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IMF Professional Monitor IV

hello
you mention renovating imf crossovers for clients, which makes me hope you would do so for me, i may have misunderstood, but it your up for it i would happily pay to have my crossovers renovated.
please let me know
thankyou
from adam zisserman

[email protected]
 
A little off-topic nostalgia...

I bought an Aiwa AD 1800 from KJ back in the summer of 1978, after trying my best to find a DT600 for 200 quid as advertised by some 'stack 'em high' outlet in Essex-they were out of stock and would not order another one for me at that price. The deck that I REALLY wanted (but could not afford) was the Sony TC 177SD, which KJ did have in stock that day-until the salesman turned his back and some 'customer' waltzed out of the door with it- and no, it wasn't me either.

As good as the AD 1800 was, it didn't really have much HF extension, even with the bias knob dialled in just right, and turned highhats into tssssssh, tssssssh, tsssssh sounds. I still don't know why Aiwas flagship in the era when cassette decks were hugely overbuilt was only a 2-head model. I ended up using the 1800 as a fuzzbox for my first electric guitar, by plugging it into one of the mic inputs and then sliding the gain knob to the max!

DSJR said:
P.S. My Uncle bought an AD1250 from me thirty years ago and loved its performance until it started a squeak - he oiled it....................................................
Click to expand...
 
DSJR said:
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..
Click to expand...

Thanks for the input - makes interesting reading after all these years!

I can't remember where KJ in Watford was - could it be where Richer is now?
 
On the corner of Langley Road and St Albans Road. A big white painted building with glass windows (wonderful for acoustics - not!). It became Acoustic Arts after the big KJ selloff in the mid eighties (KJ Uxbridge eventually became Martin-Kleiser which recently moved to Beaconsfield, KJ Harrow reverted back to Harrow Audio, KJ W1 moved and remains under different ownership, Fleet St closed and Croydon had a huge fire...............). Amazing though, that many industry proprietors/higher-uppers worked at KJ at some point - the Walrus guys, Listening Rooms, Rob Follis (audio PR guru) off the top of my head, but there are more around and about...

When I started, we had all the "in" stuff - all the IMF's, AR speakers (including the magnificent LST's), big and smaller JBL's and some awsome (for the period) Crown electrostatic hybrids skulking in the corner (£1200 in '74 equates to £8-9K now I think). We also had the big Monitor Audio MA1 and MA3, along with BC3's and the big Celef models and, of course, the Tannoys, which sounded a bit raw and coloured on the flat toned solid state gear we used but obviously much better now once restored on the refined sources and subtle sounding amps of today...
 
Hi,

I stumbled upon this site/thread while trying to decide what to do – replace my IMF Professional Monitors with more "spouse friendly" standmount speakers + subs, or to revamp the IMFs. The money would be easier to justify for the former of course – and there is the third option of doing nothing! Reading through this site has moved me towards the latter two choices, but I would appreciate any views! More about the options in a moment, but first a tiny bit of my IMF history in case it is of interested:

~1976 I bought a pair of TLS50 MkII from KJ Leisuresound just off Tottenham Court Road in London. Took em home to Hounslow by taxi – amazing what fits in a London cab! I had be stunned at the difference between different speakers in the pretty expensive £250-£300 bracket (at least £2500 in relative terms today, or double that if related to house prices! The RSPMs were about £500 I think. None of the subtle differences that took a reviewer a whole weekend to hear the difference between a Linn LP12 and other turntable (Technics?) at a similar price three or four years later: speakers make a bigger difference than anything else!

Very happy with the TLS50s. Then in ~1991 I spotted a pair of Prof Monitors for sale for £350 – and snapped them up! My brother in law, who had been following the then modernist line of thinking on speakers and had Naims (can’t remember the model) gladly chucked them for my old TLS50s! He still has them, going strong.

And I still have the PMs. They are, I think, the Mk I (No plinth, and no Mk number) – the owner had had a pair of low and very solid stands made, just enough to lift the castors off the floor – to which I added spikes, and he’d also apparently had some modifications done to the crossover. Maybe not as good as later versions, but still pretty satisfying! Best I ever heard, though, was once when I had a party in the garden – nothing like free air loading and good volume to make them sing, and the bass was incredible – which I can never achieve indoors (despite 22’ x 14’ living room).

I’ve been using them all that time with a Musical Fidelity P170 power amp, which seems an OK combination.

But when a pre-amp fault blew one of the B139s recently (managed to find a replacement on e-bay), that started me thinking about the longer term if things go wrong, and also about whether modern drivers might be better, especially in the upper registers. And the thought of the cost of that made me wonder if there was any way of achieving as good a sound in a more ‘spouse friendly’ package.

