How to Set up a Home Studio (Part 5)
Wiring A Patchbay
Part 5: Patchbay wiring. David Mellor proposes a more practical wiring system for your studio.
Dashing through the undergrowth, one false move and your foot becomes entangled in a wire noose. The trap is sprung and the tree branch snaps upwards, leaving you dangling upside down and helpless. A scene from the latest Harrison Ford movie, or a typical day in your home studio? David Mellor proposes a more practical wiring system. Read on...
I have a crusade against cables; I hate them! But a typical home studio can contain several hundred metres of cabling, and a professional studio may have miles, literally. But there are ways to keep the cables out of the work space and get them into a sensible arrangement where they will do most good, and cause you the least amount of inconvenience.
At the heart of a good cabling system is the patch bay - or 'jackfield' if you prefer old-fashioned, un-Americanised English. The patchbay is simply a device to place all the equipment connections within easy reach, and in a logical format. There is no need to grovel about in dark corners plugging in equipment. Nor is there need to keep a multitude of adaptor cables - phono to XLR, XLR to jack, jack back to phono again, etc. Let's get down to the basics...
You will not be unaware that every piece of audio or electronic musical gear you own has an array of connectors on the back. Neither will you be unaware that to make a studio work, all these items of equipment have to be connected together. That's the starting point. But how to make all these connections?
The usual way most people start in home recording is to have just a small amount of gear and to connect cables directly from equipment to equipment. Let's say you have a 4-track cassette deck, similar to a Portastudio. Add to that a synthesizer, a stereo tape recorder, monitor amp and speakers. At the very least, this amounts to five line-level cables, typically:
1 jack to jack (synth to 4-track)
2 phono to XLR male (4-track to stereo tape)
2 XLR female to phono (stereo tape to monitor amp)
Already this is a fine assortment of different cable types. As the set-up increases in size and complexity, the assortment grows. Eventually you find yourself in an immense tangle of leads every time you want to re-configure your equipment, or perhaps want to do something special for a musical effect.
With a patchbay - even a very rudimentary one, as in this case - connection and reconnection become a lot easier. Now, all the inputs and outputs of the various pieces of equipment are wired to rows of jack sockets, all on one panel. Standard cables with identical connectors - patch cords - can then be used to connect the equipment together in any way you wish. No fuss, no bother.
Let's now progress to a very simple practical example. I'll stick to the 4-track cassette, one synth, tape, amp and speakers combination and add to it an effects unit (possibly a reverb). The first step in patchbay implementation is to make a list of equipment connections. Like this:
4 inputs (jack)
1 auxiliary (effect) output (phono)
2 auxiliary inputs (phono)
2 main outputs (phono)
2 monitor outputs (phono)
1 output (jack)
1 input (jack)
2 outputs (jack)
Stereo Tape Machine
2 inputs (XLR female)
2 outputs (XLR male)
2 inputs (phono)
Two things to note. Firstly, this is the very simplest system I can think of, without becoming too trivial - that's why the synth has only one output! But still, this will provide a good example. Secondly, that speaker wiring has no place in the patchbay system. There are such things as loudspeaker patchbays, but they bear the same relationship to the home studio as a Centurion tank does to a Ford Fiesta.
Figure 1 shows how the system would be connected without using a patchbay. To make connections via a patchbay, we first need to design a sensible patchbay layout. Figure 2 shows the initial stage of patchbay layout. In this example, the patchbay would have 13 jack sockets in each row, and nine rows. It may look wasteful on space, but this is just for starters, and has the advantage of showing the signal flow clearly.
As you might have noticed, each row consists of either all outputs or all inputs. Output rows and input rows alternate all the way down the patchbay. The primary signal source is the synthesizer, therefore its output is on the top row. Directly below it is the input of the 4-track to which it will normally be connected - Input 1.
Next in the signal chain is the 4-track's auxiliary (effect) output. Directly below that is the effect unit's input. And so on. In the next row of outputs appear the outputs of the effect unit. Beneath them are the 4-track's auxiliary inputs. Get the picture? Rows of outputs and inputs always alternate. Outputs and inputs which will normally be connected together are paired up vertically.
Now we can make the diagram more simple and practical by shrinking it into just two rows. Row 1 contains all the equipment outputs, row 2 has all the inputs, as in Figure 3. With just eight patch cords, the entire system could be hooked up very simply, and with no confusing diagonal connections in normal tracklaying use. When the final stereo mix is complete, the output of the stereo tape can be patched into the monitor amp for auditioning.
Now that we've covered the basic theory, it's time to look in more detail at a real patch bay. And why not go straight to the top - to a professional quality GPO-type patchbay of the kind used by recording studios, radio and TV stations, the world over. Photo 1 shows a patchbay in use in a theatre installation. It may look large and complex, but it is just a grown up example of what I have described above. The principle is no different.
A typical patchbay unit comes as a 3U rack-mounting panel containing three rows of 24 jacks, totalling 72 connections. Some types have more rows, others have different numbers of jacks in each row. Figure 4 shows the overall construction of the patchbay. Figure 5 shows the configuration of the individual jack sockets. The jack socket, of the type conventionally employed, has five metal tags to which wires may be soldered. It seems like two tags too many, so what can they all be for?
Obviously, three of the tags must be for the balanced audio cable (two signal conductors plus the screen). The other two tags go to switched contacts in the body of the socket. These switch contacts press against the two signal contacts when the socket does not have a jack plug inserted, but are forced apart when the plug is placed in position. The switch contacts can be used to connect equipment together, using an important technique known as normalling.
Going back to the simple example outlined earlier, you can see that the patchbay was designed to suit the normal way the equipment will be connected together. For every studio, there is a configuration of equipment that will be good for 90% of the tasks undertaken. Using the normalling technique the patchbay can be used to make all these regular connections, through the switch contacts of the jacks, without any patch cords being plugged in, by the attachment of wire links at the rear of the panel. If the engineer wants to do something out of the ordinary, and reconfigure the connections between the equipment, all he or she has to do is to overplug the normal - which means that when patch cords are inserted in sockets to make new connections, the switch contacts of the jacks come apart and the previous connections are temporarily broken.
In the simple example, normalling can be used to make all the connections necessary for the track-laying and mixing process. No patch cords are necessary. When the time comes to audition the final stereo mix, two patch cords are used to take the outputs of the stereo tape recorder to the inputs of the monitor amp. The act of plugging into the monitor amp's jacks disconnects the original link from the 4-track's main outputs.
The upshot of all this is that you could walk into a studio that has maybe 20 rows of patchbay, and be able to make a recording and mix it without using a single patch cord. But if you want to try something fancy, all you do is make the new patch you want and the original connection will be unmade automatically.
That's it for now. Next month's instalment will describe the hooking up of a 16-track system, complete with a full patchbay. If a full patchbay sounds like too much of a trial for you, don't worry: I shall definitely be including ideas for simplification.
Canford Audio, (Contact Details).
Studio Spares, (Contact Details).
Raper & Wayman, (Contact Details).
EMO Systems, (Contact Details).
Larking Audio, (Contact Details).
Kelsey Acoustics, (Contact Details).
Feature by David Mellor
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