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Old 7th August 2006, 10:50 PM   #1
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Default MOSFET power amp help

Hi;

I was wondering if anyone has had any experience with a project published in Radio Electronics back in the mid 80's written/designed by Reinhard Metz? It was a 250 wpc FET outputs power amp. I tried raising someone at the ATL web site, but no response...I suspect they don't support this amp at all.

Anyone else built one or familiar with the amp? It is a bit of a brute and has no safe guards for the output FETs from shorted speaker leads. I cooked the outputs in on channel (shorting a speaker lead) and need to replace them. They are connected in parallel and are all current matched. I am not sure how far back I have to go in the circuit looking for components that got taken out by the short. Any thoughts?

thanks,

Paul
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Old 8th August 2006, 03:53 PM   #2
anatech is offline anatech  Canada
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Hi Paul,
Look at the drivers, keep going back until you start hitting good ones.

-Chris
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Old 9th August 2006, 01:05 AM   #3
clem_o is offline clem_o  Philippines
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Hi all,

Wouldn't the drivers have a better chance of surviving given the insulated gate of the MOSFETs?

Hmmm, on the other hand if the MOSFET silcon melts down then the gate wouldn't be insulated anyway... oh well...

Cheers!


ps re the amp - my brother's subscription to RE ended about the mid-80's - not sure if I can dig it up! How about posting the schematic? :-)
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Old 9th August 2006, 02:16 AM   #4
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Hey Clem_o;

I can post the schematic as soon as I dig it up. Any rules on the forum re: intellectual property for posting schematics?

Paul
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Old 9th August 2006, 02:21 AM   #5
clem_o is offline clem_o  Philippines
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Hi Paul,

There are, i.e. if the gear is commercially being produced, if there is good technical support etc.

OTOH, mid-80s would put it at 20 years, probably out of any claim to copyrights, and you haven't gotten any support from ATL...

Chris (anatech), watcha think?

Cheers!

Clem
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Old 9th August 2006, 02:39 AM   #6
anatech is offline anatech  Canada
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Hi Clem,
There is a ton of other stuff posted. I wouldn't worry about this one too much. The manufacturer can always request it's removal if it came right down to it.

With regard to the mosfet gates shorting. Yup. Sometimes the protective zeners from gate to source (if used) will short instead. In any event, just keep going back until everything tests good. If it was a mid 80's Yamaha home amp, that puts you at the input cap to the diff pair.

-Chris
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Old 9th August 2006, 03:15 AM   #7
clem_o is offline clem_o  Philippines
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Quote:
Originally posted by anatech
If it was a mid 80's Yamaha home amp, that puts you at the input cap to the diff pair.

OUCH!!!! :-) :-)

Thanks Chris!
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Old 9th August 2006, 09:19 PM   #8
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Default MOSFET Power Amp Help

Hi Guys;

I will scan and post the schematic as soon as I can find it. I am in the middle of moving and I think it has been packed and put into storage already. I will look around a bit more, but if I can't find it, I will post in September.

thanks,

Paul
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Old 9th August 2006, 10:56 PM   #9
anatech is offline anatech  Canada
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Hi Clem,
I left out the worst part. No silk screen on the pcb, no bottom access. Warranty claims.

-Chris
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Old 10th August 2006, 12:29 AM   #10
clem_o is offline clem_o  Philippines
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Hi Chris,

Some manufacturers can really make a service tech's life difficult! I'm surprised they didn't pour silicon rubber or epoxy to seal up the thing! :-)




I'll have a look if I can locate those RE magazines.... that is, if the termites haven't feasted on them yet!

Paul, I think you can give it a go even without the schematics anyway - expert guide is here (Chris)... :-)


Cheers

Clem
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