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Music Reference RM-4 Input-Loading and Gain-Select plugs

I have been using Music Reference RM-4 pre-preamp with MCC cartridge Denon DL103R for quite some time. This cartridge has an output voltage of 0.25mV and output impedance of 14 ohms. I am aware that the Music Reference RM-4 has some switchable Input-Loading and Gain-Select plugs. Unfortunately, I have purchased RM-4 with no user manual. And I was not able to locate one on Internet. I wonder what those Input-Loading and Gain-Select plugs are and how they could be used to match RM-4 to Denon DL103R cartridge "better". I would also appreciate any help in getting a copy of the user manual (regardless if it is PDF of just the mobile phone photos of the manual pages).
esputnix
imhififan's avatar
imhififan
2,129 posts
 
I beleive you need to take off the top cover of your Music Reference RM-4 pre-preamp and look inside if the gain plug is 30dB, if it is 30dB then you should connect the RM-4 outputs to phono stage MM input, because most MM input of a phono stage will provide about 40dB of gain and give your Denon DL103R a total of 70dB gain!
Usually the MC input of a phono stage provide about 60dB of gain and give you total gain of 90dB! It will hurt the overload margins of your setup.
With RM-4 adding a 30db of gain, how much its output voltage will be if the incoming voltage is 0.25mV the MCC cartridge outputs?
= 7.9mV
http://www.sengpielaudio.com/calculator-amplification.htm


roberjerman
4,319 posts
 
@imhififan : +1! You've got it right! The RM-4 is a linear-gain (no equalization) stage to boost a low-output mc cartridge's voltage (below 1 mv) by adding gain (30db). I have a Marcof PPA-1 (battery-powered) which does the same thing. In the old days these were called "head amps" or pre-preamps. They should only be plugged into the MM jacks of preamps with phono stages or separate phono stages.
roberjerman
4,319 posts
 
If there are no loading options on the front or back of the RM-4 leave it alone! I'm sure that the late Rodger Modjeski knew what he was doing when he designed/built it! 
Post removed 
hjak
3 posts
 

I realize that the OP has probably resolved their issue by now, but I am posting this to help anybody now who gets one of these units with no documentation. In 2014, I wanted a tube head amp. At the time, Music Reference, Audion, and Dulcet Lector appeared to be the only folks making a dedicated tube MC head amp. The Audion and Dulcet Lector units were over $2k, while the RM-4 was $1250. Also, the RM-4 was pretty much the original commercially available unit, having been introduced in the ’80’s, so I went with it. It took 10 months from order to completion, and was an amusing and somewhat surreal purchase experience. I knew that no one had ordered one in quite awhile because the website showed the price as $750. When I called, I was told it would be $1250. I told Roger it would be nice if he would give me the info to be able to set the loading and gain with discrete resistors rather than having to buy a bunch of plug-in modules. He kindly included a hand-drawn note showing how to do this.

I can’t seem to be able to upload an image of his note to my response. I just sat here trying to see if I can explain it in words, but it’s a bit complicated. If anyone happens on this post who wants the loading and gain info, you can either let me know if it’s possible to upload an image, or just contact me through the website, and I can email you a scan of it. It’s pretty self-explanatory if you have a little basic electronics knowledge.

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