Thanks for the interesting article Paul. I haven't played an LP for almost 30 years, but it brought back memories of decades of doing battle with the many demons of that medium. My first turntable was a Thorens TD124 that dented my then small budget (ca. 1965), fitted with a 12 inch SME tone arm. According to its already fantastic reputation it should have been a remarkable experience - but no. Incredibly, it rumbled: thumpity, thumpity . . . I was fortunate (?) to have loudspeakers capable of real bass. The reason was quickly determined. It was a "professional" broadcast turntable, with "instant start" capability for timely segues, and multiple speeds to play many versions of discs. That meant an idler wheel and puck, and it was the puck driving the inside rim of the turntable that generated the rumble (no different from the much-despised changers
. I contacted the distributor who manfully provided me with a selection of new pucks. They all rumbled, but generated different patterns of "thumpity, thump". I had constructed a nice custom cabinet for it, so it was easy to get my money back in a trade in for a simple massive belt drive Empire Troubador turntable that was superbly quiet. A legend, yes. A great turntable, no. Later models were greatly improved for consumer use and I owned one (TD-125?). I ended up my tenure with LPs using two Professional Technics SL-1000 turntables (allowing for perfect segues during listening sessions with friends - we used to take turns playing disc jockey exercising my large LP collection while enjoying good Scotch). They were as flawless as anything I encountered, needing only some mechanical isolation from very low frequency building vibrations.
A puzzle: why did the audio press get so wound up about some downright crummy turntable designs? One still talked about was simply a slab of MDF board sitting on hard rubber feet, with the turntable bearing and tone arm rigidly attached, and the belt-drive motor somewhat isolated. It didn't rumble inordinately, but it suffered from horrendous acoustical feedback. Even the dust cover was attached to the MDF board! It was a microphone. A test: place the stylus on a stationary record, and play some music from another source into the room. Turn up the volume and record the output from the cartridge. You will hear a bass-heavy version of the music, and whatever you hear is error - it should not be there. In some of these dreadful machines it was possible to record dictation while talking to the disc, especially a low mass disc. This is another case where clamping the disc to the mat improves things. In the extreme there could be low-frequency feedback howl - "tight" bass was impossible. I remember being at Harry Pearson's "reference" room, in which the bass had to be turned down when he played LPs on his multi-kilobuck turntable - a giant floor-standing visual work of art, but . . . The solution: put the turntable in the next room.
When I began to investigate tone arms, I set up an arrangement of one tone arm suspended precisely above the one playing the record. The lower arm was balanced to neutral, no tracking force at all. The upper arm provided the tracking force through its stylus that was placed on the top of the lower headshell. So, one could listen to the lower cartridge playing the record, or to the upper cartridge "playing" the vibrations in the headshell that held the lower, main, cartridge. Now, in a perfect system there would be no vibrations in the headshell because
any movement at audio frequencies is an error. Believe me, the error was huge. Very distorted versions of the music came through clearly. The most egregious offenders, not surprisingly, were the then fashionable "low-mass" tone arms, especially the unipivots - they exhibited measurable and audible arm resonances, including torsional modes because they could twist on the pivot. Likewise perforated headshells, intended to reduce mass, also reduced stiffness - and they bent. And finally, low-compliance cartridges, then mostly moving coil, generated more force on the headshell than did high-compliance cartridges, thereby generating more errors. All this was unreported in the enthusiast press that lacked the capability or interest in doing measurements, or even asking the right questions. But they heard things and the reasons were always kind of mysterious.
The perfect headshell, therefore, is a "brick". But that requires perfectly flat records, and they don't exist. So we must use the sturdiest, most massive arm/headshell combo that can play the records you have. and seek out high-mass, typically flatter, discs. This is assisted by those few turntables that clamped the LP to a sculptured mat. Flat mats are a waste of time, including the occasionally praised felt. The label area and perimeter are thicker which lifts the groove area away from the mat. The groove area needs to be in contact with the mat to damp vibrations, and vibrations are what the stylus picks up.
The final breakthrough innovation was the "stabilizer", introduced, I think, by Shure in the V-15. It allowed the use of a relatively massive, sturdy headshell while still tracking warped records. But some purists found a reason to not like it, and other manufacturers were annoyed because they hadn't thought of it, and were then prevented from using it because of patents. Meanwhile, many of us simply got on with enjoying more records in a superior fashion, without the headshell wobbling all over the place, generating low-frequency rubbish and pushing the transducer into non-linear regions generating all manner of distortions.
All of these adventures with playback apparatus were documented, with measurements, in articles I wrote for now defunct Canadian audio magazines. They are still relevant.
And then came (uncompressed) digital . . . phew!
Again, thanks for the reminder of things past.
Floyd
