univox uniwah questions..

[pinkjimiphoton]

hi guys,
i picked up one of these bad boys the other day, had one years ago..
since it's really not worth all that much, i wanna modify it with a power supply jack so i can run it at 9v with the rest of my stuff.
i've just spent a couple hours tinkering around trying to come up with a decent power supply daughterboard for it, but i'm missing something...
all i've done is smoke some resistors. got a good buzz on right now. 

yikes...

this thing is weird, it's ALWAYS on..it's an opto volume/wah thing with a weird variable inductor inside it...different from most others, i'll post pics shortly.

so forget t/b, and forget batteries...3 c cells just doesn't last very long.

so...like...what would be the simplest way to drop the voltage to around 4.5 v? i know i'm missing something.

first i tried to use a couple diodes to get it in the ballpark similar to what worked on the heathkit ta 28 project a week or so ago, based on one of steve daniel's projects. i THOUGHT...well, self, i said to myself, maybe if ya change out the resistor from say, 10 k for 1.5v, if you divided it to about 1/3rd, that may get ya 4.5 v.

nope. tried a whole bunch of resistors, some got hot, some smoked, but i can't seem to get it anywhere in the ball park.

i know (?) i can use a trimmer to drop voltage wired as a voltage divider, but that will i assume get hot too.

i was thinking, maybe use a 7805? figuring the lamp inside the pedal is most likely 6.3v, so running at 5 instead of 4.5 should be ok...

what would you guys suggest for a newb like me to figure this out? it's a great sounding pedal when the voltage is right.. unique, not a crybaby or morley sounding wah at all...kinda..."liquid".

i appreciate the advice...i don't wanna "smoke" this thing, figure there's something stupider than my dumb arse can figure out myself..

[pinkjimiphoton]

duh...4733 reverse biased to ground, a 100u cap and a 470r resistor seemed to do the trick...

what was throwing me, was there was/is something else wrong with the pedal...gonna replace all the electros inside it i think.

when all's said and done, i figure running it at 5.1 v should be ok, right? pretty close to 4.5...

any caveats?


thanks brothers!! (for putting up with me, in particular!!)

[joegagan]

i had one that worked for a while. i sold a whole summer's worth of my edamame crop to buy a the C cell batteries to try it out.

they sound horrible in my opinion, and others have concurred. i hope you can do some magic to yours.

[pinkjimiphoton]

well,
no real magic possible, i don't think...
it's that freekin' weird inductor...when it WORKS, they sound fairly good.
when.

i've got something screwed up... i roasted that zener diode, for the second time now.
i replaced all the electros on the pcb, which helped quiet it up some...

when it works.

when.

so..do ya think the 470r resistor is preventing enough current for the thing to turn on? it sounds great...when it works.

if i use a dedicated 4.5 wart, it's fine. (bypassing the daughter board) if i use a 9v with the daughter board, it's fine..

for a minute. then the dang diode blows, and the lamp won't light up.

advice needed!!

joe...this thing ain't even a good doorstop.

ahhh...nostalgia... sucks.

[joegagan]

DON"T SAY doorstop!

one of my fave local bass players, carlos cordova tells how his dad found an old fuzzface ( long before any reissues ) in the garage, left by carlos' brother when he left home.

his dad said " what the F is this?", got out a hacksaw to saw the pots flush and it became the family doorstop for years.

[pinkjimiphoton]

my favorite kind of doorstop!!

naaah, this thing, i gotta figure out how to power it.
seems to me the diode/resistor trick would work, but it gets too hot and pops the diode.

thinking maybe a 7809 to regulate it down some?

stumped and stimpy-ish here brothers...

[pinkjimiphoton]

err...780FIVE...

did the trick...couple diodes and caps and a regulator...

it's running...still sounds like poo. really crummy design, but i got it sussed out...there's a magnet inside that comes loose from the top of the metal "spring" over the inductor..if it slips out of place, you lose the "wah", which is weak to begin with. a little crazy glue, and repositioning, and a completely different beast.

also had to reverse the switch...the way it's set up stock, when you go heel back it kinda "chirps" on the wah and makes the volume function wrong...better to have the switch "up" for volume, and "down" for wah. had to swap ONE wire on one side of the switch, and cut traces and make jumpers on the pcb to reverse it on the other side...it's a DOUBLE dpdt switch...the poles go all the way thru the switch, and into the circuit board. pain in the...but it made a huge dif in the "playability" of the wah.

so...electros replaced
inductor fixed
power supply and jack fitted to the pedal
switch "reversed" to be useful

not done yet. gonna play with the circuit some more. it's maddeningly inconsistent right now...ya never know what the hell it's gonna do.

ay.

[pinkjimiphoton]

fwiw, after replacing the caps and making sure the magnet is in the correct place (and fixing one trace cut for the switch i had to jumper) this is now a really nice, useful sounding wah, completely unlike the turd i got from ebay the other day.
thinking about maybe changing to a 7806 instead of a 7805, right now it's reading about 4.91 on a 9.46v wart.
if i bump it up a little bit to 6 v,  (the lamp is 6.3v) i think i may get JUST enough headroom to make the bypass/volume function not suck.

gonna keep playing with it...SPT to come...