Octave Audio

Developing a Replacement Top Platter for the TD-124

Written by Urs Frei, CH-Troinex

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At the beginning of 2005, shortly after delivery of the first non-magnetic main platters, Juerg Schopper again raised the issue of the top platter. A replacement was needed for warped, bent, damaged and missing top platters, but the original manufacturing dies, tools and machines were long since unavailable. In other words: retro-engineering was required, a situation we are well acquainted with!

I made some technical sketches and starting inquiring at well-equipped Swiss companies with excellent references. My usual optimism was hard pressed when I received back only negative replies: "can't be done", "not in our production program", etc. Well, if they don't want to shape the platter by rolling the metal, why not cast it? After much discussion with our technical specialists, we finally found one of our suppliers who was willing to give it a try. After some months of waiting for the dies and finishing tools, we finally had 3 samples, cast and finished from an aluminium-silicon-copper alloy. Despite some cosmetic imperfections, these were balanced and true, and thus functionally perfect. The top platters were then put through independent listening tests in a number of different systems.

The listening tests of the top platters and other improved replacement components clearly showed that different manufacturing solutions produced clearly audible differences. Above all, we were amazed by the clear sonic superiority of the new top platter. It not only sounded different, but produced music with far greater inner coherence. Some of the audio freaks taking part in the tests wanted to buy the new platter immediately: it was simply impossible for them to go back to the old top platter!

The whole story could have stopped there, if not for the desire to see if we couldn't do still better! Pilgrim's staff in hand, along with the samples, I returned to one of the machinists who'd previously turned me down, and convinced him to make some new trial versions of the top platter from aluminium alloys. There followed an endless series of listening tests with top platters cast at different temperatures and with different finishing techniques, from which a hard alloy platter eventually emerged the clear winner. It became clear to us that the original top platter, by selectively absorbing small vibrations, introduced a coloration which was not unpleasant or unmusical, but which deprived the music of some of its emotional drive. Zeroing in on small but increasingly perceptible differences finally led, by a process of elimination, to the final choice of raw material and manufacturing process.

"All" that remained.was to now produce an exact replica of the original Thorens top platter! This proved extremely difficult, as the new alloy was much harder and more difficult to shape than the original, lighter pure aluminium. The first 100 wound up on the scrap heap. It took many, many experiments in the production process to produce a successful clone of the original using the much harder alloy. At last, the final test day arrived, with the listening team (including myself) assembling at Jürg's. After carefully checking the usual parameters (tonearm, cartridge, cable) the candidate was put to the test!

Anyone thinking we had to listen and concentrate hard to locate minute nuances of sound is hugely mistaken. With every record we played - classic, jazz, blues - it was obvious that only the machined hard alloy platter was capable of conveying the full emotion of live music, totally free of stress, strain or the lingering desire to hear something missing. Suddenly, the cast platter that had won our hearts showed its limits, smoothing and concealing essential musical differences. Even the originally planned anodizing of the top surface showed its subtle but unmistakable contribution to homogenizing the sound, and so was discarded.

In the 1950's, the original TD 124 top platter was a hi-tech product, contributing to the well-deserved success and survival of an audio legend. It has now been surpassed. Having reached our goal with the final production of a top platter , which Jacques Basset would have loved to have made himself had he been given the resources, Jürg gave the go-ahead for series production. The first replacement top platters, tested and packed in Sainte-Croix like the original, will be available at the end of May 2007.

I want to heartily thank all those who took part, by contributing their patience and skill, in developing this marvelous musical component.