Smokey the Pot says ' only YOU can prevent bench fires ' ...

[petey twofinger]

i was going to go with "smoke on the potentiometer ' for the thread title , but its too many sillyballs .

So i have this 2 transistor led blinker circuit that i breadboarded to run an led for a home made vactrol that is going into a crybaby mod .

anyway the circuit has 2 sets of resistors , one set determines the brightness of the leds , the other sets the blink rate . i believe it is called an astable multivibrator .



i changed the values of r1 and r4 , or maybe it was just r1 at the moment , i am using one led for the vactrol and the other to mount on the chassis as an ooh ahh .

for r 2 and r3 i cut in a dual 50 k pot instead , so i could alter the blinkie rate .

heres the good part , if the pot is set to all the way up , dimed , or "zero resistance" , you guessed it , smokey time in fuzzlab . ( my wife wasnt amused , but my kid got a kick out of it ) . ohms law works very well when applied properly , i prefer to utilize " peteys law " when it smokes , unplug it ...

so i am thinking ( never good ) i prolly should go to guitar center and , just kidding  i should install low value resistors on that pot so when i turn it all the way down , its not going to have smoke problem .

heres the thing , i THINK i cut this resistor in in series , not parallel , but i am not sure ... also i really dont want to play trial and error with smokey time for pot pot might shorten lifespan of pot pot . 

thanks , and happy fathers day to all the Dads  !

[Seljer]

We've managed to burn up big wirewound 10 ampere potentiometers in classes, lots of smoke 

Your problem is when the potentiometer for R2/R3 is turned to 0ohms, theres a direct bath from the postive voltage supply to ground through the base emitter junction of the transistor, which is basically a diode, so you've got 0.6 volts of voltage drop and very little resistance, which is very inviting to let all the current possible flow through there and elt the magic smoke inside the transistor escape.
Put small resistors in series with both R2 and R3 to basically limit the current and maximum rate and you should be fine (probably 100ohms should do it).

[petey twofinger]

thank you for replying , i figured something like that was going on ...

after i posted this thread i went and spliced in a coupla 2k2 resistors to the wipers of the pots . i turned it all the way up and ran her for ten minutes with no sparks or magic smoke .

i am thinking a pedal that has a top mounted socket , so you could drop in a cap or something , engage the second switch , which would activate something like a booster or ring mod , but also slam the drop in component to the point of releasing said smoke could be practical for some applications .

i did a quick search for smoke before iposted this , but there are a ton of things coming up , smokey amp , smoke from 20 , smoke from a pot , pot smoke ... nothing on the first page was relevant so figured i would embarrass myself .

i also swapped the 50k pot out for a hundo , and got it to slow down even more , just past the usable range by a bit . with the original pot in place , utilizing the 2k2's at top , or just a btit below it was acting oddly , triggering on and off at a medium rate . very strange...

[Seljer]

If you read up on multivibrator circuits like the one you have there you'll find the formula f = 0.721/(R*C) , where R is the value of R2 and R3 in your schematic and C is the value of C1 and C2.

So if you want it slower (i.e. the frequency is lower) you can increase either those two resistors and/or capacitors and vice versa for making it faster

[Paul Marossy]

I thought bench fires were started by smoking pot(s). 

[Jdansti]

Was the smoke black or white?  You may have elected a new pope! 

[pinkjimiphoton]

and here i thought this was about my favorite passtime back in the day...lol


speaking of which, what the heck ever happened to the old "smokin' pots" website?


petey...i watched your metal amp video. it was awesome!! lol

[petey twofinger]

thanks for watching , that sucker KILLED us . it took way too long .

actually now that i think about it , the cops came too ....

almost put me off of amps forever , well at least for a week or so .

its really tight in there , that thing is just , its crazy . what a bad idea ...

my new one blows it out of the water , its really somethin special to me . i will be doing more videos , eventually , there is some goofy legal stuff going on so ...

thanks for watchin man , keep the SPT comin , i live for those . i actually was watching those way before i sgned up here .

[pinkjimiphoton]

it was cool as f&&&!


so the cops came? damn, dude, it wasn't THAT loud!!

[petey twofinger]

yeah it isnt ... at all .

something else was going on , but i did get to do a lil show and tell for the officers ...

[pinkjimiphoton]

always fun with officers. i remember trying to explain to one once when working up my princeton, that because i couldn't afford an oscilloscope, i HAD to run it full tilt boogie to chase down the microphonic feedback whine it exhibited at stage volume...

he looked at me real funny....but he GOT it. i was expecting much worse. and he went away, and i went back to my horrible noise making unscathed. i told him i needed it for work.

cool cop.

sometimes that doesn't work out that way tho, i understand...believe me.