I mentioned in the RAAL-requisite SR1a thread, that I’d post a bit more info on the custom interface/headphone cable I built for them:
I wanted something a bit “prettier” and more “audiophile” than the stock cable, as well as wanting to experiment with different cable resistance, as this has a noticeable difference on the treble-response of the SR1a. I built versions in 0.05 Ω, 0.1 Ω and 0.2 Ω and would up preferring the 0.1 Ω configuration.
Cable basics are:
- Proprietary* dual-interleaved, quad-helix, geometry.
- Ultra-low resistance** and capacitance.
- High purity, oxygen-free, pure-copper wiring.
- High-density, plated copper-matrix shielding.
- Electron-beam irradiation (EBI) - for improved flexibility and reduced microphonics.
- Cryogenic treatment - because … “Why not?”
- Reflective and Glow-in-the-Dark cable sheathing.
Raw parts cost is as follows (with shipping included, since each part comes from a different vendor):
| Part | Price | Qty | Total |
|---|---|---|---|
| Eidolic 3.5mm TRRS Connector | $30 | 2 | $60 |
| Neutrik 4-pin Female XLR Connector | $10 | 1 | $10 |
| Splitter | $16 | 1 | $16 |
| Sheathing (per foot) | $1 | 12 | $12 |
| Sundries*** | $5 | 1 | $5 |
| Total | $103 |
The cable itself is a complex assembly/winding involving four conductors per channel, with cotton spacers and a special wrap to maintain the geometry. The raw wire is $6 per conductor/foot; so that’s 4 x $6 = $24 per channel on raw wire, with another $4 per foot for the spacers, wrap and shield - so $28 per channel/foot. Or $56 per stereo foot, and thus $336 for a 6 foot run of the 0.1Ω configuration.
So that’s a total of $439 in parts, and cryo and EBI treatments come to $25 total.
Grand Total: $464****
The 0.05 Ω version requires twice as many conductors which would double the cable costs (total would be $875 with $772 in cable), and requires ditching the shield in order to avoid the cable becoming too heavy and inflexible.
The build itself is not particularly challenging, except for a) winding and binding the cable assemblies and b) ensuring the overall resistance of the cable is under 0.2 Ω (which is the maximum permissible):
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You could, in theory, build a 0.2 Ω version of this cable using something like Canare Star-Quad cable, which is much less expensive at about $0.50 per foot. That’d be just $6 total for the two 6 foot runs required, so would save >$300 on parts (and a LOT of time in assembly, since there’s no cable to wind and bind). Though it’d be thicker, heavier, less flexible and a lot plainer looking (unless you stripped the jacket and re-sheathed it). You’d also need a bigger splitter and would have a lot of fun getting two runs of it into the back of the XLR connector!
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Measuring very low resistances does not work with basic/inexpensive multi-meters. For that matter, it isn’t really precise enough with expensive, calibrated meters either. My Fluke 289 measures anywhere from 0.08 to 0.19 Ω just directly connecting the probes together (the variance comes from exactly where they touch and how much of them are actually touching). Meters with a “Relative” mode (like the 289) help some, here, as you can cancel out the inherent resistance of the probes. But it’s still more variable than we want. In reality you need to do the four-wire (“Kelvin”) approach with an appropriate meter (which is, incidentally, how I do it for things like this).
A final word on resistance if you are going to make such a cable yourself. Cleanliness of the solder points, contact area between them and the conductors (as much as you can get!), and the quality of your solder and soldering all will be factors here, especially if you’re attempting a longer cable. For the 0.05 Ω cable, after doing the basic assembly, I used a hot-air station to reflow the joints and cooled them over a 20 second period, instead of the natural 1-2 seconds you’d get when you simply remove the iron from the joint.
I do not want to dissuade anyone from making their own cable here. If you’re careful, are proficient at soldering/cable making, use the right materials (most importantly a suitable gauge of wire and avoiding cheap knock-off connectors which may have more resistance on their own than you can afford for the whole cable), take your time, and keep the length to 6 feet, then building a 0.2 Ω version of the cable will likely work “on faith” (i.e. without having to measure the resistance or take special measures, at all).
*It’s possible that other cables use the same geometry, but I am unaware of any.
**As low as 0.05 Ω for a 6 foot cable.
***Heat-shrink, grommets, hot-glue, speciality solder etc.
****Without labor or accounting for tools, so you couldn’t sell or buy this cable for that price.