Punter
Active Member
- Joined
- Jul 19, 2022
- Messages
- 236
- Likes
- 1,156
The concept of a needle running in a modulated groove has been around since the first wax drum recorders were launched by the Edison Company in 1877. The original stylus was an assembly with a bar and the stylus attached. Play-only styli were rounded in profile while record capable styli were squared off to provide a cutting surface to remove wax from a blank cylinder. The stylus mounted on a hinged plate and was coupled to a foil diaphragm which vibrated in sympathy with the vertically modulated groove on the drum. Mounted on the diaphragm housing was a horn that acoustically amplified the audio. A headset could also be attached to the same mount via a hose for more personal listening.
As the technology of recorded music changed from the drum to the disc, the mechanics of the stylus changed also. The disc groove was modulated laterally so the arrangement of the stylus and diaphragm was flipped on its side.
The principal of operation was the same but as the surface speed and duration of the disk was higher so the fiddly arrangement of the stylus on the drum phonograph was replaced with disposable steel styli that were supplied in bulk, around 200 per can on average.
Needles came in different grades, loud, medium and soft which related to their shank diameter. A thicker shank transferred more energy to the diaphragm but at the cost of accelerated wear. Needles came in this sort of quantity because a conscientious user would change the needle for every play of a disk. It was possible to get 2-3 plays but the risk of damaging the record was high if this number was exceeded. A lateral cut 78 would be showing noticeable signs of wear after about 30 plays with loud needles, 40 plays with medium needles, and 50 plays with soft needles.
The peak of phonograph needles was the “Tungstone” sold by Victor. They were touted as being good for two hundred plays but in reality they lasted for roughly 40-60. The Tungstone stylus had a steel shank but a tip of metallic tungsten which has a Rockwell hardness of 31 as opposed to steel which is around 58 depending on the alloy. The tungsten was easier on the groove surface and could be used until the tip was worn away. Speaking of wear, the amount of pressure on the needle of a phonograph was significant compared to a more modern tonearm, up to 100 grams.
With the advent of the “Microgroove” LP and electronic amplification, a new transducer was needed as well as a new type of stylus. Columbia Records released the first long-playing “Vinylite” microgroove record, spinning at 33 1/3 revolutions per minute and holding about 23 minutes each side, in June, 1948. RCA had refused to collaborate with Columbia and counterpunched with their 45rpm record but by the summer of 1949 it was obvious that the 33.3 rpm LP was becoming the dominant format. Both of these competing formats would have been useless without a method of playing them though. Unsurprisingly, the development of the microgroove record was concurrent with the development of the players. Columbia chose the Philco Company to partner with and also made the choice of building a catalogue of music prior to releasing the new Vinylite disc to the public. Philco produced console style machines and portables which subsequently had four speeds to make them compatible with all of the new disc formats which were battling it out in “the disc wars” where there were four competing speeds.
From the consumers perspective, the stylus and pickup on the tonearm was of little interest but it was a crucial part of the player and the format. First and foremost, the pickup had transitioned to an electromechanical device rather than purely mechanical. In this early stage the pickups were commonly of the crystal or ceramic type. The stylus itself was often made from sapphire but some were made of osmium even though it was prone to wearing out fairly quickly.
A crystal cartridge employs a piezoelectric crystal to convert the vibration from the stylus to an electrical signal. The early Philco cartridges used Rochelle Salt (Sodium Potassium Tartrate) as the crystal element. Due to its high sensitivity, the output from the pickup was in the range of 1 to 3 Volts, and capacitance in the order of 800 pF. The crystal had an almost perfect built-in mechanical equalization. All that an engineer had to do was to feed the signal to the grid of a valve triode which the crystal would drive easily. The alternative to the crystal cartridge appeared in 1946 called the Sonotone, using ceramic titanates to produce the piezoelectric effect. The only downside with these cartridges was a much lower output in the order of a few hundred milli-volts, and capacitance as high as a few thousand pico-farads. The cartridge produced 0.95 V (at 1 kHz using RCA test record), and had a flat response to records cut with LP, NAB, and AES, characteristics. Subsequently, a more capable amplifier was needed to make it useful. Unlike magnetic cartridge (MM or MC), where the output is proportional to the velocity of the stylus movement; the output of a ceramic (piezo-electric) cartridge is proportional to the amplitude of the stylus deflection. The signal generated by a piezo-electric cartridge is almost inherently flat. Hence, ceramic pickups are considered constant amplitude devices because, for the most part, they do not require equalization.
