If you’ve done any sort of home theatre setup, then you’ve likely seen pre out or line out on an audio device such as a DAC, amp, or preamp.
Confusion between these two normally leads to an improper setup and a less than stellar experience. So what is the difference? Let’s discuss pre out vs line out and when to use each one.
What Is Pre Out vs Line Out?
Pre out or ‘subwoofer pre out’ is a very common household audio connection type that is meant to connect to an AV receiver to a powered amplifier or subwoofer.
It produces a variable signal and so adjusting the volume control adjusts the output signal level since a power amp is normally a fixed gain device.
On the other hand, line out, alternatively known as ‘audio out’ or ‘sound out’ is an audio connection type which allows external speakers to be connected.
It is normally a fixed voltage signal that is unaffected by the volume control.
Comparing both pre-out and line out helps us understand what type of sound output we should expect and how to get it using which connection type.
But why use one or another? Why pre out vs line out? Since you already understand the distinction between both, let’s look at understanding what type you wish to get.
What Do A Pre Out and Line Out Look Like?
Pre-out(s) look like a set of RCAs (Originally stood of “Radio Corporation of America” in the 1940s) jacks on the back of the receiver.
The RCA cables use a color code system to indicate the correct socket for each plug.
Line out looks somewhat the same like the RCA audio jacks, only with a set of different colors in most cases.
Why Use Pre Out vs Line Out?
Getting a receiver for your amplifier is sometimes a great idea, though their functions sometimes overlap.
The advantage is that a good-quality stereo amp does a better job at amplification and providing music and left and right front-channel audio than any receiver would.
However, if additional amplification is not needed, this additional amplifier in the signal path may just degrade the sound.
In general, you want to use pre out when connecting to an external amplifier because you will need to adjust the signal to adjust the external amplifier’s gain.
While on the pother hand, you use line out when connecting directly to speakers from a receiver with a good preamp and when no external amplification is needed.
Why Use Pre Out With Receiver/Amp Setup?
When using pre-out, it is easier to connect the outputs from the receiver directly to the amplifier and then connect the speakers to the external amplifier instead of the receiver.
This takes the load off the receiver to drive the speakers as the amplifier will take over that job. Remember, while AV receivers will have an amp, external amplifiers are more powerful and suited for high gain power amplification.
In other words, the pre-out which is a volume-controlled source is best associated to the pre-ins of an outside power amplifier to use rather than the power amplifiers incorporated with the receiver.
The receiver is now acting as a pre-amp and provides variable signals for all the audio processing, volume control, etc. while the amplifier provides the power. The pre-out/main in provides another dimension of flexibility to the receiver.
Why Use Pre Out With Receiver/Subwoofer Setup?
Connecting the pre-out to your subwoofer reduces the burden on the main woofers, at a very low frequency and allowing for high levels of volume with little to no distortion.
As said earlier, after making the right connections, the pre-out signals are sent to an internal amplifier.
There are subwoofers that utilize a port or opening to tune it to a specific recurrence to guarantee an ideal recurrence reaction.
Recurrence reaction refers to the scope of bass, mids, and treble that a speaker or sub can deliver without causing distortion.
It is generally alluring for the speakers and subwoofer to be tuned to about a similar recurrence.
Why Use Line Out?
The biggest advantage for line out is that you don’t have to worry about feedback and that you can model the tone without worrying about positioning, angles, mics and so on.
It is a fixed volume connection and so is a good choice for connecting to devices that already have a pre amp, especially if you don’t need additional amplification.
For example, if you’re connecting to a receiver or DAC that already has a pre amp, then that device will have some sort of volume or signal control mechanism.
If you add another amplifier in the mix, that’s another device in the signal path which could degrade the sound’
Line outputs usually present a source impedance of from 100 to 600 ohms. The voltage can reach 2 volts peak-to-peak with levels referenced to −10 dBV (300 mV) at 10 kΩ.
The frequency response of most modern equipment is advertised as at least 20 Hz to 20 kHz, which corresponds to the range of human hearing.
Line outputs are intended to drive a load impedance of 10,000 ohms; with only a few volts, this requires only minimal current. Interfacing a low-impedance burden, for example, an amplifier (generally 4 to 8 Ω) to a line out will basically cut off yield circuit.
Such loads are around 1/1000 the impedance a line out is intended to drive, so the line out is typically not intended to source the present that would be attracted by a 4 to 8 ohm load at ordinary line out sign voltages.
The outcome will be a low frequency sound from the speaker and conceivably a harmed line out circuit.
Unlike using subwoofers which are intended to work inside a determined volume to accomplish ideal execution.
Line output converters are sometimes also needed to install a new stereo in a vehicle with a separate factory amplifier.
They’re used in conjunction with vehicle-specific wiring adapters to make the new high-powered stereo work with the factory amp.
Adding a line output converter to a car’s stereo system is a great way to get more volume out of the car speakers and more clarity and profundity to music when it’s being played.
When To Not Use Pre Out vs Line Out
When You Shouldn’t Use Pre Out
The use of a subwoofer only augments the bass capability of the main speakers and allows them to be smaller without sacrificing low frequency capability.
This is intended to work inside a determined volume to accomplish ideal execution.
A subwoofer does not necessarily provide superior bass performance in comparison to large conventional loudspeakers on ordinary music recordings due to the typical lack of very low frequency content on such sources.
Pre-outs are just signals, unlike line out which has the amplified signal and has to go through the line level filters to get the signal, therefore, more processing and less clarity. Pre-outs impart a line level sign and that sign must be intensified.
Normally the pre-outs are utilized to interface an outer enhancer to control the speakers as opposed to utilizing the beneficiary’s intensifiers.
When You Shouldn’t Use Line Out
Line out has a fixed voltage signal unaffected by volume and which comes directly from the DAC (Digital to Analog Converter).
Functions like source determination, volume control, DSP (Digital Signal Processing) and different impacts are constrained by the receiver, the power amplifier just drives the speaker.
The DSP which is supposed to take real-world signals like voice, audio and so on, and manipulate them mathematically to produce quality output, is being constrained.
Using a pre-out often guarantees more volume control than using a line-out. Line out would remove the influence of the speaker, which is an important component of the overall tone.
When it comes down to it, the biggest difference between pre out vs line out is function and tone. Do you need volume or signal control?
Then use pre out. If you already have a preamp in the device you’re connecting to, then you can use line out to avoid double amplification in the signal path and two volume/signal controls. One sounds different than the other.
So, before anything else, find out which sound you prefer with the amps and mics you have available. This determination should also depend on the specs of the devices you have. All the best!