Build a Vibration Measuring Machine

How To

Build a Vibration Measuring Machine

Rega founder and designer Roy Gandy has often said that there are no other turntable designers who he can turn to do discuss the topic that is obviously close to his and our hearts. He feels that few if any of his peers fully understand what’s required of a turntable, which is essentially to measure vibrations in a vinyl groove with as greater accuracy as possible. Obviously his peers would disagree but none have explained their thinking on paper in quite such comprehensive and informative fashion as Gandy has with the help of Paul Messenger in this substantial tome.

A Vibration Measuring Machine is largely written by Gandy’s friend Bill Philpot who tells us about Roy’s background and the history of the company in clear and entertaining fashion. As Roy once said “I’ve never had a passion for hi-fi. I have a passion for music”, he built his first turntable because he couldn’t afford to buy a decent one with his salary at Ford’s Dagenham plant, ditto the loudspeakers that he initially made out of concrete building blocks. But the first product he sold was a transmission line loudspeaker, the first turntable, the Planet took significantly longer to develop as it actually involved having parts made. Rega was registered in July 1973 by Roy and his then business partner Tony Relph, (Re(lph) Ga(ndy)). The early turntables were made by Roy in his evenings and weekends, he didn’t leave his ‘day job’ for two years.

Rega Planar 3
The Planar 3 introduced the first glass platter to the world of turntables but its development was not straightforward, only long hours with glass supplier Rankins making them economical enough for the job. The Planar 3 was launched in 1976 and “sold like cold cakes” to begin with, but within a year it had overtaken the Planet and established itself as the poor man’s LP12.

Dissatisfied with having to buy in tonearms Roy tried to get a one piece arm made in Japan but had no luck and put the idea on the back burner until 1982 when the RB300 started to take shape. The first one piece tonearm proved to be a major challenge for casting companies and required early use of computerisation to produce, it took 18 months of R&D to get right but formed the basis of all subsequent Rega arms. In the eighties they developed their first cartridges, Bias, Elys and Exact with fixed styli and started building the Ela, a small transmission line speaker.

The first Rega electronics came about when got an old friend contacted Roy about an amp he had built. It sound good but the “birds nest of wires” proved to be beyond the ability of its designer to turn into a viable product. Enter Terry Bateman, an engineer from pro audio who’d had no experience of hi-fi, yet he managed to turn Frost’s creation into Rega’s first amplifier, the Elicit, which went on sale alongside the Elex in 1990. These amps were the first to use cast aluminium clamshell cases, a distinctive and solid solution but one that was to cause the company all sorts of grief over subsequent years. Another source of problems was finding adequate space for the growing company, Roy has always been keen on owning rather than renting and in the first twenty years was personally involved in renovation and constructing Rega’s facilities. The current Temple Farm building was built from scratch on what is now an industrial estate in Southend, designed by Gandy its construction resulted in a lengthy legal battle with contractors but gave the company a space in which it has grown and prospered.

Original Planet turntable with Acos Lustre arm

Linsley-Hood
More electronics and loudspeakers followed in the nineties including the entry level Brio amplifier, Kyte bookshelf speaker and an FM tuner based on a NAD circuit design. Turntable R&D continued with the P9, the first turntable to have an aluminium oxide platter. 15 years after CD’s introduction Rega launched the Planet, a top loading player with a Sony mechanism in 1997. The P25 turntable marked Rega’s 25th anniversary and in 2011 Terry Bateman developed the circuit that underpins all the current amplifiers apart from the Osiris. This is based on a 1970 Linsley-Hood design he found in an ancient copy of Wireless World, and produced the best selling electronic product Rega has yet made, the Brio-R. Terry also built the Isis CD player and Osiris integrated amplifier at the other end of the budgetary scale, both are remarkable pieces, the Isis in particular being the best CD player I have had the pleasure of using. Speaker development followed with the RS10 incorporating a BMR midrange and a Rega tweeter in a transmission line design.

Over the last few years Rega has been working on something rarely seen from the company, a develop a cost no object turntable. The project that spawned the foam cored plinths of the RP8 and RP10 and the brace that couples main bearing to arm on the majority of Rega’s current turntables. The Naiad turntable for which all the work was done is yet to be finalised and even when it does will only be made in small numbers. The first 40 were sold to commemorate the company’s anniversary in 2013!

The Engineering
The second section is called ‘The Engineering’ and in it Paul Messenger explains Roy’s ideas about how to construct an accurate Vibration Measuring Machine. It starts by explaining that a turntable, arm and cartridge need to be able to measure or read vibrations down to the micron level, and that any movement in the turntable itself will undermine its ability to do this. It points out that airborne vibration is more detrimental to this process than that transmitted through furniture, which is one reason Rega has never made a suspended subchassis design. The only benefit they see in that approach is that it results in a low mass plinth, Gandy had a bad experience in the pre-Rega days when he built a concrete plinth in an attempt to improve his first turntable. He came to the conclusion that mass is a bad thing because energy can be more easily transmitted from a heavy to a light object than vice versa. Hence Rega turntables have relatively heavy platters in comparison to their light but stiff plinths. The thinking being that lighter plinths are less able to transmit motor and bearing noise into the platter.

