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IMF Professional Monitor IV

These old seventies speakers were designed with a rather fulsome bass end which can get way out of control if not partnered properly.

DM2A's *could* sound way inferior to KEF R104ab's if you got the amp wrong - all sloppy in the bass and of course the BD139 flapper in the 104ab's didn't like Linn vinyl either (much better on good digital and modern LP sources... (the "ab" was MUCH better than the first version and Wilmslow Audio did these crossovers at one point in the recent past).

I'm currently very much enjoying a crown D60 on my headphones. It has no headroom - clipping point is just that unless you have two, bridged mono! - but the ability to hear straight through it to the recording (a recently re-acquired AVI pre-amp helps enormously, it's line buffering makes the sound better ordered than a "straight through" feed for some reason) is a huge plus. A later D75 or D150A mk2 may be even better, as I believe they went balanced and the 150's top end was tamed a little, without losing the huge damping they have on the bass. My D60 has original caps (some were mil spec) and seems fine, as they run stone cold and don't put huge demands on the supply.

I'd avoid capacitor coupled amps with IMF's perhaps, unless you love the richness this'll bring to the bass. An A60 used in anger would swamp the room I suspect, but I could be wrong. Naim amps (160 and 250) didn't sound too hot either (loose bass) but 135's were better in this respect and let the other positive Naim qualities through to some TLS80's a friend had for many years. He replaced them with '84 vintage 'briks (mine!) and the bass was better but the mid not...
 
Hi people! I'm new to this forum, happened to stumble across this thread on Google search looking for info on my IMFs. I'm an IMF freak too! Started off with the TLS 50, then added the ALS 40 MKII, and then the Prof Mon MKIII. I love them all.

The TLS 50 give wonderful tight controlled bass, but the high end is a little exaggerated for my liking and the mid-range a little recessed, although setting the control at the rear to the '+' position helps bring out the mids a little better.

The ALS 40 MKII don't go quite as low as the TLS 50 but psychoacoustically make up for this with a slight mid-bass bloat, and overall they sound more pleasant to my ears than the TLS 50 (treble not quite as exaggerated and a little more mid-range airiness), especially with the control set to '+'.

But my favourites have to be the Prof Mon MKIII. The soundstage is just so damn big, the mid-range is much more detailed and liquid, and the treble is detailed but softer than the other two. Most realistic and complete sounding speaker I've heard. Only downside is the bass is not as tight/controlled as the TLS 50 or ALS 40 MKII. Don't know if this is a limitation of the B139 driver, or a limitation of my amplification, or a limitation of my room (suspended wood flooring that literally shakes as you walk across it and wildy varying bass response as you move to different parts of the room certainly doesn't help matters, does it?!). To rule out amplification, I am driving them with the best I've got, a 165wpc Pioneer SX-1250. I'm not very knowlegeable on technical issues like current drive, impedence matching, damping factors, etc. Do you think I'm ok with this Pioneer?

Thanks in advance for any help!

Richard

PS - I am at the tender age of 22. I'd have loved to been around in the 70s/80s to witness the golden era of speaker building. I envy those of you who got to demonstrate IMFs for a living! :p
 
if you look elsewhere on the audio forum, you'll find threads dedicated to spec vs listening tests and very pro and negative vibes regarding either view.

The Pro Monitor mk3 is a classic case of being designed "of its time." It desperately needs an amp with very low output impedance and "high damping factor," which as I understand it is the ability to control the bass drivers, which in this case have little physical or electrical control of their own and are inclined to flap uncontrollably.

If you can find a "good" Crown vintage amp like a D150A or D60/75 (150 has more watts, 75 is an update on the 60) you'll get all the control you'll need. As a nod to the above mentioned thread, the Crown D150A can have a bright, fingers down a blackboard sound into modern speakers, but sounds absolutely marvellous into the Pro Mon 3 using reasonable speaker cables (2.5mm Van damme would be fine in most domestic lengths around 5m each). Run the mid control on "+" and the tweeter control (if there is one) either flat or "-." If you can lift the cabinets a few inches off the floor with coping bricks or a breeze-block you may get a slightly tauter bass response too, although the above mentioned amps will mostly sort it.

