Studio Wiring: A Practical Guide, Part 2

Tips & Techniques

Published in SOS May 1994
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Technique : DIY

Having addressed your studio mains wiring, you can now turn your attention to the connections between your equipment. PAUL WHITE explains the undoubted benefits of a patchbay system. This is the last article in a two-part series. Read Part 1.

 

Patchbays are designed to bring some degree of order to the potential wiring chaos of the recording studio -- though some people seem to put off installing patchbays for as long as possible, usually because they are worried that both wiring them up and using them will be complicated. It's true that you can get into a real mess if you try to install a patchbay system without first planning what you actually want to achieve -- which is where this article should come in useful.

While many of the connections in a typical studio can be left alone, many more need to be changed on a daily basis. For example, you may have a compressor that needs to be patched into different mixer insert points as required, or you may want to move an effects unit from one send to another. You might need to copy a DAT tape, perhaps via an equaliser and enhancer, onto cassette, and later in the day might need the enhancer to process a stereo subgroup on your mixer, or the equaliser to process a couple of input channels. No matter how you try to rationalise your system, you never seem to get away without having to repatch things.

Patching without patchbays is awkward, mainly because most bits of studio gear have their connections at the back where you can't get at them easily. Even if you can get at them, the chances are that they're labelled in black on a black background, covered in dust, and positioned in the darkest corner of the room. This certainly applies to most of my synths and effects units, though the current fashion for Macintosh-grey boxes means that some are now labelled in beige embossed on beige!

Mixer insert points may or may not be easily accessible, depending on the make and model, but most use stereo jacks, so unless you have an endless supply of Y-leads or adaptors, they're not easy to use. Aside from the fiddle factor of having to patch directly between the individual pieces of equipment, a studio completely devoid of patchbays soon ends up looking like a mad woman's knitting. By the same token, building a patchbay that allows you to route anything to absolutely anything else is likely to be over-complex, and over-expensive.

That's where the planning comes in -- you have to decide what you can afford to leave permanently patched and what you are likely to want to move on a regular basis. For example, if you have more effects sends and returns than you have effects units, you could leave your effects permanently wired in rather than use a patchbay. You might then bring any spare console sends and returns out to the patchbay to enable you to patch in effects which clients or friends might bring into your studio.

WHAT IS NORMAL?

At its simplest, a patchbay can be regarded as a system of extension cables that brings all your input and output points to an easily accessible panel, enabling you to patch any input to any output using a short patch cable. Most semi-pro studios use standard jack patchbays for this purpose because they are relatively inexpensive, and because they interface with most musical equipment, such as synths, effects, pedals, guitar preamps and so on. Professionals use the more expensive Bantam mini-jack, which allows more patchbay to be crammed into a smaller space, but has the disadvantage that you need adaptor leads to plug any real-life equipment into it.

The most popular form of jack patchbay is the one that also uses standard jacks on the rear, which means you can wire up all your system using conventional jack leads. This scores highly in the convenience stakes and also makes it easy to reconfigure your patchbay when you want to integrate a new piece of equipment. You can also buy 'hard-wired' patchbays, where the rear connections are soldered directly to your cable harness; this is cheaper and, because it cuts down on the number of plugs and sockets, more reliable. However, wiring up a patchbay of this type is tedious and time consuming, and any change to the patchbay wiring calls for major surgery.

Where a patchbay is used to provide access to the ins and outs of effects processors, to the input channels of a mixer, and so on, a basic, non-normalised patchbay is required. In other words, the socket at the back of the patchbay connects directly to the socket on the front and nowhere else.

Another type of patchbay, known as normalised, is required for use with insert points. The reason for this is that the stereo jack commonly used for mixer insert points includes a pair of switch contacts which route the insert send directly to the insert return when no jack is inserted. If this were not the case, there would be no continuous signal path through the mixer channel unless a processor of some type was plugged into the insert point.

Once you plug a patchbay into a mixer insert point, the mixer's internal signal path is broken because the insert point assumes you've plugged a processor into it. This is clearly not good news, because it means that whenever you don't have a processor plugged into the patchbay, you have to join the insert send socket to the insert return using a patch lead, otherwise the signal has no way through. Fortunately, the so-called normalised patchbay uses internal switch contacts to do this for us automatically; when no connection is made to the patchbay, the input jack is connected to the output jack.

