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I have two old Aiwa P22 amplifiers.

When I turn one amplifier on I hear small 'click' noise from the inside of the amplifier 2-3 seconds after I turn the amplifier on, when I turn the amp off again I hear the same click 1-2 seconds after I flick the switch.

The second amp (which has recently stopped working) doesn't make this 'click' noise at all.

  1. What is this click noise?
  2. Do you think the lack of the click noise and the amp not working are related?
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Did the 2nd amp used to make the click noise? –  Andy aka Jul 18 '13 at 19:17

2 Answers 2

up vote 1 down vote accepted

JoshP's answer is good and I'd like to add more detail about the relay action. When amps switch on without the anti-pop relays incorporated, it's a lottery how the push-pull output transistors come into correct working - one transistor may become switched-on several milli-seconds before the other and this will inject a pulse into the speakers which may damage them or just prove annoying.

The relay may be used for other things but basically it is supported by a small circuit that monitors the output from the power transistors to check that they have stabilized following application of power. The relay contact then connects one or both speaker wires to the amplifier in the knowledge that there won't be a big popping sound.

Because the relays are magnetically driven switches there is no significant contact resistance to add colour to the signal reaching the speaker. So on power up and soon after you hear the relay click. When you power down there will be a small delay while the relay coil circuit (the thing that creates the magnetism to close the relay contact) discharges its energy thus a small click after power is removed.

I would say there's a fair chance that because the relay can directly disengage the speaker from the power transistors that this may be the culprit in your failed amp. Alternatively it may be doing its job and preventing a shorted (or partially shorted) transistor doing the speaker damage.

Output capacitors can also fail and this will cause the same problem - a large amount of dc onto the speaker - the relay protects against that too. Alternatively the AC power supply section in the amp may have died and nothing will work unitl this section is mended.

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The clicking noise is likely the relay switching on/off. The relay is a safety device for your speakers, which abhor DC current.

I'm not schooled enough in the electronics to describe it in detail, but I found a nice write-up about it here.

Excerpt:

An important feature of an audio amplifier is to provide a system to protect your speakers in case the amplifier breaks down and puts DC on the speaker terminals. No speaker will take kindly to the presence of 50V on it's voice coil, so that has to be prevented. One way of doing that is to include a VI limiter in the amplifier or power supply. However, it's hard to design one that doesn't negativly influence the sound quality when the amplifier is driven near it's maximum (which happens sooner than you might think). Other solutions include polyswitches, fuses, etc. But the best solution, in my opinion, is a relay with DC sensor. Relays have no non-linear components and their resistance is small.

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