So…

Possible replacement bass driver in the PM is the Volt 250.8 (suggested by Wilmslow Audio for this loading). Scanspeak R2904/710003 tweeters (chosen for their better dispersion than the ring version, ATC SM75-150 mid. WA say they can design a suitable XO. Any observations on this bass unit, or alternatives, for this enclosure? Any comments in general? Easy to assume that the best of modern drive units will be better, but the big question is, will they???

The other thought was standmounted 27 litre asymmetric reflex cabinets with downward firing ports, using same mid & hf as above, with Scanspeak 22w 8851T00 bass. These partnered with one (spouse preference) or two (if needed) BK Monolith subs. The biiiig question is, how would this setup compare with the IMFs. I expect the mid-high to be better on the basis of the drivers, but am very concerned about the bass, in the absence of TL loading, and using smaller cabinets supplemented with a sub (probably from about 60Hz). Anyone have experience of the Scanspeak bass units in this size reflex, and/or experience of the BKs? Re crossover: For ~£250 (parts only) Wilmslow Audio can supply suitable passive XOs matched to this specific speaker combination (so they say), noting that the ATC has particular demands. Alternatively for £100 more I could get a Behringer DCX2496 3-way active XO, and a pair of secondhand amps such as Samson Servo 170, and go for triamping with easy control over XO frequencies/slopes/EQ. I've no knowledge of these amps other than the specs, but that would mean cheap amps not on a par with my existing MF P170, vs passives that are less tweakable.

For reference my main use is music listening (from heavy/progressive rock, to classical, both chamber and dramatic orchestral, and opera, also playing a sampled piano.

All comments gratefully received!
Paul
 
Well, you need to go back to the fundamentals of TL design to calculate if the length and taper of the PM B139 Line specifically designed for that unit in your PM's will be suitable for Volt woofers. Somehow I doubt it, and I'll wager WA haven't done that either...

It's very easy for WA to say they can provide replacement units, they would, wouldn't they as that's what they're in business for, but I doubt very much the resultant sound will have anything approaching the sound an original IMF makes. My advice is to go back to square one and look at what you're trying to create. If it's a new speaker using a TL design, then I suggest you look at Dave Duglos's TL site for ideas, and links into the TL underworld!

If on the other hand you want small TL's beacsue of the open bass a TL gives, which are almost but not entirely an impossibility, then a look at PMC's will be educational.

I'd leave the IMF's alone if it were me.....
 
Yeah, I'd agree with the above.

If you wish to carry on as you are, get the MF fully serviced with new uprated electrolytic caps (especially the supply ones). Use a good gauge speaker cable such as Van Damme 4mm or 6mm as short as possible to maintain damping and if there's a midrange control on the back, turn it to "+." very old IMF's aren't going to be worth huge dosh, but I'd rather keep them original as much as possible (why did I chuck out those old HiFi Sound mags - they were IMF fans as I recall).

Look on eBay for a set of spare drivers. You often get old Kef Concerto's (or Kefkit 3's) being broken up and the B139's (wide metal surround or the later neater black one) and B110 mids can be sourced that way - at a price now probably. I can't remember the tweeter units on early PM's ("my" era had the Celestion HF1300 and HF2000 I think) but these come up too quite often. A shame Elac/TDL didn't keep their factory going, as at least you could have updated that way (later Mk2 IMF's eventually switched to the TDL drivers and when IMF went under, TDL started making speakers to put their drivers in, taking John Wright as MD, hence the continuation).

If you want to make new speakers from scratch then great, but obviously the spirit of your old PM's lives on in their MB2 model (forget the cheaper tall slim boom-boxes, they don't begin to compare IMO). If KJ West One has any lasting "fame" it'll be that Pete Thomas bought some PM mk3's there and this got him hooked on Transmission lines - the rest is history.
 
Just a word of caution as far as sourcing replacment B110's is concerned.

The B110 SP1003 type which was used by IMF had very heavily coated cones done I believe in-house by IMF, most of the ones you will see on eBay are standard untreated types. I'm sure it isn't impossible to replicate, there's a huge variety in the application of the finish between units, so it doesn't appear too scientific!

From memory it was a thick PVA that was painted on, but if anyone knows for sure exactly what it was, I for one would be very interested to know.
 
Hang on, is this the extra white doping that 3/5A lovers wet themselves for? Paul Pulse-Studio, WE NEED YOU!!!!!
 
Yes. It's certainly the same stuff that produces the B110 "White-belly" effect that as you say, LS3/5a and also Isobarik owners get very worked up over.

