Infinity Black Widow Tonearm Rebuild



A friend gave me a rough Thorens TD-165 with a very broken Infinity Black Widow tonearm.

The Black Widow was made by the speaker company Infinity in the mid '70s to early '80s and was a very desireable arm; as a matter of fact, it is considered a classic by many audiophiles to this day. This BW is classified as an ultra-low mass arm and was designed to work with low mass, high compliance moving magnet cartridges. This arm has a double knife edge bearing with a conventional bearing pivot.

The lore of the Black Widow was that it was the first arm to employ carbon fiber (called graphite in it's day) for it's light weight, high torsoinal strength, and low thermal expansion coefficient. The BW is also said to be somewhat rare, but rare is an overused word these days. There is not a whole lot of solid, factual information on the Black Widow on the internet, so I would like to share through pictures and words what I have learned and how I have rebuilt this little audio gem. I will also try to include closeups and measurements when possible.


First thing I discovered is that this arm has absolutely no carbon fiber/graphite. The first clue was the metalic silver edges of the broken arm tube - this is really 4.5mm black anodized aluminum tubing with a very thin wall. This tubing is inserted into a larger tube that is in turn connected to the bearing fixture. The counterweight assembly is also bolted on to the bearing fixture with a thin gasket of rubber.

I then thought that the larger tubing was carbon fiber as you could see a bit of grain, but as I popped out the tube retaining pin, a small amount of metal was displaced causing a lump on the edge of the hole - this cannot happen with carbon fiber as it is not malliable. Nope, no carbon. It is almost certain that Infinity would have used this information in their marketing. After a little more searching, I found that the early Black Widow had a two piece aluminum wand while the later model used a one piece carbon fiber wand.

I decided to use carbon fiber to replace the broken arm anyway. Why? Because after searching the net for the few suppliers of thin walled metric aluminum tubing, I would have had to purchase a large and expensive order. I would have also needed to surface mill and anodize to match the outer tubing. That's an awful lot of time and expense. Pulltruded carbon fiber tubing, on the other hand is readily available in a diameter close to what I needed (.180" = 4.58mm), comes in a nice satin black color, and is available one tube at a time. Cool beans.


Another compelling reason to use carbon fiber tubing is because carbon fiber is supposed to have low resonant characteristics. I found an interesting article that mentions the structural resonance of the Black widow . Since I cannot duplicate the test, nor can I directly compare my rebuilt BW with an un-modified unit, I will (very un-scientifically) assume that the carbon tubing will have more desireable resonant characteristics and also because a carbon fiber arm wand is a pricey but better sounding upgrade/option for other arms such as the Well Tempered Arm. Looking at it from this point of view, a regular repair becomes a spectacular upgrade! Gotta love turning lemons into lemonade :)





Page created by James L Woodley © 2006 Page last updated 28 February 2020