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RM-4 vs. MCP-33

I have recently purchased the Audio Research MCP-33 phono pre-pre amp, and compared it to my heavily modified Music Reference RM-4 pre-pre(Dynamicaps, Vashay nudes, Blackgate caps, fred diodes, premium power cord, etc) RM-4.
Here is the listening impression so far. My regular phono preamp Counterpoint SA-9 is out to Mike Elliott for upgrads, so I have borrowed my friend's Wright Sound WPP-200C for the audition.

My modified RM-4:
very transparant, lots of details without sounding bright, a little polite sounding, instruments a little thinner than the ARC unit, very smooth and silky, better micro dynamics

MCP-33:
I had to change the tubes to Amprerex Buggle Boy 6DJ8s since the stock Telefunkens sounds too thin and bright to me.
This unit has definitely more macro dynamics than the RM-4, so it is more suited for jazz and pop with rhythm. The RM-4 is more polite and silky smooth sounding, so classical music is good with the RM-4.
So, the MCP-33 has somewhat more apparant (macro) dynamics, a little more foward in the midrange, a little thicker sounding than the RM-4, while the RM-4 is more transparant, smoother and has better resolution and more detail. Occasionally, I felt a little hardness in the high frequency from MCP-33, but I need more listening before I can be sure. Guess the premium parts installed on the RM-4 has paid off (parts alone cost over $1000). The MCP-33 indeed sounds very good, and I am sure stock MCP-33 would outperform unmodified RM-4.

If I had to pick one of them, I would pick the RM-4 because the transparancy of RM-4 is quite addictive. Maybe I would change some parts on the MCP-33 and find out if it gets better.

Any thoughts on the comprasion?

My system is VPI TNT 5/JMW 12.5/Shelter 501 II/Modified Acoustat Servo OTL power amps/Acoustat model 8
Steve
sojs
dwbwbw
1 posts
 
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?

Many thanks.

Tom
s23chang
617 posts
 
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.
sojs OP
13 posts
 
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.

Steve
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