One Last Dip in the Groove

One Last Dip in the Groove
Two old friends of mine recently asked me for advice on setting up a vinyl playback system, so I explained what sounds best and how to do it cheaply. One of them loves Martin Scorsese-directed films so much that I just knew his renewed interest in records has a lot to do with the new Scorsese-created TV show called Vinyl– to such an extent that I did not even bother asking. Anyway, since most of the advice I gave was about phono cartridges, and how they can sound wildly different and can employ differing technologies, it occurred to me that I should make one final blog post related to vinyl records – and make it specifically about phono cartridges (the most critical aspect affecting sound quality). So here goes:

Moving Magnet Cartridges
Most phono cartridges you have ever heard – or the most common – are “moving magnet cartridges.” These are not the cartridges most audiophiles tend to use, although certain classic ones have a devoted following (such as the Shure V15 series). Generally speaking, moving magnet cartridges are the lowest rung on the ladder for sound quality. Many use a cheap, conical stylus attached to an aluminum cantilever which will do the most bare bones job of tracking a record accurately, giving a rolled off sound quality (more on turntable needles later). This is why, in most cases, moving magnet cartridges are the cheapest. Moving magnet cartridges do not sound extremely detailed or lush, but they tend to sound warm and mellow and a bit lush - and are mostly affordable!

A moving magnet cartridge, as the name indicates, employs a small magnet attached to the backside of a record needle. When the needle moves back and forth on the groove, the magnet moves to and fro between two small coils (left and right channels). A small AC current is created by this action which travels to the pins on the backside of the cartridge, down through the tonearm and out to a phono stage or preamp (which uses an RIAA curve, which essentially boosts the lower frequencies and a bit of the mid frequencies of the signal in order to produce a flat frequency response). The phono stage/preamp also boosts the gain (effectively the volume of the signal).

Moving magnet cartridges, just like any other cartridges, can sound different depending on the materials used in the makeup of the cartridge. Different types of wire with differing purities of metal are used for the coils and tiny wires used in different cartridges. This can make the cartridge sound warmer, colder, more detailed, more dark or more bright. Even the cartridge bodies affect sound quality. That is why some higher-end cartridges are placed in wood, aluminum or other material bodies (they typically range from plastic to very exotic natural materials); the natural resonance frequencies of these materials color the sound a bit and you would choose a body type depending on your listening preference.

The sound of a moving magnet cartridge, just like any other cartridge, can be greatly changed by upgrading the needle. One way to do this is by upgrading the cantilever (the rod part of the needle) to a thinner and lower mass and of better dampened material; the other is upgrading the stylus (the actual tiny needle part at the end of the cantilever that tracks the groove) to one that tracks better. Such changes can make a cartridge sound much more detailed. For instance you will notice details you have never heard from your records before. The very top of the line turntable needles give a sound quality that seems to provide as much detail as a high resolution digital file does, or close enough. There are various stylus profiles, such as conical, elliptical, line contact, shibata and micro ridge, to name a few.

Up until recently a company called Jico in Japan would sell very high-end cartridge needles that you could swap into certain moving magnet cartridges called SAS (Super Analog Stylus) – but unfortunately, at the time I write this blog post, the SAS is discontinued.

Moving Coil Cartridges
Moving Coil cartridges have traditionally been the audiophile’s choice in phono cartridges and are usually not what most beginners use. They can be very expensive (in the thousands), but some are as affordable as most moving magnet cartridges. Instead of a moving magnet, a moving coil is seated around the cantilever back inside the cartridge body (which is the exact opposite of a moving magnet design). When the stylus moves the movement of the cantilever moves the coils and a signal is generated. A benefit of this design is that the coils are a lower mass than in a moving magnet (in fact they are placed the exact opposite where the coils are placed in a moving magnet design, with the magnets seated near the coils). This provides a more detailed sound, and for some reason moving coil cartridges can sound incredibly lush, warm and beguiling. In fact, they are my favorite sounding cartridges. But there are a few complications involved in using them. Most are “ low output ” – so low output that the small AC signal they pass needs an additional boost in gain before the phono stage, using a device called a step up transformer (some phono preamps have a built in moving coil cartridge input where the gain is boosted so you do not need a separate step up transformer). Some moving coil cartridges are “high output ”; they sound great, no step up transformer is needed and they will work in any moving magnet phono stage (these would be my first recommendation to someone wanting to enjoy listening to their records on the cheap). Low output moving coil cartridges generally sound better however.

Moving Iron Cartridges
A moving iron cartridge has a design just like a moving magnet cartridge, but instead of a moving magnet sitting on the back end of the cantilever, it is a very small piece of iron. And the iron piece can be made very, very small. The advantage of this is that the cartridge needle has less mass on top of it, allowing it to track the record more easily and accurately. The only high end moving iron cartridge I have tried was a very good performer but sounded a little too cold for my taste, even when housed in a wooden body.

Strain Gauge Cartridges
Strain gauge cartridges use a radically different design than other phono cartridges. And they do not work in a traditional preamp. They require a strain gauge preamp which sends a DC voltage out to the cartridge pins. The displacement of the stylus as it moves on the record grooves modulates this DC signal - which effectively creates the audio signal in the strain gauge preamp, where it then gets converted to AC and sent out to an amplifier or receiver. Strain gauge cartridges do not require an RIAA correction curve. There is also no mass on top of the needle (no magnet, coils or piece of iron), which makes tracking the record accurately easier. Because of all of these factors, the audio signal generated by strain gauge cartridges is just about the clearest and “close ” sounding I have ever heard a record sound. However, they tend to sound too CD-like for my taste. There are vintage strain gauge preamp and cartridges one can buy affordably. On the other hand I know of one company that makes new ones and the cost is in the several thousands of dollars. I made my own strain gauge preamp once and ultimately I found the sound not to my liking. But others would disagree. Technically they are really excellent.

I hope this post proves useful to you in buying your first or next phono cartridge. If you ever wind up banging and breaking your phono cartridge’s needle, do not panic. There are a few companies you can find online that can retip your cartridge with stunning results, although it will cost you a few hundred dollars and the wait can be a few months. In my case I eventually taught myself how to retip my own cartridges, and the process taught me a lot about how phono cartridges work. And the hobby is still a lot of fun. Keep those records spinning!

-Jay Oliver


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