Thorens TD 165 / Hadcock Unipivot Tonearm

This is my Hadcock GH 228 unipivot tonearm. It has a base, mounting pillar and bias assembly from the earlier Unipoise tonearm with a GH 228 arm wand and weight assembly attached.

There are differing opinions regarding the Hadcock (and many other Unipivots). Because of their design, they are succeptible to mechanical anomolies that you will not get with traditional designs. Even when properly set up, there is still some amount of rotation of the arm that will affect the azimuth, or how level the cartridge is over the record surface. Many unipivots (including the GH228) use a counterwieght that has a low centre of gravity to help overcome this tendency to twist, but this can also cause difficulty when tracking warped records. Some felt the early Hadcocks were just too 'Heath Robinson' to really merit consideration as proper hifi. I have heard comments that they never worked without post purchase modifications and that they were just too fiddly to ever really get the most from. It is true that they are very fiddly (or at least my early version is). There are no markings or calibrations anywhere on the thing, so adjustment and setup is time consuming! With most unipivots you have to make careful adjustment to the low slung counterweight to make sure that cartridge is level and then hope that the thing does not slip under the affects of gravity. All in all, not a tonearm for the impatient.

This pic shows the Goldring mounted on the Hadcock GH228. The headshell does not have slots and so does not allow you to align the cartridge properly. You can overcome this by using smaller than nomal (M2 or M2.5) nuts and bolts, these allow you to twist the cartridge to get proper alignment. You can see the difference in angle between the headshell and the cartridge nounting plate.

All that fiddling, why do I bother? I would have to say that I like the simplicity and the idea of a unipivot. Why have all that excess guff like bearings etc. when a simple sharp bit of steel will do the job? Without spending a fortune I reckon this offers me a good chance of high performance. The advantages I think I have are in a reduction of interference with the cartridge for improved tracking and less succeptibility to distortion. I have not yet made up my mind on whether the soundstage and stereo image is better because of the arm or just because of the general improvements I have made to the system. Certainly stereo image is in part due to the rigidity of the platform the cartridge sits on, and a unipivot is not rigid. I think that it is improved by the use of the Shure because I think that the compliance of the stylus assembly is higher. Therefore the stylus will move more easily and the vibration is less likely to travel into the arm and cause swing or rotation, pitch or yaw! Whatever the reason I am very impressed with the clarity of records and I do think that the Shure M91 (and now the M97) seems to be a good match on the Hadcock arm. I certainly enjoy the sound of this set-up more than the old Dual that served me so well for so long!

The Hadcock has been modified a bit. Mine came with both an early 228 and a Unipoise arm/bearing. The old Unipoise arm tube was removed from the bearing and replaced with a 1/4" stainless steel tube. This is more rigid (and heavier) than the original aluminium tubes. The resonance with the Shure M91 is still OK at 9Hz though. The counterweight on the Hadcock was never particularly satisfactory, as the decoupling rubber seemed to have changed over time. There was some slip between the counterweight and the bearing assembly and it did not seem to be that stable a connection. I had the opportunity to aquire a slightly damaged Decca unipivot at low cost, so took the opportunity to canibalise it for the heavier screw adjustable counterweight, which was relatively easy to adapt to fit the Hadcock. This is a lot easier to adjust than the original Hadcock (especially seeing as I had abandoned the Hadcocks screw mechanism some time earlier as it was too fiddly). Adjusting the azimuth is still done by rotating the counterwieght. I have also replaced the antiskate string and weight (it was far too light) with a new peice of monofilament (Korbond colour blend nylon sewing thread) and a fishing weight.

Thorens TD165

Initially the modifications to this classic deck have been pretty minor. I have set the arm up on my Thorens TD 165 (using the original arm hole, luckily preserving the tonearm lift and original top-plate of the deck). I have replaced the tonearm internal wiring (less difficult than I imagined but you have to be wary of any drag or force where the wire comes out of the armtube) with some Cardas wires and replaced the external wiring with a very nice silver cable, DIY of course.

As with many Thorens decks, the mechanical speed change mechanism continues to lack reliability. The mechanism fails to move the belt consistently to the 45rpm section of the pulley, but it is such a common problem and I play such limited numbers of 45s that I have not perservered for more reliable switch over. If it is misbehaving I set it with the platter off then replace the platter for play. Return to 33 is no problem.