Hi,
The most intriguing part was the construction of the tonearm. That such a simple concept, the unipivot, works so well, and is so easy to implement, is amazing in itself.
This arm was made at home, with materials on hand. The arm material is teak, approx 12mm square with rounded edges, and length to come close to a 12" tonearm. The headshell was shaped from the armpiece itself, for a single point cartridge mount. That way the cartridge angle can be adjusted easily. Since the arm material is lossy in itself, absolute rigity is not a consideration here. The end where the counterweight sits was rounded and threaded to match threads within the counterweight body. This is another easy adjustment to dynamically balance the arm and apply tracking force to the cartridge. The counterweight is an aluminium piece cut from the counterweight of an old table lamp.
On selecting the cartridge, an old Supex SD900 Super, using its weight, the pivot point was determined, to give some adjustment with the given counterweight. A hole was drilled in the arm, at the pivot point, to a depth just above centerline of the arm. A small metal disc was embedded at the end of the hole. This was the support for the metal point of the unipivot.
That point was a simple ball point tip. Embedded in a wood support pillar, the height of which was determined to run the arm parallel to the record surface, with the selected cartridge. The position of the support pillar was to provide the proper arc, tracing the cartridge to the centre spindle of the turntable.
Balancing the tonearm showed the true character of the unipivot - a tendency to shift and flop the arm! Obviously, some additional support was required. I eventually put in some teflon sleeves in the hole in the arm, reducing the flop. This is one area where more thinking and experimentation is required!
Wiring from the cartridge to the RCA sockets is single conductor 30 gauge insulated winding wire, using old clips to attach to the cartridge pins. The wires are taped to the underside of the arm up to the pivot point.
The angle of the cartridge was set using a protractor. The tracking force was set to 1.8 grams using the Shure stylus gauge (by turning the counterweight).
Perform, the arm certainly does! The lossiness of the wood does not seem to be at all detrimental in recovering information from the record grooves. The 360 degree freedom of movement (not there yet in this arm!), and the high pressure point support is clearly showing its benefits.
The music is clear and lively. There is a solidity to the image which is captivating - as is said "more there there!" The best part is the resulting tone. Strings being reproduced with so much vibrancy and body. Brass with texture and bite. Piano is percussive and tonally rich. Voice projected with great realism. Thoroughly enjoyable!
Some credit ought to go to the cartridge too. The Supex is used and old - has been sitting with me for over 25 years! That it still works, and the cantilever support has not dried up, is amazing. I understand these cartridges were designed by the legendary Sugano. That's why they are tonally rich. No desire to change to anything else at all.
I'm going back to listen to some more LPs.
'Bye,
Viren
