This classic turntable needed a lot of TLC but it had the makings of something great. The original plinth was a bit tatty, missing the lid and barely held together by failing glue. So I scrapped it and built the plinth you see here in solid Tulipwood, complete with a brand new acrylic dust cover, updated hinges, adjustable feet, laminated base and a vastly improved structural design over the original.
Open box plinths can be prone to resonance. A layered plinth with an exact cutout for the motor board and mechanics can overcome that. However, those plinths are high in mass and tend to absorb unwanted vibrational energy rather than dissipating it quickly. A good compromise is to build a framework that is extremely rigid, not just from corner to corner but also across the span of the vertical panels, and to create a balanced array of defined points of contact between that structure and the supporting surface.
The new plinth is a lot stronger, can be adjusted for level, and provides a far superior support to the floating top plate than the original ever did. This is done via solid blocks directly mounted to the frame, in turn mechanically interfaced to the bass support blocks. Any energy that passes between the top plate and the plinth can be quickly dissipated through the base, rather than remaining within the plinth structure.
The feet are made from 2 layers of Corian. They’re heavy and dense, helping to reduce transmission of feedback from the supporting surface into the plinth. The feet in this case contribute some mass to what is a relatively light turntable, and they provide a path for any energy that does find its way into the plinth to be transferred away. But they’re dense enough that unwanted energy from the supporting surface doesn’t make it through the feet into the rest of the structure.
the baseboard is a low-resonance high-pressure laminated MDF sold for paneling bathrooms that is very rigid and drastically improves the torsional stiffness of the plinth. The rest of the plinth is solid Tulipwood which was reclaimed from a scrap doorframe.
The PL-12D was the budget turntable of choice in the 1970s and centres around a steel top plate suspended on four springs of different compliance, positioned according to the distribution of weight within the chassis. The springs are damped with foam cylinders which reduce their metallic ‘ring’ when excited by vibration, and prevent some of the ‘bounce’ in the top plate which will occur under external influence such as footfall. I realised early on that the type, density and quantity (diameter and length) of foam significantly affects the performance of the isolation system.
You typically see people who restore these cut up sponges and stuff them into the springs. It is impossible to cut a perfect cylinder from the foam unless you use a stamper but that is exactly what you need. After a lot of trial and error I found the ideal type, density, diameter and length of foam, and engineered an economical way to cut them. I now offer these for sale.
Spring-suspended turntables nearly all suffer a lateral twist that occurs as a result of isolating the plate on springs. The PL-12D doesn’t suffer this to the extend of an LP-12 or Thorens suspended subchassis as the motor and platter share a common chassis, so the belt tension cannot cause a twisting effect. The foam dampers help to combat this somewhat, and I installed additional rubber damping into the blocks that support the springs.
The main bearing was refurbished by polishing the bearing shaft and replacing the steel ball bearing with a ceramic ball of the correct size. This reduces friction to negligible levels, causing the platter to spin for ever and a day without the load of a belt. I used a 100% synthetic oil with no additives, cleaning agents or other nasties. So-called ‘black oil’ is sometimes recommended for these turntables, but this oil can damage the liners of some bearings and also causes excessive wear to the soft steel that the spindle is made from so is not recommended. A lightweight synthetic oil, or a light gearbox oil is all you need.
Just when I thought I was finished, the motor failed. So I swapped it for the motor from a MK II model, the better of the two motors offered in the PL-12D generations. I stripped, cleaned and lubricated the motor with the same lightweight synthetic oil as above, aligning the cage and magnet to give me the lowest possible noise and the least possible vibration when holding the running motor in my hand. Be very careful doing this as dangerous voltages are present, do not attempt this unless you are confident in doing so. I could have fitted new grommets for better motor isolation, but the originals are still soft and pliable and perform as well as they ever did. New grommets are available from a chap in Sweden if you need them.
The switches were cleaned and the two arc suppression capacitors replaced with modern safety-spec components. Be wary of some sellers on eBay advertising parts for these that are not safety rated. In this application it probably doesn’t matter, but you should at least ensure the parts you are buying are of a suitable voltage rating to exceed (by a margin of at least 10%) the nominal mains supply in your part of the world.
The arm has been adjusted to minimise the play in the bearings while being as low in friction as possible, not that there was much play to begin with. It is a fine example of the PL-12D tonearm and still has its factory lateral balance weight present which most of these turntables are missing. A Pioneer headshell completes the original ‘1970s lineup, on which I mounted an Audio-Technica AT91 cartridge. A Japanese AT91 for what it’s worth, sold by the kind folks at IPT who grabbed a load of stock when Audio-Technica discontinued the AT91 officially.
It’s a fine cartridge and a great match to this budget arm, and takes the excellent IPT Audio XTC (extended contact) stylus upgrade for the AT91 as an easy upgrade. It has the slightly warm, forgiving sound characteristic of the ‘1970s, but better dynamics than the Shure cartridges these turntables were typically fitted with. Given that it has been around for move than 4 decades, I’d be willing to bet a few PL-12Ds ended up with AT91s during the 1980s. They’re great for playing styrene 45s, and can take the stylus of the AT3600L which tracks at 3 grams and may better suit worn out discs. You can even fit 3-mil and 2.6-mil styli to them for playing 78s, though this turntable doesn’t facilitate a 78RPM speed. And there are aftermarket elliptical and line contact options available too. It’s a highly versatile cartridge.
A fine old turntable lives to give another 50 years of faithful service. These turntables are virtually maintenance free, simple enough to be fixed with minimal tools, and as rugged as they come. By no means an example of advanced precision engineering, but a very nice way to play records and certainly better than most of the budget options made today. You can find two excellent articles on PL-12D restoration on Mr Ives’ Blog.
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