T/T Drive Systems - various conundrums and conclusions
In a discussion with Mike (Shian7) recently on the SL-1210 thread he mentioned that Roy Gregory was going somewhat 'ape' over the £12k direct-drive Grand Prix Monaco turntable in Hi-Fi+. Intrigued, I obtained a copy; and what I read put a huge smile on my face because as I was reading it what he was describing was almost an exact facsimile of my feelings on the performance of the KAB-modified Technics SL-1210 (and original SP10) which are available at a mere fraction of the price! It confirms what I've thought all along that direct-drive, done well, is unquestionably a superior drive system solution to going the low or medium-mass belt-drive route. And getting the all-important issue of highly accurate speed stability right with a belt-drive T/T takes high-mass construction to ridiculous levels and a serious amount of required expenditure. The SP10 and SL-1210 in my opinion solve the issue far more elegantly via the use of their near-flawless direct-drive mechanisms.
Allow me to elucidate further on the importance of accurate speed stability with a turntable... Roy Gregory wrote:
Now what Mr Gregory fails to mention is that the "hunting" effect described above only applied to the cheap direct-drive turntables of the day which were deeply flawed, the result of which was that they gave the 'side' a bad name, and along with the Linn marketing machine at the time that was telling everyone who was willing to listen (and those who were not were simply made to listen anyway!) that the LP12 was the best thing since sliced bread and unquestionably the 'de-facto' turntable of choice. Direct-drive T/Ts, despite when done well being technically superior, were pitched to audiophiles as 'inferior' and simply 'cheap Jap crap'. Consequently, they were relegated to 'low-fi' use in mass-produced midi-systems of the day.I'm afraid that given the essential dichotomy at the heart of turntable design. A stretchy belt isn't exactly a high-tech response. The problem facing any turntable designer is to create a player that resolves at accurate stable speed and does so quietly (meaning, without excessive mechanical vibration). The trouble is that accurate, stable speed control demands a close-coupled drive system and the motor just happens to be the biggest single source of vibration in the unit.
Hence the use of belt-drive, which doesn't just decouple the motor noise, it also helps solve the far thornier issue of real-time variations in speed, through the twin devices of elasticity and slippage. So, far from subtle changes in motor speed are evened out by the belt into less jagged and intrusive variations. Like I said it may not be sophisticated, but it is surprisingly effective. So much so that it drove off [with the help of the ferocity and misguided principles of the Linn marketing machine of the 70s - Marco] the commercial threat of direct-drive with comparative ease, despite the latter's clear theoretical benefits.
You see, even if you coupled a decent, quiet, direct-drive motor to a well-engineered bearing (which actually isn't that difficult) the Achilles heel was the speed control system, which used servos to hunt the correct speed. The end result was arguably a platter that turned constantly too fast or too slow, but most damaging of all, was constantly changing speed, a subtle distortion the ear detected all too readily. The advantage of a belt drive is that those fluctuations in speed are far more gradual and thus less intrusive.
This was indeed a sad state of affairs but undeniably true. It just shows how easily people will believe in a concept if it is marketed cleverly and successfully enough! Unfortunately because of this misinformation the feeling that direct-drive is inferior still exisits amongst many audiophiles today, and the reputation of the excellent SL-1210 is further marred because DJs have adopted it for use because of the high torque (and thus quick start-up time) of the direct-drive motor and the deck's rugged construction, but it was of course never originally designed for the purpose of 'DJ-ing'. Ironically, though, the SL-1210's use as a 'DJ deck' is what has enabled the unit to remain in production today. It was of course originally made as a cost-no-object (to Matsushita Electric) audiophile turntable, which National Panasonic (Technics) are able to sell today at ridiculously low cost due to economies of scale and the 'refined down to a fine art' nature of their mass production techniques.
However, in order to solve the inherent problems of other direct-drive systems on the market at the time, Technics introduced a D/D mechanism with Quartz movement using linear frequency generators, as opposed to the somewhat flawed position-updating systems used by the cheaper direct-drive turntables of the day, which suffered from none of the issues of "hunting" as referred to earlier, and delivered near-perfect accuracy and W&F results of 0.025% - almost identical to that of the Grand Prix Audio Monaco, which achieves 0.002%. It is precisely this mechanism that is used in the SL-1210 today, and the fundamental reason why its audio performance (after minor weaknesses in some ancillary parts have been addressed) is so astonishingly good.
Mr Gregory may have omitted to mention this fact because of copy restrictions but perhaps it was also because he didn't wish to advertise the fact that the sort of performance which is delivered by the G.P.A Monaco is also available at a frankly ridiculously low price (when judiciously modified by the likes of KAB) from a company with a far less desirable audiophile badge, i.e. Technics?
Your thoughts please on this, gentlemen, and on where you stand on the thorny issue of belt-drive (and idler drive) versus direct-drive?
There are numerous other issues Mr Gregory raises in his article which I would like to discuss, and which I feel rather succinctly summarise my own thoughts on the superiority of direct-drive (done well) but before getting to that I would like to deal with issues concerning my question above.
Marco.
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