Cartridge Types

he phono cartridge is the collective name for the stylus, cantilever and generator assembly that is mounted at the end of the tonearm. The stylus is the carefully shaped tip that actually sits in the groove, while the cantilever is the beam to which it is attached and sticks out below or in front of the cartridge body. Just to confuse you, together they are often referred to as a stylus assembly, especially when talking about replacement parts. The cartridge body is the rest of the generator assembly to which the stylus and cantilever are attached and which also mounts the small connecting pins for the tonearm wires. Historically, cartridge bodies were generally boxy in shape, with a can or housing shielding the delicate internals, but these days there are an increasing number of naked-body cartridges that warrant particularly careful handling.

Phono cartridges are about as basic as electrical signal generation gets: a stylus on one end of a lever is used to generate relative movement between a magnet and a set of coils at the other, resulting in a signal that can then be amplified. That signal is incredibly small, the generator producing it also tiny and the micro-engineering involved difficult to appreciate unless you’ve experienced it firsthand. The fact that anything meaningful, let alone something as complex as a full-range musical signal, can be reproduced in this way is little short of miraculous. Fortunately, we don’t need to worry too much about how this happens. Instead, we’re more interested in the results and their implications for setup and interfacing with the rest of the system. For those purposes we can divide cartridges into two basic groups and identify a couple of key parameters that we need to consider: output level and compliance (or how stiff the cartridge suspension is).

Although over the years a number of different topologies have been tried, most cartridges fall into two camps: those that move a magnet relative to an array of coils and those that move the coils relative to a magnet. Each approach offers its own advantages and tradeoffs, and both are widely available. What’s important is that they can require quite different amplification.

Moving-magnet (MM) cartridges – As the name suggests, these work by moving a small but powerful magnet relative to the coils mounted in the cartridge body. It’s an arrangement that offers several advantages. The more turns in the coil, the more signal generated, and as the coils are fixed elements, they can be wound to produce a healthy output level -- normally around 4.0mV. This flexibility in the generator system means that it is easy to define the electrical parameters of MM cartridges and achieve standardized output and interface requirements, simplifying the necessary amplification considerably. All moving-magnet cartridges should be designed to work into the standard 47k-ohm input impedance provided by low-gain (or MM) phono stages. They also offer good mechanical characteristics and a smooth frequency response. They are generally of medium compliance (around 20+ cu), making them compatible with a wide range of medium and low-mass tonearms. The higher the compliance of the cartridge, the softer its suspension and the lower the effective mass of the 'arm required (although these days most 'arms fit the medium-mass description, making mechanical compatibility much less of an issue).

You also find these cartridges referred to as moving-iron designs, which they technically are not, while the moving-flux topology used by Grado is actually different in operation but conforms to the same electrical standards and requirements. Most MM cartridges offer replaceable stylus assemblies, meaning that changing a worn stylus is a simple plug-in operation.

Moving-coil (MC) cartridges – Again, the distinction here is fairly obvious. Instead of mounting a magnet on the other end of the cantilever from the stylus, an array of four small coils is arranged relative to a large, fixed magnet, producing the necessary left and right, positive and negative signals. The advantage is that the coil assembly can be much lighter and thus more responsive to the groove than the magnet used in an MM cartridge. The disadvantage is that low mass also depends on a low turns count, meaning that optimizing the performance of MC cartridges generally means accepting a much lower signal level than you get from MM designs. Because the coils have to be wired to the output pins on the body, it is not possible to offer replacement stylus assemblies for moving-coil designs, although most manufacturers offer an exchange price on the old cartridge against a new model. This does of course mean removing the old cartridge and installing the new one from scratch.

High- (or medium-) output MC cartridges – There are a large number of cartridges described as high-output MC designs. These use larger coils to generate a higher output, but must perform a balancing act to retain the potential benefits of lower moving mass. The result is that although they are designed to interface with a standard-sensitivity, 47k-ohm phono input, they often deliver output levels in the 2.5 to 3.0mV range, rather lower than many MM designs. Although they are often sound more detailed and transparent than the MM alternatives, it is important to ensure that your system has enough gain and a quiet enough phono stage to work with this lower input level.

