Setting up a decent patchbay system for your studio can seem like a lot of hassle. Is it worth it? Paul White considers the ins and outs of patchbays, and concludes that the potential benefits far outweigh the initial effort.

Just as the majority of the human body is made up of water, it is my contention that at least 90% of every recording studio is made up of cables! At least, it certainly seems that way. This poses no real problem as long as the cables go exactly where you want them to go, but the nature of recording is that we need to change things around on a fairly regular basis; we may want to use different effects or processors during a mix, we might want to run the cassette deck back through a mixer line channel to add sound effects, or we may need to plug a friend's multitrack into the system. It would be exaggerating only slightly to say that the possible permutations are infinite, and if a studio is to run smoothly, some form of patchbay system is essential.

For those who've yet to incorporate patchbays into their systems, it should be stressed at the outset that although a large patching system can look daunting, the underlying concept is quite simple. In reality, all a patchbay does is get all the inputs and outputs that you might need to access out to a central area where they can be linked as required using short patch cables. The alternative is to fiddle about around the back of equipment which is, as often as not, located in some dim and inaccessible corner, only to find that the legend is embossed in black on a black background and is totally unreadable without a torch!

PATCHBAYS

In professional studio installations, the patchbays are often wired for balanced operation and are fitted with small, specialised jack sockets known as Bantams. They are relatively reliable, easy to service and compact — but they cost a fortune, and you can't plug any of your standard instrument leads into them without using an adaptor or special cable.

For the home and project studio, unbalanced, quarter-inch jack patchbays have become the norm; they accept standard jack plugs and they're reasonably cheap. Until recently, most jack patch panels were limited to 16 pairs of sockets, or at best 22. However, recent designs have managed to squeeze in 24 pairs which is more convenient for those working with 24-track recorders.

A typical patchbay is shown in Figure 1. In addition to the front panel sockets, there are further sockets at the rear which facilitate the connection of the patchbay to the rest of the system. Alternative versions are sometimes available with solder connections on the rear, and though these are more difficult to wire up, they offer several advantages; they save the cost of the jack plugs needed to connect them to the studio wiring harness, there are no plugs to accidentally pull out, and the signal path is more reliable because there's one less plug and socket for the signal to pass through. Convention has it that the bottom row of sockets is used for signal inputs while the top row is used for outputs. There is invariably provision to label the sockets, and it pays to do this as neatly as possible — it saves a lot of frustration.

NON-NORMALISED

The simplest form of patchbay is the so-called non-normalised type; this acts purely as an extension system to bring inputs and outputs to a point where you can get at them. In other words, the patchbay sockets behave exactly like the input or output sockets on the back panels of the various pieces of equipment connected to it. A typical application of this type of patchbay is to bring out the signal connections for outboard effects and processors, and to make certain mixer connections more accessible, such as aux sends and returns, and line inputs.

NORMALISATION

There are some patchbay applications where a non-normalised connection doesn't do the required job, the most obvious example being console insert points. The idea behind insert points is that an external device can be inserted into the signal path, and to do this, the existing signal path must be broken or interrupted. This is achieved by using a special stereo jack socket, which has an extra pair of contacts known as 'normalising' contacts. When no plug is inserted, the contacts are closed and the signal path is unbroken; when a plug is inserted, the contacts open, breaking the internal signal path — so now the signal takes a detour via whatever external processor has been plugged in. If a plug is inserted, but not connected to another piece of equipment, then the signal path will be broken, the signal will have nowhere to go — the mixer channel will go dead.

If we were to connect the insert send and return points (the ring and tip of the stereo jack plug) to a non-normalised patchbay, there would be no problem when an effect or processor was plugged into the patchbay, but if no device was connected, then the insert point would remain open and the signal path would be broken — exactly as in the case of a console insert socket. This is clearly of little use; you'd need to connect all the unused insert send and return points on the patchbay using patch cables to restore normal signal flow, which would be very cumbersome, not to mention expensive in leads.

"The alternative to a patchbay is fiddling about around the back of equipment which is usually located in some dim and inaccessible corner, only to find that the legend is embossed in black on a black background and is totally unreadable without a torch..."

The practical solution is to use a normalised patchbay. These use sockets with built-in normalising contacts so that when no plugs are inserted into the front of the panel, the top and bottom jacks are automatically connected together. A more correct term for the type of system used in conventional patchbays would be semi-normalised. Here, plugging a jack into the low socket breaks the circuit, allowing an external signal processor to be inserted into the signal path, but pushing a plug only into the top socket leaves the normalising intact. There is a very good reason for this: it allows you to use the top socket to take a feed from an insert point without affecting the normal mixer operation. In other words, it provides a convenient way to split a signal.