Even though there was a prevalence of piezo cartridges, it didn’t stop equipment manufacturers looking for a better way and this saw the development of a moving coil cartridge by Ortofon.
Ortofon launched the cartridge in 1948 designed specifically for mono microgroove vinyl records. Indeed, Ortofon filed a patent in 1946 to cover the design.
As with all things, technology marched on and in the early ‘50’s the stereo LP was born. This time however, due to the technology behind the stereo LP, the pickup needed a significant re-think not only as to the electromechanical aspects but also the method by which the stereo signal was imprinted on the disc and how it would be retrieved. Shure partnered with Columbia records to produce the first stereo phono cartridges, the M3D, which was released to the market at the same time as the launch of the stereo long playing vinyl record. As I outlined in a previous post, stereo LP’s weren’t a runaway success due to the inertia caused by so much mono equipment being in people’s houses. The first stereo pressings came out of a small outfit in new York called “Audio Fidelity Records”.
As I mentioned in my “The Truth About Vinyl Records” post, the job of creating a groove in a vinyl disc that contained the information for two separate channels but would still reproduce a mono signal was solved by recording a vector matrix onto the disc rather than two separate channels. If the engineers had taken the easy way of using the lateral as one channel and the vertical as the other, a user playing on a mono device would only hear the lateral channel. Ultimately, a brilliant solution was conceived, albeit one requiring a bit of clever mathematics. The “LEFT” (L) and “RIGHT” (R) channels can be rearranged as “side” (S) and “mid” (M). Mid refers to the vertical movement of the stylus and side refers to the lateral movement. “side” contains everything that’s the same in both L and R, and “mid” contains everything that’s different between them. To encode into mid-side: (L+R)/2 = S and (L-R)/2 = M. To decode back into stereo, M+S = L and M-S = R. If the stereo signal is converted into mid/side for cutting, both aforementioned problems are solved. The “side” channel moves in the lateral side-to-side dimension, resulting in perfect compatibility on a mono player. Remember: S = (L+R)/2. The “mid” signal moves in the vertical dimension, and as long as bass frequencies are kept in-phase and close to the middle of the stereo field, there will be few large vertical excursions which might cause the stylus to skip. The brilliance of this is that the cutting head in the lathe encodes the matrix mechanically into the groove and it is then decoded mechanically by the stereo pickup. The electromechanical servos in the cutting head are at 45 degrees to each other and so are the active elements in the pickup.
As far as stereo pickups went, there were two competing types of stereo cartridge the moving coil (MC) and the moving magnet (MM).
In the MC design, the two coils are attached to the cantilever and, by oscillating between the two magnets, they form the modulated signal. Due to the internal construction, the STYLUS cannot be replaced as it is attached to the cartridge. To reduce the weight on the moving parts, the number of coil turns is restricted, which generates a fairly low output signal, between 0.25 mV and 0.55 mV. The coils also have to be electrically connected to the output terminals of the assembly making the internals of the MC type very delicate. More recently, manufacturers have boosted the magnetic field of their MC cartridges. They are known as High Output MC cartridges. Their output level spans between 0.80 mV and 3.3 mV
Pros:
Advantages:
Weak points:
The moving coil and moving magnet designs have become the most common now but they weren’t the only designs on the market in the early days. There were a few alternative magneto-mechanical devices vying for commercial success.
IM Induced magnet cartridges (derived from MC cartridges).
