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.

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