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Old 21st April 2005, 03:51 PM   #1
Gasho is offline Gasho  Croatia
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Unhappy Unusual behaveour of Marantz

Does anybody have a simmilar problem with Marantz PM7200 output section.
Everything is working fine until I try to switch on loudspeaker ouputs (No speaker connected) , than the quiescent current on both channels rise and i must turn of the output binding posts before mad heat up.

I dont know what can go wrong by switchin on only output relays .
this only happends when class A mode is used. Help please. I am pretty pist off with that problem .[SIZE=3][COLOR=blue]
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Old 24th April 2005, 07:51 PM   #2
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Hi Gasho,

This amplifier is known to run hot in class-A - it is meant to.
One friend fried a DAC that he had sitting on top !


Cheers ....... Graham.
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Old 24th April 2005, 08:30 PM   #3
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Quote:
Originally posted by Graham Maynard
Hi Gasho,

This amplifier is known to run hot in class-A - it is meant to.
One friend fried a DAC that he had sitting on top !


Cheers ....... Graham.

Indeed. And, if the heatsinks get too hot to touch more than a few seconds, they may still be less than 50 degrees Celcius. We don't really know what HOT means anymore

Jan Didden
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Old 25th April 2005, 09:31 AM   #4
Gasho is offline Gasho  Croatia
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I understan that class A means hot heatsink , but this is too much . When I measure the voltage across emiter resistors (0.18 ohm) it is too high , about 490mV . That is not OK.

This only happends when I switch on the output relay for loudspeaker.

Somethig is very wrong here. I must run some tests to locate a problem wich is very srange.
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Old 26th April 2005, 05:59 AM   #5
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Hi Gasho,

Does it do the same with a loudspeaker connected ?


Cheers ......... Graham.
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Old 27th April 2005, 02:12 AM   #6
Leolabs is offline Leolabs  Malaysia
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Looks like a short circuit problem
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Old 27th April 2005, 09:14 AM   #7
Gasho is offline Gasho  Croatia
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I solve a problem!

I cant belive it! It was the thing with outpur LCR filter. When I remove output coil , the rest of filter have too much of paralel capacitance (about 400nF ). I put the new paralel RC combination of 100nF +10ohm . Now everthig works fine.
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Old 27th April 2005, 09:56 AM   #8
moamps is offline moamps  Croatia
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Quote:
Originally posted by Gasho
.... Now everthig works fine....
Why did you remove output inductor?
Did you check amp stability with oscilloscope?
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Old 27th April 2005, 11:43 AM   #9
Gasho is offline Gasho  Croatia
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Yes

Yes
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Old 27th April 2005, 07:46 PM   #10
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Hi Gasho,

I'd love to hear what you think of the sound of this reasonably priced amplifier.

Reviews say that it has reasonable power, a decent phono input stage and useful pre-amplifier options.

Is it a good basic amp, and has removing the output choke improved it ??


Cheers ......... Graham.
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