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Old 8th February 2009, 02:20 PM   #1
OMNIFEX is offline OMNIFEX  Jamaica
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Question More power with less capacitance. Why?

Right!

So, my Peavey Electrolytic modification was a success and, I have now moved on to some of my Crown Amplifiers.

Looking at the Schematic the amplifiers offer Capacitors with the following ratings:

Macrotech 600 = 7800 MFD

Macrotech 1200 = 10000 MFD

Macrotech 2400 = 6300 MFD

I am going to upgrade the MA 2400's with a pair (two for each amplifier, six in total) of these in the near future.

Does anyone know why Crown would offer 6300 MFD Capacitors in the MA 2400 while, offering more capacitance in their 1200 & 600 models?



Cheers!
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Old 8th February 2009, 02:34 PM   #2
AndrewT is offline AndrewT  Scotland
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possibly because the high voltage caps cost too much to supply the correct/adequate capacitance.
I suggest you buy 8 (+-50mF/channel) if they can fit the space available.
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Old 8th February 2009, 03:03 PM   #3
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Could be the supply is designed to sag under heavy load to save the inadequate output stage from failure. Just a thought...
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Old 8th February 2009, 03:58 PM   #4
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Default very very possible

Quote:
Originally posted by MJL21193
Could be the supply is designed to sag under heavy load to save the inadequate output stage from failure. Just a thought...
especially if we think that some of these models work the otherway arround like all collectors grounded ....
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Old 8th February 2009, 09:51 PM   #5
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I agree with Andrew on the cost issue, but to my understanding both output power and energy stored in a capacitor are proportional to the square of supply voltage, so there is basically no reason why higher power amp should have more capacitance in the supply.
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Old 9th February 2009, 04:21 AM   #6
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"I suggest you buy 8 (+-50mF/channel) if they can fit the space available."

There is only one cap per channel, they're bridge amps.

If we did take your advice we would see rectifier failure.

6800F gives 90% regulation on 60hz, 8200F on 50hz (4R loads).

The Crown Macro Reference, a 1500W per channel amplifier that was highly acclaimed by Stereophile magazine (for its sound quality), limps by with only a pair of 6300F cans.

http://www.crownaudio.com/pdf/legacy/mrschematics.pdf
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Old 9th February 2009, 09:14 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by djk
If we did take your advice we would see rectifier failure.
Are you sure?
Is soft start fitted to the transformer?
Is slow charge fitted after the secondary?

These two remedies should already be there. If not then fit them.
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Old 9th February 2009, 01:38 PM   #8
djk is offline djk
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"Are you sure?"

Yes, see the schematics.

The schematic I showed for the Macro reference does have inrush limiting, the Macrotech/Microtech/Powertech/Powerbase 600/1200/2400 do not.

http://www.crownaudio.com/pdf/legacy...5-4%20revf.pdf


"Is soft start fitted to the transformer?"

No.

"Is slow charge fitted after the secondary?"

No

"These two remedies should already be there. If not then fit them."

A big job, and needed if you re-design the supply as you suggested. I suggest leaving them alone, they work OK as is. The only thing I would add would be bypass caps to the main filter caps, and film bypass the electrolytic coupling caps, etc.

(or buy a Crest)
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Old 9th February 2009, 02:28 PM   #9
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So I take it, having 6300 MFD in the MA 2400 is a mystery.

Nevertheless, should I upgrade the bridging rectifiers when I begin this project?

They are 35 A 200 volts. One for each channel.

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Old 9th February 2009, 03:16 PM   #10
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the rectifier failure problem is not from start-up. the problem is the repetitive high current spikes during operation that keeps the caps charged. these high currents are somewhat mitigated by the fact that as the rated voltage of an electrolytic is increased, it's ESR rises as well (it's partly due to the fact that the oxide layer on the plates is thicker and the conductive portion is thinner)
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