In theory, they are an upgrade. Instead of the coil, a small soft iron rod is attached to the cantilever and moves within the field of a powerful and heavy permanent magnet. This setup reduces the weight of the cantilever, improving their behaviour for treble frequencies and transients. However, these cartridges are heavy and must be associated with heavy tonearms.
VR Variable Reluctance cartridges
Variable reluctance cartridges are neither MM, MC, nor IM cartridges. Their magnetic circuit consists of a thin soft iron rod that moves inside the air gap of a magnetic circuit polarised by a permanent magnet. These cartridges have low sensitivity, and the stylus is quite difficult to replace (DECCA London MK5, B&O MMC 20S).
VMS Variable magnetic Shunt cartridges
Developed by ORTOFON to overcome the flaws of MM and MC cartridges. In this case, the magnets and coils are stationary. When the cantilever starts moving under the effect of the modulation in the record groove, it short-circuits part of the magnetic fields generated in the ring magnet, which creates electric signals in the coils that recreate the record's original recording. This solution reduces the weight of the stylus/cantilever assembly and the cartridge, which makes it compatible with almost all tonearm types.
MI Moving Iron cartridges
Very similar to VMS cartridges. This solution uses very specific magnets and was invented by Norman C. Pickering. Nowadays, the principle is used by GRADO.
Despite these variations, MM and MC cartridges maintained their popularity and became the most utilised designs. I think when all of this innovation was going on, we are seeing the seeds of the Audiophile hobby with users experimenting with their equipment and being more critical of the audio quality their gear was reproducing. Ceramic cartridges were not dead in the stereo era however and models were created with two piezo elements arranged to capture the stereo signal but these were (and are) mostly found on low-cost equipment.
Another significant development in the world of cartridges was the removable head shell which became necessary to swap between 33 and 78rpm discs. The stylus tip profile was different for each record type and 33’s wouldn’t play with a 78 stylus as the tip was much larger. This was more of an issue in the mono days but the utility of being able to detach the cartridge easily from the tonearm was particularly useful in radio studios to replace styli and for the growing number of “HiFi buffs” wanting to try out new and better cartridges. This development also kicked off a de facto ½” standard for cartridge mounting provisions which is still used today.
Mechanically, all these types of cartridge/stylus combinations worked in a similar fashion. The stylus was mounted on the end of a thin metal rod called the cantilever which had a pivot to permit movement. In the case of an MM cartridge the cantilever passed through a pivot made of high durometer rubber or a synthetic equivalent which was roughly at the centre of the cantilever. On the opposite end of the cantilever was mounted a tiny permanent magnet which is flanked by a pair of coils disposed at 45 degrees from each other. In the case of an MC the pivot is at the opposite end of cantilever to the stylus, the coil is mounted next to the pivot and is flanked by two permanent magnets in the same 45 degree configuration as the MM design. The vibrations of the cantilever, driven by the stylus, cause a weak signal to be produced by the coil element on the cantilever.
By the time stereo LP’s had begun to penetrate the market, the stylus element of the pickup was almost universally made of diamond. Sapphire was still around but used mainly on low cost gear. The diamond stylus could be made of either gem or industrial quality material. Industrial diamond is usually a translucent brown colour while gem quality is transparent. The other variation in this element is the mounting of the diamond which can be either “bonded” or “nude”. In the bonded type, the shaped diamond is bonded to a post or pad on the cantilever and in the case of a nude diamond, it is staked through the cantilever.
Having dealt with the electromechanical aspects of the stereo phono cartridge it’s time to explore the business end, the stylus. Debate still rages today with respect to the tip profile of the stylus. The tip diameter and basic angles have to conform to the groove width which is around 0.003in and is really set by the profile of the cutter on the mastering lathe. But this is really the only accepted common dimension from there, we delve into the murky world of spherical, elliptical and other exotic profile shapes. As with all things associated with playing vinyl records, different tip profiles have their pros and cons and also their champions and detractors so it’s a somewhat tricky proposition to choose one design over another. The driving force behind the development of stylus tip shapes comes from the desire to maintain constant contact with the groove sides and thereby achieve optimal tracking and by dint, accurate reproduction. As a note, it is not desirable for the stylus tip to ride in the bottom of the groove, the stylus should float along with its tip clear of the vee of the groove. If it rides down to the bottom, it will increase noise and accelerate wear of the disc. The groove itself does not have a hard angle at the bottom but a slight radius. The actual force on the contact patch where the stylus touches the vinyl can be around 42tons with a tracking force of 7 grams.