Low-output MC cartridges – The true thoroughbreds of analog replay, low-output moving-coil cartridges are expensive and demanding when it comes to delivering their best performance. Intent on reflecting every last kink or deviation in the groove wall, they reduce moving mass to the absolute minimum, meaning fewer turns in their coils and a correspondingly lower output. Most low-output cartridges deliver around 0.4mV -- one-tenth of the signal from a MM design, one-10,000th of the signal generated by many CD players! In some cases outputs can drop below 0.2mV, although thankfully that is rare these days, while there is also a trend to (slightly) higher outputs, helped by improved magnet technology and finer wire for winding the coils.

But this low output level is only the start of the problem. Electrical parameters vary enormously, while the cantilever assembly itself is mechanically undamped, making the input impedance of the phono stage a critical factor in achieving an evenly balanced performance and avoiding the rising top-end response that plagued many early MC designs. So, not only does the phono stage have to handle possible outputs ranging from less than 0.2mV up to 0.7mV, often demanding variable gain, it must also offer a range of load impedances, different cartridges demanding anything from 50 ohms to the standard MM setting of 47k ohms. Finally, MC cartridges also use stiffer suspensions that not only demand medium- or high-mass tonearms, but drive more energy into the tonearm assembly, in turn making it a more critical element in the replay chain.

Choosing a top-flight moving-coil cartridge thus becomes a case of matching its potential performance to an appropriate tonearm and the right phono stage -- at least it does if you actually want to hear what the cartridge can really do. Is it worth all the trouble? Yes. Despite the eye-watering cost of really high-end cartridges, working at their best they deliver what is still the finest possible audio reproduction. But that’s an important caveat, and really getting the best from such a cartridge takes considerable care and experience. It’s one situation where the help and advice of a good dealer are invaluable. The better the cartridge, the more important that advice becomes.

Mono cartridges – These days mono cartridges might seem like an anachronism, especially as stereo cartridges will play mono LPs. However, there are good reasons why you might want to play original mono pressings -- and why you should ideally use a mono cartridge to do so.

Although by the 1960s stereo was well established, there were still a large number of pop and jazz records being pressed in mono. For many collectors and critics, these sound better than stereo alternatives (even if the latter are available) with early discs from Dylan, the Stones, the Beach Boys and the Beatles being prime examples. Meanwhile, many of the jazz greats continued to record in mono, with stereo issues simply adopting a hard left-right pan effect that is actually distracting. Although classical labels were early adopters of stereo techniques, they were on a steep learning curve, meaning that early efforts were patchy to say the least, while the equivalent mono recordings benefited from considerable experience, the result being that the mono releases often exhibit better tonal balance and instrumental weight. Add to that the fact that many truly great classical performers were already past their prime when stereo appeared and being able to play mono discs takes on a whole new importance.

But why not just use a stereo cartridge? Because stereo cartridges read both horizontal and vertical information from the groove, necessary to generate the four axes of movement they require (left and right, positive and negative). Mono cartridges only read horizontal information, meaning that the depth of the groove was of no concern to the cutting engineers. The result is that stereo cartridges reading original mono pressings often generate a constant rumble or whooshing sound as they replay spurious vertical information -- a situation made worse by the tiny tip dimensions of many modern cartridges, allowing them to sit even lower in the groove. Play these records with a true mono cartridge that only reads horizontally and you’ll be amazed at the way the noise floor drops away and the instrumental colors and dynamic range improve. It’s like a whole new recording -- and in many ways that’s exactly what it is.

Should you invest in a mono cartridge? Only if:

• You own or plan to invest in original mono pressings. Modern 180-gram reissues of mono recordings are cut with stereo cutting heads and do not benefit from playback with a mono cartridge.

• You have the facility to use it alongside a stereo pickup. That means having an 'arm with an interchangeable headshell or armwand, or a deck that will accept a second tonearm. Ideally, a second tonearm means a second phono input too, so bear that in mind.

• You have the patience and dedication to actually swap the cartridge and/or phono input when required. Only you can answer this question, but be honest with yourself before you spend the money.

If the answer to all of the questions above is yes, then how much should you invest in a mono cartridge, relative to a stereo one? That depends on your record collection and musical interests, but there are many classical and jazz collectors whose mono cartridges cost more than their stereo pickups. Again, only you can make this judgment, but listening to original mono recordings with a true mono cartridge is one those things that you’ll either get or you won’t. Try it and see, but it’s likely that you’ll decide very quickly whether this is something you need -- or not.