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Marantz PM 80 mk2
Marantz PM 80 mk2
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Old 9th January 2018, 09:49 AM   #1
Joanito is offline Joanito  Portugal
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Default Marantz PM 80 mk2

Hi all,

I am considering simulate one channel of this amplifier in LTSpice. I've been seeing the technical details of this amp and i also want to know more about it.

Here is a link to service manual download:

Marantz PM-80-Mk2 Service Manual, Service Manual, Repair Schematics

The amplifier operates in both classes ( AB and A ). It even has a button to do the switch. What i understand after i saw the service manual is that: when it operates in class A, the voltages in the rails must drop to 24.9v and -24.9v, correct ?

image MPM80 1.jpg

So i can see the power supply providing the correct voltages... :

image MPM80 2.jpg

... But i don't see the power supply providing the 24.9v and -24.9v. And i can see the button to switch classes in the schematic but i don't understand how this circuit works... After all this voltages must come from somewhere, right ?

Or the voltages in the rails, when switched to class A, remain +56.7v and -57v, but what they mean is that they can be reduced to 24.9v and -24.9v if we want, is that it ?

Thanks.

Last edited by Joanito; 9th January 2018 at 04:11 PM.
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Old 9th January 2018, 10:04 AM   #2
Joanito is offline Joanito  Portugal
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Is this a very good amplifier ? It claims to have a very low THD value considering other comercial amplifiers. Would that THD be true ?
Thanks.
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Old 12th January 2018, 06:43 AM   #3
chermann is offline chermann  Austria
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Hello

i got the manual from this page
Download Marantz PM-80 Service Manual

If you look at Page 10 you will see the connection to the switch (Class a switch) PSIO (board) JSI2. If you press this Clss A botton the ralay (L851) is switching its 2 conntact and the power transformer provide you the "magic" 17.3V AC -after filtering you get about 20.5VDC.
Maybe in the future this relay contact get worse...so you have to change the relay because the contact ar gone.

regards
chris
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File Type: png Class A_Power Rail for Marantz PM 80.PNG (887.0 KB, 108 views)

Last edited by chermann; 12th January 2018 at 06:52 AM.
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Old 12th January 2018, 09:48 AM   #4
cumbb is offline cumbb
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"Is this a very good amplifier ?"
No;-)
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Old 12th January 2018, 10:21 AM   #5
chermann is offline chermann  Austria
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give it a try

...if you want to pimp this old amp then try to change the PSU electrolytic caps and then the others...first electrolytic.
I did that for my 28 years old Preamp Accuphase C200V and it worked perfectly! Watch out the polarity and the size of the caps in some area !


greetings
chris
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Old 12th January 2018, 12:31 PM   #6
Joanito is offline Joanito  Portugal
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Thanks guys,

...So if i want to simulate one channel of this amp operating in booth classes in LTSpice, i just have to replace like this:

img tr.jpg

... and the new switch defines if we want it operating in class A or in class AB ?
Is that it ?
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Old 12th January 2018, 03:46 PM   #7
chermann is offline chermann  Austria
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Quote:
Originally Posted by Joanito View Post
Thanks guys,

...So if i want to simulate one channel of this amp operating in booth classes in LTSpice, i just have to replace like this:

Attachment 656333

... and the new switch defines if we want it operating in class A or in class AB ?
Is that it ?
sorry ..i dont get your point. What do you want with the left drawing? it looks to me like a opto coupler.You want to change this to a switch??
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Old 12th January 2018, 04:17 PM   #8
Joanito is offline Joanito  Portugal
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Yes, that opto coupler closes or open the circuit that defines class A or class AB, right ? Can i do it ? ( i mean the repleacement ) ?
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Old 12th January 2018, 07:50 PM   #9
chermann is offline chermann  Austria
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Quote:
Originally Posted by Joanito View Post
Yes, that opto coupler closes or open the circuit that defines class A or class AB, right ? Can i do it ? ( i mean the repleacement ) ?
hmm looks not bad... should work....
but why change the switching function? try in clss A for listening and for party mode release the button
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Old 12th January 2018, 08:52 PM   #10
Joanito is offline Joanito  Portugal
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Because it would be my first constructed and simulated circuit in LTSpice and i'm afraid i can't found opto couplers in component menu :-D . And i i'm not very experienced with LTSpice also and replace the opto coupler by a switch makes circuit more simple...

Thanks.
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