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Music Reference RM-9

24.229.102.39
Posted on March 1, 2014 at 11:28:07
TMASLAR
Audiophile

Posts: 27
Joined: April 3, 2002
 Hi Kevin,

I am in the process of bringing a Music Reference RM-9 back to life. I have heard that you had done some modifications to these amps.
Are there any areas that you feel offer worthwhile improvements in this amp based on you previous experience with it? I have obtained the power supply chokes from Roger that will bring it up to what is called MKII status. I will be installing them as I get the amp up and running.
Thanks,
Tom

 

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RE: Music Reference RM-9, posted on March 1, 2014 at 11:39:59
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I actually did less modification and more repair, but I did do a few things that were beneficial.

First, I replaced the big power supply electrolytics with the same value, but from the superior sounding Panasonic TSHB line (Mouser or Digi-Key). Second, the input board was grounded to the power supply and output stage through the stand-off mounts on the amps I worked on, which is a distinct "no-no". I isolated the stand-offs from the PC board ground trace and took a separate wire from that ground trace back to the star ground in the amp. Of course, you can change the coupling caps, too, to change the sound, but I will let you decide what's to your taste.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Music Reference RM-9, posted on March 2, 2014 at 08:53:02
TMASLAR
Audiophile

Posts: 27
Joined: April 3, 2002
 Thank you Kevin.

 

RE: Music Reference RM-9, posted on March 19, 2014 at 12:54:01
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Hi Kev, I am having trouble with my rm9 as the bias is down. From what I understand there are zener diodes that determine the bias voltage, along with the bias pot ? If that is correct do you know the value of the zeners or do you know where I can get a copy of the schematic for this amp? thank you very much, dak

 

RE: Music Reference RM-9, posted on March 19, 2014 at 16:43:15
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001



In one of the amps I was taking care of I had to replace the bias trim pots. They were thermally damaged after so long in service.

I've attached the only RM-9 schematic I've ever seen. It's not a particularly clear picture. I assume it is a few generations removed from the original, but don't now remember where I even got it. I've never seen a Mk II schematic, but from the looks of the one I serviced the differences are minimal.


Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Music Reference RM-9, posted on March 19, 2014 at 19:42:33
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Thanx a million Kevin. I noticed that there are 3 zeners per channel. Unfortunately, I can not make out the values of those zener diodes. Is it possible for you to tell me that. best regards, Dak

 

RE: Music Reference RM-9, posted on March 20, 2014 at 03:22:05
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I'm afraid I have no memory of the zener diode part numbers or voltage values (if I ever knew them), but it's easy to place a voltage across the zeners with a current limiting resistor to measure what they are. I would be careful about blaming the zener diodes for your problem until you've assessed the other components that comprise the bias network. Zeners are typically very rugged unless asked to pass way too much current.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: Music Reference RM-9, posted on March 20, 2014 at 10:40:13
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Thank you for the tips. I will go in there and take a better look at things. I know the bias circuit was problematic when I bought the amp maybe 10 years ago. Since the previous owner gave me the replaced parts which was a cap and a pot. The amp worked ok but was not the sound I wanted so I sold it to a buddy. Now several years later the bias is giving problems again. regards, dak

 

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