The simplest profile is the conical tip. While it conforms to the exact size and shape of the cut groove, conical styli tend to have a larger tip radius than an elliptical design. The primary downside of the conical tip is that the contact area is quite small and is basically two circular dots either side of the stylus. The elliptical tip generally has a smaller tip radius and so sits a little deeper in the groove. The contact area is larger and consists of two elliptical patches either side. A later development was the “Shibata” profile which is classified a “line” contact stylus the trailing part of the of the tip is chamfered on either side behind the contact patches, this is to promote better tracking by reducing the effect of the stylus being “pinched” as it tracks higher frequencies. The most modern tip shape is the “Micro Ridge” or “Optimised” which is also classified a as line contact stylus but in this case the tip shape is formed so that the only material that can touch the disc is the contact patches. The front and rear of the contact patches is carved away. The other advantage of this kind of detailed construction is that tracking mass can be reduced while still achieving high tracking accuracy.
It’s pretty well settled that the advent of solid state amplifiers really marked the start of the mass market HiFi enthusiast. Solid state amplifiers were a far more approachable technology than valves and it was also possible to include features in a solid state amp that would be difficult to implement in a valve design, not to mention increasing the cost. Also, valves were now considered old fashioned and the appeal of having an amplifier without components that would wear out and fail was strong. As manufacturers piled into the market, there were improvements across all aspects of HiFi equipment and new speaker designs were joined by improved turntables, radio receivers and eventually tape decks. There was no question however that the pickup was seen as an essential component to “get right” on your setup. With the vinyl LP as the gold standard, the swelling audiophile market recognised the cartridge as the critical first stage in reproduction. Established manufacturers flourished and specialised manufacturers began to pop up with their own take, aimed at wooing the HiFi punters into believing they had the answer to perfect reproduction.
As the pickup had taken its lofty place in the HiFi hierarchy the debates over the stylus, the method (MM or MC) and other factors took on great importance. One of these factors was “compliance”. At one stage, this factor assumed centre stage as it was deemed that no less than your entire tonearm should be matched to your chosen cartridge based on its compliance. Compliance itself was nothing more than the relative stiffness of the material used to form the pivot for the cantilever. The lower the stiffness, it was deemed, the higher the output by dint of a greater range of movement and velocity which would provide a cleaner signal. Manufacturers tried to outdo each other by creating higher and higher compliance designs. New, lighter tonearms were needed to match these high compliance pickups and other factors like anti-skating and tonearm resonance needed to be considered so it could do its job accurately.
Total (tonearm system) mass can be calculated by using the formula M = 10⁶ : (f² x (2π)² x C where:
f - Cartridge resonance frequency in Hz
π - 3.14159265359...
C - Cartridge compliance in µm/mN
NB: Total (tonearm system) mass M is a sum of Mass of cartridge, Mass of head shell and screws and Effective mass of tone arm (all values in gram)
As technology progressed and HiFi systems became more technically advanced, the pickup continued to evolve but in essence, the improvements were largely in the details and in some cases materials (beryllium and boron cantilevers for example) Makers continued to tinker with the stylus and developed subtly different shapes. This activity probably peaked in the 80’s when vinyl still ruled the roost with names like Dynavector and Glanz becoming some of the prominent manufacturers. Behind this though was either an MM or MC architecture. It would be interesting to see the relative fortunes of companies as the vinyl record gave way to the CD, I’m certain most of them thought they’d hit their “Kodak” moment. But when you do some research now, it’s obvious that there’s still a thriving business in phono cartridges, no doubt assisted by the “renaissance” of vinyl.
