The Thorens TD280 MK IV turntable

I like to  fix up old turntables, especially odd or unloved examples. I've posted blogs on other decks , and back in November I saw a Thorens TD280 on ebay at a very low cost,  close to where I live. I prefer to collect, as decks need careful packing.

In the end I bid and won the deck, a Thorens TD280 MK IV. I am very familiar with the Thorens brand, my father had a classic TD150 MkII followed by a TD 160 - both classics from the Golden era of the 70's.

I read that the deck was a late model, and while not a classic Thorens, was widely liked by people who had owned one.  the TD280 is from the mid 80's when CD had started to put a lot of turntable manufacturers out of business, and like the Ariston Q-deck, was a bit of a final gasp from a declining industry. I got the auction for £64 as the external power supply had been lost, but I was sure I could source a new one.

A bit of research indicated the external power supply is 16v AC,  and I happened to know this is the same as is used by some older Scalextric slot car and Hornby model Train sets. Back to ebay,  I found a Hornby G8025W AC Adapter 16V for £5 and ordered it. I will confirm here and now that this adapter works fine, the plug fits the deck, and I'm still using it now.

While I was waiting for the power supply to arrive I had to have a look inside :)

Unlike almost all other Thorens decks, the TD280 does not have a floating sub-chassis , a device Thorens are famous for. This is where the platter and arm are connected to a plate inside the box or plinth of the deck. This plate is suspended from springs. These springs isolate the replay of the records from external vibration , from within the room and from the motor.
The TD280 has a simple MDF plinth, box section. In the picture you can see the main components. On the base of the plinth was a hardboard base-board with 4 sprung rubber feet to provide some isolation. The base board is held on by screws. I removed the platter, mat, sub-chassis and fixed the arm in its cradle then flipped the deck on its lid laying on a soft carpet

Inside the TD280 MK IV

You can see where the power supply connects top left in the picture. The motor is a low voltage AC motor which has a bright yellow sticker. Then as we move from left to right you can see a complex circuit board. This takes the AC supply from the external power supply and re-synthesises an AC supply which it drives the motor with. the motor is connected to the board via a connector, and includes a feedback circuit so that the motors speed is continually being adjusted to a precise 33 1/3 or 45 rpm, selectable from the front switches.

Between the motor and circuit, and a little lower you can see the underside of the main bearing bush. Further down on the left are the interconnect wires which attach to the arm wiring, then we have the underside of the arm bearing and the auto-raise mechanism which wires back to the circuit board. A mechanical linkage links the arm lowering mechanism to the front switch.

very simple and tidy internally, the main innovation being the power supply circuit.

TP35 tonearm

The turntable features a tonearm, and being the MK IV variant (there were 3 previous versions with different arms), it comes with the Thorens TP35 arm. This features adjustable tracking weight at the rear, with ant-skate implemented with a common weight and fishing line method. Unusual though is that the arm has a lateral balance adjustment via a small dial close to the rear counter weight. This is less common. the deck came with an Ortofon OM series cartridge

Motor pulley, mount and bearing well

With the main and sub-platters removed you can see the bearing well. This was a surprise to me as the service guide for this deck states the MK IV has an inverted bearing, where the platter sits on top of a ball bearing on a column. However this example has a more conventional rounded machined spindle which sits in a brass sleeve with a plastic thrust plate at the bottom.

I have since seen or contacted 2 other owners and there examples are like mine. Possibly the inverted bearing in the MK IV service manual was never used ? It is why, I believe, that the Mk IV is the only Thorens  deck where they recommend grease as opposed oil for the main bearing. Grease is used for inverted bearings to prevent it from dripping out as oil would.

the motor is coupled to the plinth by a plate with 3 screws. This is different to most decks I have worked on where the motor is decoupled using rubber bands or mounts to isolate motor noise. Thorens must have been confident that this motor was vibration free !

sub-platter with integral spindle, and drive belt in place

Issues and fixes 

Noisy motor

OK - so the power supply arrived, and I plugged it in. Operating the deck, the motor was buzzing though the deck appeared to operate fine and kept reasonable speed using a printed strobe disc. However the buzzing from the motor was detectable in the plinth through my finger tips - this wasn't so good. Errant vibration is not good for optimal sound quality.

