Phono Cartridge Basics 101

Lenten Entre 1 – Mounted in a Hadcock GH228 Super Unipivot Arm

As I am now in the market for a new cartridge, and maybe a new head amplifier or pre-amplifier, I thought a quick refresher course on cartridge basics would clear my head and help others who maybe in the same boat.

Cartridge specifications alone are not terribly helpful to the prospective buyer in order to determine what it will sound like in their system. There are some basics that should be understood about the the mechanics of the cartridge(s) and the way it interacts with, in particular, your tonearm.

Before buying any cartridge you need to read as many reviews as possible. No matter how many reviews you may read, for a given cartridge, while you may find a general similarity between the reviewers comments you are just as likely to find significant disagreement as to “sound” of a cartridge. Try to find a review using a similar tonearm and phono amplifier to your own or you maybe disappointed after spending what could be many hundreds of dollars.

In the end you can never tell what a cartridge will sound like until it is installed in your system, and been used (broken in) for tens of hours.

Principles of Operation

There are six types of phono cartridge:

1. Moving magnet
2. Moving iron
3. Moving coil
4. Optical
5. Strain gauge
6. Ceramic/Crystal

For further information on the optical and strain gauge cartridges please click on their links. Ceramic or crystal cartridges are based upon the piezoelectric effect, are generally a long way from audiophile, and so will not be discussed.

The first three are all based upon the same electrical principle of electromagnetic induction; a varying magnetic field (flux) within a coil of wires will create an electrical current. This techniques is accomplished by any one of the three ways:

1. Moving Magnet (MM). The magnet is attached to the cartridge moving cantilever with the fixed coils mounted around it. The moving mass is the highest.
2. Moving Iron (MI).  A piece of ferrous material is attached to the cartridge cantilever that sits inside a fixed magnetic field that is surrounded by a fixed coil. Movements of the ferrous material vary the magnetic (flux) density, generating an electrical current. Medium moving mass.
3. Moving Coil (MC). The coils are attached to the cartridge moving cantilever and sit inside a fixed magnetic field. Lowest moving mass (usually).

The Moving Magnet Principle

The Moving Coil Principle

The Moving Iron Principle

The electrical output (in mV – thousandths of a volt) from these cartridges, depends upon how strong the magnetic field is and how many turns of copper wire make up the coils.

1. MM – High output – typically 3.0-5.0mV
2. MC – High or low output – typically 3.0-4.0mV or 0.2-0.5mV respectively.
3. MI – High output – typical 3.0-5.0mV. Low output MI are also available see Soundsmith.

The output voltage and the moving mass of the cartridges cantilever are important parameters to consider.

Cartridge Output Voltage and Loading

Most common phono pre-amplifiers are designed to accept high output phono cartridge signal levels and have gains between 36dB and 42dB. They also provide the correct RIAA equalization in order to obtain a flat frequency response. Some more expense pre-amps will have switchable amplification (gain) that allows for the connection of the lower output models, up to 66dB gain. Alternatively high level phono pre-amplifiers can be driven by an external head amplifier  that is designed to bring the low level output up to the level required by the pre-amplifier. These head amplifiers need to be very low noise and distortion and have a very flat and extended frequency response. They may be an active amplifier, a passive transformer or a mix of both. Typical gains will be 20dB with signal to noise figures better than 70dB.

Lentek Active Head Amplifier – Purpose designed for the MC Entre 1

The load or impedance that the cartridge “sees” when connected to a head amplifier or pre-amplifier can significantly affect its sound. ALL high output cartridges are designed to be connected to the standard 47K resistive, 200pF capacitive input of most phono pre-amplifiers. The sound of some high output cartridges can benefit to changes in these values, but few pre-amplifiers of this type offer such adjustments. Low output cartridges always need to be correctly loaded with either a purpose designed head-amplifier designed specifically for the cartridge, or pre-amplifiers that offer various resistive and ideally capacitive loading options in order to optimize the sound of the cartridge. Typically most low output cartridges require a load of between 100 and 470 ohms and a capacitance of between 200 and 400pF.

So be warned. Buying low output cartridges will often entail buying a suitable pre-amplifier or dedicated head amplifier as well. These very high quality pre-amps range tremendously in price from as little as $250 to $5,000+! So choose your cartridge solution wisely.

Cantilever Moving Mass & Stiffness

The comparitive mass of the phono cartridge cantilever assemblies was previously listed. Why is this important? The tip of the cantilever carries the diamond (stylus) that traces the vinyl grooves. You want the diamond to exactly follow this cut, keeping in intimate contact with it at all times. You also do not want this cantilever assembly to have resonances that can add to or detract from the movement of the cantilever. The mass, its damping and stiffness of the cantilever effects both its tracing ability and resonances.

A high mass cantilever assembly has a lot more inertia than a low mass one. In other words a high mass cantilever is more difficult to stop moving in one direction and then move in another. The energy to do this comes from the vinyl tracks and is absorbed by the cartridge, the arm and the vinyl. The higher the moving mass the more energy that has to be used to start and stop the diamond tip and the more that has to be absorbed by the arm and cartridge. This process and interaction is complex and can seriously affect the sound of the cartridge, record wear and can give rise to miss-tracking, resulting in the need for increased tracking weights, and fluid damped arms.

Low mass cantilevers do not magically fix the above issues. They all still exist, but generally to a lesser extent.