As always, I don't intend this post to be the last word on anything, I intend these articles to be the start of conversation and knowledge sharing. I'm happy to be corrected or schooled on anything herein.
As the technology of recorded music changed from the drum to the disc, the mechanics of the stylus changed also. The disc groove was modulated laterally so the arrangement of the stylus and diaphragm was flipped on its side.
The principal of operation was the same but as the surface speed and duration of the disk was higher so the fiddly arrangement of the stylus on the drum phonograph was replaced with disposable steel styli that were supplied in bulk, around 200 per can on average.
Needles came in different grades, loud, medium and soft which related to their shank diameter. A thicker shank transferred more energy to the diaphragm but at the cost of accelerated wear. Needles came in this sort of quantity because a conscientious user would change the needle for every play of a disk. It was possible to get 2-3 plays but the risk of damaging the record was high if this number was exceeded. A lateral cut 78 would be showing noticeable signs of wear after about 30 plays with loud needles, 40 plays with medium needles, and 50 plays with soft needles.
The peak of phonograph needles was the “Tungstone” sold by Victor. They were touted as being good for two hundred plays but in reality they lasted for roughly 40-60. The Tungstone stylus had a steel shank but a tip of metallic tungsten which has a Rockwell hardness of 31 as opposed to steel which is around 58 depending on the alloy. The tungsten was easier on the groove surface and could be used until the tip was worn away. Speaking of wear, the amount of pressure on the needle of a phonograph was significant compared to a more modern tonearm, up to 100 grams.
With the advent of the “Microgroove” LP and electronic amplification, a new transducer was needed as well as a new type of stylus. Columbia Records released the first long-playing “Vinylite” microgroove record, spinning at 33 1/3 revolutions per minute and holding about 23 minutes each side, in June, 1948. RCA had refused to collaborate with Columbia and counterpunched with their 45rpm record but by the summer of 1949 it was obvious that the 33.3 rpm LP was becoming the dominant format. Both of these competing formats would have been useless without a method of playing them though. Unsurprisingly, the development of the microgroove record was concurrent with the development of the players. Columbia chose the Philco Company to partner with and also made the choice of building a catalogue of music prior to releasing the new Vinylite disc to the public. Philco produced console style machines and portables which subsequently had four speeds to make them compatible with all of the new disc formats which were battling it out in “the disc wars” where there were four competing speeds.
From the consumers perspective, the stylus and pickup on the tonearm was of little interest but it was a crucial part of the player and the format. First and foremost, the pickup had transitioned to an electromechanical device rather than purely mechanical. In this early stage the pickups were commonly of the crystal or ceramic type. The stylus itself was often made from sapphire but some were made of osmium even though it was prone to wearing out fairly quickly.
A crystal cartridge employs a piezoelectric crystal to convert the vibration from the stylus to an electrical signal. The early Philco cartridges used Rochelle Salt (Sodium Potassium Tartrate) as the crystal element. Due to its high sensitivity, the output from the pickup was in the range of 1 to 3 Volts, and capacitance in the order of 800 pF. The crystal had an almost perfect built-in mechanical equalization. All that an engineer had to do was to feed the signal to the grid of a valve triode which the crystal would drive easily. The alternative to the crystal cartridge appeared in 1946 called the Sonotone, using ceramic titanates to produce the piezoelectric effect. The only downside with these cartridges was a much lower output in the order of a few hundred milli-volts, and capacitance as high as a few thousand pico-farads. The cartridge produced 0.95 V (at 1 kHz using RCA test record), and had a flat response to records cut with LP, NAB, and AES, characteristics. Subsequently, a more capable amplifier was needed to make it useful. Unlike magnetic cartridge (MM or MC), where the output is proportional to the velocity of the stylus movement; the output of a ceramic (piezo-electric) cartridge is proportional to the amplitude of the stylus deflection. The signal generated by a piezo-electric cartridge is almost inherently flat. Hence, ceramic pickups are considered constant amplitude devices because, for the most part, they do not require equalization.
