smokin' pots revisited

[pinkjimiphoton]

so i used joe davidson's fuzzface calc for shits n grins and built up yaff the other nite.. with the particular q's i used (156 and 162 hfe si) it reccomended a 220r resistor between the stages rather than the more common 330 or 470 (or 1k)... so i slapped one in there.  fired it up, worked great... until the fuzz pot smoked. like... flash of light, puff of smoke kinda smoked.
i'd used trimmers for the 33k and 8.2k resistors, and a 100k in the fb path, 50k and 10k... it wanted to see about 18k c q1 and 4.7k c q2.

i used a 1/8th watt resistor for the 220r, and a 1/4 watt for the 100k.

so... knowing scary little of actual electronics, i'm wondering if i am correct in assuming i should have used more like a 1/2 watt resistor instead of 1/8th?

if the value is right to bias the circuit, but its drawing too much current somehow, am i right to go up in the physical current handling of the resistor? the resistance value should stay the same, right? just go upward on the power it can handle?

sorry for the dumb question, but figured i should ask before i smoke another pot. lol... that sounds dumb, coming from me, doesn't it?

fwiw, the smoked pot was one of them little 9mm board mount apha's

thanks guys!

[anotherjim]

I think it's the pot that needs the higher wattage Jimmi. Or else you need more resistance outside the pot to lower the current. Trouble is, when the pot position leaves only a little of the track active, the current is maximum and there is only that small area of track to dissipate the power and you get smoke.

I'm woefully unfamiliar with fuzz face variants, but does it really have to have current so high it can smoke things?

[pinkjimiphoton]

hi jimmy,

beats me, i wouldn't think it would need that much current. i found the 220r sucks the life outta the feedback loop too, so only about the last .25% or so of the sweep even matters.

i was i guess wondering if maybe i should go with a higher wattage resistor there.

it may have been cuz i recycled the pot, but i'm thinking the resistor has to be it, i've built around 100 ff's and never encountered this before.

its a weird planet, bro

[anotherjim]

Well, if you had a pot for Q2 collector then that alone is tempting the smoke. Have at least a 1k fixed R in series. I can't see how it would want to be lower than that & then you should be able to twiddle any little trimmer pot as low as you want without frying anything.

[pinkjimiphoton]

great tip bro! 470r even. it may have just been a bad pot cuz i recycled it. after switching the 220r to 470 no more problem.