June 2012 Issue

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June 2012 Issue
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IMF Reference Standard Professional Monitor  loudspeaker





My system has grown somewhat haphazardly in recent years but I’m now homing in on a definitive set up - or trying to. There is one cast in stone element, which I’m loath to change. At the end of the signal path, and occupying two corners of my living room is a pair of IMF Reference Standard Professional Monitor Mk IVs. These transmission line monsters are even bigger than the IMF TL80s by some margin, and something of a family heirloom, being my dad’s before I got my hands on them. They were purchased as liquidated stock from the Hi-Fi Surplus Store in the early 80s, when IMF sadly went out of business. So big were they, that we had to put one speaker in the back of my dad’s Capri with the seats down and tailgate open, and one on the roof rack!


Fortunately I have no near neighbours so they can be used loud, which is a good thing because they need to be moving a lot of air before they really get going. Feeding these hungry beasts I have a pair of Conrad Johnson Premiere 12s.


So far so good. I love the IMFs, but I’m aware that they are a bit on the slow side, but really nothing quite gets those low furniture vibrating bass notes quite like these do. I like all sorts of music, but have a fondness for Prog for which the IMFs excel, particularly if there’s a bit of Moog or Mellotron action.


Moving forward and this is where it all starts to get a bit messy. I’m currently between pre amps, having jettisoned an Audio Research SP – I can’t remember what one (it was the valve hybrid one)! It never really sounded convincing to my ears. In temporary residence is a Hitachi HCA 8500 Mk2, which is actually pretty good, but not exactly in league with the CJs. It has a surprisingly good phono stage with a good choice of gain settings for various cartridges, but that said I’m using a World Designs phono stage and power supply.


Finally there is the Technics SL-120 Mk2. It’s a lovely thing in excellent condition and was fitted from new with an SME Series III S arm, which I realise is a limiting factor. I’ve fitted my trusty Dynavector Karat 17D3 and have so far modded the Technics with upgraded feet and mat from Sound Hi-Fi. At the moment the deck has the pace that I was expecting, but is a bit bass light, which I put down to the arm. Certainly CDs currently have more oomph, but I’m fairly clear on the upgrade path, which will involve retaining the Dynavector and fitting a more up to date SME and probably remote PSU and upgraded main bearing.


I’m quite keen on having a punchy, metronomic and up-front turntable set up, because frankly I think the IMFs need to have something to think about, or they’ll just wallow. Equally, I do wonder whether the CJ 12s really have the grunt required. Would the IMFs benefit from some serious horsepower to get the best out of them? I’m thinking of the big engine analogy here. I’m not wedded to valves and my inclination is towards a big sound, which the IMFs deliver, but with some wallop and control too, which currently they don’t quite manage.


And of course in the middle of all this is the pre amp. Which way to go? If I’m sticking with valves, then the only pre that has really caught my attention is the Icon Audio  LA-4 and frankly with the way high-end audio is going these days price wise, £1000 is about the maximum I’m willing to spend. Of course there is always the second hand route.


So any advice gratefully received. I suppose it all comes down to the speakers. If you guys had a pair of these monsters in residence, how would you get them to perform at their optimum?

Steve Bennett,






Inside the IMF Reference Standard Professional Monitor loudspeaker. A KEF B139 bass unit was acoustically loaded by a long, damped transmission line, ported at the front of the cabinet. This gave big bass that ran deep, a feature of IMFs, but they need high damping factor amplifiers for control.






Technics SL-120 Direct Drive turntable. It has metronomic timing and suits the IMFs. Fit it with a good, modern arm like an SME309, we suggest.



Hi Steve. Those are great loudspeakers. Your dad was brave to buy them; they are rare birds and produce bass like few others. The KEF B139 bass unit loaded by a long ‘Transmission’ line is quite a load and demands current. Of all the loudspeakers that need the grip and current delivery of solid-state, this is the one! You would be best off siting a monoblock power amp near each one, but suitable models like the Electrocompaniet Nemo don’t come cheap. NAD will be updating their M2 Class D technology power amplifier soon, so an old M2 might become available at low cost and Nu Force make technologically advanced Class D power amps with a tight, clean sound.


I am not saying Class D is better, but generally they sound dry and tight. You just have to be aware that many have rotten transfer functions that modulate distortion terribly and they have nasty treble and are none too detailed or delicate. Hypex modules are an exception with  a clean sound and can be found in Channel Islands amplifiers.


Roksan make amplifiers with the right sort of balance for your IMFs, meaning punchy, dry and very controlled. Their M2 power amplifier would be a very good choice. But don’t get a Naim, as they have a low damping factor and will not exert enough control.


If you use an integrated amp., site it reasonably close to the loudspeakers and use stout loudspeaker cables.


Try and audition before buying as many won’t cut it with those loudspeakers, and don’t buy blind from eBay for the same reason.

In front of your solid-state power amplifier use a valve preamplifier, or possibly a passive preamp, or even a Music First Audio transformer preamp., if your budget can stretch that far. The Icon Audio LA-4 may well suit; it’s 6SN7 small-signal triodes are the smoothest, most relaxing valve you will ever hear, but it has fulsome bass and I am uncertain how this will suit your big IMFs.


You are spot on with your turntable upgrade suggestions. Get an SME309, a lovely arm by any standards and upgrade the SL-120 with Sound Hi-Fi parts. Consider a Benz Micro Ace (low output) MC cartridge at least if you want to move up from the Dynavector.




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