Wednesday, 19 February 2014

A 12 inch Wooden Tonearm

Hello to everybody, this week I want share something untypical for the TrueFi blog and my understanding of the analogue audio chain. As the most people know, I am selling a conversion kit for classic SME tonearms. This conversion is dedicated to the classic medium weight arms into the heavier and stronger MK1 version in order to improve the pick up process with low compliance cartridges. The famous Ortofon SPU, the Denon DL103 and the more expensive japanese handmade cartridges from Koetsu, Ikeda and several others will tremendously profit from the heavy weight armwand. All existing twelve inch transcription arms are medium weight arms, so my kit makes a lot of sense to improve the dynamic abilities with this cartridges.
But there are some other extremely good vintage moving coil cartridges which unfortunately do not match the medium and heavy weight transcription tonearms. They were designed mostly in the later 1960ties or in the 1970ties when high compliance was advertised and all makers followed to nowhere. Here the famous Supex cartridges as predecessors of the unique Koetsus and their equivalent Linn cartridge line made by Supex in this time has to be named in a foremost stage. As well the successor of the SPU, the Ortofon SL15 is a wonderful cartridge almost a copy of the SPU with alnico magnet, similar assembly but with 15x10-6cm almost a high compliance cartridge. Some exotic cartridges of the 1970ties like the Toshibas or the Sonys need a lightweight arms to work with the best dynamic response. So what to do?

For this reason I always liked wood as light weight material in mind, wood has very musical properties and can be machined easily. I always wanted to test a wooden arm wand in my different SME tonearms since years, I never made it work. But I did buy rounded wood strips made from different wood sorts years ago for this reason. I had bought several broken tonearms in order to check their compatibility for my plans, a whole box with arms was stored away some years ago. So now it came into proof, I wanted to test it out.

Metal cased micro ball bearings

For that reason I looked for well designed bearings with low tolerance clearance either
for the vertical support and as well for the horizontal axis. Low tolerance micro ball bearings are in demand, if the material will be wood. The combination of relatively soft materials, like wood and precision metal work is a delicate design approach. First I did weight the standard stainless steel arm wand without interior damping wood. My ss armwand weight around 50 g, a comparable sized stick of hard wood like mahagony, oak or walnut differs around 20 g. If the cartridge holder is made as well from wood the completed armwand has almost the same weight like former used aluminum tubes of the originally 9 inch long tubes. This has another advantage, the counterweights can be still used even with the longer arm wand. The design has a overhang of 308mm and the cartridge carrier is angled off 18°. This geometry is a quite common design and is used be several arms of this length.

Wooden armwand from underneath, closed slot and a piece of copper foil for earthing the wirement

I had to cut a slot from the underside into the woos stick. For that reason I needed to make a tool to fix the round stick in position, when it will be tracked at my table saw. So I did cut a 2 mm wide and 4 mm  deep slot into the underside of my stick. I did use walnut for both parts, the armwand and the cartridge holder. Into the holder I did mill two slots for the standard 1/2 inch mounting of the cartridges. As internal wirement I did use my silvered copper litz with teflon insulation. In order to prevent hum problems the four wires needed to be screened in the wooden stick. Here a thin copper foil was used to surround the four cables. This copper foil together with the metal parts of the bearing assembly got wired together and lead out for separate grounding.

Unfortunatly this new arm is not the luxury edition, it does not have any extras like lowering device, vertical tracking adjustment, gravity free pressure alignment, a anti skating mechanism and variable geometry. It is simple and very basic, it requires one qualification – a "quiet hand".

Coming to the real experience with this tonearm. I have set it it up at my Platine Verdier turntable, mounted were normally my SME 3012 (MK1) is located. My standard pick up is the SPU Gold with the bakelite headshell, I did mount a Linn Asak (made by Supex, identical with Supex SD1000) directly at the holder.  This cartridge is very similar in characteristic with the SPU, its very dynamic and musical. Taking into account that now here a standard cable from silvered copper litz  was used, the first impression had a quite fresh taste. I did expect a very smooth, let us say more than that, a over mild general characteristic as first impression. But it came out different, a solid quite balanced soundstage of good depth and width was the first impression. Of course it did not have the pure dynamic attitude coming from the stainless steel armwand with the SPU in favorite task, but the combination was still a lot better than the cartridge with the heavy SME or even their standard aluminum armwand in the 3012. I switched to other program material. With classic music, for example with larger scaled orchestral music or with string orientated chamber music this combination is very good. A brilliant refinement of the complete mids and upper tonal range is the result of the damping qualities of the wood, the other side of the medal is a little lack of attack and dynamics. The domaine of this wooden arm is not the dynamic jazz ensemble, were punch is a important part of the realm coming true, but even there the arm works quite well. It has to be seen that this approach is a quite cheap alternative to other twelve inch arms in the upper 1000 plus region. I like its purist appearance in design, function and materials. It is an approach towards musical performance, for that it is a bargain...

If there are some interested people out there, which would like to have such a wooden twelve inch arm, you should get in contact with me. I will have some of these and they will be sold piece by piece through Ebay soon. If you are interested, you might make me an offer…

Read on soon, Volker