What Does "AF Out" Mean?

AF out stands for audio frequency output. It is a line-level or speaker-level signal output that carries the audible part of the audio spectrum — roughly 20 Hz to 20 kHz — out of a device so it can be sent to another stage of the signal chain.

You will see the label on power amplifiers, mixer amps, KTV processors and some active speakers. In most cases, AF out is a line-level output designed to feed another amplifier, a powered speaker, a recording device or a second zone.

It is not a standardized connector type. Depending on the device, AF out may appear as:

  • RCA jacks
  • 6.35 mm (1/4") TRS jacks
  • XLR connectors
  • Euroblock / Phoenix terminals
  • Speaker binding posts (when the output is already amplified)

Always check the manual or the label next to the jack to confirm whether the AF out is line level or amplified.

AF Out vs Pre Out vs Line Out

These three terms are often used loosely, which causes wiring mistakes. Here is the practical difference:

  • AF out — audio frequency output. Usually line level, sometimes amplified. Carries the full audible band.
  • Pre out — preamplifier output. Line level, volume-controlled, intended to feed a power amp. Very common on AV receivers and mixer amplifiers.
  • Line out — fixed or variable line-level output. Similar to pre out but not always tied to the master volume.

The key question is not the label but the signal level. A line-level AF out (around 0.3–2 V) must go to a line input, not to a speaker terminal. An amplified AF out must go to a loudspeaker and never to a line input.

Common Uses of AF Out in Pro Audio and KTV

AF out is a practical tool for system design. Typical uses include:

  • Linking two amplifiers — feed the AF out of amp A into the line input of amp B to run a second zone or more speakers.
  • Recording or streaming — send the AF out to a recorder, interface or streaming encoder.
  • KTV systems — route the mixed vocal and music signal from the KTV processor to a separate power amplifier or active speaker.
  • Subwoofer feed — some amps provide an AF out that can feed a powered subwoofer.
  • Distributed audio — cascade AF out to multiple zones in a bar, restaurant or retail space.

When you cascade outputs, watch for signal loss and ground loops. Use balanced connections where possible and keep cable runs short.

Wiring AF Out Correctly

Follow these steps to avoid the most common mistakes:

1. Identify the level. Check the manual: is the AF out line level or speaker level?
2. Match the input. Line-level AF out goes to a line input (RCA, TRS, XLR). Speaker-level AF out goes to a passive speaker.
3. Check impedance. Line inputs are typically 10 kΩ or higher; keep the source impedance low.
4. Avoid double amplification. Never feed a speaker-level AF out into another amplifier's line input.
5. Control the volume. If the AF out is volume-controlled, set the master volume before adjusting downstream gain.
6. Test with a known signal. Use a test tone or music at low volume before pushing the system.

If you are building or upgrading a venue system, tested used amplifiers and processors from Acoustrade's power amplifier and audio processors ranges are a cost-effective way to add AF out routing without buying new.

AF Out in Used Equipment: What to Check

When buying second-hand gear with an AF out, inspect the following:

  • Jack condition — worn RCA or TRS jacks cause intermittent signal.
  • Label clarity — confirm the level and pinout, especially on older KTV amps.
  • Noise floor — listen for hum or hiss on the AF out with no input signal.
  • Channel balance — compare left and right AF out levels.
  • Documentation — a manual or schematic makes wiring much easier.

Acoustrade tests used amplifiers and KTV equipment before shipping, so the AF out and other outputs are verified working. Browse the KTV systems and mixers categories for options.

FAQ

Is AF out the same as a subwoofer output?

Not always. A subwoofer output is usually filtered to low frequencies, while AF out carries the full audio band. Some amps label a full-band output as AF out and expect you to set the crossover downstream.

Can I connect AF out directly to a speaker?

Only if the AF out is speaker-level (amplified). If it is line level, you need a power amplifier or active speaker between the AF out and the loudspeaker.

Why is my AF out signal weak?

Line-level AF out is intentionally low voltage. If it seems weak, check that you are using the correct input, that the master volume is up, and that the cable is not damaged.

Does AF out carry video or digital audio?

No. AF out is an analog audio-frequency signal. Digital audio uses different outputs such as coaxial, optical or AES/EBU.

Can I use AF out to daisy-chain many amplifiers?

You can cascade a few units, but each stage adds noise and can load the source. For more than two or three amplifiers, use a distribution amplifier or a matrix processor.