The stiffness of the cantilever will also effect what you hear. You want all the movement of the stylus to be replicated exactly at its end inside the cartridge. That is where the mechanical energy is turned into its electrical equivalent. If the cantilever distorts or resonantes in any way it will color the sound by adding additional resonant frequencies or loosing energy and impact as the cantilever distorts. The majority of cantilevers are manufactured from various types of hollow aluminum alloy tubing. Some of which are coated with various exotic coatings to help stiffen them and reduce any resonances. Many exotic cartridges use more rigid materials like Carbon, Saphire and Ruby, but at a significant cost increase.

Types of Cantilever

Cartridge Compliance and Your Arm Mass

An often overlooked issue.

The cantilever assembly is held in place by a complaint mount that allows the cantilever to move and follow the vinyl grooves. The stiffness or compliance of this mount is measured in cm/dynes. Low compliance cartridges (a stiff mount) measure around 10cm/dyne, high compliance cartridges (a very flexible mount) measure up to 30cm/dyne. This “springiness” of the mount will interact with the arm and cartridges combined masses to have a resonant frequency. What you do not want to happen is have a resonant frequency that is in the audible range, or of such a magnitude that it causes the cartridge to miss-track or even jump out of the groove, particularly with wrapped records. Ideally you need to keep this resonant frequency between 7-12Hz.

Types of Cantilever Mounts

The general rule is: low compliance cartridge/high mass arm (>20g) and high compliance cartridge/low mass arm (<10g). This general rule is not carved in stone, and some arm designs will perform equally well with both high and low compliant cartridges, particularly if they use liquid damping like my Hadcock GH228S, a medium mass unipivot arm shown above.

If you know the cartridge mass, compliance and effective arm mass you may calculate its resonance here or here or here .

Stylus Profiles

There are now a large range of profiles available for the diamond stylus tip. In increasing cost and performance we have:

1. Conical/Round (least expensive)
2. Elliptical
3. Line contact
4. Shibata/Line Contact
5. Exotic:
   1. Micro Line
   2. Micro Ridge
   3. VanDenHull
   4. FritzGeiger
   5. SAS
   6. Paratrace

The purpose of these different diamond profiles is to fit the diamond stylus shape into the groove in the best way possible in order to match the way the cutting lathe made its cut. And to get perfect contact between the stylus and the groove wall to exactly trace it. This will produce excellent tracking and extract the maximum amount of information. It will also prevent the stylus from loosing contact with the vinyl and producing tracking distortion and will reduce vinyl wear. See here at Soundsmith for an excellent introduction to stylus shapes.

Styli Groove Contact

Image Credit – Soundsmith

These profiles provide a significant difference not only in cost, but in the audible performance of the cartridge and its ability to extract/accurately trace all of the groove information and minimize the amount of surface noise. Many medium cost cartridges use the very popular and cost effective Elliptical stylus.

See here at Soundsmith for additional styli closeup images.

NOTE: The new HD vinyl albums due to be released later this year are supposed to have the vinyl grooves optimally laser cut to fit the tracing stylus. I assume that once available there will be additional optimized styli profiles released to support this new laser cutting technique.

The Sound

Trying to characterize the sound of a cartridge design is borderline at best, especially once you start spending hundreds or thousands of dollars on them. It is a complex interaction between cartridge, stylus, cantilever, arm, amplifier and speakers. But here goes:

MM cartridges tend to have a warmer profile as inertia from a higher moving mass broadens the cantilever strokes, and having lower detail resolution leads you to focus more on the mid-range. Where as MC designs provide improved dynamics and HF detail with often a very open mid-range. Well-designed moving iron (MI) cartridges can offer a blended MC-MM experience, which can be very musical in nature. Depth and width of image and stereo positioning is often a function of the cartridges channel separation and the stylus shape. While tight, extended and well controlled bass is not only a function of the individual cartridge design, but on how the arm and cartridge are damped.

Higher compliance cartridges often produce a fuller bodied sound compared with the more dynamic sounding low compliance cartridges that have stiffer cantilevers.

Other Factors

Remember that just buying an expensive high end cartridge doesn’t mean that it will sound fabulous. It is all in its setup. Correctly aligning the cartridge and arm is essential in order to obtain the best aural experience. Incorrect geometry and arm adjustment can seriously hamper the performance of a cartridge and even make them sound very poor, despite their pedigree.

In the end, the limiting factor when deciding on the choice of a cartridge rests to some extent on the equipment you own (and your wallet). But do not let that limit your choice of cartridge. Remember one day you may want to upgrade your system. It is extremely important to ensure that the compliance of the cartridge matches your tonearm for you to extract maximum performance. While the decision between MM, MI and MC, and of course stylus profile, depends very much on the sound balance that you want to hear for playback.

Careful pairing of output voltage and impedance matching to your phono stage is of equal importance. Too much gain will limit headroom causing distortion and add noise, to little will just result in low levels of replay and lack of dynamics. While MM and MI cartridges are generally very tolerant to loading, incorrect MC loading can provide loss of top end response, impact bass performance, image depth and mid-range.

Ideally try to find a vendor that can provide you with an audition of the cartridge in a similar arm and/or one with a generous return policy.  Specifications and reviews are for our eyes, but its our ears that listen.

Click here to see what I am looking to replace.

So what am I giving serious thought to, and eventually purchased?

• Hana SL (low MC & low compliance) – Excel Sound Corporation, Japan – (purchased – review here)
• Sumiko EVO III (low MC & low compliance)
• Musical Fidelity MX-VYNL pre-amp – (purchased – review here)
• Soundsmith MCP2 pre-amp.

Sumiko Blue Point Special – EVO III Low Output MC Cartridge

Hana SL Low Output MC Cartridge

For more information on turntables, arms and cartridges see the following posts:

• Cartridge Alignment – An Introduction
• Tonearms 101 – An Introduction
• Optical Turntables and Laser Cartridges-Are They The Future?