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

Good luck! What ought to be very simple don't need a manual, turns out its not even clear if the RM-4 is a phono stage with RIAA equalization or just a pre-amp with no EQ! The one picture I could find of the inside isn't clear. Even owner's don't seem to know what they have. Further complicated by their being made to order, with different gain, and no way of telling. So good luck!  https://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=36348

Some general info that may be helpful: the whole entire reason for changing loading is to be able to fine tune the sound to your taste. Therefore, if it sounds good, do nothing. Be happy.

Some of these things the loading can only be changed by soldering resistors. This sure looks to be one of those. Its a Roger Modjeski hot-rod with high quality parts strung together RAM knows how. If you know even a little bit about phono stage circuits you'll be able to follow the hot leads from the inputs to the first resistor, read the value, and figure it out. In other words you don't need no manual. If you do get a manual that is what its gonna say: solder.  

Because the only other way loading is changed is with switches, which there aren't, or by swapping RCA with different resistors, which requires an extra set of RCA connections, which again there aren't. So you're SOL on loading unless you can figure it out. 

Following the input is literally as simple as following the wire (or circuit trace) and you won't have to go far, the resistor you're looking for will be the very first thing it comes to. Resistor values are color coded, look on line to decode and get the value, which will probably be 47kOhms as that is pretty much the industry standard. 

0.25mV MMC output > RM-4 > Phono Stage > Pre Amp > Amp > speakers

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? Should the output of RM-4 be connected to MMC or MCC input of the phono stage?

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

@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.

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! 

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.

@hjak 

I am posting this to help anybody now who gets one of these units with no documentation.

Great! it definitely help, thanks!

I can’t seem to be able to upload an image of his note to my response.

You can upload those image to your system page, and provide a link to it in your post.

Oh cool, thanks. I'll give it a try.

Ok, here it is......I've posted it as my system photo. Search systems for "hjak's system."

@hjak 

Thanks! This is the image form your system page: