Power Switch 'pop's frequency?

[cent88]

What is the frequency that causing speaker to 'pop' from on/off the power switch?
As I know PSRR of voltage regulator is lower on higher frequency.
I have some power rail wire twisted previously and couldnt hear any pops.
Is the twisted wire act like inductor/resistor to surpress it?

[DF96]

What frequency are you hearing?

Direct movement of voltage rails tends to be low frequency. Induced spikes can be higher frequency.

[cent88]

Just poppp. I don't know the frequency.
Shall I use low-esr reservoir cap instead of general purpose(datasheet written up to 120Hz only)? or twist the wire will do.

[Mooly]

Does the amp "pop" if you disconnect power cord rather than use switch ?

If it is the switch then it could be arcing and causing a burst of RF energy that is getting into the front end circuitry (radiated). I doubt it's disturbance of the power rails.

[cent88]

It happens to all the switches in the house.
Normally what is the pop's frequency? We cannot hear RF from speaker right?

[Michael Bean]

My money is on RF burst from power switch arcing, it usually can be tamed by putting an AC rated cap across the switch terminals. In my experience one in the .01uF to .047uF range seems to work well.

Mike

[Mooly]

Originally Posted by cent88

It happens to all the switches in the house.
Normally what is the pop's frequency? We cannot hear RF from speaker right?

Right

But RF can overload and be demodulated by the front end transistors in an amp and the result is an unpredicatable pop.

What is the amplifier ? Is it homemade ?

It might be worth trying a simple filter on the mains supply to the amp. Very hard to diagnose at a distance though. If all your switches cause the problem it sounds like a design/build flaw with the amp.

Does the amp continue to run for a second or two when power is turned off... running on its reservoir caps. If so disconnect from mains and quickly have someone operate a light switch and see if it still pops. Have just the amp and speakers and NO external leads/source components at first to try and narrow it down.

[DF96]

Yes, my guess is an RF burst, or it could be poor house wiring giving a voltage jump when a load is applied/removed. Does a battery powered AM radio show the noise too?

[Speedskater]

Power line switches work much like an old-fashion spark-gap radio transmitter. They both create a wide band-width energy bursts. It's best to place the filter at the source.

[gootee]

It's almost-certainly broadband RF, getting into the amp. It gets rectified in your input stages and give a DC pulse out. Pop!

You need RF filtering on your amp's inputs. The problem is that for RF, the inputs include the output, the power supply inputs, and the signal inputs, plus every length of wire and PCB trace, depending on whether the RF is conducted (through AC lines) or radiated (through the air), or both.

If it's a commercial amp, you could place a low-pass filter (probably just a parallel capacitor) in the wall outlet, unless you want to open up the amp and put it there.

If it's a DIY amplifier, there are several things you should probably do, in addition to filtering the AC power.

First, see section 7 of ADI - Analog Dialogue | Op Amp Applications Handbook .

You need to make sure that you have proper decoupling capacitors on every point where DC power goes to an active semiconductor device.

You need an RF low-pass filter on every input to every amplification stage (i.e. every opamp, etc). Sometimes you only need a 220pF cap across each amp's input pins. Other times, you need multiple RC filters. Resistance in series with each low-power output is also advisable, if it's possible with your circuit.

If your speaker cables are acting as antennas, then you might need to place an inductor and parallel resistor in each of the high-power output paths.

You should also have a Zobel network (snubber) on each output.

Tom