A quick note on damping factor. Crown amps of old (and possibly new ones like the K2, which works well with domestic speakers too) had damping of around "1000." HiFi World magazine regards a figure of "40" as being high, which is probably the case with transformer coupled valve amps. This is all part of the art of system building and "synergy" and one of the improvements wrought in the RSPM IV was to add significant amounts of damping to the interior of the line and perhaps sacrifice a few Hz of extension (yours go below 20Hz to around 11Hz as I remember where doors and windows rattle) for a much tighter, drier and better upper bass balance. it was possible to dial in huge extra capacitance to roll the bass off slightly higher in the mk4 and this worked a treat when springy, belt drive turntables became fashionable with the LP12, which sounded awful with the mk3 - of course, it was a fault in the speaker, not the precious turntable..... Surprising though how good the mk3 sounds with master quality material (and possibly the majority of CD releases)...

Hope this helps...
 
hello
sorry to but in, but i need help
i bought a pair of rspm 1v (i assume that that means reference standard professional monitor mk iv (4) speakers a long long time ago - 1987. they were second hand and cost me £700. they were the best speakers i have ever bought and served me well for 20 years. i had quad amps, but then about a year ago something went wrong, it could have been the caps in the crossover wearing out, i don't know but my quad power amp broke (405-2) and somehow the speakers were damaged - as i said it could be the caps.
anyway i have now got naim amps and spender speakers, but it's just not as good. i really want to restore my imf speakers, i will happily replace all drive units and crossovers. i would really appreciate any help/advice you can give me
thankyou
adam zisserman
 
DSJR said:
if you look elsewhere on the audio forum, you'll find threads dedicated to spec vs listening tests and very pro and negative vibes regarding either view.

The Pro Monitor mk3 is a classic case of being designed "of its time." It desperately needs an amp with very low output impedance and "high damping factor," which as I understand it is the ability to control the bass drivers, which in this case have little physical or electrical control of their own and are inclined to flap uncontrollably.

If you can find a "good" Crown vintage amp like a D150A or D60/75 (150 has more watts, 75 is an update on the 60) you'll get all the control you'll need. As a nod to the above mentioned thread, the Crown D150A can have a bright, fingers down a blackboard sound into modern speakers, but sounds absolutely marvellous into the Pro Mon 3 using reasonable speaker cables (2.5mm Van damme would be fine in most domestic lengths around 5m each). Run the mid control on "+" and the tweeter control (if there is one) either flat or "-." If you can lift the cabinets a few inches off the floor with coping bricks or a breeze-block you may get a slightly tauter bass response too, although the above mentioned amps will mostly sort it.

A quick note on damping factor. Crown amps of old (and possibly new ones like the K2, which works well with domestic speakers too) had damping of around "1000." HiFi World magazine regards a figure of "40" as being high, which is probably the case with transformer coupled valve amps. This is all part of the art of system building and "synergy" and one of the improvements wrought in the RSPM IV was to add significant amounts of damping to the interior of the line and perhaps sacrifice a few Hz of extension (yours go below 20Hz to around 11Hz as I remember where doors and windows rattle) for a much tighter, drier and better upper bass balance. it was possible to dial in huge extra capacitance to roll the bass off slightly higher in the mk4 and this worked a treat when springy, belt drive turntables became fashionable with the LP12, which sounded awful with the mk3 - of course, it was a fault in the speaker, not the precious turntable..... Surprising though how good the mk3 sounds with master quality material (and possibly the majority of CD releases)...

Hope this helps...
Click to expand...

Thanks DSJR. I've just flicked through all the owners manuals of the amplification I have for damping specs. Most of my amplifiers are quoted as damping factor 40, the Pioneer is the worst at 30 while my Technics SU-V9 DC is the best at 80. I suspect damping isn't the only contributing factor since the bass sounds better defined on the Pioneer than it does on a few of my other amps quoted at 40. Perhaps I'd only notice a real difference by stepping up to an amplifier with a damping factor of 100 or higher. The Crown D150A you mention sounds interesting. Is this an integrated amp or just a power amp? The strange looking inputs are confusing me! It looks a bit industrial for someone used to looking at pretty eye candy that is 1970s Japanese-built receivers. ;)

PS - I am currently using cheapo Gale XL-189 cable that retails in RicherSounds at 99p/m, and the lengths are approx 8m. I used to use Gale XL-315 but it's too darn thick to squeeze into vintage gear...

Out of curiosity, did you ever get to test the amplifier IMF released, what was it, the IMF galactron? Did that have a good damping factor?
 
I only heard the Galactron once and it was OK, but so long ago.

My comments regarding Crown refer to the mk3's and their siblings, the mk4's being much tighter in the bass. The D150 series are power amps and of this series, the D60 is the best for general modern use with all sorts of speakers. The 150 worked well with the mk3 and I suspect the manufacturers may have used them at the time. Regarding other amps, if you like the sound and the deep bass is musical and not too "breathy" or "pushy" then you're fine.

