12-inch tonearms

8/12/2025. Although we think of the 33⅓ RPM discs as being introduced in 1948, this was only true of the introduction to the public. Discs spinning at 33⅓ RPM pre-dated the commercial LP by twenty years. The 33⅓ RPM speed was originally chosen increase the playing time of shellac records for synchronised audio in the cinema where the system was known as Vitaphone; the first commercially successful apparatus for the "talkies".

Using a disc nearly 16 inches (about 40 cm) in diameter and rotating at 33⅓ RPM, the playing time of one side of a record was increased to 11 minutes which matched the running time of 1000 ft. of film at 90 ft./min (24 frames/s).

Although the Vitaphone system had been overtaken by sound-on-film systems by the mid-thirties in the cinema, the format of the 16 inch, 33⅓ disc was retained in radio broadcasting by the networks who needed a standard format to distribute programmes to affiliated, local stations.

To play these broadcast transcription discs, we need a tonearm longer than the almost standard nine-inch (230mm) type. Twelve-inch (305mm) tonearms were standard in broadcasting; in order that 16" discs could be played, and broadcast players existed right up to the 1960s to contend with these discs.

But what of vinylistas who insist longer tonearms are beneficial — even if we play only 12-inch LPs?

They argue that lateral tracking error is less with a longer arm, so distortion must be commensurately lower too.

There is some truth in this. After all, an infinitely long tonearm would have zero tracking error. But, if we do the maths, as the arm length is increased beyond seven inches (178mm) which is the minimum dimension of a practical tonearm to play LPs, a law of diminishing returns exists. Little practical benefit is gained by an increase over 9 inches (230mm). Indeed, the appreciation of this fact is the grain around which the standard nine-inch tonearm design crystallised. (The maximum angle error in a correctly aligned nine-inch (230mm) tonearm is 2.33° and that due to a 12-inch tonearm 1.75°. This translates to a theoretical improvement in distortion from 0.74% to 0.54%.)

A further advantage is claimed for the longer tonearm. The optimum crank (offset)angle in a nine-inch tonearm is about 23°, whereas the optimum for the longer type is about 17°. Side-thrust (or skating force) is proportional to the tangent of the tonearm offset angle, so the required anti-skating force is reduced by about 26%.† Whilst this is useful, it doesn't eradicate the need for side-thrust compensation. The tone arm design isn't thereby simplified, and the asserted advantage is largely illusory.

†Tan 23° = 0.42; and tan 17° = 0.31

Against these fragile arguments looms the major disadvantage the longer tonearm: it is heavier. Given that the moment of inertia of a thin rod of length L and mass m, perpendicular to the axis of rotation, rotating about one end (as illustrated left) is given by the expression, ⅓mL² , it will be appreciated that to manufacture a 12-inch arm with the equivalent inertia of a 9-inch version, the weight of the arm would have to be about one half of the latter. (This is based on the calculation that (12/9)² = 1.78.)

The case for a longer tonearm turns on the argument that an increase in the mass moment of inertia is justified by a small reduction in theoretical distortion. It's a tenuous argument unless ‐ of course ‐ you need to be able to play 16-inch transcription recordings.

The Needle-drop Handbook contains an extended version of this argument, with the working.

For further information write to sales@phaedrus-audio.com

Amplifier clipping

1/12/2025. Let's start with a simple maxim: power amplifiers must not be driven into overload. Even the advocates for the argument that all amplifiers sound the same are quick to point out that the minimum requirement is that "overload precautions have been observed."

Could this be the missing x-factor in our assessment of power amplifiers and why so many critical listeners claim to be able to hear differences between amplifiers when scientific testing proves they sound the same? Are we inadvertently operating our power amplifiers with inadequate headroom?

We conducted the following experiment* to determine the degree of clipping we might be able to tolerate before declaring the onset of obvious distortion. We prepared examples of tones and music with peaks extending to 0dBFS. We then manipulated the data mathematically to clip all values above various thresholds. The illustration below is an example of the multitrack session in the DAW. Track #1 is of the original audio, track #2 was the value-limited version. Note, track #2 was not produced by dynamic limiting with time constants: this was brutal clipping of all values above a certain level.

