Schematics on the Adcom GFA-5802 - diyAudio
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Old 3rd January 2004, 09:14 PM   #1
K-amps is offline K-amps  United States
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Default Schematics on the Adcom GFA-5802

Does anyone have the schematics of the Adcom GFA-5802. I am interested in repairing a faulty turn on circuit.

The power amp section is fine but seems to run too cool. Ballast resistors are 0.33 ohms so I am guessing 24mV across each will do?

Anyway without the schematics I don't know how it is supposed to turn on the amp.

There are two jumpers near the power on relay and shorting them turns the amp on but it seems like all the current then passes through the Current rush limiter (ST electronic's CL-101) also same as Digi-key's parts number KC024L-ND.

I would think normally the power transformer should not be in series with the current Limiter all the time only for half a second or so till a relay shorts it. But in this case all the amp's load went to the current limiter over heating it.

In the Adcom it seems like the relay never shorts it out... weird.

Any help will be appreciated,

K-amps
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Old 4th January 2004, 12:45 PM   #2
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IIRC, Adcom still sells manuals for about every amp they've ever marketed.

I've only opened up 3 or 4 different models of Adcom amps, but several of the newer ones had inrush limiters with no relay at all...IOW, the limiter was in the circuit all the time. However, if your's has a relay for a soft-start, then I'd ahve to suppose that it should jumper the inrush device.

BTW, if the number you gave is correct for Digikey, seems odd that the limiter no-load value is so low. But I never use these things, so....
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Old 4th January 2004, 12:47 PM   #3
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Quote:
Originally posted by EchoWars
several of the newer ones had inrush limiters with no relay at all...IOW, the limiter was in the circuit all the time.
I thought it was supposed to work like that. No?
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Old 4th January 2004, 01:38 PM   #4
K-amps is offline K-amps  United States
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I'd like to think that you would have the limiter in circuit for a second and then short it out with a relay for direct connection.

Right now the limiter is in series with the Toroid's primaries all the time meaning at full power, 7 or 8 amps @120VAC are flowing through it. It started to smell after heating up, that can't be normal can it?

The part has ST on top and CL-101 labelled on it.

Thanks!
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Old 5th January 2004, 03:32 AM   #5
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Quote:
Originally posted by millwood


I thought it was supposed to work like that. No?
Apparently so, since that's the way they are built.

Every soft-start I have ever seen that used an honest-to-gosh relay used a limiting resistor, like a 4-ohm 10W or some such, instead of an inrush limiter. Every inrush limiter I have ever seen had no relay (besides the speaker output relay). So I honestly don't know whatcha got there K-Amps.
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Old 5th January 2004, 11:56 AM   #6
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Aha, so inrush resistors have relays not current limiters then?

In that case it makes sense. However this sucker should not get hot and begin to stink.... unless that normal.
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