PRACTICALITIES

In reality, most patchbays can be configured for normalised or semi-normalised use — you don't have to worry about two different versions. The illustration in Figure 1 shows a normalising link which may either be made using a short length of wire or by running a blob of solder between two printed circuit 'pads'. A simpler approach is that adopted by P&R Audio (Contact Details), who have devised a reversible patchbay circuit board which is normalised one way around and semi-normalised the other. The fact that each pair of sockets is independently configurable means that a single patchbay can be wired with a mixture of normalised and semi-normalised sockets if required.

One of the easiest ways to wire patchbays is to use foil-screened cable, because it is easy to wire up, reasonably thin, and offers excellent screening. Depending on the complexity of the patching system, the wiring may be carried out with individual cables, or a suitable multicore cable of the type that contains several individual, foil-screened cables inside a single outer sheath. Suitable types are available from Studio-spares (Call (Contact Details) for a Studio-spares catalogue). It is advisable to support the cables so that they are not pulling directly on the rear of the patchbay, as this may lead to cable fractures or plugs working loose.

It is also sensible to locate the patchbay as close to the mixer as possible, as most of the interconnections will be between the mixer and the patchbay. As in any audio installation, the shorter the cable run, the better. With line-level signals, cable resistance and capacitance is unlikely to have any detrimental effects when using cable runs of only a few metres.

The cable run from the effects rack should also be kept as short as possible, and if it is not possible to route this through under-floor ducting (unlikely in home studios), consider threading it through a length of vacuum cleaner hose to keep it tidy. This method is particularly effective when the effects are mounted in a mobile rack. Proprietary cable tidying systems are also available for this purpose, and range from simple cable ties to corrugated plastic sheathing.

SUMMARY

Some form of patching system is essential if a studio is to run smoothly, but there is a valid argument in favour of making as many permanent connections as you can to cut down on the number of plugs and sockets in the signal path. Normalised patchbays are potentially the most trouble prone, so when choosing these, don't skimp on quality; go for a model with gold-plated contacts if you can afford it. Non-normalised patch panels are less critical, but even then, don't always go for the cheapest. Figure 2 illustrates typical patchbay applications.

Even with unbalanced patchbays, there can be advantages in connecting them to a balanced line input, and the article 'Earth Loops Are Easy', which was published in the May 1993 issue of Recording Musician shows how this can be achieved. The result is a much improved immunity from hum-causing earth loops. In a studio with mainly balanced equipment, balanced patchbays should be used; most patchbay manufacturers offer balanced versions for only a small extra cost. Note: some designs of patchbay have a common earth connection running along the panel joining the ground or cold pins of all the jack sockets together. I feel this type of design invites ground loop problems; models where each socket pair is independent of its neighbours (and not grounded to the front panel) are more electrically 'hygienic'.

Patchbays arranged vertically will accumulate less dust and debris than horizontal ones, so if you must use a horizontal bay, cover it with a clean cloth when not in use. Finally, clean your patch lead plugs regularly with a rag soaked in WD40 or isopropyl alcohol, and make up decent quality patch cables rather than using budget moulded types.

Connect mastering machines to the mixer via a patchbay. This allows mixing to be done onto any machine and makes it easy to copy from one stereo machine to another, for example, when making DAT to cassette copies. Sensible use of normalisation will ensure that the most common taks can be accomplished without patching, a typical example being that a DAT machine might be the default mastering machine and the console's two-track return points may be normalised to the DAT machine's outputs.

The inputs and outputs of all effects units and signal processor may be connected to a non-normalised patchbay. Equipment inputs are located on the bottom row and outputs on the top. Side-chain access points should also be brought out to the patchbay where appropriate.

Effects sends and returns should be wired to a non-normalised patchbay. Sends are wired to the lower row of patchbay sockets and returns to the top. Tape Returns may also be normalised to the Line inputs.

Console channel, group and master insert points may be connected to a patchbay for easy accessibility. The patchbay myst be normalised (ideally semi-normalised - see text) to allow an uninterrupted signal flow when nothing is plugged into the patchbay. Insert sends are wired to the lower row of patchbay sockets and insert returns to the top.

Other Applications

The outputs from MIDI instruments are best connected via a patchbay and may be normalised to feed the console line inputs if that is the most common mode of operation. Studio monitoring and headphone systems may also be made more flexible by providing patchbay access. It may be an advantage to connect normalised patchbays between the console's group sends and the multitrack inputs allowing direct access to the multitrack when necessary. Similarly, the multitrack outputs could be fed via a normalised patchbay allowing individual tape outputs to be intercepted for copying purposes. In general, any connections that need to be changed on a fairly regular basis may be fed to a patchbay.

WARNING: Loudspeaker level signals should never be fed via a patchbay as the propensity for expensive accidents is unacceptably high.