I disconnected the deck, removed the platter and sub-platter and then removed the screws holding the motor in place. I then removed the base board and the wires from the motor to the circuit board. These all use push connectors, so removing the motor is very easy.

taking the motor out and rotating the pulley it seemed a bit stiff. I squirted some Servisol 10 contact cleaner into the upper and lower bearing on the motor to try and clean any corrosion or dirt. Quite possibly the deck had been unused for some time. It seemed to ease up, and so I worked the pulley round with my fingers, and then left the motor over night for the Servisol to work, then more  rotation. Finally using a precision oiler I placed a single drop of oil on the motors upper and lower bearing. The movement seemed much easier.

I put the motor back in the deck, refitting the plate and screws and plugged it in. This time the motor ran silently and has been silent ever since. No noise vibration, even with my ear really close I can hear nothing as it turns. I was very pleased.

VTA

One odd aspect of this deck was the VTA (Vertical Tracking Angle). VTA is the slope of the arm , or rather the arm should be parallel with the record surface when playing in order to present the stylus at the correct angle. on this deck the arm sloped downward  quite severely with no adjustment at the arm base as exists on some decks. My good friends over at the vinyl engine forum explained that the deck came with spacers that go between the cartridge and the headshell to raise the cartridge end relative to the arm pillar when playing.

I didn't have any spacers but decided to stack a couple of mats to raise the level of the playing surface. I had a spare heavy rubber mat from an Ariston Q-deck, and a cork mat I'd used. placing these on the platter and the original Thorens mat on top raised the playing surface such that the arm was level in play

Here you can see the extra thick triple mat - rubber, cork and rubber

Even with a deep cartridge like the Denon DL110, I still needed the extra mats

Vibration

I noticed that while the motor caused no detectable vibration in the deck, acoustic feedback in the room from the speakers was detectable via my finger tips in the original light weight baseboard. It may not have been an issue, but I experimented with an 18mm plywood based board, which I had cut to size by a very reasonable supplier on ebay sheetmaterialscut_essex. I sat the plywood base on some 40mm sorbothane domes I previously had used on another project. It was quite hard to use the original screw holes, so in the end I fixed the deck to the base board using 4 pea-sized pieces of blutak, arranged around the underside internal lip. After some thought I placed the peas at the centre of each side, so the plinth sits on the base at 4 points between the 4 feet, not directly above them. My thinking was that attaching at the centre of each side would dampen any resonance in the 2 front and back and 2 side pieces of MDF at their most resonant point.

There is much less vibration detectable during loud passages of music

I could have used the original feet, but I decided tho leave the original base board as is , I can go back if I want it original

Conclusions

I really like this deck. Its not a classic Thorens and there is very little information about it , even on the excellent www.theanalogdept.com, home of all things Thorens . However now properly setup with my Denon DL110 cartridge it sounds very good to me. I cleaned and re-oiled the main bearing, set the tracking weight, anti-skate AND the lateral balance, as described in the service manual which can be found here 
http://www.vinylengine.com/library/thorens/td280.shtml

The speed stability is exceptional. It does sometimes not engage its auto-raise at the end of the side, but I can live with that. Otherwise it presents music in a very appealing way.

if you get the chance to get a working example, especially discounted because of a lost power supply, I'd say its a great deck

Coda

Well despite having other decks lined up to be used, I'm still using this TD280, it just works. A very kind seller of one shared these pictures of the alternative MK IV with the inverted bearing, and I include these for completeness. It  appears that a black motor pulley, printed serial number means an inverted bearing, while a brass pulley wheel and hand-written serial number means conventional bearing. Any former Thorens employee's care to comment ?