[DecibleDude]

So upon turning the amp on or off there's a click after a few seconds which I always thought was to prevent power to the speakers for a few seconds. Today I noticed because the volume knob was up slightly that the music comes on immediately after pushing the power button on. I wouldn't have noticed this earlier because I always turn the volume fully down before turning the unit off. Anyway, after a few seconds the relay clicks but my confusion comes from the fact that I thought there wasn't suppose to be any sound possible until you hear the click. Is something wrong or am I just misunderstanding the meaning of the click when I turn the unit on or off? Thanks

[danielgk]

The relay is in the power supply circuit, not the audio circuit.
When the amp first turns on, a fairly large resistor and inrush current limiter allow the large power supply capacitor(s) to charge slowly.  After a few seconds the relay clicks on and the resistor and inrush current limiter are taken out of circuit (shorted out).  The result is a smooth, noise free, power up called a "soft start".  The same circuits are in the SET500 and M750.

The other way to do it would have been to put the relay in the audio path, wait until the amp came up, check the voltages to make sure they are right, and then energize the relay to connect the speakers.  This does not prevent the initial current surge (which, by the way, can be as much as 400 amps (yes, amps!) for a few thousandths of a second - too fast to blow a circuit breaker or fuse, but that's why the lights flicker when you turn the old amps on) and relies on circuits connected to the audio path to work properly or the amp is "dead".  Further, Frank was a firm believer in NOT having a relay in the audio path, but he liked the soft start power supply circuit.


Dan

[veloceleste]

My SET120 doesn’t click after power up. I also get sound immediately after power on.

[DecibleDude]

So upon turning the amp on or off there's a click after a few seconds which I always thought was to prevent power to the speakers for a few seconds. Today I noticed because the volume knob was up slightly that the music comes on immediately after pushing the power button on. I wouldn't have noticed this earlier because I always turn the volume fully down before turning the unit off. Anyway, after a few seconds the relay clicks but my confusion comes from the fact that I thought there wasn't suppose to be any sound possible until you hear the click. Is something wrong or am I just misunderstanding the meaning of the click when I turn the unit on or off? Thanks

 Thank you Dan, so are you saying this is normal for my amp and nothing is wrong? Out of curiosity I turned the amp off by the power button with the volume knob slightly up and the music continued to play until the relay clicked and then the music immediately ceased, so I'm wondering if that makes sense for the amp given what I mentioned prior? Thanks

[danielgk]

Older SET120's will not have the soft start power supply and hence will not "click".

Upon power off the SET120 will continue to play until the power supply capacitors discharge to a certain level.  Usually its about half of what they normally run at.  How long this takes is dependent on how loud the music is.  If the relay clicks at the same time the music stops its purely coincidental.

It is perfectly normal to hear a click a couple of seconds after power on in a SET120 with soft start power supply and would be a problem if that "click" were to stop.


Dan

[DecibleDude]

 Thanks Dan, then I guess everything's ok, and I learned a little more than I knew about these things yesterday, which apparently wasn't a lot.