Chevin Research A-series schematic

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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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Mounted all the washers ;) , reassembled all parts, and the beast is running.
Only, can’t find a resistor bank to test it at full power. B+/- is 320VDC. Go figure.
As this is the first ‘heavy’ Chevin I serviced, I can tell I’m impressed with both the power and the sound they produce.

-=Hugo=-
 
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?


_-_-bear :Pawprint:
 
Bear,

I’m waiting for the schematic and when I have it I won’t post it because the amp is still in production.
It’s a SMPS power supply, with a capacitor bank of 20 X 1800µF/180V.
There’s no way I can test the amp at full power as I don’t 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 don’t know the class, there’s no bias regulator and the mosfets seem to be driven by op42’s. 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=-
 
Chevin uses an old Hafler patent for the power amp( called grounded emittor/source transnova?), also a Motorola or IRF patent for the power supply (electronic balast, no ic's just self oscillating with a diac and small signal transformer for driver) so nothing special here. The mosfets will produce some (most of the..10-20 dB?)gain and can be bolted without isolation as both upper and down banks are "earthed" if I am correct (it's way too long ago since I've serviced them...)
The speaker connects between earth of psu and earth of bolted together power mosfets..a bit odd when seen at first..but very smart..;-) they do get good reviews.

Testing is indeed difficult, perhaps some lightbulbs..the ones they use for rebuilding/re-decorating homes..?

the best test is half power...that will show if there's enough thermal cooling or not..full power will not generate as much heat as half or quarter of power.
Hopes this helps
 
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A1000 fan problem

Can someone help me with my problem?

I have two a1000 Chevin amp on wich the fans are dead. I traced the problem down to two burned resistors (100 Ohm) In the middle of the cooling bank. I tried replacing them but found that the IRF740 mosfet was dead to.
With my rather basic expierince in amp design after looking at the datasheet I decided I could easely bridge the Mosfet by connecting pin 3 to the massa, and therefore leaving the fans on constantly.
Works like a charm on one amp, but the other keeps blowing the resistors. Has anyone expirience with this kind of problem, and a solution?
Also a schematic of the design would be higly appreciated.
 
Thanks for the diagram,

I will try to replace the caps this weekend (I don't have much time during the week), but I have strong feelings these won't make much of a difference since the resistors just smoke away, Even 4 500 Ohm 1/2 Watt resisters in parrallel (= 110 ohm 1 Watt) are blown away really fast. I am more thinking in direction that one of the two Supply's is faulty, therefore generating to much current trough the resistors.

On both amps I'm also going to replace the hardware tot the ground instead of the mosfet by a 10 or 100 ohm resistor 5 Watt. I'm geussing these should temper the current flowing trough both 100 ohm resistors.

Is there anyone who sees a mistake in my thoughts?

DaDe
 
Good afternoon,

I bought a used chevin q6 with one of the volume knobs broken off. I recently opened the amps and put in a replacement pot. When I reassembled and powered up the amp, the red clip light for the channel remains lit and the output is shockingly low and bad. I took out the new pot and stuck back in the old one, but the problem remains.

I checked the capacitors with a multimeter and they all work fine, and nothing appears damaged.

Does anyone recognise these symptoms? Have I inadvertently damaged something?
 
Chevin Research A1000 schematic required.

Hi, I am new to this forum. I am an electronic engineer by profession but more on the digital side - not too good with analogue stuff!

I am trying to repair a Chevin Research A1000 power amp for a friend and was wondering if anyone has any schematics for this or similar amp.

Fault description: Channel A seems to work fine and the fans are Ok too. The output from channel B is noticeably distorted but seems to be about the correct volume, I think. Nothing inside looks obviously burnt, or anything.

Any help would be gratefully received!

Thanks.
 
Still no schematic or service manual for the A-series?

I have an A2000 here, but I really dont like poking around too much in SMPS units.

From the look of it, it couldl very well be an arch welder.

32 pcs of TO3 transistors. I cant find a datasheet, but I assume its 200-250w 250v exicons.
As far as I can tell, several models use the exact same config. All the way from 2x300 8r to 2x750w 8r.
Just a pot to increase voltage? :p
 
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