This topic comes up a lot due to the switch that can be found on our SX2 and TI3 line of amplifiers.
Everyone always asks "Which setting do I need to use".
The short and simple answer is:
High Level Input From Factory Head Unit = Balanced
Low Level Input From Factory Head Unit with Factory Amplifier = Balanced
Low Level Input From Aftermarket Head Unit = Unbalanced
However, if you would like to gain a better understanding of this topic and apply it to all audio equipment, read on.
Lets start with the definitions and terminology
Unbalanced / Single Ended Signal: This type of signal always has one signal wire, and another wire (usually a shield), with a common connection to ground.
This type of signal can ALMOST always be found on the low level RCA outputs of an aftermarket head unit. No head unit has this type of signal on the high level speaker outputs. Speaker outputs are ALWAYS Balanced / Differential.
This is what an unbalanced signal looks like on an oscilloscope. Channel 1 is on the center pin of the RCA and channel 2 is on the shield. Notice how the signal is only present on channel 1 while channel 2 is at 0 (ground).
Balanced / Differential Signal: This type of signal always has 2 isolated signal paths (one positive and one negative) carrying the audio signal, with no common connection to ground whatsoever, on either path. The wires carrying these signals may sometimes have an insulating layer around them that is connected to ground.
This type of signal can always be found on the high level outputs of any head unit. It can also be found on the low level outputs of some factory head units that utilize a factory amplifier. Very few aftermarket head units have this type of signal on the low level RCA outputs. RCA outputs ALMOST always use an Unbalanced / Single Ended configuration.
This is what a balanced signal looks like on an oscilloscope. Channel 1 is on the positive wire of a high level output and channel 2 is on the negative. Notice how signal is present on both channels, but exactly 180 degrees out of phase.
Connecting an audio source with an unbalanced output to an amplifier with a balanced input (or vice versa) can lead to unwanted noise. Knowing the equipment you are using, as well as knowing how to test the equipment you are using, will help prevent these issues.
So how do you test for the type of signal your equipment uses?
Simple, with a digital multi-meter (DMM) set to measure resistance/ohms.
Lets measure one of our Phoenix Gold SX2800.4 amps with the switch set to Unbalanced. Place one lead of the meter on the ground input, and the other lead on one of the RCA inputs outer shield. Notice the low resistance reading (217 ohms). This means that the outer shield of the RCA is connected to ground. This is the setting that should be used when using the low level RCA outputs of an aftermarket head unit (most of the time, more on that later).
Now, lets measure the amp with the switch set to balanced. Notice the resistance reading is much, much higher (1.3 megaohms). This means that the outer shield of the RCA is no longer connected to ground and is now an independent audio path. This is the setting that should be used when using the high level outputs of any radio, the low level output of a factory head unit that is connected to a factory amplifier, or if you come across an aftermarket radio that has balanced, low level, RCA outputs.
Lets take some measurements on aftermarket radios and see what we get. This is done in the same fashion as the amp. One meter lead on the outer shield of an RCA output and the other lead on the chassis of the radio.
First up is a Pioneer NEX4200. This one is definitely unbalanced. Pretty much a direct connection to ground. When you get a reading like this, set the switch to Unbalanced. or test the amplifier to ensure it is an unbalanced configuration. Running a signal from this head unit into an amplifier with a balanced input configuration will generate noise that cannot be removed.
Next up is an Alpine INE-Z928HD. This one is balanced. A rare find on aftermarket radio. I tested all of the aftermarket radios that we have here at AAMP and this was the only one that had a balanced low level output. Running a signal from this head unit into an amplifier with an unbalanced input configuration will generate some noise, but in this case it can be removed by adding a simple ground loop isolator such as the PAC SNI-1
So there you have it. The difference between balanced and unbalanced, and how to test your equipment to see what setup it is using!