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Old 19th April 2008, 03:59 AM   #1
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Default bridge rectifier question

I plan to add capacitance to the PS of my amp which is a Parasound New Classic 2125 model. the caps in it now are two 6800uf 80v. 105 degree rated. it has two bridge rectifiers also which are inline packages rated at 8 amp 200v. and also attached to heatsinks. I have ordered two 10,000uf 80v. 105 degree. I also, ordered 8 15 amp 600v. rated stealth diodes also to use to replace the original rect. should I replace the 6800uf caps or, add the two 10,000uf caps in paralell? also, should the new heavier duty bridges need to be heatsunk again?

http://www.enjoythemusic.com/magazin..._2100_2125.htm here are the specs and picture. Thanks!
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Old 19th April 2008, 04:19 AM   #2
TheMG is offline TheMG  Canada
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Yes the new rectifier diodes would have to be heatsinked. Assuming they have the same Vf as the old ones, the heat that needs to be dissipated will be the same.
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Old 19th April 2008, 04:26 AM   #3
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Quote:
Originally posted by TheMG
Yes the new rectifier diodes would have to be heatsinked. Assuming they have the same Vf as the old ones, the heat that needs to be dissipated will be the same.
Thanks! should the heavier duty rectifiers be able to handle the 10k caps in paralell? or should I just replace the 6.8k caps? I know just replacing wouldn't be much of an increase.


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Old 19th April 2008, 05:15 PM   #4
TheMG is offline TheMG  Canada
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Adding larger caps does not really have anything to do with the rectifier ratings, unless you go insane with absolutely extreme amounts of capacitance.

That's because rectifier diodes have a continuous current rating, and a surge current rating. This means you can actually put much more than the rated current through a rectifier diode for a short amount of time with no ill effects.

As far as which is going to be better sound quality wise, that I don't know.
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Old 19th April 2008, 05:24 PM   #5
Mooly is offline Mooly  United Kingdom
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Hi, Just a couple of points to bear in mind. Adding more capacitance can significantly increase the peak charging current in the bridge as the conduction angle is significantly reduced. This can increase the temperature the mains transformer runs at due to "copper losses" and there is a risk of the core saturating. 6800mf to 10000mf is probably fine but I would'nt go adding much more. These higher currents can also increase any radiated magnetic field, so if hum caused by induced field is a problem this can actually make it worse. Correct layout and grounding is much more important in my opinion. Just be aware of potential problems, more isn't always better.
Regards Karl
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Old 19th April 2008, 05:49 PM   #6
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The photo shows a dual mono construction with two rectifiers and two sets of filter caps. What's strange is one cap per channel looks smaller than the other. Is this a single polarity supply with a cap coupled output stage?

If this was my amplifier, I would get the schematic before going any further (actually I would disassemble it and trace it out myself, but I would still get the schematic for reference).

I would also check the data sheet for the new rectifier's 10mS surge current ratings, fast rectifiers have lower surge ratings than 60hz ones. It would need to be 150A to be safe in my mind with the parallel 6,800 and 10,000 combination.
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Old 19th April 2008, 06:10 PM   #7
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thanks for all the pointers fellas! I was just surprised when i opened the amp up and it had the same size PS caps as my Adcom GFP 6500 preamp stock, caps which, i'm driving it with. just seems that Parasound cut corners on the power supply putting that size (6800uf) caps in a power amp with the rated specs? makes me feel like i must, be laking in the bass department? even my Onkyo M-282 100 wpc. amp came stock with 10,000uf Nichicon Gold tunes and much smaller, and lighter tranny with 71v. caps which costed $200.00 vs. the $700.00 (retail) price of the Parasound which also, uses Jamicon brand caps? does this make since? or am i thinking all wrong? maybe the large tranny makes up for the smaller caps? thanks for any help clearing up my confusion LOL!
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Old 19th April 2008, 06:18 PM   #8
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Quote:
Originally posted by djk
The photo shows a dual mono construction with two rectifiers and two sets of filter caps. What's strange is one cap per channel looks smaller than the other. Is this a single polarity supply with a cap coupled output stage?

If this was my amplifier, I would get the schematic before going any further (actually I would disassemble it and trace it out myself, but I would still get the schematic for reference).

I would also check the data sheet for the new rectifier's 10mS surge current ratings, fast rectifiers have lower surge ratings than 60hz ones. It would need to be 150A to be safe in my mind with the parallel 6,800 and 10,000 combination.
hi djk! the smaller caps are rated at only 63v? so i really don't know what their purpose is. I think your right! i'd better try to find a service manual. Thanks!


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Old 19th April 2008, 07:04 PM   #9
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Quote:
Originally posted by djk
The photo shows a dual mono construction with two rectifiers and two sets of filter caps. What's strange is one cap per channel looks smaller than the other. Is this a single polarity supply with a cap coupled output stage?

If this was my amplifier, I would get the schematic before going any further (actually I would disassemble it and trace it out myself, but I would still get the schematic for reference).

I would also check the data sheet for the new rectifier's 10mS surge current ratings, fast rectifiers have lower surge ratings than 60hz ones. It would need to be 150A to be safe in my mind with the parallel 6,800 and 10,000 combination.
these are the specs on diodes. if i understand correct, these should handle 200 amp surge yes or no? Thanks!

http://www.fairchildsemi.com/ds/IS%2FISL9R1560PF2.pdf
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Old 20th April 2008, 01:20 PM   #10
djk is offline djk
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Yes, the 8.3mS (60hz) 200A surge is adequate.
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