Voltage into Potentiometer = Smoke!

[Bishop Vogue]

I'd heard that pots don't take voltage well but one day when I built the Dwarfcraft Great Destroyer, I noticed that the starve function on the circuit was just a simple 9v - 2KB pot - pin1 of the IC, using the pot as a rheostat. So I thought that a simple starve like this must be viable.  I actually built a starve into my 'testing box' so I could audition a starve function on all new designs.  I used this setup for ages without issue - it worked great.  But today I noticed a wisp of smoke come out of the pot and thought: oh dear god... that could have been a pedal I sold to a customer. I am so thankful I discovered this on my test box! Dodged a bullet there.  But I'm left with a question: how does one make a good starve without frying a pot?

(Full disclosure: the pot in my test box was not a 2K but a 5K... could that be the difference?)

http://tagboardeffects.blogspot.com/2012/08/dwarftcraft-great-destroyer.html

[PRR]

You have got 9V. Most small parts can take 0.125 Watts. How many Ohms fed 9V makes 0.125W?

V^2/R = P
V^2/P = R
9^2/0.125 = 648 Ohms

NEVER let the total resistance ins a path from +9V to -9V(gnd) be less than 650 Ohms without more thinking.

Putting 680r in series with any pot which COULD take full battery voltage is a wise rule of thumb.

However a "starve" pot is normally in series with the whole pedal-guts. Which is usually a lot more than 648 Ohms. I suspect you have a short.

[antonis]

I'm with Paul..

A short on middle lug could lead to overheating 5k pot "active" body resistance of less than 13%..

[EBK]

But today I noticed a wisp of smoke come out of the pot and thought:

[antonis]

I'd like to know if your reaction would be the same in case of your own smoking pot, Eric.. 

[Bishop Vogue]

Does this mean the Dwarfcraft Great Destroyer is a poor/unstable design and liable to burning out, I wonder?

[PRR]

Is this the plan?

https://musikding.rocks/wbb/index.php/Attachment/356440-DGD-GIF/

If so, that's fine. You have a building error.

[lars-musik]

Thanks PRR,

that solves an ancient mystery from my early days of building electronic circuits. I built this Syntom II (a quite nice srum synth) that had a pot going up in flames when I presented it to a band mate. He was really impressed.

Here's what I think now was the culprit (12V to ground, besides the cheapest pots I found back then):

[ElectricDruid]

Here's what I think now was the culprit (12V to ground, besides the cheapest pots I found back then):

Not if you correctly put a 100K pot in there.

V^2/R = P

So

144 / 100K = 0.000144 = 1.44mW. Even cheap pots can stand that.

But 100R or 1K could easily get mixed up for such a thing. It happens. I've smoked some pot(s) myself...

[Ben N]

It happens. I've smoked some pot(s) myself...

But did you inhale?

I'll see myself out.