Even though there was a prevalence of piezo cartridges, it didn’t stop equipment manufacturers looking for a better way and this saw the development of a moving coil cartridge by Ortofon.
Ortofon launched the cartridge in 1948 designed specifically for mono microgroove vinyl records. Indeed, Ortofon filed a patent in 1946 to cover the design.
As with all things, technology marched on and in the early ‘50’s the stereo LP was born. This time however, due to the technology behind the stereo LP, the pickup needed a significant re-think not only as to the electromechanical aspects but also the method by which the stereo signal was imprinted on the disc and how it would be retrieved. Shure partnered with Columbia records to produce the first stereo phono cartridges, the M3D, which was released to the market at the same time as the launch of the stereo long playing vinyl record. As I outlined in a previous post, stereo LP’s weren’t a runaway success due to the inertia caused by so much mono equipment being in people’s houses. The first stereo pressings came out of a small outfit in new York called “Audio Fidelity Records”.
As I mentioned in my “The Truth About Vinyl Records” post, the job of creating a groove in a vinyl disc that contained the information for two separate channels but would still reproduce a mono signal was solved by recording a vector matrix onto the disc rather than two separate channels. If the engineers had taken the easy way of using the lateral as one channel and the vertical as the other, a user playing on a mono device would only hear the lateral channel. Ultimately, a brilliant solution was conceived, albeit one requiring a bit of clever mathematics. The “LEFT” (L) and “RIGHT” (R) channels can be rearranged as “side” (S) and “mid” (M). Mid refers to the vertical movement of the stylus and side refers to the lateral movement. “side” contains everything that’s the same in both L and R, and “mid” contains everything that’s different between them. To encode into mid-side: (L+R)/2 = S and (L-R)/2 = M. To decode back into stereo, M+S = L and M-S = R. If the stereo signal is converted into mid/side for cutting, both aforementioned problems are solved. The “side” channel moves in the lateral side-to-side dimension, resulting in perfect compatibility on a mono player. Remember: S = (L+R)/2. The “mid” signal moves in the vertical dimension, and as long as bass frequencies are kept in-phase and close to the middle of the stereo field, there will be few large vertical excursions which might cause the stylus to skip. The brilliance of this is that the cutting head in the lathe encodes the matrix mechanically into the groove and it is then decoded mechanically by the stereo pickup. The electromechanical servos in the cutting head are at 45 degrees to each other and so are the active elements in the pickup.
As far as stereo pickups went, there were two competing types of stereo cartridge the moving coil (MC) and the moving magnet (MM).
In the MC design, the two coils are attached to the cantilever and, by oscillating between the two magnets, they form the modulated signal. Due to the internal construction, the STYLUS cannot be replaced as it is attached to the cartridge. To reduce the weight on the moving parts, the number of coil turns is restricted, which generates a fairly low output signal, between 0.25 mV and 0.55 mV. The coils also have to be electrically connected to the output terminals of the assembly making the internals of the MC type very delicate. More recently, manufacturers have boosted the magnetic field of their MC cartridges. They are known as High Output MC cartridges. Their output level spans between 0.80 mV and 3.3 mV
Pros:
- Very low distortion level
- Excellent transient response, very good dynamic range
- Very good tonal balance, soft sound with a lot of density
- Low output level, requires a preamp or transformer (except for some references)
- Stylus cannot be replaced
- Expensive
Advantages:
- High sensitivity, high output level
- Stylus is easy to replace
- Robust
- Affordable price
Weak points:
- Variable response consistency
- High distortion (at the time)
The moving coil and moving magnet designs have become the most common now but they weren’t the only designs on the market in the early days. There were a few alternative magneto-mechanical devices vying for commercial success.
IM Induced magnet cartridges (derived from MC cartridges).
In theory, they are an upgrade. Instead of the coil, a small soft iron rod is attached to the cantilever and moves within the field of a powerful and heavy permanent magnet. This setup reduces the weight of the cantilever, improving their behaviour for treble frequencies and transients. However, these cartridges are heavy and must be associated with heavy tonearms.
