Thorens TD125 + SME 3009 II Fully Restored

MikeC's Audio Craft
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Thorens was a well-established Swiss brand of quality turntables long before Linn and its peers appeared in the 1970s. The idler wheel drive TD124 remains one of the revered tables among collectors today, with fully restored machines on exotic plinths fetching many thousands of dollars. It's a fascination I can't comprehend fully, perhaps never having listened to it's song, but the relatively high mechanical noise from the motor seem to me difficult to tame and prevent from affecting the sound quality.

The TD125 came a bit later, after Thorens had introduced the modest but successful TD150, its first belt drive model, with a floating suspension similar to the AR turntable introduced in 1961. The TD125 was intended to be the state of the art for vinyl playback in 1968, and featured advanced features and build quality that remains impressive even in this day of computer controlled lathes.

A decent quality sample of the TD125 came into my hands early this year. It was not without issues, naturally, being a machine over 40 years old. It was outfitted with a tonearm that has also achieved legendary status, an SME 3009 II. I already had a couple of Lenco turntables on the go in my workshop, as well as a Thorens 160 and various other promising vintage turntables, but this TD125 was such an interesting challenge that I decided to spare no effort to bring out its former glory.

THORENS TD125 BASICS

The Linn LP12 has become the posterboy of all suspended subchassis turntables, and most audio enthusiasts are familiar with the concept of a platter/main bearing bolted on a subchassis that is suspended on springs riding on bolts which extend down from the top plate. The motor is secured to the top plate and isolated from the platter/tonearm by the springs and resilient belt. This is the design invented by Acoustic Research , copied by Thorens in the TD150, and by Linn in the LP12... and dozens of others since.

An Aside: Looking with the clarity of hindsight, the floating subchassis introduced another variable for speed instability, the very real possibility of relative movement between platter and motor, either due to external shock, or transient increase in drag from a highly modulated part of the groove or even a burp on the AC line. This has the potential to affect speed stability. Awareness of such issues didn't escape the engineers of the time, surely, but one thing the soft spring subchassis turntable did better than all its competitors — when properly placed on a rigid stable table — was to avoid acoustic feedback and reject external vibration. It was, at the time, so much better than anything else, that perhaps the other factors paled in comparison

The TD125 differs from the orignal breed of AR, its own TD150 and Linn LP12 in a couple of important respects.


Scan from original TD125 brochure (courtesy of thorens-info.de)

First, the visible top plate in which the platter/bearing rides is suspended, in a kind of reverse of the floating subchassis. You could call it the floating main chassis, a massive cast alloy that weighs 7kg by itself. A steel structure beneath this floating chassis has the motor bolted on the left, and three plastic height adjustable cups which hold the springs. Take off a couple of transit screws and a few ground wires, and the entire cast chassis, with platter, main bearing and tonearm, can be lifted straight up and off the bottom chassis. You'd have to be careful doing so as the total weight exceeds 12 kg.

An exploded image of main parts from the service manual may help visualize this.

The 16-pole AC synchronous motor is driven via a Wein bridge 2-phase electronic circuit, which provide switching for 33, 45 and oddly, 16 RPM, plus fine speed adjustment at each speed. The brushed aluminum control control strip features stylized rectangular switches, including the cue control for the stock Thorens arm. Strobe markings underneath the inner platter are viewed through a lit mirror system from the front panel to check and adjust speed with ease. Looking back at it today, it was clearly a tour de force of technology and design in 1968. It sold when first released in the UK for £70, which translates to about £1,136.52 in 2015, which is an excellent value considering Linn's base model Majik LP12 sells for over US$4,000.

THIS TD125 SAMPLE

The plinth (wooden base) of my TD125 sample looked a bit beat up, and there were lots of scratches on the metal control panel and slide switches. Here's a quick visual tour of the original.


This Thorens TD125, when it first came into my hands.

With outer platter off.


Front left of plinth cracking.


The back stem of the SME 3009 II was sagging due to worn rubber bushing within, the rubber grommets on the base mounting looked complete gone, and it was covered with dust and grime, but... all in all, not bad.


The motor and metal parts looked fine, except for the yellowing of the plastic motor pulley, which is harmless.


The motor electronics PCB looked OK, no leaky caps, but they're 40+ years old. It is routine among electronics restorers to replace electrolytic capcitors, which degrade fastest.


This crack on the inside of the back panel was pretty bad. It could have been repaired by injecting the right type of glue in behind the cracks, but since the veneer was in bad shape and it was only chipboard underneath, I opted for a completely new plinth.

The main bearings looked OK under a bright LED flashlight, the platter spun without discernible wobble even at the periphery (well under 0.5mm variance over a complete turn), and the motor ran extremely quietly. So my initial goals were:

  • Build a new, better, stronger plinth from hardwood, not veneered particle board.
  • Fit a strong bottom board to further strengthen the plinth.
  • Examine, clean & repair every part of the turntable and the tonearm.
  • Replace all the electrolytic capacitors in the electronics.
  • Find a way to eliminate or hide scratches.
  • Fine-tune, adjust and set up to make it sing again.

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