How can I reduce mechanical turn on and turn off noise? - diyAudio
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Old 26th October 2003, 02:24 AM   #1
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Default How can I reduce mechanical turn on and turn off noise?

On the subwoofer I have mentioned in many other posts, I have the AC cord coming in, into a toggle switch, then through the transformer. from the switch, I get a noise on turn off, and want to get rid of it. Would a cap in line with the transformer and switch work for this, and if so, what value. I would use something like 150V (I have a .5uf with 1600V, if that would work).

Thanks, Mike
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Old 26th October 2003, 02:44 AM   #2
tool49 is offline tool49  Canada
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I'm throwing an idea here, but perhaps you could try to bypass the switch with this cap, I'm pretty sure it will lower the thump (prolonging the life of your switch in the process). Others might correct me here tho.

Hope this helps,
Sébastien
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Old 26th October 2003, 12:35 PM   #3
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You mean connect the cap across the switch's 2 connectors? I may be wrong here, but would't that sort of bypass the switch and keep it on all of the time?
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Old 26th October 2003, 12:54 PM   #4
tool49 is offline tool49  Canada
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Exactly bypassing the switch. No it won't keep the device on all the time. In fact, a capacitor can be seen in this position as a device that will absorb part of the stress caused by the spark that will occur in the switch, thus reducing the intensity of the spark and the turn on/off stress for the switch. By making the current flow behave this way, I believe it would somewhat make the thumps you're experiencing softer.

This being relatively simple to do, I suggest you try it, and report how it goes. I did it for quite a few of my newer amps, and it prevents the switch from deteriorating as fast. Since I'm using a muting circuit for the thumps, I've no idea to what extent it does correct the problem. (The capacitors I usually put in this position are 0.1uF/400V Wima MKS, so your 0.5uF/1600V would be even better)

Hope this helps,
Sébastien
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Old 26th October 2003, 12:54 PM   #5
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you should make sure that you aren't getting a DC transient into your subwoofer on "Turn-On". You could place a snubber across the switch contacts if you suspect arcing -- the snubber allows some current to pass as the contacts come into proximity. Take a look at the Quencharc series from Mallory. I have a bag full of them if you email me privately.

I suspect that as with many home-built amps yours could benefit from inrush current limiting, however.
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Old 26th October 2003, 01:08 PM   #6
ronc is offline ronc  United States
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I just leave my amp on 24/7.
ron
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Old 27th October 2003, 06:10 PM   #7
macboy is offline macboy  Canada
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Consider using a solid-state relay. Use a zero-crossing type. This type of relay will only turn on or off when the voltage crosses zero, avoiding the inrush current and associated spark.
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Old 28th October 2003, 01:25 AM   #8
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After experiencing problems with the amplifier's connection and the shaking of the speaker causing it to loose connection for a second and pop, and the heatsink not having enough thermal greese and the chip going into protect mode, I took everything out, fixed the heatsink, and ran newer, nicer wire. The sound is now much better, and the thing doesn't overheat. I also noticed that there is almost no pop unless I put my head up to the speaker and listen. I will still use the cap, and report how it works. Just to make sure, I connect is across the contacts of the switch.

I like the idea about leaving it on all of the time, but I am not confident enough in myself to do that. Also, I don't know how the chip will work if it is constantly on. And I don't know how much heat it puts out when there is no signal.

Thanks for all of the help, Mike
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Old 28th October 2003, 01:43 AM   #9
JoeBob is offline JoeBob  Canada
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The chip should put out a very low amout of heat when it isn't driving a signal, it's Class-A/B and has a very low bias current, so heat wouldn't be a problem in leaving it on 24/7.

If you're using the LM series of chips (I haven't tried the OPAs) they get mighty cranky when they overheat that might be why it sounds better when properly conected to your heatsink.

I understand what you mean by leaving it on 24/7, I don't trust myself enough to do that either, I'd always be constantly woorying that something might blow and I'd have to redo all that work again!
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