VR Variable Reluctance cartridges
Variable reluctance cartridges are neither MM, MC, nor IM cartridges. Their magnetic circuit consists of a thin soft iron rod that moves inside the air gap of a magnetic circuit polarised by a permanent magnet. These cartridges have low sensitivity, and the stylus is quite difficult to replace (DECCA London MK5, B&O MMC 20S).
VMS Variable magnetic Shunt cartridges
Developed by ORTOFON to overcome the flaws of MM and MC cartridges. In this case, the magnets and coils are stationary. When the cantilever starts moving under the effect of the modulation in the record groove, it short-circuits part of the magnetic fields generated in the ring magnet, which creates electric signals in the coils that recreate the record's original recording. This solution reduces the weight of the stylus/cantilever assembly and the cartridge, which makes it compatible with almost all tonearm types.
MI Moving Iron cartridges
Very similar to VMS cartridges. This solution uses very specific magnets and was invented by Norman C. Pickering. Nowadays, the principle is used by GRADO.
Despite these variations, MM and MC cartridges maintained their popularity and became the most utilised designs. I think when all of this innovation was going on, we are seeing the seeds of the Audiophile hobby with users experimenting with their equipment and being more critical of the audio quality their gear was reproducing. Ceramic cartridges were not dead in the stereo era however and models were created with two piezo elements arranged to capture the stereo signal but these were (and are) mostly found on low-cost equipment.
Another significant development in the world of cartridges was the removable head shell which became necessary to swap between 33 and 78rpm discs. The stylus tip profile was different for each record type and 33’s wouldn’t play with a 78 stylus as the tip was much larger. This was more of an issue in the mono days but the utility of being able to detach the cartridge easily from the tonearm was particularly useful in radio studios to replace styli and for the growing number of “HiFi buffs” wanting to try out new and better cartridges. This development also kicked off a de facto ½” standard for cartridge mounting provisions which is still used today.
Mechanically, all these types of cartridge/stylus combinations worked in a similar fashion. The stylus was mounted on the end of a thin metal rod called the cantilever which had a pivot to permit movement. In the case of an MM cartridge the cantilever passed through a pivot made of high durometer rubber or a synthetic equivalent which was roughly at the centre of the cantilever. On the opposite end of the cantilever was mounted a tiny permanent magnet which is flanked by a pair of coils disposed at 45 degrees from each other. In the case of an MC the pivot is at the opposite end of cantilever to the stylus, the coil is mounted next to the pivot and is flanked by two permanent magnets in the same 45 degree configuration as the MM design. The vibrations of the cantilever, driven by the stylus, cause a weak signal to be produced by the coil element on the cantilever.
By the time stereo LP’s had begun to penetrate the market, the stylus element of the pickup was almost universally made of diamond. Sapphire was still around but used mainly on low cost gear. The diamond stylus could be made of either gem or industrial quality material. Industrial diamond is usually a translucent brown colour while gem quality is transparent. The other variation in this element is the mounting of the diamond which can be either “bonded” or “nude”. In the bonded type, the shaped diamond is bonded to a post or pad on the cantilever and in the case of a nude diamond, it is staked through the cantilever.
Having dealt with the electromechanical aspects of the stereo phono cartridge it’s time to explore the business end, the stylus. Debate still rages today with respect to the tip profile of the stylus. The tip diameter and basic angles have to conform to the groove width which is around 0.003in and is really set by the profile of the cutter on the mastering lathe. But this is really the only accepted common dimension from there, we delve into the murky world of spherical, elliptical and other exotic profile shapes. As with all things associated with playing vinyl records, different tip profiles have their pros and cons and also their champions and detractors so it’s a somewhat tricky proposition to choose one design over another. The driving force behind the development of stylus tip shapes comes from the desire to maintain constant contact with the groove sides and thereby achieve optimal tracking and by dint, accurate reproduction. As a note, it is not desirable for the stylus tip to ride in the bottom of the groove, the stylus should float along with its tip clear of the vee of the groove. If it rides down to the bottom, it will increase noise and accelerate wear of the disc. The groove itself does not have a hard angle at the bottom but a slight radius. The actual force on the contact patch where the stylus touches the vinyl can be around 42tons with a tracking force of 7 grams.
