Unusual behaveour of Marantz

Gasho · 21st April 2005, 03:51 PM

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]

Graham Maynard · 24th April 2005, 07:51 PM

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.

janneman · 24th April 2005, 08:30 PM

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

Gasho · 25th April 2005, 09:31 AM

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.

Graham Maynard · 26th April 2005, 05:59 AM

Hi Gasho,

Does it do the same with a loudspeaker connected ?

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

Leolabs · 27th April 2005, 02:12 AM

Looks like a short circuit problem

Gasho · 27th April 2005, 09:14 AM

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.

moamps · 27th April 2005, 09:56 AM

Quote:

Originally posted by Gasho
.... Now everthig works fine....

Why did you remove output inductor?
Did you check amp stability with oscilloscope?

Gasho · 27th April 2005, 11:43 AM

Yes

Graham Maynard · 27th April 2005, 07:46 PM

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.

21st April 2005, 03:51 PM	#1
Gasho diyAudio Member Join Date: Nov 2004 Location: Zagreb	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]

27th April 2005, 11:43 AM	#9
Gasho diyAudio Member Join Date: Nov 2004 Location: Zagreb	Yes Yes

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24th April 2005, 07:51 PM	#2
Graham Maynard diyAudio Member Join Date: Dec 2003 Location: UK	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.

25th April 2005, 09:31 AM	#4
Gasho diyAudio Member Join Date: Nov 2004 Location: Zagreb	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.

26th April 2005, 05:59 AM	#5
Graham Maynard diyAudio Member Join Date: Dec 2003 Location: UK	Hi Gasho, Does it do the same with a loudspeaker connected ? Cheers ......... Graham.

27th April 2005, 02:12 AM	#6
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Looks like a short circuit problem

27th April 2005, 09:14 AM	#7
Gasho diyAudio Member Join Date: Nov 2004 Location: Zagreb	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.

27th April 2005, 07:46 PM	#10
Graham Maynard diyAudio Member Join Date: Dec 2003 Location: UK	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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