The main thing that may have failed on the mk4's could be the caps in the crossover. I believe the crossovers can be removed by loosening the thumb nuts on the bottom plates and gently easing the plates from the cabinet. It's unlikely the drive units are damaged, check the crossover first. I knew someone else who used a 405 with mk4's and found the combination a good one - good luck. Mk 2 405's can be serviced easily and in the absence of new boards from Quad, I understand DADA Electronics (Netherlands is the European distributor?) make new boards I understand, with all the latest components and tweaks.

Naims with IMF's can be a hit and miss affair, either harsh up top or lumpy in the bass if you get it wrong. Naim pre amps do well into Quad power amps by the way...
 
If it's any help, having used both I find the Quad 606 is a lot better than the 405 with IMF's, I use 606.2's, they're a natural with the TLS80.2 and RSPM 1V, not quite so happy with my SACM's which benefit from a bit of extra damping because of the TDL/ELAC bass unit. I am told the Crown's work well with them, but when I tried them out I didn't lake the overall sound so much. I'm still looking for something I like to go with them that I can afford, in the meantime I have stuck with the 606.2's.

NetAudio in the UK are another excellent source of upgrades etc. for the 405 range, I've had quite a few items from them which have been excellent.

The RSPM crossovers can be easily accessed by unscrewing the covering plate, and then unscrewing the crossover out of the bottom of the box after unsoldering the wiring harness. Don't lose the little red fibre isolating washers when you take them out that go either end of the PCB stand-offs. Replacing the caps is uncomplicated, but the actual tracks are likely to be quite fragile so a little gentle extra care when removing caps will save time later.
 
Fraser said:
Well i've listed them (along with some classic technics seperates) in the classified ads section of the forum, to be honest i'm open to offers as i want them to have a good home rather than just sell them for all i can get. I adore these speakers and with more cash and space would be having them overhauled myself. So if anyone wants to make me an offer i'm open to suggestions.
Click to expand...

hello
sorry to bother you
i have same wonderful speakers which need help, if you were to get yours overhauled where would you take them? i need new crossovers, some-one must be doing this
thankyou
adam zisserman
 
I don't think anyone is re-manufacturing the crossovers for old IMF's, but in the UK, Wilmslow Audio should be able to supply capacitors etc. of the correct value. Sadly, John Wright passed away some years ago and his speaker designer for TDL, Clive Gibson, is buried in a research lab somewhere I understand...

I wish I had the room (and an understanding wife) to take on restoration of some mk4's. I loved these at the time and the better bass damping works wonders with modern gear. I'd happily agree that a 606 is a better bet most of the time over a 405-2 and they are fairly affordable too (mk1's go for typically £360 or so). I understand that everything from supply caps to the internal wiring loom can be upgraded if you wanted to as well. I don't know what Quad did with the 606.2, but stone cold it sounded like a 606mk1 warmed up and got better again (they seemed to need a couple of hours for the cases to warm through).
 
Most of the IMF crossovers are pretty bullet-proof apart from the inevitable electrolytics, and I always recommend to leave well alone apart from replacing all the capacitors when I'm renovating them. On some models L1 ( the bass line inductor) can get fried usually because some misguided soul thought they'd make good disco speakers.... Falcon is another good and cheaper source of capacitors in the UK.

As I understand it ( happy to be corrected) the main internal differences between the Quad 606.1 and the 606.2 are a much beefier power supply with a toroidal transformer in the Mk2 giving much more "grunt" and reliability ( not that was ever much of a question mark over these beasts anyway!) , and the Mk2 also upgraded and consolidated all the various improvements in circuitry and component changes Quad made during the Mk1 manufacture period. For certain, not nearly so many Mk.2's were made, and they don't come up for sale much. The Mk.2 can be easily distinguished by bevelled top fins and a faceplate with different graphics.
 
AH, so there were a few more tweaks in the 606.2 other than "just" the mains transformer. I could never understand the audio industry's (or was it the dealers only) apparent lack of respect for this amp. As long as it was given a smooth 6 Ohm upwards load, it sounded superb - very spacious and no grain or harshness. I think this may have got even better with the 707/909 which are all you could ever need from a general purpose power amp - unless you had some awful speaker loads to drive...

Oh to hear Dark Side Of The Moon on some big IMF's again......:D
 
I never really liked the 707 and the 909 isn't so much different from the 606.2 from the good reports I've heard. The 606 ( and especially the Mk 2) is a very good solid and reliable workhorse that does well what it what it says on the tin. I've inadvertantly done some dreadful things to mine over the years, driving it fully shorted out for several hours on one channel being the worst. Just turned it off, removed the short (loose banana plugs touching from testing some other speakers), turned it back on again, end of problem.

