loud snaps from other devices switching

[Arx]

I've built a 6 channel lm3875 which I plan to use for tri-amping.
Currently I'm just testing it with the subwoofers on one pair of channels, and the main speakers (2 way) on another pair of channels.

Whenever anything nearby switches on or off, like the refrigerator's compressor etc, I get a pop from the speakers.

I have a fluorescent lamp in the room, and if I unplug it, it'll sometimes make a VERY loud snap.

It's not really a big deal as things are now, but I don't really trust my tweeters to take that kind of abuse after I switch to some nice big caps for dc protection.


The current configuration is AC -> Line Filter/Fuse -> 600VA 25+25 Transformer -> Large bridge rectifiers -> 68000uF per rail -> umbilical -> amplifiers

The amps are wired in P2P configuration with fairly short signal paths, using the same basic schematic as the audiosector kits, with no zobel.

I was originally thinking it might be noise getting in through the power supply, so I unplugged the amp, which will run for 20 seconds or so off the supply capacitance, and tried unplugging the lamp. It still popped, so it's obviously getting in through the air.

Any suggestions how to deal with it?

-Nick

[!]

I hate to argue with the results of your experiment in unplugging the amp and still getting a pop, but these kinds of disturbances don't generally travel through the air.

Is it possible your source, not the amp, signal has this pop in it from the lamp/etc power change? If it's AC powered, try with an isolated source like a MP3 player/etc. If the source does't have sufficient AC filtration on it, filter that as well.

What's your amp AC filter look like? One of those small filteres built into an AC socket is ok for higher frequencies but you'd need a larger external inductors or LC filter for some higher magnitude noise. One thing at a time though, I'd check the source first.

[BWRX]

Originally posted by !
Is it possible your source, not the amp, signal has this pop in it from the lamp/etc power change? If it's AC powered, try with an isolated source like a MP3 player/etc. If the source does't have sufficient AC filtration on it, filter that as well.

It's not just possible, it is the cause of the pop! Arx has demonstrated this nicely by disconnecting the amp's power supply from mains power.

Is all of your equipment plugged into the same outlet? Try moving your amp and source to the same outlet and your light to a different one. If the house wiring is all tied together it probably won't make any difference.

[Arx]

Originally posted by BWRX


It's not just possible, it is the cause of the pop! Arx has demonstrated this nicely by disconnecting the amp's power supply from mains power.

Is all of your equipment plugged into the same outlet? Try moving your amp and source to the same outlet and your light to a different one. If the house wiring is all tied together it probably won't make any difference.

I still get the pop with no audio source connected, and no AC source to the amp.

My paper shredder also made a lot of really nasty hf hash on my speakers. I moved it about half way across the room, and I get considerably less noise, though it's still very noticible.

Looks like it's definitely going through the air.

-Nick

[!]

Are you completely disconnecting everything? Turning a device "off" is not a disconnection, ground currents are still a factor.

Le'ts suppose for a second that you really do have noise floating through the air. It would have to be high frequency, and it would be effectively shielded by the (metal) case. If you do not have a metal case, ground (or ground coupled) with all significant openings appropriately shielded, that should be priority #1.

[Arx]

Originally posted by !
Are you completely disconnecting everything? Turning a device "off" is not a disconnection, ground currents are still a factor.

Le'ts suppose for a second that you really do have noise floating through the air. It would have to be high frequency, and it would be effectively shielded by the (metal) case. If you do not have a metal case, ground (or ground coupled) with all significant openings appropriately shielded, that should be priority #1.

Yes, completely disconnecting everything. Unplugged cables from inputs, unplugged cable from line connector.

I probably should have mentioned that I haven't completed the chassis yet. The amplifiers are currently mounted on a piece of 3 inch aluminum angle which will make up one half of the chassis.

Hopefully when I finish it will no longer pick up the noise.

-Nick

[BWRX]

How close are your input and speaker wires to the AC wires of all these devices near your amp? Are the input wires and output wires at least twisted?

[abid_rehan]

In my experience this sort of problem occurs when you are using same electric line for different electronic equipmet you could try connecting your amp to a different AC line, hpefull it will resolve the issue if it doesnt you could use an AC capacitor at the mains of your toroid or transformer whatever you are using.

[Arx]

Originally posted by BWRX
How close are your input and speaker wires to the AC wires of all these devices near your amp? Are the input wires and output wires at least twisted?

Varying distances, but not particulatily close. The paper shredder, for example is about 4 metres away. The Fluorescent light, which gives the worst noise when turning off, is about 1.5 metres away, but the wiring is running fairly close to where the amp is.

The wires aren't twisted. They're all 14Ga magnet wire, done point to point. It gives the physical structure as well as the electrical. The feedback, input, and output wiring are all quite short though, so even if I could twist them, the improvement would not be the orders of magnitude I'm looking for.

Originally posted by abid_rehan
In my experience this sort of problem occurs when you are using same electric line for different electronic equipmet you could try connecting your amp to a different AC line, hpefull it will resolve the issue if it doesnt you could use an AC capacitor at the mains of your toroid or transformer whatever you are using.

As I explained, I get the same effect when running off the DC caps with no connection to the AC line, so putting a cap on that line isn't likely to help me.

-Nick

[Leolabs]

Is your transformer a toroidal???