Turntable Clamps and Pucks

by: Pierre Lurne

Editor’s Note: This month, we are excited to present a new article by Pierre Lurné, the founder of Audiomeca.

Views expressed in this article are those of the author, and they do not represent the position of Dagogo.

A little article on the Analogue clamp! Is there so much to say about such a little accessory? What’s that gadget for? Indeed it maintains and flattens the record against the platter and also helps vibration control. Is it so important? Why? To tell the truth, you can perfectly live without it. Clamp or no clamp, you will recognize your favorite bands and singers and enjoy music. The Phonographic process is a good boy and always works. So be tolerant and kind. But if you are looking for the best, if you ask for full respect of all the delicate and delightful musical nuances and emotions hidden in the minute groove, if you are curious and sensitive, and above all, if you love music, your Turntable does need a clamp.

1. The clamp main job

2. The clamp next job

3. How it works

4. The most usual kinds of clamps

5. A few mistakes to avoid

6. Conclusion

1. The clamp’s main job

Any Audiophile and Dagogo reader is supposed to know that the Effective Mass of the pick up Arm + cartridge assembly, combined with the cartridge compliance, make a critical combination, a wonderful oscillating system. Imagine a stone upon a bed string. This is it!

In physics, any free Oscillating System leaves its stable position and starts moving in response of

the slightest excitation or impulse. The frequency of the oscillation depends on the Mass and the Compliance and is called the Resonance Frequency. A heavy stone lowers the frequency and increases the amplitude of the movement which looks slow. A light stone gives a faster oscillation, and the amplitude of the movement looks shorter and faster. Similarly, compliance variations lead to same findings.

Arm/cartridge resonances range from 5 to 20 Hz. Values around 9 to 12 Hz prove to be the most usual ones fortunately, as a too-low resonance frequencies could be excited by the record wrap and off-centering, and too high by the lowest notes of the engraved music. Today, the resonance of almost any Arm combined with almost any cartridge happens in the safe area.

Always check this graph when you contemplate buying a new cartridge or Arm. “The perfectly centered and perfectly flat record does not exist”. The record off-centering is normally no problem as it is very regular and low (1/2 Hz approx). Wraps are a real pest. Some of them can easily reach the resonance frequency of the arm/cartridge combination. When wraps set the resonance to ring, distortion increases drastically. The stylus gets out of control and, in the worse cases, is literally ejected out from the groove and scratches the record. High Fidelity you said?

You guessed and anticipated the solution: a clamp will flatten the record wraps and as the phenomenon is not linear, any clamp will reduce it to a remaining, more or less, one third only. A great improvement, as the Arm/cartridge resonance at 8 Hz only is not dangerous anymore. Besides, “He who can do more, can do less” and in all cases a clamp eases the tracking.

2. The clamp’s next job

Another little reminder will be useful here again: the minute size of the groove.

Groove width on vinyl record ranges about from 0.025 to 0.035 mm. In comparison, a human hair is typically 7 times bigger! The tiny Tracking Force, let’s say 2 grams, applied on the minute areas of the stylus contacts, reaches an amazing high pressure that the record withstands only thanks to the record rotation. The usual values of acceleration are even more unbelievable and scarcely seen in physics. But the most incredible fact is the size of the engraved signal at very low levels such as -50 or -60dB, which means you are hearing movements of the order of a few millionths of a millimeter! The Phonographic Process is a miracle definitely!

Consequently, it is no surprise that the slightest vibration affects the musical results. In opposition to all random bad vibes coming from the outside, which can be considered as simple noise, the worse parasitic vibrations come from the tracking itself because their harmonic content is directly related to the music being played. They are the very music itself, distorted, corrupted, delayed, they invade everything and naturally they come back to the stylus where they are tracked again and again. This phenomenon quickly decays but it is continuously excited and replaced by the music being played blurring the sound and reducing the dynamics.

‘Sound Propagation’ is a very complex branch of Physics which studies this kind of problems. So far, Hifi design does not deal with it seriously enough and sadly keeps on focusing on always the same macro-problems for several decades. Spikes and mechanical grounding are very rudimentary exceptions. Analogue clamps, or pucks, are known to help vibration control and sound propagation principles explain why.