The simplest profile is the conical tip. While it conforms to the exact size and shape of the cut groove, conical styli tend to have a larger tip radius than an elliptical design. The primary downside of the conical tip is that the contact area is quite small and is basically two circular dots either side of the stylus. The elliptical tip generally has a smaller tip radius and so sits a little deeper in the groove. The contact area is larger and consists of two elliptical patches either side. A later development was the “Shibata” profile which is classified a “line” contact stylus the trailing part of the of the tip is chamfered on either side behind the contact patches, this is to promote better tracking by reducing the effect of the stylus being “pinched” as it tracks higher frequencies. The most modern tip shape is the “Micro Ridge” or “Optimised” which is also classified a as line contact stylus but in this case the tip shape is formed so that the only material that can touch the disc is the contact patches. The front and rear of the contact patches is carved away. The other advantage of this kind of detailed construction is that tracking mass can be reduced while still achieving high tracking accuracy.
It’s pretty well settled that the advent of solid state amplifiers really marked the start of the mass market HiFi enthusiast. Solid state amplifiers were a far more approachable technology than valves and it was also possible to include features in a solid state amp that would be difficult to implement in a valve design, not to mention increasing the cost. Also, valves were now considered old fashioned and the appeal of having an amplifier without components that would wear out and fail was strong. As manufacturers piled into the market, there were improvements across all aspects of HiFi equipment and new speaker designs were joined by improved turntables, radio receivers and eventually tape decks. There was no question however that the pickup was seen as an essential component to “get right” on your setup. With the vinyl LP as the gold standard, the swelling audiophile market recognised the cartridge as the critical first stage in reproduction. Established manufacturers flourished and specialised manufacturers began to pop up with their own take, aimed at wooing the HiFi punters into believing they had the answer to perfect reproduction.
As the pickup had taken its lofty place in the HiFi hierarchy the debates over the stylus, the method (MM or MC) and other factors took on great importance. One of these factors was “compliance”. At one stage, this factor assumed centre stage as it was deemed that no less than your entire tonearm should be matched to your chosen cartridge based on its compliance. Compliance itself was nothing more than the relative stiffness of the material used to form the pivot for the cantilever. The lower the stiffness, it was deemed, the higher the output by dint of a greater range of movement and velocity which would provide a cleaner signal. Manufacturers tried to outdo each other by creating higher and higher compliance designs. New, lighter tonearms were needed to match these high compliance pickups and other factors like anti-skating and tonearm resonance needed to be considered so it could do its job accurately.
Total (tonearm system) mass can be calculated by using the formula M = 10⁶ : (f² x (2π)² x C where:
f - Cartridge resonance frequency in Hz
π - 3.14159265359...
C - Cartridge compliance in µm/mN
NB: Total (tonearm system) mass M is a sum of Mass of cartridge, Mass of head shell and screws and Effective mass of tone arm (all values in gram)
As technology progressed and HiFi systems became more technically advanced, the pickup continued to evolve but in essence, the improvements were largely in the details and in some cases materials (beryllium and boron cantilevers for example) Makers continued to tinker with the stylus and developed subtly different shapes. This activity probably peaked in the 80’s when vinyl still ruled the roost with names like Dynavector and Glanz becoming some of the prominent manufacturers. Behind this though was either an MM or MC architecture. It would be interesting to see the relative fortunes of companies as the vinyl record gave way to the CD, I’m certain most of them thought they’d hit their “Kodak” moment. But when you do some research now, it’s obvious that there’s still a thriving business in phono cartridges, no doubt assisted by the “renaissance” of vinyl.
As always, I don't intend this post to be the last word on anything, I intend these articles to be the start of conversation and knowledge sharing. I'm happy to be corrected or schooled on anything herein.
