MMC20CL



MMC 20CL


Manufactured: 1979 - 1985
 Designer: Jacob Jensen
 Colours: Silver

The top of the range cartridge from B&O, this boasted a single crystal sapphire cantilever and a Contact Line stylus derived from the Pramanik stylus of the MMC6000

The MMC 20 CL was the top of the range of the MMC 20 range. Designed to work with the tangential tracking turntables of the time, MMC 20 CL was the first B&O cartridge to use a single crystal sapphire cantilever. This offered a very rigid but light structure and was fitted with a naked contact line diamond, a version of the Pramanik diamond found on the MMC6000. The profile was such that this cartridge was recommended as a replacement for MMC 6000 should quadraphonic reproduction be required. The CL was available with either ½" or P mounts so that it could be used with other turntables. It received a number of glowing reviews at the time of its introduction from the audio press, not normally renowned for their love of B&O. It achieved something not many B&O products ever managed - it was described as offering value for money!!




Extract from ‘Gramophone’ July 1979 (page 118)

The MMC 20CL is distinguished from the more lowly models in the new series by its contact line stylus contour (hence ‘CL’) but even more so by something really unusual. For the first time in a commercial cartridge we find the diamond stylus mounted in a cantilever rod not of aluminium tube, or beryllium  - but single crystal sapphire. The special virtue of this unusual cantilever material is said to be its high stiffness for a given thickness, five times stiffer than aluminium and 21% stiffer than beryllium. The effective tip mass is a very low 0.3mg which should ensure low record wear and a high stylus resonance well beyond the audible range.

A transparent guard projects in front of the cartridge body to protect the stylus and yet give clear visibility of the tip. The body itself forms an effective Mu-Metal screen against stray hum fields. The cartridge is supplied in B&O’s usual beautiful Perspex box complete with screwdriver, stylus brush, stylus balance (simple but very useful) and the usual hardware including spacers and a wedge to optimise the working height and vertical attitude in the (unlikely) event that this cartridge is used on a stacking autochanger. The package also contains a penrecorded response curve and other test measurements as well as clear operating instructions.

How it performed

Not having a Bang & Olufsen turntable/arm immediately accessible to my test bench, I ran the usual tests on a standard SME Series III arm, without damping, mounted on a MicroSeiki DQX-1000 turntable—that is their latest model permitting up to three pickup arms to be fitted at a time—an essential feature of my cautious procedures for double checking every aspect of objective as well as subjective assessinents. Once vertically and horizontally aligned, the cartridge could be checked for optimum playing weight and sidethrust compensation. The 1-gram recommended playing weight would indeed cope easily with the vast majority of records, though 1.1g was necessary for the highest velocity test bands. Incidentally, the gauge that B&O supply was reasonably accurate and read only about 0.1g high compared with my laboratory gauge. This order of playing weight, helped by the long contact stylus shape, should keep record wear very low indeed.

The moderately high compliance quoted does imply the use of a tow inertia arm and I checked the low frequency resonance with the SME at a practically ideal 11Hz. The resonance peak was high enough to make moderate damping, via the SME dashpot, a good idea. Low arm friction is stressed as a requirement in the B&O leaflet and would be another good reason for coupling this cartridge with a decent arm—either B&O or some other reputable make.

As Fig. I shows, the frequency response is very smooth and well matched in the two channels. There is a gentle slope at the extreme treble end, using the recommended loading, and I feel that a little less capacitance as found in many modern arms may actually be beneficial in making the treble hold up further. Crosstalk is also shown in Fig. 1 and is remarkably low over the full spectrum. Sensitivity is quoted as greater than 212mV for 5cm/sec lateral velocity and I found the slightly higher values shown in the table. This is still a rather low figure and it would be a pity to use an amplifier with abnormally low sensitivity or indifferent noise figures. However, most of today’s amplifiers will present no problems.

When it came to listening, via Quad 33/405 amplifier and IMF TLS80/II loudspeakers, I was immediately impressed by the anonymity and just plain naturalness of the sound. Voices and instruments were clear and easily distinguishable, so that Sylvia Sass (for instance on her recital record, Decca SXL6921) who has recently joined my select band of female voices providing both listening pleasure and audio test material, was immediately recognisable against Joan Sutherland, Janet Baker and Elly Ameling. The best of the new direct-cut and digitally mastered discs were also reproduced with maximum clarity and marked left to right and front to back spread.

No problems with tracking or hum induction were experienced. The lack of tracing distortion attributable to the stylus shape, and indeed the very low value of any sort of distortion, added up to a refreshing clarity which I would compare favourably with any other cartridge around— including the very expensive moving coils. At its reasonable price, considering the outstanding standards of performance, the B&O MMC 20CL goes straight into the very small company of cartridges that can be safely recommended to even the most fastidious record enthusiast.


MMC stands for 'Moving Micro-Cross'; the patented moving-iron principle upon which all B&O cartridges were based. This unique system employed a cross-shaped armature which, among other advantages, guaranteed exceptional stereo separation since each channel moves on a separate axis.

The job of any pickup cartridge is to transform the record's physical profile (groove modulation) into corresponding electrical signals (which are then amplified or enlarged by the amplifier and turned into audible sound waves by the loudspeaker.

A cartridge must perform three separate and exacting tasks if it is to do this job successfully. It must function mechanically (the movements of the stylus in the groove); it must function magnetically (using the physical movements to create changes in a magnetic field); and it must function electrically (using the changes in magnetic flux to generate an electrical current). At each stage, one type of energy is transferred into another, quite different, type. And the transfer must be perfect, with no energy lost and none added from extraneous sources.

No cartridge will ever reach this ideal unless the Laws of Physics can be repealed. However, by understanding the relationships between the three transfer stages and continually applying refined engineering techniques, B&O's belief was that each stage of cartridge improvement would bring each successive cartridge closer to the ideal.

Record wear and the cartridge

If you take music seriously the value of your record collection is likely to be high. Many of your records are likely to be irreplaceable. You will also know that the signals pressed into your vinyl discs are very fragile indeed. The pickup cartridge can be the disc's worse enemy since an ill-suited cartridge can mark a record for life in a single play.

While B&O is aware that cartridge specifications are inter-related, their research shows consistently that Effective Tip Mass (ETM) is one of the major factors affecting record wear. ETM is the equivalent of the amount of inertia the groove 'sees' in moving or accelerating the stylus tip. Consequently, the higher the ETM value, the higher the force required for a given constant acceleration. Obviously, more force results in more wear.

Three elements contribute to ETM. The stylus tip (diamond) contributes with its entire weight and mass. The armature contributes between 5 - 20% of its weight and mass; the cantilever around 30%. B&O has been able to reduce ETM substantially by refining these elements and building them into an integrated unit. The result is a system which not only reduces damage to the groove walls dramatically, but also provides exceptional performance at all frequencies.


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I'm running this business part-time whilst I raise my first child. My daughter Issy is 23-months old, the apple of my eye, my teacher and the beneficiary of your purchases. (She says THANK YOU VERY MUCH!). I endeavour to source the HIGHEST quality electronics, mostly B&O HiFi and will have owned most of the models in question at some time in my life. This gives me a real experience of the merits to share with you. I'm a time-served Sound Engineer and use my trained ear to check each audio item. It's not just sonics though, look out for the weird and wonderful – as long as it's well made!