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Old 21st October 2004, 06:12 AM   #1
rs1026 is offline rs1026  India
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Unhappy How to prevent capacitor draining?

When ever I switch off my amp I can still hear music for about 10-15 seconds and it gradually fades away. Is there a way to eliminate this capacitor draining problem. I am sure this problem would have occured to many of you guys. Please let me know a sloution for this.
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Old 21st October 2004, 07:11 AM   #2
HDTVman is offline HDTVman  United States
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Why is this a problem? That is the normal function for a chip amp, or any amp for that matter and depends on the size of the filter caps you're using and the current demands of the amp. Use small filter caps and have a short discharge time. Use big caps and have a longer discharge time. Use monster size caps, or a bank of caps and the thing will play for a long time after power down. If your using the National lm3886 controlling the mute pin will let you kill the sound at power down.

Later BZ
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Old 21st October 2004, 10:20 AM   #3
rs1026 is offline rs1026  India
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Default But I thought Big is better!!

I thought large capacitors give good filtering.If I reduce the value/size then what about the filtering ??Wouldnt it effect the sound qaulity.
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Old 21st October 2004, 10:49 AM   #4
Jennice is offline Jennice  Denmark
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Default Re: How to prevent capacitor draining?

Quote:
Originally posted by rs1026
Is there a way to eliminate this capacitor draining problem.

RS1026,

The short answer would be: No.

More specifically, every capacitor has some shunt resistance, causing it to drain itself slowly, even if nothing is connected to the terminals of the capacitor.

However, I would not call your issue a real problem. It just shows that your capacitors are in good shape, and capable of supplying your amp for a long time after the power transformer is switched off.

This phenomenon it related to, but not identical to the issue of filtering ripple from the supply. Yes, lowering the capacitor value to very low values cause poor ripple suppression and lower the peak current capability of your PSU, but this is just as much a matter of finding a capacitor with low ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance) for ripple suppression. Alternatively, use ceramic capacitors in parallel with your electrolytic ones to lower ESR and ESL.

Your setup works fine, and nothing is wrong. As someone suggested, you may want to use the mute pin. Alternatively, use a relay on the live terminal of your speaker to disconnect them from the amp during power-up/ -down.

Jennice
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Old 21st October 2004, 11:47 AM   #5
rs1026 is offline rs1026  India
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Default Thanks

Thanks guys. Your inputs will surely help. I will think about adding a relay and the ceramic capacitor.
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Old 21st October 2004, 12:09 PM   #6
Jennice is offline Jennice  Denmark
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In my non-chip-amp designs, I use the relay to avoid turn-on "popp" sounds in the speakers.
If you don't have any popp-sounds (probably not with a chip-amp), the use of a relay is only for the puspose of not hearing the capacitors drain. The phenonenon still happens... it's just a matter of avoiding to hear it.

Ceramic capacitors have lower ESR and ESL than electrolytics, especially at higher frequencies (the harmonics of the rectified mains frequency). If you like the sound of your setup, there's no need to make any change.

Jennice
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Old 22nd October 2004, 08:43 AM   #7
rs1026 is offline rs1026  India
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Default not good to hear

I am not liking the sound of the system.May be its got to do with bad drivers.I also see lot of cone movement. I dont know if I am clipping the amp!!
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Old 22nd October 2004, 01:50 PM   #8
Jennice is offline Jennice  Denmark
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When you play loud, visual cone movement is normal. During what conditions do you see this movement?
If it's during loud music, and you don't like the sound, then your amp may not be the amp you need/want... Maybe you need a more powerful amp for your needs.

Jennice
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Old 22nd October 2004, 08:15 PM   #9
Tim__x is offline Tim__x  Canada
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If it really bothers you, you could use this EDN Design Idea.
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Old 22nd October 2004, 09:15 PM   #10
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You seem to hear music for a heck of a long time too, just how big are these caps? My output fades away in about 2 seconds.

"I am not liking the sound of the system."
Could it be you have to much capacitance?
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