Here's an off topic question for all the electrical engineers out there. I recently bought a new receiver that got very hot in the cabinet I had it in. Instead of doing what most people do, take it out of the cabinet, I thought... "oh yeah, time for a project!" So I installed a cooling fan in the cabinet and wired it to a simple $10 Home Depot thermostat.

My problem is that when the thermostat kicks on, because it's connected to a fan, it creates a surge or pop that comes through speakers and makes the TV flick.

What can I place between the switch and the outlet to prevent this pop? It's a standard 120V line, and the fan is a 4" Radio Shack 120V fan. Is there something I could wire in parallel between the two leads?

Thanks,
Brad

If it were all running on DC instead of AC, I would say that any one of the Radio Shack noise filters designed for car audio would work. However, I know nothing about AC.

I had a similar problem in my old Volkswagen. Every time I stepped on the brake pedal, there would be a pop coming out of my amplifiers as the brake lights kicked on. I fixed this by literally putting a noise filter on the wire leading to the switch above the brake pedal under the dash.

I would think that the cooling fan you're using would be noisy when you're watching a movie, though. If it were me, I'd be re-arranging my cabinet to allow for more proper ventialtion (amplifier on the bottom with a 6" space above it) instead of adding a noisy fan.

Hmmm... although it's not 100% clear what your thermostat is, I would guess it is a device with a relay built in to turn on the fan? If so, then it could be one of two things. The fan is probably an inductive load (motor) and as you switch it, you will get a large current spike. If this is plugged into the same mains feed as your amp, then you may hear this as a pop. You could filter this with a mains filter, and seperate the feeds to your amp and the fan by using different mains feeds. It could also be radiated RFI from the relay as it switches the load - a current spike could result in flash-over between the contacts at the time of the switch. If your amp is not properly shielded, this could cause the pop. You would need to solder on supression caps to the relay of an appropriate voltage rating to stop the spark. Mind you though if your amp was that sensitive and poorly shielded, I would buy another one . I have no idea how big your fan is, or how much current it takes - but if it takes enough current to cause flashover and RFI then it is either too big, or faulty, or the relay unit is duff/using poor relays/etc. I suspect this is a case of "You pays yer money...."

A mains filter and seperate feeds would be the first, easiest solution. A second step would be to use a more expensive switch that uses a thyristor switch instead of relays; after that, I would start drilling big holes in the back of your cabinet....