, but not pass signal.
head stumper.
but i did take voltages. none seem good. first, without the transistors, all knobs full, tho it made no difference if they were 0 or 10.

b+ 8.80v

q1

c 8.76 b 0.0 e 0.0

q2 c 8.79 b 8.76 e 0.0

with transistors in it
q1 c .63 b 0 e 0

q2 c .021 b .648 e 0.0
i have checked continuity for shorts and run a blade thru all the strips. no issues apparent.
this is REALLY weirding me out.
but still thinking… its possible i got a bad batch of caps or something.

to me, likely culprit would be the 10n to ground, c2. i suppose if it were shorted, it could shunt the signal to ground, and would probably make b of q1 look like its shorted to ground, right? i mean, the most obvious answer usually works… except in this case. i DID use a cap from the same bag.
the voltages on q2 seem to be on lsd, too. totally not what i expect.
did not check the hfe on the 3904’s i just chucked ’em in my  chinese tester thingy to confirm pinout. i’d assume the usual 300-ish.

so… the plot thickens, as another circuit that should be working does exactly the same thing!

can’t wait to hear ya’ll’s thoughts on this sucker! 😉

thanks!
p.

 

[Anonymous]

so… the plot thickens, as another circuit that should be working does exactly the same thing!

HUH!???

Have you been smokin’ some bad stuff?  ANOTHER board…same problem??

[Anonymous]

you know i only smoke good stuff, wilkie 😉

yes, another. exact same symptoms. this is CRAZY, ray!!

i kept thinking… ok, we’ll try replacing the next part, which i HATE to do…no diff.

i mean, what are the odds of two completely independent builds doing EXACTLY the same thing, with the same symptoms?
i’ve not yet begun to fight, yada yada… but this is ridiculous. i’ve built these in the past with zero issues whatsoever!
i even switched from 16mm to 9mm pots to make sure that it was different. different bag of jacks. footswitch is irrelevant, as its not even wired into the circuit at this point. i even disconnected the ground for the led to the footswitch to ensure no leakage possible, nothing.

man!

this one’s a head scratcher!

 

[Anonymous]

Put it aside for a day.  Work on something else.  Come back to it with a clear head and start with simple steps.  Get the power supply working.  Then the input…next…you get the drill..

[Anonymous]

yeah, i sure do, lol.

i’m guessing its gonna be that 10n cap to ground. yeah…lol

stay tuned  8)

[Anonymous]

messed with it a bit more. that 10n cap is not it. seems like the entire ground side of the circuit is showing continuity to ground, which literally should be impossible.
weirder and weirder.

[Chuck]

I’ve only ever built one Mastodon and it has worked perfectly for ages so I’m as worthless as teats on a bore in this thread.  I do however have a lot of experience with seemingly perfect builds that don’t work – what Wilkie said works great.  Set it aside for a day, week, month, or a year.  You’ll probably see the obvious, glaring oops very clearly and leave a large pink palm print on your forehead.

Chuck

 

[Cybercow]

Jimi – Damn! I shoulda brought some popcorn. I feel ya. I’ve experienced such a scenario twice before in my electronics journey. Two fresh PCBs and each had the exact same issue with no signal passing properly. All values were correct, continuity was correct, voltage measure at crucial components were correct, . . . everything indicated they should work. After futzing with them for weeks, I procured a third PCB and started over. It fired up correctly. WTF????? I cleaned up one of the previous PCBs and replaced with all fresh components, pots & jacks. No go. All I could ever surmise was that I got two bad PCBs. A fluke I know, but I’ve experienced the same with Peavey amp and even Yamaha synth repairs too. Such flukes are rare but can happen. I believe it’s possible that a dog hair or tin-whisker can caught up in the works (layers) of a PCB or two during a production run.

I certainly hope that’s not it, but there’s just something else to ponder.

I’ve even had socket pins break between the top of the plastic socket housing and the bottom. Troubleshooting that kind crap is so rewarding when found.

Ever have a stray clipped-lead-bit bounce off something on the bench and wedge itself between two conductors on a board in such a way that it can’t be seen until a socket or some other part is removed? It’s rare, but that too can happen.

I’ve seen solder splashes create the tiniest of bridges in the strangest of places.

What kind of jacks are you using? After encountering three shorted Switchcraft 1/4″ jacks one year, I quit using them. I only use Lumberg or Neutrik 5-pin enclosed stereo jacks these days.

In any case, there’s my 2¢

Good luck. Looking forward to learning what you discover.

[Anonymous]

hi mark and chuck,

yeah, i have abandoned the pcb as it was kinda over worked with me trying to debug it. probably order another from barry cuz at this point i need this thing off my bench so i can get my job – job done 😉
the vero is sitting next to me. i showed it to my bro dennis, he went to school for electronics engineering, and he went over the entire thing as well, and couldn’t find anything that appeared wrong on either board.
sometimes it can be a resistor that LOOKS good, but is broken off at one end and still connected, or a bad cap, or even a bad solder pad that gets lifted from too much heat.

pia!
i use them enclosed plastic stereo jacks from tayda usually. i’ve got switchcraft ones for boutique stuff if someone asks for them too. tried both. no difference.
something is dumping the circuit to the ground plane as far as i can tell. but there’s really not much anywhere in the circuit i can find that could cause it.

i’m’a’gonna let this suckah ride for a day or two. one of the guys in one of my bands needs an envelope follower, so gonna build one of them tomorrow to give him sunday. so maybe sunday nite or monday i’ll revisit it.

crazy shit.
its almost like the enclosure doesn’t want the circuit to work, cuz as soon as ya touch the enclosure, any signal being passed stops.  yikes.
more soon.
lol

[Anonymous]

oh, you guys are gonna freekin LOVE this one. i did NOT get the pcb working. i may mess with it at a later date. the vero, i DID get working… the connection to the 500k pot was off by one rail, which i cannot believe i did lol. so that was the stupid part, which we all expected to find.
but i am always doing dumb shit. so this time? i made this into a kinda quasi octave fuzz by making q1 a reverse biased 3906 …yeah… a PNP… and a bc547, which is reverse pinout-ed ….errrrr… is that a word? anyways, it freakin screams.
the 10n to ground off q1b was too much for my ear, so i just eliminated that, as well. the tone control thing works more than well enough, and this way, you can make it really scream for a guitar.

he wanted a unique fuzztone, well, i dunno what kind of happy accident it was, cuz i found the wrong transistor working before i found the bad connection… but it may be worth burnin a cheap q if ya got a socket on the q’s and trying this combo of transistors.

all i know is its one off, sounds great, is literally the guitar pcb circuit minus the couple changes i mentioned and the guy i think is gonna be stoked. and i even beat the living crap out of it against my bench to make sure it can take a licking. boom.

thanks for helping me sort thru this madness, friends. you guys rock
peace
PjP

i will try and get a little video of it before it launches, too 😉

[Cybercow]

PjP – well that’s good news! Thanks for sharing the BJT selection. We all get a little something out of such interactions. Now I gotta try that when I do my Mastodon build.

Hope the envelope follower went smoother than the MaFu build.

 

• “Solder will get you thru times of no money better than money will get you thru times of no solder.”

[Anonymous]

Go celebrate!

[Author]

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