RB300 single piece cast tonearm

Rega also eschews belts that drive the periphery of a platter because this can introduce speed variations and undermines the potential for inertia to maintain consistent speed by attempting to control this energy with an elastic belt. They accept that compromise is a part of any engineering challenge but believe that driving a subplatter with a short belt to be the best available option. The use of multiple belts is applied to iron out variations in belt consistency; the RP8 and RP10 have two belts, the Naiad three.

Platter stiffness, or more precisely coefficient of restitution (COR), is important in Rega’s view; aluminium oxide has 0.004 higher COR than glass yet this translates into an increase in musical detail. Which makes you wonder whether COR is the only factor. It describes plastic (acrylic) platters as having a “church like reverberation” that whilst appealing is an addition to the signal, as a former enthusiast of that material I have to agree. They eschew clamps because they introduce stress into the vinyl disc and this produces an audible resonance. Much the same argument is made for the change of clamping arrangement of the Rega arms, the original large nut on the base of the arm was replaced with three screws to reduce tension in the plinth.

Ideal versus real engineering comes up with regard to a turntable bearing’s thrust or contact point, ideally this would be a single small spot but in reality bearing precession means that the tip of the spindle does not remain in the same place. With regard to arm bearings there is a particular concern that movement outside of the required planes be kept to a bare minimum in order for the stylus to be able to read the groove accurately. They describe the various arm types; unipivot, gimbal, parallel tracking and their preferred ball race type and explain the pros and cons of each and the reason for their choice. It’s “not the specific design direction but rather how well it is executed” that counts. Interestingly it mentions three non Rega tonearms of yore that offer good performance, none however are still in production. The assessment of carbon fibre in tonearms is that it lacks strength and thus rigidity under compression, and that aluminium alloys “give superior results”.

When it gets to cartridges Gandy reasserts his opinion that rigidity of arm fixing is more important that having the ability to adjust VTA or SRA (stylus rake angle). Measurements are included that show second harmonic distortion with the test record at four different heights to emulate different vertical tracking settings. These do show very small differences, the measurement with the vinyl raised 6.5mm above the platter being 2dB better than lower positions but this results in the arm nearly touching the edge of the disc. It also makes the point that the cutting head angle in vinyl mastering hardware varies between 0 and 20 degrees and actually changes as it cuts the groove. That VTA/SRA is not critical is one of Gandy’s most controversial claims and there are many who take the opposite view, but only a very small fraction of that group produce record players that come close to Rega’s best.

Rega Planet CD player

The various aspects of cartridge design are also considered including the opinion that anything that reduces output is to be avoided, they cite mumetal coil screens as reducing output by up to 20%. The removal of a tension or tie wire in the Rega MC cartridges is also an interesting innovation as it reduces mass and removes a source of resonance. It also allows Rega to build cartridges that do not need hand tuning.

Myths
This section is probably the most entertaining in the book, including as it does phrases like “fiddling around with VTA is entirely futile” and the observation that structure borne feedback measures 40dB below the air borne variety, so keep your turntable in the other room from now on! In many respects this section repeats more concisely the theories found in Book Two, including “heavier plinths will transfer more unwanted energy into the disc than a lighter example”. But it also advises against aftermarket arm rewiring because this usually causes more trouble than it’s worth, with silver wire being singled out because its stiffness increases friction in the arm.

With regard to measurement of record players the company is not entirely dismissive but considers “the current technology and available measuring techniques fall far short of the ideal.” Presumably they consider that the stethoscope, used in a recent high profile P3 review, is even less useful. Those looking for set up tips will find them a little thin on the ground, for instance tonearm bias: “a good compromise could be to add a little bias correction without undue concern regarding the amount.” But the beauty of Rega turntables is that they require so little setting up, in most instances it’s just a case of finding a level surface, fitting the counterweight and dialling in the required downforce. Quite a dramatic contrast to the many more expensive yet musically less compelling alternatives on the market.

The People
The last section of the book consists largely of Rega people in conversation with Bill Philpot. Here you get to learn a bit more about Roy Gandy, effective company MD Phil Freeman, former Lesney toolmaker Ken Palmer, long time audio salesman and Americana nut Paul Darwin, designer Mike Stopps, electronics guru Terry Bateman, Ky Gandy who works with suppliers, Simon Webster who does nearly everything else including much of the photography in the book and designer Colin Dilliway. There is even a piece about glass supplier Daniel Dunwoody-Kneafsey who cracked the challenge of the RP6 and RP8 platters, an achievement that clearly made an impression on Roy. Finally writers Bill and Paul Messenger get to say a bit about themselves.

Roy Gandy with glass maker Paul Rankin

This is a fascinating book that gives a lot insight into the trials of manufacturing in Britain and the challenges of making audio components at sensible prices without resorting to international outsourcing. The fact that Rega remains the only privately owned British audio company that consistently makes musically compelling equipment is a testament to the people and the ethos that make it happen. A Vibration Measuring Machine is essential reading for anyone designing a turntable and, for that matter, anyone thinking of going into manufacturing whether that’s in the audio industry or beyond. There’s a lot to learn on both fronts.