Sorry for not contributing earlier, and also post is longish, many questions were asked...
I have not found any particular tweaks to improve RM2s over their recommended usage. I tried various placement schemes, also lifting a speakers a bit, but that summed up only as a different combination of trade offs, not a real advancement. For me, a quality of their usage depends mostly on their placement within a room, the room itself, and source and amplification. RMs are very transparent, and with them I generally preferred electronics that is regarded as neutral. Before trying them with Ampzilla 2000 amplifiers, I thought RM2 bass is a bit too slow compared to the rest of the spectrum. RM40s are much more forgiving to amplifiers in terms of bass speed and control.
Although my system is chosen to be compatible to my ears using VMPS speakers, I did not choose my electronics in some particular order, but mostly tried one component (CD, DAC or preamp), and when I had a favorite, then I tried power amp, and then with favorite amp another DAC and so on... It took long time, but was fruitful. Let’s start with preamp. Of course, my findings are only relevant for my ears…
I tried some 10 preamplifiers from many different topologies, have had them six or seven at once for direct comparison. I finally decided on resistor based passive unit (Audio Synthesis Passion, ASP later in text). Compared to the others it lacked nothing, and added less that any other. Besides, output and input electrical values of DAC and amp I use are ideal according to ASP recommendations, and I use short cables, which is both important with passive units, so ASP can really show what it can do. Next best thing was Sowter transformer based passive unit, which was also nice, but compared to ASP it somewhat smoothed the transients across the spectrum. That's nice sometimes, but sometimes not, and I felt it is a coloration. Later I heard measurements support my findings, showing that these preamps are rounding the edges of square impulse signals. Third favorite was SE solid state design from Nelson Pass many DIYers use. It is a great preamplifier, can wake up some lazy power amps, but compared to ASP, it has just a bit less transparency. Nothing much, but it's audible on good recordings. Next were several tube designs, and frankly I had not really like any of them. There were four different topologies, all of them very well executed, SE triode etc... even some Audio Note design from some ten years ago, which then was priced around 9000GBP. While tubes were beautiful on the top or through the mids (but not more than ASP), and while some added 'richness' was welcomed at some recordings, it was also not welcomed at the others, and I also felt it is colored in the end. Some other SS preamps were in a way 'attractive', emphasizing deepest bass, or both extremes, but were audibly less transparent than ASP.
To choose a DAC was somewhat easier than anything else. I never felt much difference among already good DACs, but after even a short try, it appeared that I love one custom design more than the others. It’s an 8x Philips TDA1543 non-oversampling design, without digital and analogue filters too. For my ears this DAC sound smoother than ‘properly’ designed DACs, music just easier happens, and easier get back to silence, otherwise I never noticed some tonal differences compared to good 24/96 DACs. Having 8 DACs in parallel makes it easy to drive amplifiers without active preamps.
Amplifier was a hard one. After Ampzilla 2000 showed me what RM2 really can do, it was hard to go for something else. But it was also hard to go for 4xA2000, since I learned that however good amp is, RMs are even better when biamped. To find the amplifier for ribbons only was a bit easier, since many amps had enough power, and many of lower powered amps were very open, detailed and smooth. Bass amp was hard to find. It is even not necessary for RM2 that amp is incredibly powerful, I mean over 300W or so, but it must have the needed speed and control for 30cm bass. Surprise was two monoblocs called by their maker as Mini-Aleph, with only 15W per channel 8Ohm. They were wonderful across the spectrum, for as loud as they could go, many much more powerful amps were slower even when played at lower volumes. Finally I decided to make a custom amp, with primary purpose to be the bass amp for VMPS. I asked my friend whether we could build something powerful, but simple, like Gamut amps that use a low number of powerful output MOSFETs, only with a fewer gain stages. He, who is a kind of single-ended solid-state guru said he has one old scheme (other guy says it might be from Citation amps from long ago, but nobody is sure) which can be called as double-single-ended, and which should provide 400W per channel 4Ohms with only 2 pairs of special MOSFETs (not like those in Gamut, but better and cheaper ones) with very simple execution (signal path is literally some 3cm). We made it pure double mono, with only limitation that we putted 2x500W transformers, while ideally would be 2x1kW, but it was an experiment after all… Result is that this amp is VERY nice across the spectrum, I simply love it, it's easy to drive with a DAC, and I will build another one with only one pair of MOSFETs per channel for mid/treble in biamping. It sounds very detailed, open, without any harshness on many recordings. Again, I love it. It also run almost cold and is quiet, which is very important to me.
RMs are very sensitive to amplifiers, it’s easy to have a ‘smooth’ amp, but which does not bring sound to the life. While this is also may be a pleasant sound, and often it is, RMs can do much better. I’m constantly amazed how good these speakers are, being so transparent for various ‘perfect’ electronics.
Another issue of RM2 is some listeners complain speakers do not disappear. In my experience, position where everything clicks-in can be found in many spaces, I have it too, but it requires longer experimentation, and very small movements are important. Axis of speakers in my room are some 2.6m apart, they are toed in so I can just see the outer side of them. I listen some 3m from the plane speakers make, in a room 7.6m wide, 4.6m deep. Speakres are 1m from the back wall, room is a bit live. Usual mid/treble control position is from 1 to 1:30. Size of putty removed is a ball of some 6mm. Still, with my amp bass is as deep, powerful and fast as I wish. I use some custom silver and DIY Kimber PBJ IC's, and OCOS speaker cables.
I tried two Original subwoofers with both RM2 and RM40. It is a pleasant addition for orchestral and organ music. It takes some time to do it right, and it requires everything as usual, very good and quick amplifier (but since I used active xover wit a cut at some 25-28Hz at 24dB/oct, amp has a bit simpler task than to play to some 200Hz and higher). Subwoofers were in phase with main speakers (main speakers work full range, no cuts), and a good thing was to aim them to a sides. Drawbacks are that setup is pretty large, and system easily shows that some recordings are apparently monitored and equalized in bass range on speakers with 4” bass drivers.
However, having electronics as I described, and for now, biggest improvement over standard RM2 is FS tweeter and Auricaps upgrade. I don’t know how much contribution can be putted to each of them respectively, but combination sounds very much like near RM40 experience, and in some respects better than standard RM40. Sound is much more open, without being a bit more harsh. Contrary, it is even more liquid, strings sound so nice and vivid, drums and cymbals are almost real. Really. Since everything is more open, it allowed the mid/treble controls to be attenuated a bit more without a feeling than any information is lost, which leads to an impression that bass is stronger too. Warmest recommendations for FS and Auricaps.
These RM2 FS in white oak will be presented at Frankfurt 2003 High End Show (29th May - 1st June).
