Tuesday, September 29, 2009

Audio - Speaker Spades

A
few weeks ago I made a blog entry about the construction of some balanced interconnects for my home audio system. At the same time I put together some speaker wires.

The speaker wires are made from similar materials as the balanced interconnects.

Wire materials:

  • 16AWG dead soft .9999 silver wire
  • Teflon insulation for 16AWG wire
  • 1/4" O.D. (outside diameter) sleeving
  • WBT solder
  • Heat shrink

Since my system is bi-amped, I have four pairs (eight conductors) of speaker wires, each 2m in length. The wires have a banana plug for the speakers (Magnepan IIB) and a spade for the amps (Bryston 4B SST). I was able to pick up some cheap rhodium-plated, expanding banana plugs, but I wasn’t happy with the spades on the market, in particular their prices. For the price of eight gold-plated spades, I could easily purchase the materials to make my own solid silver spades. Given the choice, and my unrelenting propensity to Do-It-mYself, I decided to manufacture my own speaker spades.


Dimensions
Spade materials:

  • 1" x 6" of 12AWG (2mm) sterling (925) silver

Tools:

  • Vernier caliper
  • Hacksaw, vice
  • Files, sandpaper, Dremel rotary tool
  • Drill press, drill bits, center punch


Blanks and finished spades
This being the first time I’ve played around with a chunk of silver, I first practiced on a piece of less costly aluminum. The malleability was significantly different but I was able to work out sizing issues on the rough prototype.

The Bryston 4B SST Owner's Manual[PDF] specifies the ideal size of a spade for its binding posts. The 1" x 6" 12AWG sheet was the perfect size for eight 1" x 5/8" blanks with only a sliver of silver remaining after the saw cuts. Each blank had two holes drilled, four more short cuts, and some careful bending, filing and finishing.

Combined with the hydrogen sulfide (H2S) floating around in the air, silver (Ag2) turns into silver sulphide (Ag2S), also known as tarnish.

H2S + Ag2(s) → Ag2(II)S + H2


Soldered connection and
finished product
Tarnished silver does not conduct electricity as nicely as pure silver. It is important to clean and prevent the tarnishing of silver contacts. I used some CAIG DeoxIT® D5 to clean the surfaces of the spades. DeoxIT is supposed to cleanup oxidation – but silver tarnish is a sulfide... so I’m not sure if it’s the right stuff to use but it seems to work. CAIG marketing materials says it’ll work...

I am quite pleased with the fit and finish of the final product. I won’t claim that there is an audible difference, but it does look pretty cool ...and so does my shop floor with about ten dollars worth of sparkly silver bits.

Sunday, September 13, 2009

Automotive – Porsche Speedometer Replacement

S
urprisingly, having a low-miles, all-original 1984 Porsche 930 can be a real bummer. It’s a ridiculously fun car to drive, and even washing it can be a sensual experience. The problem is that I never get to work on it. Nothing goes wrong (which, actually, is great) and making “upgrades” to such an OEM car is criminal. However, as a habitual tinkerer, having such a fine example of German engineering in my driveway is a huge temptation. This is why I’ve decided to gut it and convert it into a competitive drift car – – joking.

Luckily I’ve been able to satisfy my DIY urges on my VW Super Beetle (and it needs it!). Having said that, I still jump at the opportunity to do work, even if very mundane work, on its more mature, but “├╝bermensch" sibling, the 930. The latest thing I’ve done is replace the speedo (not to be confused with the like-named, tight-fitting, TMI swimwear).

You can find a lot of Porsche 911 Turbos on eBay with questionable odometers (if you plan to buy one, I highly recommend first investing in an AutoCheck account). However, in this case what I’ve done is actually replace the speedometer with the original factory speedometer – a restoration if you will.

When the car was new, it was imported into the United States as a “gray market” car since Porsche was not exporting the 930 model to the US from 1980-1986. As a “Euro” car, it was converted to American standards, which including de-metric-izing the speedo/odometer. The gentleman who did the import and conversion, the original owner who I bought from, was thoughtful enough to keep the original German equipment, and I thank him for that. I live in Canada and I benefit from the superior metric system, thus my motive to do the swap back.

The American miles odometer has about 20,000miles (about 32,200km). At the time of putting it back in, the original had only about 340km.

The replacement is easy with only a few considerations – primarily where to hookup each wire. The instrument pulls out without any tools (but a good amount of fingertip strength is required and maybe a push from the back). Once out, grab your toolbox camera and take a snapshot of the existing wire hookup. Compared to the metric instrument, the terminals in the same locations can be used. The internals of the instrument are clever enough to accommodate the differences in scale as well as different upper range of 300km/h (186mph) instead of 150mph (241km/h). And yes, its documented top speed is 278km/h (173mph) – fourth gear at 6750RPM...and remember, this is a stock production car in 1984! And no, I have never driven that fast.

Now don’t worry, I plan to keep the “miles” speedometer with the car as part of its history – and not pass the car off as a 400km car. That said, I am curious how my local Registry of Motor Vehicles will handle the swap – have I just done something illegal? I’ll follow up next year when I get my next Motor Vehicle Inspection.