Psionics Missing Link
A cable tester and junction box that can test or interconnect XLR, jack, phono and DIN leads
The level of technology used in music equipment is now so high that the humble lead gets taken rather for granted. It is, however, a recognised fact that most failures are attributable to faulty leads, and this can only be avoided by regular checking and preventive maintenance.
A simple lead tester is not difficult to build but, because of the different sized sockets (and hence holes to drill) and the fact that it isn't particularly exciting, it tends to get pushed to the end of the queue.
Psionics use this national apathy to their advantage by offering a ready-built lead tester at an affordable price and, when not in use as a tester, it may be used as a one or two channel junction or splitter box.
It is not necessary to describe the front panel in any detail except to say that the LEDs are green. The heavy gauge steel case is about six inches square and two inches deep, being finished in black satin paintwork with white legend.
A PP3 battery provides power for the circuitry and this is housed at the side of the case in a drawer which looks rather like the ones found in mortuaries, except that it is very much smaller and made of plastic. The biggest difference is that a live battery is placed in the drawer and eventually evicted when it is dead.
Inside the box, the wiring is neat and the simplicity of the circuitry precludes the need for a PCB. The whole thing has a solid, professional feel and stands daintily on four white, stick-on, rubber feet.
A small toggle switch on the front panel doubles as battery test/cable test, or single/double channel junction box selector. When set to 'battery test,' LED 2 and 3 will light up as the selector switch is rotated to those positions. Switching to cable test, no LEDs will light up unless a lead is inserted between one socket in channel one, and one socket in channel two.
If a balanced lead is being tested, then LEDs one, two and three will light up, one at a time, as the selector is rotated to those positions, all other lamps being off.
If an XLR lead is being tested however, a fourth LED labelled 'case' will illuminate if the screen of the cable is connected to the case. In the event of a faulty lead being checked, more than one LED will come on if there is a short circuit and at least one LED will refuse to light if there is an open circuit.
When checking mono jacks, LEDs two and three will come on together because the box can't tell a mono jack from a stereo with a sleeve-to-ring short, but this is easy to interpret.
Switching the selector switch to 'off' allows the unit to be used purely as a passive junction box, no battery current being drawn in this mode. When the toggle switch is set to dual channel operation, channel one and two are electrically isolated and may be used as independent junction boxes. When switched to single channel operation, all the sockets on the panel are wired in parallel (except the Left and Right phonos which maintain their stereo integrity) so that, for example, two male or two female XLR connectors may be linked together.
It's well made, attractive and it does its job well. At the modest asking price of £58 plus VAT, it's really not worth drilling all those awkward holes to make one yourself, even though we are usually the first to promote the virtues of home construction when appropriate.
Why not buy one and do your leads a favour, after all, the value of the plugs presently dangling at the ends of your faulty lead collection is probably greater than the cost of this box.
The Missing Link usually retails at £58 plus VAT from Kelsey Acoustics, (Contact Details). However, HSR readers may take advantage of a special offer price of £45 plus VAT (inc p&p). Further details in this issue.
Review by Paul White
mu:zines is the result of thousands of hours of effort, and will require many thousands more going forward to reach our goals of getting all this content online.
If you value this resource, you can support this project - it really helps!