Patch Boxes; Multi-Purpose Audio Adapters

• Change from one type of connector to another
• Connect multiple Audio signals to the same source
  • Parallel Wiring
  • Series Wiring
• Sum a series of signals together into a single Audio feed

Always use the best connectors that you can afford (I recommend Switchcraft). Avoid gold plated connectors unless these Patch Boxes are intended to remain connected in a studio or rack mount environment once put into service. The gold on any gold plated connector will wear off very quickly if the Patch Boxes are used frequently.

What wire to use:

• Patch Boxes used for Low Level audio signals: 22 gauge or larger wire.
• Patch Boxes used for High Power audio signals: 18 gauge or larger wire.

Since these wires will all be under 6 inches in length (15 cm), I don't use sheilded cable. In situations where you expect low level audio signals and all the wiring will be Parallel connections, use a metal case to install the connectors in.

Most Audio gear use some combination of 1/4 in Phone, RCA Phono and 1/8 inch Phone jacks/plugs. The Phone plugs can also be stereo, which adds another level of confusion to the equation. You will often be in a position where you have to an audio device that has one of these connectors to something that needs one of the other connectors.

1/4 inch Phone Jacks/Plugs are commonly used on:

• High Impedance Guitars and Bass Guitars
• Pro-Audio Synthesizers / Keyboards
• Pro-Audio Effects/Mixers/Signal Processors

1/4 inch Stereo Phone Jacks/Plugs are commonly used on

• Headphones
• Stereo Microphones
• Some Multi-channel Mixer Boards
• Some Stereo Pro-Audio Special effects.

RCA Phono Jacks/Plugs are commonly used on:

• High and Low end Home stereo equipment
• Component CD Players
• Turn Tables
• Home-Audio Synthesizers / Keyboards

1/8 inch Stereo Phone Jacks/Plugs are commonly used on

• PC Based Sound Cards
• Portable CD Players
• Portable Cassette Decks.
• Headphones
• Stereo Microphones

Your need will be to have at least one of each possible connector type wired to each of the other connector types. This way, you can connect a 1/8 inch stereo cable to a 1/4 inch stereo cable, or break out the stereo signal to a separate left and right phono jack, and a left and right 1/4 inch phone jack. You will often find that you need this when you are playing live and suddenly need to patch a stereo cassette deck or a portable CD player into your PA system and find that none of your cables are compatible. Suddenly, you'll find yourself unable to play some important recording. Sometimes someone will show up with an instrument that needs to be connected to your PA system and it will not have been wired with the right connectors. This patch box typically deals with low level signals (but not always). In general, this would be wired in a metal case.

When you are recording, you'll often find that 50% of what you need to connect together has the wrong connectors on it. A common problem is connecting to a Sound Card in a PC - these usually have 1/8 inch Stereo connectors (many high end Sound Cards have Phono Jacks). The rest of your audio gear is likely to have 1/4 inch Phone Jacks.

You can either buy every possible cable combination that you can think of, or build a few Patch Boxes that convert the connectors. This way, you only need a few specialty cables, and they will have the same type of connectors on both ends. You'll use the Patch Box to convert to the right connections for you.

The goal of this patch box is to allow you to connect a number of wires to the same signal. This could be used to wire speaker cabinets in Parallel, or connect the same low level audio signal to 2 separate pre-amplifiers. Its often used to splice 2 audio cables together to make a longer wire (for example, if you have 2 20 foot cables, but you need to run a cable 30 feet, you can connect the 2 20 foot cables into the patch box, and now you have the equivalent of a 40 foot connector. This is my most common use of this sort of Patch Box. Its simple to build. All you need to do is wire 2 or more of the same type of connector in a single box.

These should be put in a non-conductive box, otherwise, you may require special connectors that have isolated ground connections. These are typically used when wiring Speaker cabinets in series. There are 3 connectors on the box and the input is specifically marked, and the outputs are also specifically marked - the connectors do not provide interchangeable functions as in Patch Box #1 or #2. Warning: Never run a Tube amplifier without a full speaker load. If using a Series Adapter, make sure all of the speakers are plugged in before turning the Amplifier on

Sample Usage

Note: The In/Out Jacks on the Monitors are wired in parallel as shown at Floor Monitor Concept Plans

• If the 4 floor monitors are 4 ohms each, the total load will be 4 ohms

• If the 4 floor monitors are 8 ohms each, the total load will be 8 ohms

• If the 4 floor monitors are 16 ohms each, the total load will be 16 ohms

This effectively makes the speakers wired up as Series/Parallel - Use 18 gauge or heavier wire.

