Amp makes popping noise when lights are switched or stuff plugged in

Started by 133MHz, January 26, 2008, 09:42:12 pm

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Hi everyone! ;D

I've built myself a nice surround amp for my computer based on a TDA7386 chip and a linear power supply. The thing is that it makes a loud popping noise through the speakers when somebody flips a light switch at my house, or when I plug something like my soldering iron, a lamp or a desk fan into the wall. Googling only returns 'plug the amp into a surge protector', but it's already plugged into my PC's surge protector! I know I'm missing some power filtering component because commercial equipment is usually immune to that problem, but I don't know what exactly. A ferrite bead? a ceramic capacitor in parallel with the transformer primary?  ???

Anybody with experience on medium-high end audio equipment? Thanks in advance ;).


Hey I also have that problem! :o Every time I turn on a lamp close to my computer my speakers make this huge pop sound. I've always wondered why it does that ???


When you turn on the lamp, the switch generates a spark on the inside when the contacts get close, this spark is electrical 'noise' and travels down through the wires as a small power spike, your speakers catch and amplify it. Most commercial good audio equipment I've seen doesn't suffer from that problem, so there's some spike filtering component I need to add to my amp, but I don't know what exactly. I have one of those small coils used in computer monitors as line filters, I might try adding that later.

In fact, an electrical spark is a huge source of RFI (Radio Frequency Interference). The very first radio transmitters in existence used a controlled spark as a transmitter!


Bad news, tried fitting ferrite beads on the primary and secondary wires, and putting an AC capacitor in parallel with the transformer primary, and nothing >:(


Have you tried a UPS or some form of line conditioner? That might be overkill, though. I think if it's really important you could have that line switched to another circuit.


I have it plugged to one of these (supposedly a surge protector):

I'll try plugging it to the UPS when I find a suitable adapter (it's got IEC plugs instead of normal ones).

Milky B

I have these TDK computer speakers and they do the same thing.

I think the filter would be some kind of capaciter, that's what old guitar amps have instead of being grounded.  what size cap are you using?


a 0.47 uF 250VAC cap in between the transformer primary. Tried smaller ones and also in the secondary, and nothing >:(.