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Old 3rd December 2007, 08:01 AM   #1
Itsme is offline Itsme  United States
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Default Capacitor problems

Hello, I had posted earlier about a Memphis 16-ST1500D With some bulging output capacitors.
The specs are 200 volt 10uf Non-Polarized (Samwha BP M7A) Anyway I can not find replacements anywhere. Perry gave me a model number through JBL, But they are out and could be months before they are in stock. So I ordered some non-polar 100volt 4.7uf's {The only thing I could find at Mouser} And was going to parallel them together, But the problem is even together they are only half the physical size of the bad one. Is this going to hurt the sound quality? I know it's just a sub amp but I don't want to lower the SQ in any way. And I am replacing 4 caps all together along with 8 IRF3205's. I've uploaded a picture of the old cap's next to the replacement cap's. Thanks.

Please let me know if anybody knows where I can find these cap's. I have tried Dogpile & Google search and Mouser, Digi-key, All Parts, and 7 or 8 other supply houses.
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Old 3rd December 2007, 01:25 PM   #2
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Those are only 100 volt caps. What's the rail voltage in the amp?

If the rail voltage is less than 100v, the caps may hold up. When testing, you need to drive the amp hard (into clipping on peaks) into its lowest rated load while monitoring the temperature of the caps. If the caps become uncomfortable to touch, they probably won't hold up. The amp should be driven like this for at least 30 minutes.

When testing have the bass boost at the minimum setting and the crossover set to the highest frequency. Test with music that has a wide range of low frequencies.

You should wear eye protection. If the capacitors are not up to the task, they could explode.

If they hold up and have the same capacitance as the originals, there should be no degradation of sound quality.
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Old 3rd December 2007, 01:55 PM   #3
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Parts Express has bipolar caps in 10uF, 100V ratings. $0.55 each.

Most likely, as Perry has indicated, the 100V caps will be fine. However, the half sized capacitor will potentially cause an early rolloff of the low frequencies. You'd have to know a little more of the design to know for sure. Might not make any difference.

The other possibility is to series two 22uF, 100V capacitors together. End result is a 11uF, 200V bipolar cap. Advantage here is you can get away with using polarized caps, which are typically smaller in size. Difficulty is getting it all to fit on the circuit board.
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Old 3rd December 2007, 02:07 PM   #4
djQUAN is offline djQUAN  Philippines
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that amp is class D and with most class D that I have seen with those caps, those are used for the output zobel (10uF + ~4R) so that the output stage doesn't blow up if you run the amp without a speaker connected.

I don't think it would affect sound quality.
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Old 3rd December 2007, 02:35 PM   #5
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Default Re: Capacitor problems

Quote:
Originally posted by Itsme
Hello, I had posted earlier about a Memphis 16-ST1500D With some bulging output capacitors.
The specs are 200 volt 10uf Non-Polarized (Samwha BP M7A) Anyway I can not find replacements anywhere. Perry gave me a model number through JBL, But they are out and could be months before they are in stock. So I ordered some non-polar 100volt 4.7uf's {The only thing I could find at Mouser} And was going to parallel them together, But the problem is even together they are only half the physical size of the bad one. Is this going to hurt the sound quality? I know it's just a sub amp but I don't want to lower the SQ in any way. And I am replacing 4 caps all together along with 8 IRF3205's. I've uploaded a picture of the old cap's next to the replacement cap's. Thanks.

Assuming these caps are on the output stage
P=V^2/R
1500Wrms at 2 ohm is 54.77V rms
peak voltage is 1.414 times rms =77.45V peak. If its in a zobel then the series R will also disipate some of the energy. Those caps should work while you wait for the correct ones to come in.
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Old 3rd December 2007, 03:26 PM   #6
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I've never worked on a 1500 but in the 1000, the caps are directly across the output. They work with the output inductors to filter the carrier from the audio.
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Old 3rd December 2007, 05:17 PM   #7
Itsme is offline Itsme  United States
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If I parallel 2 0f those 100 volt 4.7uf I should end up with a 200 volt 9.4uf capacitor right? When you parallel it doubles the values on both voltage and micro farads right???
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Old 3rd December 2007, 05:21 PM   #8
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It only doubles the capacitance, not the voltage.

To double the voltage, you have to connect two in series. When you connect them in series, you double the voltage but the capacitance is cut in half (as was previously stated).
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Old 3rd December 2007, 06:26 PM   #9
Itsme is offline Itsme  United States
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Quote:
Originally posted by Perry Babin
It only doubles the capacitance, not the voltage.

To double the voltage, you have to connect two in series. When you connect them in series, you double the voltage but the capacitance is cut in half (as was previously stated).

That's right, I don't know what I was thinking.
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Old 7th August 2008, 09:46 AM   #10
Itsme is offline Itsme  United States
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Hello, again!
I finally put some Sprague 100v 20uf's in series and fired up the amp and I get a clicking noise from the tl494cn card and the protection light flickers on and off. Also my IRF3205's are heating up. So I checked voltage on the tl494cn pins and this is what I have.

Pins:
1: 0
2: 4.9
3: 0
4: 3.6
5: 1.4
6: 3.6
7: 0
8: 11.9
9: 0
10: 0
11: 11.9
12: 11.8
13: 4.9
14:4.9
15: 4.9
16: 0
No Negative Voltage.
Not sure were to go from here?
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