Thats interesting of the work done on the RM-4.
I use to own a RM-4 for about 5 years when it first came out.
I used it with the ARC SP-8 for moving coil head amp
reproduction.As I recall you could solder in your own resistor to load it too the proper value you needed.
Even stocked the unit has a wonderful bloom in the midband
and a very musical unit at that.Roger Modjeski used very high quality tubes with this unit.
The RM-4 is a great find if u can locate one on the open market used.
I have done many experimental mods using Vishays myself
and I'm very familiar what this resistor is capable of.I.E.
A huge reduction of the noise room floor,A very,very transparent resistor,which opens up this vast 3D Soundstage
that is locked tight with perfect imaging around the instruments playing in this soundfield.
I have not audiotioned the ARC Head Amp your refering too
But I'm sure if this was moded out it would sound much better then the RM-4.
Totally agreed with Steve.
RM-4 is the best head amp I've came across and it is still in my current setup. I only bought it because I had Roger modified one of the tube amp for me and recognized his good work. I then bought the RM-5 preamp and the phono section realized the phono section was really good ( much better than the line stage to match my system.)
I've used both the Counterpoint and Audio Reseach and neither came close to what Music Reference RM-4 offered.
I've tested the stock RM-4 with Arc SP-8, SP-11 MK II, Counterpoint 5000 and H.K. Citation I MM sections to mate with RM-4. They all worked out well with my VDH Black Beauty Cartridge.
Not only it is quieter and smoother sounding, it also has much better dynamic than both ARC and Counterpoint.
The ARC and Counterpoint has too much hiss when compared to RM-4. I've compared to many good step up transformers and I still prefer the RM-4.
You'll be surprised vintage stock HK Citation I phono section for MM is better than ARC SP-8, SP-10, SP-11, counterpoint SA5000, Lehman Black cube and etc.. Compared them in many setups and this preamp really sound better than the most. The line stage needs upgrade to better resistors (Carbon was a little bit soft and lack of focus than metal film type) and power supply caps then it will be as good or better than the most of the modern line stage. I wish Stewart Hegeman had design more of these timeless tube gears other than two amps ( Lafayette KT-550 and HK Citation II ) and this preamp.
Don is right about Vishays. I have noticed the RM-4 to be extremely quite after installing Vishays (along with Caps).
My cartridge has about .4mv output, so tube hiss is not audible at normal listening level. So, my analog setup is deal quite at the listening position. It's pretty amazing with all tube head amp and phono preamp. With about .2mv output cartridge I would get slight tube hiss with regular NOS tubes. Low noise tubes will be dead quite, but it's hard to find NOS with low noise. Registers can be soldered to change input impedence. The RM-4 has about 30db of gain, which is a little too high for me. I am using SA-9 phono preamp volume control (providing only 0db to -15db range), and I have to use the lowest volume setting and it's not low enough for me.
I have compared the RM-4 to Counterpoint SA-2 about 15 years ago. Counterpoint sounded too thick and colored. It also emitted DC voltage when the AC line voltage changes slightly, which the factory could not fix and recommended usage of power conditioner. Even with the power conditioner my Apogee Duettas bass panal was moving badly.
I heard good things about the HK Citation One. Will try it if I have a chance.
I have ordered Bent audio TX-103 transformers and will post how it compares if you are interested.
Dear Steve: Something that can do an improvement on your RM-4 is to change the Dynamicaps for V-caps. This ones can do a great difference ( for the better ) in the quality sound reproduction.
Regards and enjoy the music.
I have thought about using V-Cap oil caps. The Teflon caps are too expensive in my application since the RM-4 uses 5.0uf value. A very reputable person in audio modification told me that V-cap teflon is 9 if Dynamicap is 10. So, I am holding off that mod for now.
Dear Steve: Before I use the V-caps I try: Wima, Sonicaps, Aeon, Solen, MIT, Audicaps, Dynamicaps, Hovland, etcc.. on my speakers crossover.
For me, the V.caps hands down any of the others ones. I think that you have to try, not with the Teflon ones but the metallized prolypropylene ones. High recomended !!!!!
Regards and enjoy the music.
The V-cap oil caps were not as preferred as the dynamicap by some reviewer on AA. He gave V-cap TFTFs 2 thumbs up. However, Teflon version doesn't come in 5 uf size from Chris's website. It will probably be surper expensive to make a teflon version that size.
I wonder if you loose the warmness after replaced the original caps with Dynamicaps.
I could not tell the sonic changes of replacing the original caps with Dynamicaps, because I have changed lots of other parts together at the same time. I know I should have modded one part at a time. The original caps are yellow colored Rel-Caps. I have also tried Auricaps at this position, and found it sounded too forward and loose. Dynamicaps are more neutral.
I had 2 different versions of Counterpoint SA-5 preamps. One was older model with yellow Rel-Caps, and the other used white Wondercaps. The one with Rel-Caps sound significantly better. It sounded very delicate, warm, detailed, and very musical. I was disapointed with the Wondercap version (dry and transistor like sound).
Hi Steve, thx for your reply.
Yes. Both the RM-4 and the Counterpoint SA-2 I have are the yellow Rel-Caps. Exactly like what you described.
Rm-4 had additional by-pass cap to enhance or clean up high frequency response.
I guess the SS power supply is quicker and more dynamic than the tube version in SA-2.
I bought a RM 4 some time ago without a manual. Could someone please advise me on how to use it properly.
On the OUTPUT Gain terminals, my guess is that for each channel (say the left channel), one connects a resistor the signal (the center) to the ground (the outer) to achieve the gain as shown on the back of the RM-4. This is to be repeated for the other channel.
The gain would then be realized at the "Attenuated Output" terminals. The "Direct OUtput" terminals are for output NOT affected by the insertion of the resistors (i.e. no gain).
On the INPUT Source load, my guess is that it is for impedance matching with the cartridge. Thus, one would put a say 47 kohm between the center and ground for each channel.
I used the above setup (with about 6 db gain) and used it as a head amp, connecting to the phono input of an Audio Research SP-11 Mk2 pre-amp. It sounded really good, but it tripped the power amp (solid state Krell) after 2-3 minutes of playing. The SP-11 was not tripped.
My questions are (1) is the setup correct? (2) is the RM-4 NOT meant to be used as a head-amp?
Would someone sell me a copy of the manual?
I have the SP-11 MK II and I also tried to test the RM-4 for the MC cartridge. The gain is too high that it doesn't work well with SP-11 unless you use super low output cartridge like .2mV. Make sure you have subsonic filter turn on when you use a lot of gain.
I have 2 versions of the RM-4. The first one has only one transformer (later model). It has input impedence loading socket and output gain socket. I was able to have custom value male socket made by Music Reference. The output gain was not changed even with the factory made socket.
The second RM-4 is an earlier version with 2 smaller transformers. I have called MR to find out if I can lower the gain to about 20db instead of stock 30db. I have followed their suggestion (adding a register), but it did not change the gain.
Tom: (1) yes, the input impedence is changed by inserting a register from hot to ground.
(2) yes, it is a head amp.
About tripping the power amp, maybe you can check the output DC with multimeter to see if excessive DC is present at the output. Maybe your placement of output gain registor is incorrect. Call RM to make sure it is ok.