HSR Patchbay Project
An inexpensive, easy to construct accessory for the home studio.
An inexpensive but vital piece of studio equipment that can be built by anyone who is capable of soldering a jack plug.
The patchbay described here consists of 16 pairs of jack sockets, each pair mounted on a small PCB and fixed to a 19" wide x 2U high rack panel. Connections to the rear of the patchbay may be hardwired or made by means of phono connectors and a wire link is fitted to each PCB so that a normalised or non-normalised configuration may be implemented.
In the normalised mode, the top jack socket of the pair is normally connected to the bottom one unless a plug is inserted into the bottom socket, in which case the circuit is broken. If a plug is inserted into the top socket, however, the circuit remains unbroken allowing some signal to be tapped off for processing without disturbing the existing arrangement (Figure 2).
Normalised pairs of sockets would generally be connected to the insert points on the mixer whilst a further row of non-normalised sockets would be allocated to effects. In this way, the effects unit can be patched into any required location by means of short jackleads, thus eliminating the need for an expedition into the jungle of leads behind your mixing desk.
There will be a detailed article on the use of patchbays in the very near future but now we'll concentrate on building it.
The PCB is designed for use with PCB-mounting jack sockets, but as these are not generally available in small quantities, a standard jack may be modified by cutting the tags as shown in Figure 1.
Solder the modified jack sockets to the PCB and fit the link if appropriate. Next fit the PCB-mounting phono sockets to the PCB (if required) and solder these into place. The soldering is not quite as straightforward as it could be due to the large holes required to accommodate the tags, and so care must be exercised in order to prevent the solder from running through the holes and down the legs of the sockets.
Once all 16 PCBs are fully assembled, put them to one side and mark out the front panel in accordance with Figure 3 ready for drilling.
Drilling is easily accomplished by means of an electric hand-drill providing a few simple guidelines are followed. Firstly, centre punch the hole positions and then, setting the drill to its slow speed, drill through the panel using a small drill bit of ⅛" diameter.
Next, fit the large drill bit and drill all holes about halfway through. (If you drill completely through you'll probably end up with a huge burr which is difficult to remove.) Turn the panel over and drill the holes through from the other side, not forgetting to place a piece of scrap wood below the panel first to drill into.
The next step is probably to swear at me because, despite the above precautions, you've still got a burr around each socket hole to remove. Fortunately, aluminium is quite soft and so a Stanley knife or similar will remove them fairly easily. When you've had the stitches out and cursed me again, rub down the front panel with wet-and-dry paper or wire wool in a hot soapy water and then dry it using a grease-free cloth.
Painting is best achieved using aerosol spray paint, so apply a coat of primer first followed by the main colour of your choice. A light colour is best as you can then write on the panel in wax pencil, but an alternative is to affix labels or strips of white Fablon to the panel.
When the paint is thoroughly dry, fit the sockets through the panel then replace the nuts to secure the assembly in place and the patchbay is complete.
Make up the leads that will plug into the rear of the patchbay by using the best quality screened cable that you can afford ensuring that it will fit through the holes in the phono covers. It is always best to go for a cable with a woven screen, but the simple wrapped-screen type will do at a pinch for short runs of line level signal, although you run the risk of picking up some interference if you're unlucky.
If you only have a limited requirement for patching facilities, the panel may be split so that normalised insert points are connected to the first few pairs of sockets and the rest may be left un-normalised for use with effects units and in this way, the entire patching requirements of a small studio can be accommodated quite easily by only one patchbay unit.
PCBs are available in sets of 8 at £6.50 each. Sets of 16 phono sockets cost £5.00 each. All prices include VAT & p&p. Please make cheques payable to Music Maker Publications Ltd and allow at least 28 days delivery and please send to: HSR (Contact Details).