Both my IMFs TLS80's have a similar coating, it's the same on all I've seen or renovated, but judging from the still clearly visible brush strokes over the cone surface, the stuff IMF used was even thicker. So there must have been at least 2 types - or in the case of IMF B110's, maybe multiple coats. Maybe IMF put another coat over a KEF painted coat of the stuff after delivery?

The technique was used by many manufacturers, not just KEF.

I was always told it was a thick PVA type "gunge" that was painted on, it was apparently called Plastiflex, but I have no more information on it or what would be a modern equivalent. Every now and again there's an inconclusive discussion on this on various forums, but I don't have the spec. to compare against anything. The reason was to cure a resonance that was produced by the bextrene material of the cone.

If you pick up on this, Paul, any info?
 
Hi
Yes the IMF mid driver B110 SP1003 was given a few extra coats of Plastiflex, the now equivalent would be something like C37, a German made lacquer, I have not tried it but have read some good reports, but it is like anything mystical there is of course a high premium. The reason for the additional layers of dope to the B110 as a mid driver is that it was mounted from the front of the baffle, unlike the bass/mid used on the 3/5a which is rear mounted. Front mounting a B110 will add a new node of resonance that will need taming by the application of a few coats of dope, there is also a resonant node around the dust cap that is why the B110 ( White Belly ) units used in the 3/5a's are sought after, but lets not get carried away here.
Over the production years of the B110 the cone doping material changed to comply with various design requirements and also fire regulations that were introduced, there are 4 basic B110 models, and the most frequently used is the SP1003 , which is what will be in the IMF's.
The use of a hand mixed dope to apply to the cones of untreated B110's will be hit and miss affair, if you want to give it a go them mix PVA with the stuff they use for stiffening the tissue paper on model gliders, available from a hobbyist store, I can not remember the ratio's now as it was over 30 years ago, but try something like 4 parts PVA to 1 part dope, then you will need to practice on a piece of black card to get the consistency correct and the number of layers required. Some B110's were treated on both front and back of the cone, some on the back only and others only on the front, there were so many variants around during the 70-80's.
The Kef Concerto used a quite heavily doped mid driver that would be a good replacement for the IMF, but be warned they also fitted the larger magnet, B110 SP1057 from the mid 70's, these are treated on the back only, so look before you buy.
Paul
 
Thanks, Paul, for the info., very helpful. I looked at C37 following your post and decided not to bother with it having seen the cost. Ridiculous. The home-made PVA/dope mix sounds much more like what I expected, cheap, cheerful and doubtless effective!

As an aside the B110 SP1057 was fitted by KEF into the Cantata and some of the Reference range form the mid 1970's, I've never seen one fitted in a Concerto as an original, only the old faithful SP1003 version.
 
Hi

Just found this very useful forum this morning!

I've been thinking recently about replacing my IMF's - but the more I listen to the current speakers on the market, the more I realise how much I will have
to spend to gain a really appreciable improvement in sound.

I have a pair of IMF Professional Monitor Mark IV Improved speakers, which I bought brand new here in Brisbane in 1982, and extensively modified in the late 90's. Incidentally, I am more or less aware of the model progression through the IMF PM range, but does anyone know what changes were made in the "Improved" model, over the Mk IV?

The speakers are used with Tara Labs Space and Time Phase II cable, a wonderful Denon DCD 3560 cd player (which I am presently thinking of modding, if I can find out what can be done to it!!), and Linx Stratos Pre and Monoblock power amps - 120w rms a channel almost pure class A into 8 ohms; hand build in NZ in 1986 with top grade components and fully wired with Van den Hul. All owned since new, and part of the family!!

The speaker mods are as follows:

1 The crossovers have been completely rebuilt with very high grade components, and have been simplified by removing all the filters etc from the signal path.
2 The crossovers have been modified to allow the speakers to be run in a bi-wired configuration.
3 All internal wiring has been replaced with Space and Time pure copper wire.
4 The external connectors have been replaced with Eichmantech binding posts.
5 To shorten the cable path the internal wiring has been run down the front of the cabinets (behind the grilles), and the binding posts were placed on the bottom of the cabinets, as close as possible to the crossover units.

So - the cabinets are no longer original, but the with the grilles in place, no-one can tell the difference! Except for the fact that the cables meander out
of the bottom of the cabinets! Also, the LH speaker was dropped by a removalist late last year, and one of the back corners is now nicely rounded! This will be fixed if I decide to keep the speakers - I'll get them French polished.

I would be interested in any suggestions anyone might have for improving the speakers, over what I have already done. I am thinking:

1 Maybe even higher grade components for the crossovers - but I'm not sure about this as the previous crossover rebuild cost me $700, which was 25% of the new cost of the speakers.
2 Bringing the filters back into the circuit, and using these to play around with the sound.
3 Rewiring with more specialised wire.

