We've just done an 18th Birthday party and everytime we pressed the smoke machine button it crackled over the sound system. The machine itself is brand new and last time we used it everything was fine. I tried plugging it into a separate supply but still no good. Any ideas??

How seperate was the seperate supply?

Also, was the crackle heard once, sharply, as soon as you hit the SMOKE button, or was it heard throughout the time that you had your finger on SMOKE?

You could try a mains interference suppressor (Hi-fi shops) etc. Mostly effective if the sound system is plugged into it, but also effective (sometimes) if the Smoke machine is plugged into it, instead.

Also, how far from the mixer/CD-decks etc, was the smoke machine?

This can be an occasional problem on some cheaper machines which switch the pump voltage directly through the remote switch, rather than using circuitry and a low voltage to do it.

You can usually eliminate most, or all of this by soldering a suppressor across the switch contacts on the remote. If its a pump which works at mains voltage, you could also solder a Delta capacitor across the pump terminals. Either way by doing this mod, you are likely to invalidate your warranty, so perhaps taking the machine back to the distributor and explaining the problem could be the best solution.

I explained the problem to my local component supplier and he suggested the same thing as Chris said about soldering a capacitor accross the contacts,his only concern was about which side of the circuit the switch was actually on to be effective. It sounds like something for the professionals as I'm not electrically minded myself. I'm not worried about the warranty as I bought it off e-bay originally so there's no come back with it anyway.

Loz - Taking an educated guess, it sounds to me like the switch is switching on the positive side (i.e live) hence the interference. Effects / Foggers which switch on the negative or neutral side of the mains often suffer from very little interference (on lighting controllers this is often called Zero Voltage switching ).

You are not going to do any damage soldering a cap across the contacts regardless of whether it is switching pos or nagatively , so you haven't really anything to lose by trying.

If you want to give it a try, I have these capacitors in stock and if you P.M or email me your address and i'll happily post you one free of charge.

I can't tell you whether it'll work 100% but you have nothing to lose by trying