Before moving on, there's a further stage of development to consider: the concept of semi-normalisation. In some circumstances, it can be useful to take a signal from an insert send without breaking the signal path. For example, you might want to split a signal so that you can feed it both through the mixer channel and into a signal processor at the same time. To make this easy, the semi-normalised patchbay was developed; when nothing is plugged in, the patchbay output (insert send) is connected to its input (insert return). If a jack is plugged into the output only, the input still remains connected to the output, but whenever a jack is plugged into the input, the signal-path is broken. The term 'sniff and break' was coined for this type of patchbay, as plugging into the patchbay output socket allows you to 'sniff' the signal without affecting the existing signal flow, while plugging into the patchbay input breaks the signal flow.

PRACTICAL PATCHBAYS

Most patchbays on the market comprise two rows of jack sockets; the lower sockets are conventionally used as inputs and the upper sockets as outputs. Most also include some way to change individual pairs of sockets from non-normalised to normalised, the most elegant solution being that devised by patchbay specialists P&R Audio, where all you have to do is take out the circuit card, reverse it and put it back. In normalised mode, each socket on the bottom row is internally connected to the socket directly above it unless a jack is inserted into the lower ('break') socket. Inserting a jack into the upper ('sniff') socket doesn't interrupt the signal flow but does provide a split signal feed.

Both balanced (using stereo jacks) and unbalanced (using mono jacks) patchbays are available, though most home studios use unbalanced patching systems simply because most synths and preamps have unbalanced outputs. Insert points are also unbalanced on all but the very top end pro studio consoles. However, if you want to use a patchbay to provide access points between the balanced outputs of a mixer and the balanced inputs of a multitrack recorder, it is probably worth using a balanced patchbay for this application. This will require stereo jack patch leads, though most systems will allow you to use unbalanced mono jacks to feed unbalanced signals into a balanced input.

Cheaper patchbays sometimes occupy 2U of rack space but most modern designs are 1U, containing between 16 and 24 pairs of sockets each. When choosing a patchbay, check that the individual sockets are reasonably accessible for cleaning (isopropyl alcohol is good for this) and that there's sufficient room to attach labels.

WHAT TO CONNECT

It's always a good idea to bring out all your console insert points to a semi-normalised patchbay, and this should include the group inserts and the master (stereo output) inserts. If you don't want to wire up all the channel inserts, at least decide which channels you're likely to use for microphones and take their inserts to the patchbay so you can patch in compressors.

You can also use normalised patchbays between your mixer and tape machine, allowing you, for example, to plug in a DI box or mic preamp and feed this directly to tape without passing the signal through the mixer. Similarly, you might want to use a semi-normalised patchbay to bring the multitrack returns back into the line inputs of the mixer, especially if your console has no Line/Tape switch. This would enable you to patch in synths or other sources via the patchbay when the tape returns were not required.

Non-normalised patchbays are simple extension leads and are useful for bringing out the console line inputs, effects sends and effects returns, and channel direct outputs. You could also bring the inputs and outputs of all your effects, processors and MIDI instruments out on a non-normalised patchbay. Other uses for non-normalised patchbays include line level 'tie-lines', which are simply screened cables running from your patchbay to a wall-box in the studio. These may be used for any type of general-purpose connection; for example, you might want to play a guitar in the control room but have it plugged into an amp in the studio, or you might have synths in the studio area that you want to plug into the mixer in the control room. Even in the most modest home studio, if you have separate playing and control rooms, a few tie lines really make life easier.

I'll finish in the same way I started, urging you to plan first and start knitting afterwards. If some connections are seldom repatched, it may be worth putting up with the inconvenience of replugging on the rare occasion when you do need to change things around. Similarly, if you can leave your effects units permanently plumbed in, it makes sense to do so. Having decided what you should bring out to the patchbay, plan the location of your patchbay to minimise the wiring between it and the rest of your studio equipment. As most patching involves the mixer and the effects rack, it pays to keep them and the patchbay as close together as is practical. Once you've got your patchbay installed, you'll wonder how you ever managed without it.

 

LEADING QUESTIONS

Use good quality screened leads to wire everything up (but don't spend money on anything too esoteric -- we are talking line level here!), keep the leads as short as possible, and in the case of the Y-leads that you'll need for your insert points, consider buying ready made, moulded ones if you don't want to solder up your own. Keep the cables away from mains leads wherever possible and consider buying some plastic spiral cable wrap from Maplin (catalogues available from WH Smith) to keep the bunches of cable tidy.

For the patch leads, choose a soft, non-kinking cable or go for ready-made patch leads, and ensure that they're long enough to reach between the two furthermost sockets on your patchbay system. Coloured leads or plugs help you keep track of what's going where, but you can also put bands of coloured tape around standard black leads or plugs.

This is the last article in a two-part series. Read Part 1.
More In This Series:

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