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Old 20th April 2005, 07:24 PM   #1
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Default Chevin Research A-series schematic

Does anyone have a schematic of a A-series Chevin Research amplifier?
I'm stuck for the moment on a A5003.

Thanks

/Hugo
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Old 23rd April 2005, 10:54 AM   #2
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For those interested in tackling a Chevin here are some picture of a A5003.
Two banks of mosfets, Exicon ECF20P25 AND ECF20N25, 32 in total are mounted on top of heat sinks consisting of 24 alu plates, separated by spacers (don't know the exact English name).
In order to take out even one single mosfet the whole thing has to be disassembled. Also, to test the amplifier, everything must be assembled again as the heat sinks connect the upper bank sources with the lower bank.
I counted about two hours of disassembling before I even could measure something.
Boring to do and pricey for the customer.

Have fun

-=Hugo=-
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Old 23rd April 2005, 10:55 AM   #3
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spacers:
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Old 23rd April 2005, 10:56 AM   #4
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Alu plates:

Nice idea BTW to make your own heat sinks.
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Old 23rd April 2005, 01:11 PM   #5
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Not trying to be cheeky, but for your reference, those "spacers" are what we in the UK call "washers", basically a flat circular or square disk to act as spacing for a screw, usually when a hole is wider than the head of the screw
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Old 23rd April 2005, 02:29 PM   #6
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Mounted all the washers , reassembled all parts, and the beast is running.
Only, canít find a resistor bank to test it at full power. B+/- is 320VDC. Go figure.
As this is the first Ďheavyí Chevin I serviced, I can tell Iím impressed with both the power and the sound they produce.

-=Hugo=-
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Old 23rd April 2005, 03:45 PM   #7
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Ummm...

Are those little things the power transformers??
What is the rated power of this unit??

How much does the supply sag at full bore??

Stacked aluminum plates for a heatsink?
I don't think so.
What provides the thermal path between the plate with the mosfets and the next plate? Steel washers??

*Baaaap!!*

NG.

Aluminum washers? better... but without heatsink compound and without a flat, machined surface??

*Baaap!!*

NG. The thermal path is very very lossy.

Which direction are the fins - horizontal?? No fan?
Even lower efficiency.

The gap between plates matters too... that looks too thin for good "natural" flow given the length of the air path (if it was vertical...)

Must be a class AB - low bias amp, almost into class B otherwise
those Mosfets would be chunking away at something >40-60 min watts quiescent!? !?

Any idea what the circuit looks like?


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Old 23rd April 2005, 04:52 PM   #8
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Bear,

Iím waiting for the schematic and when I have it I wonít post it because the amp is still in production.
Itís a SMPS power supply, with a capacitor bank of 20 X 1800ĶF/180V.
Thereís no way I can test the amp at full power as I donít have the resistor banks and the heaviest speakers I have are 800W at 4ohm. The amp delivers 2.5Kw at 2ohm, 1.5Kw at 4ohm and 900W at 8ohm. I donít know the class, thereís no bias regulator and the mosfets seem to be driven by op42ís. http://www.hnny.nl/chevin_research/manual-ASeries.pdf

At about 150W and with 8ohm speakers the 320VDC was about 316VDC.
The heat sinks are cleverly made, washers are 3mm thick aluminium.
The mosfets are mounted on a thick alu plate, everything is horizontally stacked and the two Papst fans are modulated with the input signal amplitude. The louder the music, the faster they turn. It works, the amp runs hot but well controlled.

I remember they were once tested by a college under extreme conditions and there was no way to get them on their knees. These are one of the few amps in PA systems that really keep delivering the rated power over a long period.
IIRC they were tested with a sine wave at 2 ohm full power for several hours. Compared to other amps, most of them went into protection after five or ten minutes.

-=Hugo=-
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Old 24th April 2005, 10:33 PM   #9
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Quote:
Thereís no way I can test the amp at full power
Maybe you could start collecting the elements from old electric fires
I think maybe 20-30 1KW elements in parellel would make 2 ohm
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Old 25th April 2005, 06:45 PM   #10
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Wouldn't that be highly inductive?
I'm cooking on gas here at home.

/Hugo
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