Regardless of what you might have read before this blog or what others might tell you, how you connect things and what type of connections you're using is important. So you need to understand what types of connectors are out there and what they are intended to be used for. I can't tell you how many times I've ran across the wrong connectors being used or wired incorrectly. In some cases it was an easy fix to rewire and get things straightened out. In other cases poor wiring wound up costing people more money because of blown equipment.
Types of connections:
RCA - Sometimes called a phono connector, is a type of electrical connector commonly used to carry audio and video signals for consumer level equipment. When dealing with the consumer audio side of things, it is always an unbalanced signal, and impedance matching is simply not possible. The output impedance of the source and the input impedance of the load are almost always completely different and nearly impossible to match. You also only have two electrical connections per cable. The center conductor (the positive or signal side), and the outer conductor, which is almost always ground.
RCA - Sometimes called a phono connector, is a type of electrical connector commonly used to carry audio and video signals for consumer level equipment. When dealing with the consumer audio side of things, it is always an unbalanced signal, and impedance matching is simply not possible. The output impedance of the source and the input impedance of the load are almost always completely different and nearly impossible to match. You also only have two electrical connections per cable. The center conductor (the positive or signal side), and the outer conductor, which is almost always ground.
XLR - Invented by the Cannon Corporation, this connector was Cannon's X series of connectors, that had a Locking tab, with the female contacts surrounded by synthetic Rubber. Hence the name, XLR.
This type of connector is pretty much the standard for professionals, broadcasters and studios. And other than a few weird circumstances, they are almost always balanced and almost always impedance-matched. With that said, the range of applications for XLR type connectors is very broad. Their original use was for 600 Ohm impedance signal transmission, but then they were applied to microphones as the standard low-impedance connector. However, the mics they were built in to had impedance's ranging from 50 Ohms to 250 Ohms. Later radio broadcasting manufacturers started using the connector as its standard for 600 Ohm equipment interconnects. Not to get to in-depth with this, but then the Audio Engineering Society (AES) and the European Broadcasting Union (EBU) got together to establish the AES3 standard for transmitting digital stereo PCM audio between professional devices. And you guessed it, they chose the XLR connector.
This type of connector is pretty much the standard for professionals, broadcasters and studios. And other than a few weird circumstances, they are almost always balanced and almost always impedance-matched. With that said, the range of applications for XLR type connectors is very broad. Their original use was for 600 Ohm impedance signal transmission, but then they were applied to microphones as the standard low-impedance connector. However, the mics they were built in to had impedance's ranging from 50 Ohms to 250 Ohms. Later radio broadcasting manufacturers started using the connector as its standard for 600 Ohm equipment interconnects. Not to get to in-depth with this, but then the Audio Engineering Society (AES) and the European Broadcasting Union (EBU) got together to establish the AES3 standard for transmitting digital stereo PCM audio between professional devices. And you guessed it, they chose the XLR connector.
The XLR style of connector has so many broad applications because it has up to four electrical connections per cable and the connectors can lock into each other or the equipment they are being plugged in to. For almost all of its applications, Pin 1 is the audio signals ground. Pin 2 is positive side of the audio signal. Pin 3 is the negative side of the audio signal. And last, the case, which is either chassis (earth) ground or has no connection at all.
TRS - Named for the fact that the connector is made up of a Tip, a Ring and the Sleeve. This type of connector has a plethora of uses, sizes and names; head phone jack, 1/4" plug, TSR (wrong acronym), audio jack and patch connector are a few of them. The uses of the TRS connector are staggering. Everything from head phones to send/receive connections, so in order to understand it all you need to separate out a few things.
First, let us discuss the physical plug. There are three main types: the "phone" connector has a diameter of 1/4", the "mini" connector has a diameter of 3.5 mm, and the "sub-mini" connector has a diameter of 2.5 mm. All of these types have various uses, so there is no real correlation between the plug type and the signal type travelling through it.
First, let us discuss the physical plug. There are three main types: the "phone" connector has a diameter of 1/4", the "mini" connector has a diameter of 3.5 mm, and the "sub-mini" connector has a diameter of 2.5 mm. All of these types have various uses, so there is no real correlation between the plug type and the signal type travelling through it.
Which brings us to our next understanding. A 1/4" TRS connector could be used for connecting a stereo headphone, a microphone, send/receive on a mixer or for that matter, a guitar. However, these four examples are at the extremes of signal levels and impedance. The bottom line here is, a TRS connector is just a convenient way to make connections to various types of equipment, all of which have varying signal levels and impedance's. So you better know what you're connecting to what, and how it's internally wired or you may blow something up.
In the picture to the left, we have your typical headphone connection. Whether it's a 1/4" or a 3.5 mm type TRS connector, it'll be the same tip/ring/sleeve combination.
In the picture to the right, we have a balanced 1/4" TRS connection. The Tip is always the positive side of the audio signal, the Ring is the negative side of the audio signal and the Sleeve is the audio signals ground. One thing to note is that the Strain Relief and the Sleeve are the same electrical connection.
The next type of 1/4" TRS connection is the Send / Receive. Here the Tip is the signal return from whatever processor you're using. The Ring is the signal you're sending to whatever processor you have. The Sleeve is the common ground that must be connected to your processor equipment. You'll also see that the TRS connector is wired to two TS (Tip/Sleeve) connectors.
The next thing to cover is whether the TRS is balanced or unbalanced. This is completely based on what you're hooking the TRS connector up to. If you're plugging in a guitar or a headphone, it's more than likely an unbalanced connection. If you're plugging into the inputs of most audio mixers or a microphone, it's a balanced connection. In all cases, you need to read the manual on the equipment you're connecting from and to when using TRS connectors. If you don't, you may regret that decision later.
Now I spoke of of signal levels and impedance's above, but I should expand a bit.
What does all this mean to you? It means that you can't plug a TRS connector coming from say an amplifier into a TRS connection point that is an input to an audio mixer. Things aren't going to work out very well for the mixer. So again, please read all manuals that come with your equipment before you just start plugging things in and hoping for the best.
- Line level signals have a medium signal level and a medium impedance.
- Headphones have a medium signal level but a low impedance. The actual voltage is comparable with that of regular line level outputs but the lower impedance gives it more power (perceived volume).
- Speakers have a high signal level and an even lower impedance than headphones, producing far more power (volume).
- Microphones have a low signal level with a medium impedance. In order to hear these signals, you need a lot of amplification or gain.
- Guitars have a medium signal level but at a very high impedance. You won't need quite as much amplification to hear this signal.
What does all this mean to you? It means that you can't plug a TRS connector coming from say an amplifier into a TRS connection point that is an input to an audio mixer. Things aren't going to work out very well for the mixer. So again, please read all manuals that come with your equipment before you just start plugging things in and hoping for the best.