Also suggestions for better speaker cables, and maybe more up-to-date amps that would work well with the Mark IV's.

All the drive units are original, and are still working well - but they are not going to last forever, and I would really appreciate suggestions for sourcing
replacements before anything dire happens.

Having done all this - I would end up with beautiful sounding speakers, but unfortunately it's not possible to get away from the very dated look!

However, by modding these, my CD player and my amps, changing the speaker cables, interconnects and power cables, I would have a really great system for maybe $1200-1500. Not a bad idea really..... compared with how much would I have to spend on an audibly better new system!!

I suppose I could just simplify the whole process by buying an entirely new system and using the existing one without mods as the ultimate computer setup in my (large) home office!!

BTW - If anyone is interested, I do have copies of the crossover circuit diagrams for the Mark IV, Mark IV Improved and TLS 80 Mk IIa.

Edward
 
Seriously, I'd personally suggest you leave the speakers as they are - boutique caps will change the dynamic of the crossover and unless you can measure them..... I'm also suspicious of boutique speaker cables, but if you can borrow some for a giggle then go ahead.

I don't know the mk2, unless it refers to the TDL drivers your samples will have (slightly drier in balance as I remember). Paul could advise more (and read the crossover changes better).

I don't know what else you have, but a source upgrade (or amp similarly) could be where you're looking if you have money to burn - I think the mk4's are well up to todays top end ancillaries ;)
 
DSJR said:
Hang on, is this the extra white doping that 3/5A lovers wet themselves for? Paul Pulse-Studio, WE NEED YOU!!!!!
Click to expand...

Yes, Plastiflex was the stuff. A PVA adhesive which was as close to Resin-W as you can get. I painted this stuff on thousands of drivers for 50 pence a go back in the early 80's. I found that watering the gungo down a bit made it easier to apply and two thin coats sounded better than one thick coat and looked nicer.
 
I couldn't agree more with DJSR, it sounds to me as though you have probably done more to the speakers than most, and quite frankly, my opinion ( and I've done up a fair number of IMF's over the years now) is that anything else is not worth it, you won't get enough benefit if any from upspeccing crossovers etc.

As I'm a speaker specialist, I'll refrain from comment on amplifiers etc., other than to say I reckon boutique cable are invariably manufactured by Snake-oil Electronics Inc. Most CD's are mastered on cheap Van Damme or similar cables from what I have seen when they're used, I don't understand how spending €2000 a meter on cable is going to improve what's already there.
 
It's a bit like the "Keel" thread I and a few others have cr@pped on inadvertantly. It undoubtedly does the job, but the manufacturers have basically priced it where they think it should be, not where it "ought" to be priced at..

A total aside, but I was reading an online HiFi World critique of the Alphason turntable and tonearms. The legendary HR100S arm was originally around half the price of the Ittok back in the early eighties and apparently comfortably out-performed it (I didn't get to hear one until several years later when it was almost too late but it's superb...). People still bought the Ittok as it was the "official" arm to go on the LP12 and didn't mind paying the extra...

What the above means relative to IMF is that there are decent polyprop caps that "could possibly" go here and there in an IMF/TDL crossover to replace cheap old electrolytics, but there's no point whatever in going further to ultra low resistance ones. Internal wiring can be beefed up a little with decent gauge flexible instrument wiring I suspect but I wouldn't use chunky wires on the tweeters (totally unnecessary) and anything too stiff may vibrate internally (I'm thinking of those people who re-wired LS3/5A's with Linn or Naim cable [what difference is 6" going to make inside a speaker?])
 
I think the "Linn Hordes" will be after you if you're not careful! - I completely agree with you!

Coming back to IMF, and I think it's true of all the "classic" speakers, IMHO there has to come a point where it isn't worth spending money on upgrading components, there is no perceived benefit and also one runs the risk of destroying the speakers' character. It's a personal line, I veer towards keeping originality for character retention as much as I can in those I do up for people which is the cheapest solution. Others want to spend a fortune on replacing with gold-plated capacitors that IMO are a waste of money in terms of getting value benefit, but it's their choice.

What is also interesting is that if those ultra-worked on speakers are ever sold, with very few exceptions, they fetch the much the same, maybe a little more than an unworked-on pair, but often even less. It's the "extras in a car" value argument, basically forget them if you ever sell.
 
Personally, I wouldn't buy a tweaked pair of speakers or a tweaked anything Hi-Fi. When I buy s/hand, it has to be as original or I move on.
 
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