Astonishingly, we were able to clip the signal to a remarkable degree before it was obvious that we were doing so. With clipping set at -5dBFS (which means all audio values above 60% amplitude were trimmed), identifying the effect was uncertain.

If the original and the clipped version were directly compared (by soloing the appropriate tracks), the differences were abundantly clear. But, without reference to the non-clipped version (which is always unavailable when listening to an amplifier in isolation) the effect of the overloading was not obviously apparent. Only once the threshold level was reduced to -10dBFS (meaning all data above 32% amplitude were trimmed), was the distortion immediately identifiable as overloading.

In short, it does seem possible that many of us are operating our amplifiers with insufficient headroom and thereby, unknowingly, distorting what we hear and misrepresenting the audio signals on which we are working. Because different amplifiers overload at different levels, we infer that it might account for the observed differences between different units when casual comparisons are made.

Power monitoring

Is "amplifier sound" due to unintended amplifier clipping? It's a reasonable conjecture, but it would seem very difficult to prove.

Nevertheless, we clearly need to be sure that we are not overloading our power amplifiers. That way, we remove any chance of this variable affecting performance. The new edition of the Needle-drop Handbook offers various simple monitoring solutions to be sure we don't overload our monitoring power amplifiers.

*This is unofficial, the listening group was tiny and the correct experimental protocols for perceptual experiments weren't followed. There is also the issue that practical power amplifiers may not clip as "cleanly" as this mathematical manipulation. The results are therefore only interesting for general discussion.

For further information write to sales@phaedrus-audio.com

Particle damping

24/11/2025. We had our attention drawn to some "radical and new" damping products. The products offer particle damping, which is said to provide "more efficient and wide frequency-range vibration absorption than previous solutions."

Particle dampers are devices that work by a combination of impact and friction damping. They dissipate the energy of a system by transferring it to a bed of particles. This bed is geometrically constrained to remain inside a container fixed to the vibrating system. As such, the motion-caused interaction occurring inside the container damps the absorbed energy. Particle damping emerged in the 1960s aerospace industry when engineers sought damping methods that could survive space vacuum and extreme temperatures, in which lubricants dry out, fluids boil off, and elastomers degrade under vacuum or temperature extremes.

Does particle damping have audio applications?

Particle dampers do provide broadband damping, and prima facie, this quality is welcome in audio equipment. However, particle damping provides amplitude-dependent damping. It is highly nonlinear. The damping effect of particle dampers depends on significant amplitude of vibration, and significant acceleration — to make particles move. Particle damping is good at controlling large, transient vibrations (e.g. shock, impacts). But, at small amplitudes, particles may not move at all, or only "slosh" around slightly. The energy dissipated is thereby, negligible.

In audio equipment, vibrations are typically: very small in amplitude (microns or less); and low in acceleration. These vibrations are not enough to mobilise the particles. And, if the particles aren't mobilised, the damper does nothing. This creates a serious mismatch for this technology in the context of damping vibrations in audio equipment. It is likely to offer far less damping than constrained-layer damping, viscoelastic damping, or even well-designed mechanical isolation.

In electrical analogy terms (see afterword five of the Needle-drop Handbook ), the particle damper is modelled as a resistor in series with back-to-back Zener diodes. The damping effect is only useable above a certain amplitude of forcing function. This is the opposite of the behaviour we seek in keeping small vibrations from affecting — for example — a turntable. In theory and in practice, particle damping is ineffective or impractical at small amplitudes, such as the vibrations which trouble audio equipment.

For further information write to sales@phaedrus-audio.com

PHLUX-III Microline ships

17/11/2025. First shipment of new Microline version of PHLUX-III active cartridge.

Originally a special customer request, we are now able to supply the PHLUX-III cartridge with: a 3µm × 56µm, nude, square shank, Microline stylus. This complements the choice of: a 6.5µm × 68µm nude, square-shank, Shibata stylus; 76µm conical stylus, for 78RPM archive work; and a 18µm conical stereo cartridge for (low-wear) LP work. The cost of the new PHLUX-III with Microline stylus is the same as for the Shibata stylus version.

For further information write to sales@phaedrus-audio.com