I know what you mean about Quad and dealers, I have a feeling that Quad wasn't trendy enough for a lot of outlets, or maybe (said he rather cynically) the wholesale discounts given weren't enough......

DSOTM ( esp. in SACD) is stunning on big IMF's, but the one that really makes the windows rattle as the bass kicks in is the live version of Run Like Hell from the Pulse album. Either takes CD LF reproduction right down to the theoretical limit.
 
hello
dark side of moon may sound great, but for really superb production "pro's and con's of hitchhiking" (sp?) is the best. so damn good!
going back to my problem with mk1v monitors, what type of caps i am to ask for when replacing crossover components?
 
The original electrolytic crossover caps use by IMF were cheap and cheerful Elcaps, the reason that the IMF crossovers generally worked so well was that they were 5% toleranced ( see pulsestudios' early posts in this thread and he should know!), and I think also because IMF wound their own inductors many on iron cores which gave a very smooth sound. The Mylar caps are generally OK as they are sealed, but are an easy replacement if judged to be getting on a bit. Again normally there is no need to touch the resisitors or inductors.

I've used 5% toleranced 100V Alcaps very successfully when renovating both my IMF's and those belonging to clients, it's a cheap and effective solution that maintains the character of the speakers, and also Facel and Solen. Solen especially seem to give a brighter sound until they all settle in. There is a physical space issue on the crossover board esp. with Solens, and in RSPM's and SACM's there' can also a size issue due to lack of space inside the crossover compartment.

After that, I glaze over, I'm afraid I'm one of those people who can't justify paying any more than that for a benefit a.ka. snake-oil as far as I'm concerned that I'm told is there but is obviously so subtle that I can't hear it.....
 
DSJR said:
I have a vivid memory of playing ALS40's LOUDLY one Saturday morning with a master tape copy of Frankenstein by the Edgar Winter Group through a Crown/Amcron D150 (a good old power amp with tons of bass grip and a bit bright sounding) and possibly an IC150 preamp (not so well loved). The impact was staggering and I got a round of applause from the customers in the dem/show room when the track finished!! - We had customerS then, not one or two or none like today..

QUOTE]

I wonder if I could have been one of those customers! Went up to KJ in the West End before it moved to NewCavendish St (?) and came away with ALS40s, Yamaha CR800 (Just bought a CR600 on ebay for spares for £1.99!) and a Dual 601 (?). Still have them all but sadly the IMFs are in the boxes in the loft - space dictates but I can't bear to get rid of them. The Yammy is still going strong and has been in almost daily use for the past 30+ years. Don't make 'em like that any more! My favourite music on the IMFs was some Bach organ music but Equinoxe was also good value.
You're spot on about the customers - I remember having to wait ages to be able to part with my wedge! I returned to KJ later to look at the Nakamichi 600 but ended up with an Aiwa AD1250. Not quite up to the Nak's standards but the Nak was £300 in those days IIRC! The Aiwa was a bit more than half that. KJ then went esoteric and unless you were spending a small fortune they couldn't be bothered so I couldn't either and took my money elsewhere.
The only people I can find nowadys who can be bothered are Sevenoaks.
Click to expand...
 
I did the aforementioned dem in Watford in 1975... When the Wigmore St branch opened in late '75 most of the expensive stuff (and shedloads of new expensive stuff too) went to the London branch and we were left out in the cold. The W1 branch was snooty and arrogant in the extreme at first and featured some of the current high flyers in UK audio as staff (I won't mention names, but this arrogance is often how you climb the ladder of "success" it seems).

There is a problem when you're selling top line components, audio or otherwise. The contempt that comes down from on high regarding stuff that "ordinary" people buy is incredible. If you mention Granny's old Enfield Westminster chiming clock that's done stirling service for sixty years to a top line antiquarian horologist you'll see him visibly wince, as it was mass-produced with stamped out wheels and plates etc and has a stained or varnished plywood case.......

P.S. My Uncle bought an AD1250 from me thirty years ago and loved its performance until it started a squeak - he oiled it....................................................
 
Everything on the RSPM seems to refer to the Mk IV - what happened to I, II & III? Tried google but hardly anything materialises. Did IMF run through these like the proverbial dose of salts till they got to the Mk IV?
I've seem somthing that looks like an RSPM but with a painted chipboard front - similar to my ALS40s - rather than the veneered front of the MkIV on the IMF website and I'm trying to place them.
 
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...
 
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