You must have speaker cabinets plugged into both Out 1 and Out 2 in order for this to work.

Patch Box #4 - Passive Audio Mixer (Mono)

Occasionally you will be desperate for an additional audio mixer. It won't need to have any form of volume or tone controls, it just needs to sum together a series of low level audio signals that can be used into a normal mixer channel. This specialty box is simple to make, but I don't recommend having more than 4 inputs summed together. You'll need 4 input connectors and one output connector. You'll also need 4 1/4 watt 10,000 ohm resistors (the color code on these will be 'brown, black, orange'). The 4 input jacks should be marked as inputs (and numbered 1 thru 4) and the output jack also needs to be marked as 'Summed Output'. All that is required is that the center tap of each input jack has one side of the 10,000 ohm resistor soldered to it, and the remaining wires of the 4 resistors are all connected together, then this is connected to the center tap of the Output Jack. This should be mounted in a metal case.

Another Variation of a passive Mono mixer

In case you need to have seperate level controls for each input channel. The Variable resistors (Potentiometers) should be Audio Taper if possible, however, Linear Taper will work, but it will seem to be right as you set the levels to different positions (Your ear is not linear; Audio Taper Variable Resistors compansate for that). As above, 4 Signal In inputs is a reasonable amount. Either of these designs are often used to allow you to connect 2 mixers together to drive a power amp. If you run stereo, then use 2 of these, one for each channel.

The Type of XLR connector is not mentioned, since you might use either Male or Female depending on your need. This will allow you (using a single switch) to swap XLR input 1 with XLR input 2, allowing you to re-route microphones from one effects box to another - handy when you need to share effects. Works best if both microphones are the same type and brand. The Switch is shown in the position where Input 1 goes to Output 1, and Input 2 goes to Output 2. You could use 2 DPDT switches if you can't find 4PDT switches in your area; just rember to switch them both the same way when you use this mode.

Don't forget MIDI and XLR connectors. You'll often have need to splice cables together with these types of connectors on them. these will be more highly focused in their purpose. You won't be converting MIDI signals to anything else, or another connector type. XLR connectors imply low impedance and as such, you won't expect these signals to go to high impedance connections. These are just a variation on Patch Box #2, you will always you the same type of connector on the Patch Box, and they will always be wired as Parallel connections. In MIDI connectors, wire all 5 connections (though only 3 are normally used), pin 1 to pin 1, pin 2 to pin 2, etc. Do the same for XLR connectors - these have only 3 wires.

Construction Considerations

In order to keep things simpler in the diagrams, I use the Phone Jack and Phono Jack interchangeably. These are mono-phonic connectors. You could even use banana connectors in their place. Low level audio signals should always be in a shielded case. I suggest small Aluminum boxes (available from Radio Shack and other electronic supply houses). High level Audio Signals may have large high current voltages applied to the connectors - I often make Patch Boxes for this purpose out of wood using 1/8 inch tempered Masonite as the surface for mounting the connectors.

- = Signal Ground + = Signal (Hot) For 1/4 inch (and 1/8 inch) phone jacks, you need to verify which solder tabs go to the + and - connections, 1/4 (and 1/8) inch phone jacks have no standard for which of the solder tabs goes to what. Open cased Jacks are easy to verify - just look at it. In an enclosed Jack, you may need to use a VOM/Digital Multimeter to check which connection goes to what. The + and - relate to how the speakers are connected. The speaker should have a colored dot on it to indicate + or it will be marked with a +.

NOTE:Signal Ground will always need to be isolated by the patch box. You don't want to allow Patch Boxes to touch each other. This will be more significant if you have low level audio signal Patch Boxes laying on the floor next to Patch Boxes that are being used to correctly wire your Speakers. Always make sure that none of your Patch Boxes touch each other (tape them down to the floor with Duct Tape if you need to). What are trying to avoid?

• In low level audio signals, you will introduce ground loops
• In high power audio signals from your power amplifiers, you could short circuit power amplifiers output stages and destroy them.

All Signal Grounds in any Patch Box must be connected together. If using a metal case (such as an Aluminum Box), the case will provide the ground contact for metal Phone Plugs and some Phono Plugs. In non-metal Patch Boxes, you will have to wire the Ground connections together. Always verify that the grounds are connected visually or with an Ohm Meter. If in doubt, wire up all the Ground connections in a box as per the above schematics/diagrams. Be careful in the case of Serial connections because one or more of the connectors will not share a Signal Ground.

Questions? Comments? .

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