I'm sure the very first mkIV's had a black sprayed chipboard (?) front as I recall. The first thing we did was to remove the grilles to take a look. Later ones had the woodgrain look.
(Some of) The previous "top" models were the Domestic Monitor (early seventies I think), the Professional Monitor (I came into things at about mk3 in 1974) and the Reference Standard, which I believe was slightly bigger and with a slightly more damped line IIRC. The mkIV came along in 1976 during that very long hot summer we had. Our new manager in Watford was trying to do a cost per square foot of floor space and wanted the big IMF's out, as we didn't sell enough to justify their presence at this time (post 25% VAT and the first of many slumps in the audio market from which we never really recovered apart from a few golden years for Linn/Naim dealers in the early to mid eighties). Our "old" expert manager (something of a legend to those that know him - take a bow Jim D) had de-camped to the new West One branch and I followed in 1977 after many part time stints there...
At KJ Wigmore St we had some Pro Monitor III "improved" samples to sell through in around 1981 (after we had made our very first "single speaker dem room") and these boomed uncontrollably with the bolt up Naim 250, which despite its other endearing qualities (it's one of my favourite amps of all) just didn't have the control for them. Crown had gone the way of all those old American "pro" amps and the bigger "D" series replacements seemed to have a "fingers down a blackboard" quality with the new generation of speakers coming through.
At that time, we put all our attention into 'Briks and in the bass, with a bolt up 250 driving them, the 'Brik was in a different league where most domestic environments were concerned, although the passive "DMS" 'Brik midband was more coloured and "tubey" sounding
When I first met Robin (Epos) Marshall in '74, he was using Ref: Standards at home (bit of useless info for you).
As I've said before, the older IMF's pre mkIV had a very underdamped bass, which put huge demands on the damping control of the partnering amp. They could take off below 80Hz or so and reached well below 20Hz too (door rattles at steady state 14Hz I remember) - Dark Side Of The Moon off acetate to Dolby A tape has NEVER sounded better IMO... This is why I've w@nked on about the mid-seventies Crown/Amcron "D" series of amps, as a D150A was one of the very few amps that could drive them properly in a close to wall domestic environment, unless you had a huge room and could pull them well out from walls.
Most IMF's as I remember were an easy impedance load otherwise (8 - 10 Ohm on average), with no nasty lumps and bumps to upset early seventies amps. I chucked out my old, loft damaged HiFi Sound mags from the late sixties/early seventies, but if you can look some of these out, you'll see some very fair reviews with extensive technical measurements taken at "Hirst laboratories."
Sorry if I'm ignoring the TLS50 and 80 models, let alone the ALS40's and Compact series. They were all like smaller versions of the above models and IMF should be applauded for keeping the overall character similar from model to model...
