MOSFET power amp help

pollypocket · 7th August 2006, 10:50 PM

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

anatech · 8th August 2006, 03:53 PM

Hi Paul,
Look at the drivers, keep going back until you start hitting good ones.

-Chris

clem_o · 9th August 2006, 01:05 AM

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? :-)

pollypocket · 9th August 2006, 02:16 AM

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

clem_o · 9th August 2006, 02:21 AM

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

anatech · 9th August 2006, 02:39 AM

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

clem_o · 9th August 2006, 03:15 AM

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!

pollypocket · 9th August 2006, 09:19 PM

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

anatech · 9th August 2006, 10:56 PM

Hi Clem,
I left out the worst part. No silk screen on the pcb, no bottom access. Warranty claims.

-Chris

clem_o · 10th August 2006, 12:29 AM

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

7th August 2006, 10:50 PM	#1
pollypocket diyAudio Member Join Date: Sep 2003 Location: Ontario	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 __________________ Ride hard, shoot straight and tell the truth

9th August 2006, 02:16 AM	#4
pollypocket diyAudio Member Join Date: Sep 2003 Location: Ontario	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 __________________ Ride hard, shoot straight and tell the truth

9th August 2006, 09:19 PM	#8
pollypocket diyAudio Member Join Date: Sep 2003 Location: Ontario	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 __________________ Ride hard, shoot straight and tell the truth

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8th August 2006, 03:53 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Paul, Look at the drivers, keep going back until you start hitting good ones. -Chris

9th August 2006, 01:05 AM	#3
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	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? :-)

9th August 2006, 02:21 AM	#5
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	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

9th August 2006, 02:39 AM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

9th August 2006, 10:56 PM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Clem, I left out the worst part. No silk screen on the pcb, no bottom access. Warranty claims. -Chris

10th August 2006, 12:29 AM	#10
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	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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