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September 2012 Issue
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I noted your Letter of the Month on IMF Monitor speakers in the June 2012 issue. The IMF Monitor was the speaker of my dreams when it came out and while I never managed to own a pair I did own two sets of IMF Studios (TLS50s in England) that were smaller versions of it. 

Living in Philadelphia at the time I got to know Bud Fried (Irving M Fried, or  IMF) and we became life long pals even though he always teased me whenever I didn’t own his speakers and for my love of Celtic music that he would call tinkle music (Bud listened only to Classical music, especially opera and particularly Wagner).  

I note the writer’s concern with the slowness of the speaker which, especially with the march of the years, I agree with. Your advice to him is to the point. And I believe I can add to it. I know a couple of current IMF owners, both of whom changed bass drivers. The TDL woofers are drop-ins for the KEF B139s with the same frame, but with a concave rather than flat diaphragm. The result was much tighter, better damped bass. I assume that the Q of the TDLs is lower than the KEFs, Q improving the overall system bass control without fouling up the crossover region. The bass response is much more of a modern vein.  

These speakers are, of course, quite old. That could mean that the capacitors in the crossover have deteriorated. Changing them for more modern ones of the same value would probably result in cleaner, more defined sound from top to bottom. And it might improve the bass further also, since improving the bass harmonics should improve the overall bass sonics.  

Finally, if he can get into the mid-range enclosure, a card board tube running front baffle to back baffle, he should check the damping. My IMF studios came with a simple roll of foam. Bud changed it to a three layer system, complaining the factory was harming the mid-range in the interest of saving a few pennies. 

The back layer was now a short heavy one. The middle layer was much less dense. And the layer behind the driver was very lightly packed. The improvement in reproduction was obvious in seconds when we compared the first one that was changed to the original in the other speaker. The mid-range loading is a short transmission line and the volume right behind the driver is very sensitive to reflection if the damping there is too thick. 

If his damping is simple like mine was, I’d try about an inch of foam at the back, then a couple of inches of long hair wool or Acousta-stuf at about the classic half pound /cubic foot (experimentation is probably necessary) and finally a very, very light layer.

I still have warm thoughts of this speaker, sort of like a first love. If I had the space and the extra cash today, I suspect I’d find a pair and update them a bit as I’ve described above.  

Allen Edelstein 

New Jersey 





IMF TLS50 loudspeaker, cutaway diagram from IMF, 1975. It used an 8in

bass unit loaded by a transmission line,  a midrange, tweeter and super tweeter.


Hi Allen. Thanks for your observations. I should perhaps explain to readers that IMFs were built in the UK by IMF UK and distributed in the U.S. by Irving M Fried. Go to for more on their models and tortuous history.  

IMF UK then became TDL, run by John Wright until it closed some years ago. The TDL bass unit you mention is described as “having a thick tapered styrene cone with a plastic coating, this produced a rigid piston action and was extremely light without any cone break up and produced an excellent fast response at low frequencies”  by ex-director John Hayes. I hope your info on making improvements is a help to the  lucky owners of these monsters. NK



You ran a very interesting review of the Inspire mod of the Thorens TD160. As an owner, user, modifier of this particular turntable I can see why the company picked it as a natural upgrade! 

If you remember, you published an article about my turntable some time ago. My modifications were considerably cheaper than the Inspire ones and to be honest I think their success is more to do with the ‘don’t touch what ain’t broke’ method, than the rather more expensive mods in the review. 

For a start, a synchronous AC motor will be far smoother than a DC one, no matter how many poles the new motor has or the quality of the electronics. A DC motor is really lumpy as it moves from coil to coil in its armature. 

All you are gaining with DC is torque which, given that you are using a rubber band to connect to the platter is going to be diminished in effect in any case. If you feel that the drag of the stylus is in need of that torque then any motor control of speed needs to relate directly to the speed of the platter. Since there is no feedback mechanism then this will be largely a waste of effort. 

Greater damped mass in the platter is what is required in the TD160 to remove the ringing of the outer section. The effect is dramatic. Bass firms and rises in level. Surface noise and the effect of clicks and pops are diminished drastically. 

By replacing the plinth too there are additional benefits that relate to feedback and long term stability. I would say that my plinth is still a hollow box so it will never be like the skeletal designs from Avid or others as is the current trend. However, my plinth weighs in at more than most stand mount loudspeaker pairs and more than many floor standing ones too and is non resonant and pretty much sealed from below having over 2 inches of kitchen worktop beneath it in its construction. 

I only use a 28 year old SME 3009 fixed arm and an old Ortofon VMS20E but if something like a more recent arm were fitted the humble TD160 would take on all comers. 

From what I can see the best way of taking away some further issues of the TD160 is to isolate the AC motor from the mains by building a dedicated quartz locked mains supply which in turn will allow for electronic speed switching (just alter the clock speed in the converter) and do away with the mechanical speed change which is a liability in this turntable. I’m working on that one! Keep up the good work!  

Regards and best wishes.  

Dave Tutt 

Tutt Technology








Thorens TD-160 can be improved simply by damping the platter, says Dave Tutt.




Like quite a few turntables of the 70’s and 80’s the TD160 is a well designed and solid performer.  But any 40 year old machine is going to need maintenance and refurbishment.  All moving parts including the suspension are not going to perform now as they did all those years ago.

  The debate over AC and DC motors is likely to outlive all of us.  A DC motor when not powered but rotated by hand, does indeed appear lumpy.  An AC motor is smoother with no power, but often just as lumpy when running.  A true test would be to run both under a load and measure the vibration with an accelerometer.  An easier way would be to buy a cheap stethoscope from eBay and listen perhaps.

  If stylus drag is an issue then only a properly implemented PLL direct drive will do, or second best something with a very high mass platter like the SME Model 30. 

  I like the idea of your very heavy plinth and perhaps an SME 309 might finish it off?  A small quartz locked mains supply would be good too. I looked at the mains here in Dartmouth, Devon,  the other day; I don’t know what the neighbours are up to, but the waveform was decidedly not nice: around 2.5% distortion and an odd sloped flat top to the sinewave.  

Let us know how you get on. 

Dave Cawley, Sound Hi-Fi.




Big IMFs are great for Prog Rock, says Steve Petch. Pictured are monster

TDL Reference monitors, successor to IMFs. 

Comments (2)
right amp for speakers
2Thursday, 03 January 2013 22:35
richard johnston
hi guys,just wanted your advice on a suitable amp for my Bicor 200 spks which have lowther dx3 drive units. im loathe to go down the valve road as i live in rural ireland and know of no one to help should it break down- i have no experience of valves. i was wondering if a Sugden a21 would be a suitable partner for the lowthers. many thanks for a great mag. Richard.

Hi Richard. If you can, get a Sugden A21SE. It has a fabulously detailed yet deliciously pure sound that is a real education as solid-state goes. It is a Single-Ended design (with dynamic load) of low efficiency and power output, but it does not get burning hot and it is smoother and less glassy than the typical push-pull Class As. It's a great match for Lowthers' forthright sound. NK
Van Damme cable
1Wednesday, 21 November 2012 19:13
darren pickering
I completely agree with the comments on Van Damme cable: the 8mm version its amazing for £6 a metre. Bryston also recommend this cable for studio installs

It would be really good to see a review versus audiophile grade stuff!

Thanks Darren.
Yes, that is a good point, we must get some and give it to our cable experts.

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