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Old 27th February 2003, 05:29 PM   #1
jaybird is offline jaybird  United States
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Join Date: Jan 2003
Location: cincinnati
Default need help please

I have an adcom gfa-5500. After hours of listening only the left side of my amp gets hot to the touch. It seems to play music fine, but the right side of the heat sinks is only mildly warm. Could there be something wrong with this amp?
Thank you for any advice you can provide.
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Old 27th February 2003, 07:22 PM   #2
halojoy is offline halojoy  Sweden
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Default Re: need help please

Quote:
Originally posted by jaybird
I have an adcom gfa-5500. After hours of listening only the left side of my amp gets hot to the touch. It seems to play music fine, but the right side of the heat sinks is only mildly warm. Could there be something wrong with this amp?
Thank you for any advice you can provide.
I read about Adcom GFA-5500 in the ADCom website: http://www.adcom.com/amplifiers/gfa5500.htm

It (should) have a Quiescent Power Consumption of 192 VA.
And in the manual they say that Ampp should get hot.
It has MOSFET output. It is 2x200 Watt.

Here we have an amp with High Idle Current.
I estimate this to be in the magnitude of 1.0 Ampere/ channel.
That would make an idle power take of about 200 watt.
Then I have supposed the PSU to be +-50VDC.(=100VDC)
-----------------------------------------------------------

The case with your amp, I think, is that one channel has too low idle current.
It might have been a fault in the current setting
BEFORE the amp left the manufacturer.
Or it can have changed by some cause after that.

You should contact ADCOM and get the service manual.
If you give them your serial-number of your amp, you ought to get it.

The Owner's Manual (PDF) doesn't say how much current should be
or how to measure or set the current.
So Service Manual is what we want.
-----------------------------------------------------------

If you can't get this information from ADCOM,
you have to start figuring out, over which resistor you should measure the voltage, to get the value of idle current.
Then you could measure in the Okay (warmer) channel,
and set the other chanel to the same.

The idle current is set with a trim-pot, usually located
close to the output-transistors on the heatsink.
In this case the BIG MOSFETs.

The current could be measured over the 2 fairly big power resistors
that are also close to the MOSFETs.
Those resistors are called the Emittor Resistors in the outputstage.
Or for MOSFETs maybecalled SOURCE resistors.
As they are connected to the Source terminal.
You need of course to know the value of those resistors.
Can be like 0.1-0.3 Ohm.

/halo - can have help you with this You pay the Ticket He will come
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Old 27th February 2003, 10:15 PM   #3
jaybird is offline jaybird  United States
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Location: cincinnati
Default thanks

Thanks for the information. I called adcom and they offer a service manual for $25. It's on the way.
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