The case for MM and MI cartridges

Moving Coil cartridge design has not changed fundamentally for 30+ years.

The traditional design of almost all MC cartridges, consists of a stylus on the end of a long cantilever, with a ‘moving coil’ attached to the inner end.

This whole assembly ‘sits’ onto a soft, resilient ”suspension’ or damper’ material and held in place by a rear tension wire.

Almost all MC cartridges are  built this way. There may be variations, engineering refinements, exotic materials – but the fundamental geometry of the MC generator mechanism has not changed.

Mc cartr

So where’s the problem?

The construction of the traditional MC cartridge in particular, is geometrically imperfect.

  • The ‘rotation centre’ (or fulcrum) of the coil former is not at the exact centre of the coils, but somewhere within the suspension damper ‘block’.  Only a small discrepancy perhaps, but when you are groove-tracing in microns, this is very imprecise.
  • Additionally, the necessary soft material of the damper, means that the’fulcrum’ of rotation is vague, not exact.  These are the reasons why (in my humble opinion) most cartridge designers (of MC cartridges in particular) tend to over-emphasise HF definition – to compensate for this fundamental loss of resolution, inaccuracy of ‘image focus’.
  • The cantilever is long because of the required Vertical Tracking Angle and the presence of the front magnet pole piece.  And with the suspension at the rear, the result is that the small movements of the stylus in the groove, result in much reduced, even smaller movements of the coils.  This, together with minimised coil windings for low moving mass, means very low output voltage – requiring additional phono gain, +20dB to +30dB usually.
  • Cost – a great deal of design effort is expended on improving an imperfect concept and together with small production, the result is extremely high cost.
vdh the crimson

Van den Hul The Crimson

There are a few MC cartridges that have been conceptually reconsidered and designed differently – eg. the Ikeda 9 (OEM version, Cello/Rowland), Allnic, Tzar DST, Miyajima, Audio Technica ART1000 – but mostly, MC cartridges are variations and refinements of the above-described traditional geometry.

ikeda9

AllnicVeritoZ-1

Allnic Verito Z

tsar dst 2

Tzar DST

0716cartcoil

Audio Technica ART1000

So, perhaps it is time to re-consider Moving Magnet (MM) or Moving Iron / variable reluctance (MI) cartridges.

MM_Cartridge 2

Advantages:

  • Output voltage is much higher – 5x to 10x higher.  No need for a MC step-up gain stage or device, ie. less amplification required, shorter ‘signal path’.
  • Coils can be arranged similar to stereo record cutter head.
  • User-replaceable and less costly stylus assembly.
  • Lower cost (usually).

Disadvantages:

  • Higher internal moving mass (the magnets) – more limited tracing agility, HF and low level resolution.
  • Sensitivity to capacitive loading.

Some of the more interesting MM or MI cartridges that I am aware of:

  • Ortofon 2M series
  • Audio Technica VM series
  • Sumiko Pearl / Shelter 201
  • Clearaudio
  • Grado
  • The Cartridge Man Music Maker
  • Soundsmith
  • Garrott Brothers
  • London Decca
  • Top Wing (very low-output MM cartridges).
89bd71eaafa20a38bbcb182e2c5143d9_m

London Decca Reference MM

Top-wing

Top Wing Susaku (Red Sparrow) MM

There are of course also non-magnetic pick-up cartridges – eg. the Soundsmith Strain Gauge and the DS Audio Optical cartridges.

But that’s a discussion for another day!

 

Advertisements

2 thoughts on “The case for MM and MI cartridges

  1. The Decca/London design requires it’s own discussion—they produce a very tactile, Immediate, dynamic sound, unlike any other pickup I’ve heard. But then I’ve never heard the Tzar!

    • Hi Eric – Thanks for visiting.
      I have been using a London Decca Super Gold for a few eeks now & yes, ‘tactile’ is a good word I’d use too.
      The Tzar is a MCoil, but a unique one!
      Cheers – Owen

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s