3. How it works

The tracking process generates vibrations which can be heard if one comes closer enough. This

is called “ needle talk”. Those vibrations spread all around. They propagate into the vinyl record, into the turntable platter and so on. On the other side, they travel through the cartridge, reach the Arm headshell, keep on going and bouncing everywhere, along the Arm tube, the bearing housing etc… But let’s go back to the clamp. It is worth pointing out that the very hot point takes place right at the stylus/groove interface. This implies that vibrations run inside the vinyl record, direct and at their full strength. They are “fresh”! The mass of the turntable platter will dissipate a big part of them, but not all. Note that a correctly designed and balanced platter will dissipate more, though once again not all. Consequently any additional device could be of a great help to reduce these remaining nasty vibes, right from there. We have it. The Analogue clamp. This way, the record is firmly maintained and covered between platter and clamp, leaving only the engraved top surface available to the stylus.

Although all clamps flatten the record almost on the same way, their ability to deal with vibrations differs from clamp to clamp. The job to be done can be roughly divided in three different functions, to collect, to dissipate and to funnel away:

– To collect as many vibrations as possible from the record, the clamp-to-record contact surface must be as large as possible and secured by some pressure. If every material has its own advantages and drawbacks and its own sonic signature, it makes sense to choose a material with a similar Acoustic Impedance as vinyl. Hence Metacrylate is recommended. The rather cheap and easy-to-machine Delrin gives good results. Felt leads to overdamping and metals to the contrary.

– To dissipate as many vibrations as possible, the small volume and weight of a clamp set limits to the efficiency. A smart solution is to insert/build in a piece of lead whose physical properties are particularly welcome here.

– To funnel away as many vibrations as possible requires a firm contact to establish a “path” to the platter bearing, the only way out.

4. The most usual kinds of clamps

The simplest Analogue clamp is nothing but a “puck”. Usually a round piece of heavy material with a hole in the center to fit on the LP centering finger of the platter, flattens the record thanks to its Mass effect. Such a puck can make a wonderful job, collects and dissipates some vibrations more or less effectively depending on the materials used, but fails on funneling them away.

Another type integrates one of the many locking device solutions acting like lateral rudimentary pliers. Most of these clamps do tighten the platter centering LP finger but forget to guarantee full contact with the record. The other way round of the puck! To compensate for this drawback it is often necessary (recommended!) to exert a vertical force, downward, while mounting the clamp. A force that the platter bearing will have to withstand…

The most usual Analogue clamp uses a true clamping device which literally grips the LP finger and strongly flattens the record “in the same time” through the action of a top screw knob. The platter bearing is safe. Full contacts are complete: record to platter, record to clamp and clamp to LP finger, all together. And pressures kept within reasonable bounds. Too high a pressure could stress the record surface (Remember the minute size of the engraved low levels in chapter 2), anchor dust particles in the groove, create minute surface cracks etc… Some vacuum record hold of the past proved sometimes to be detrimental to the record integrity. Anyway, it seems they have disappeared from the market today.

Apart from these categories, a number of other variations have emerged from the designer’s imagination. From a simple lead puck (not bad) to micro glass balls covered by a thin cloth (very good), almost everything has been tried and sold. Totally crazy designs and others with keen respect to the laws of physics.

5. A few mistakes to avoid

One can find in the market a very tall clamp looking like a jar. Such high mass definitely confuses, and maybe destroys, the delicate balancing of the platter. No doubt there are good reasons behind it but no doubt as well a platter must be balanced with high accuracy for fundamental and major reasons. One could argue that correctly designed and balanced platters are scarce. Anyway adding mistake to mistake never leads to excellence.

Another clamp available in the market has been designed with a crown all around as the only contact with the record. Such a solution fails in collecting vibrations well enough and the air pocket left in between cannot bring anything good. The main purpose, if any, was probably to secure the record to platter contact, but not the vibration control.

Another one, pretty good on musical respects, jams on the LP finger. Once in due place, it becomes impossible to remove. You must disassemble it to release grip and record. A stupid error of engineering. When the angle of the grip is to sharp, it jams.

Another one again is too large and some Arm headshells come up against it before the final no-end circle of the groove, causing repetitive and unpleasant mistrackings.

6. Conclusion

May one repeat: Hifi is not an exact Science (Happily!)? Many phenomenon still remain badly understood or merely unknown; but full respect to Physics stands nevertheless as a prerequisite to musical quality. If you prefer a metallic clamp, or if you believe there is a magical material to make clamps, ask yourself and listen twice. Beware and reject “sound compensations”. Let’s keep in mind that the main purpose of the Analogue clamp is to flatten the record to improve the tracking. This job is important and generally well done. Then, adding some extra design as regard to well understood Sound Propagation principles helps vibration control. An indispensable accessory definitely.