Atari Punk Console - Sparking Pots?

[tiges_ tendres]

So I just built another Atari Punk Console from this layout http://www.aronnelson.com/gallery/v/DRAGONFLY-LAYOUTS_0/album19/album145/ATARI_PUNK_CONSOLE_VERO_001.gif.html

and I noticed that at the end of the pot travel, a little spark occurs inside the pot.  I didnt notice this on my previous build, and I understand that applying 9 volts directly to the pot isn't great practice, but is it ok that it sparks?  Or another way to phrase the question, can I avoid the spark somehow?

[Zben3129]

Hmm...

I'd love to hear the answer to this, as I recently had a sparking pot on an orange squeezer build. Then it actually made a little tiny fire inside and burned out completely. Not good

Thanks
Zach

[Wild Zebra]

tiges, Every APC I've built does this.  So I'll be looking for an opinio too.  I've never had any of them crap out....yet.

[tiges_ tendres]

It smells bad too!
I tried different pots, same thing.

Right as the spark is happening, the sound cuts off too.  Is that what happens with your builds?  I dont recall this happening with mine. 

I originally did my own perf layout which I have now lost!  I wish I could compare my layout with all of the other floating about.

[slacker]

The reason you get sparks is because there's nothing to limit the current through the pot, so when the wiper gets close to the contact with 9 volts on it the voltage can jump the gap. You also run the risk of burning out the pot because when it's turned to a low resistance you will probably be exceeding the power rating of the pot.

To stop both of these problems you just need to put a resistor in series with each of the pots, 330ohm is a good place to start because using 9 volts that will limit the power to the pot to a maximum of just under 0.25Watts which is what most pots are rated for.
Or experiment with larger value resistors because the value of the resistor will set the highest frequency of the oscillator.

[soggybag]

I've been thinking of building one of these. We should draw up an updated scheme with the addition of this new resistor.

[soggybag]

I just google up "Atari Punk Console" and found there was a Wiki article on it?!? Very funny. I wonder if the Ugly Face has one yet...

http://en.wikipedia.org/wiki/Atari_Punk_Console

[slacker]

Actually you could just add one resistor between the battery and the circuit and put a big cap to ground from there, like a lot of pedals use for power filtering. That would do the same thing. 
Separate resistors for each pot lets you tune the circuit though so I'd go with those.

[tiges_ tendres]

I will give that a shot.  Thanks for the tip, I will let you know what happens.

Also, on the layout I posted above, I noticed that it does not show 9v going to pin 4 of the IC, which it does on the orginal Kaustic machines schematic which most people have worked from.  However, there is no noticeable difference with 9v connected or not.

And Mitch, I just bought another Stylophone!  I missed mine too much!

[ianmgull]

bump


I was just wondering if anybody had any more ideas for this? I put a 330 ohm resistor in series with +9v on one of the pots and although it did stop the spark, the frequency range was far more limited.