You plugged everything in, turned it up, and it crackles. Or it hums. Or it comes out too quiet while every light on the mixer is in the red. Nine times out of ten, the mixer and the amp are fine: it is the wiring or the settings between them that are wrong.
Here is the full diagram, the gear you need, the order to plug things in, and the three mistakes that keep coming back.
The diagram
The logic fits in one line: the mixer’s master output goes into the amp’s line inputs, and the amp’s speaker outputs go to the speakers. Between mixer and amp you are at line level. Between amp and speakers, at speaker level. They use neither the same cables nor the same connectors.
The gear you need
- Two signal cables between mixer and amp, one for left, one for right. XLR to XLR if both have XLR sockets, otherwise 1/4″ stereo jack (TRS) to TRS. Both are balanced and handle long runs.
- An adapter if the mixer only has RCA outputs: RCA to jack or RCA to XLR. The link becomes unbalanced, so keep it short, a few metres at most.
- Two speaker cables between amp and speakers: Speakon preferably, otherwise banana plugs or binding posts. Never a guitar jack cable: it is not made for an amplifier’s current.
Plug in this order
- Everything is off, the mixer’s master and the amp’s gains are at zero.
- Connect the left master output to amp input A, the right one to input B.
- Connect the amp’s speaker outputs to the speakers: channel A to the left speaker, channel B to the right. Respect + and − on binding posts.
- Check the amp mode: stereo.
- Turn on the mixer and the sources, then the amp last. When shutting down, the reverse: amp first.
- Play a track, set the mixer (see below), then slowly raise the amp gains.
The power-on order is not a detail: an amp that is on while you plug in or switch on the mixer sends the thump straight into the speakers.
Which mixer output?
- Master: this is the one. If your mixer offers XLR and jack or RCA masters, take the XLR.
- Booth: a second output with its own volume, meant for a monitor near the DJ. It helps for a second system, not for the main one. Connecting a monitor is covered in how to connect a monitor to a mixer.
- Rec: fixed level, made for recording. The mixer’s master does not control it: you would lose control of the volume.
- Headphones: never. Level and impedance are not made to drive an amp.
Which amp input?
A line input: XLR, jack or RCA depending on the amp. PA amps have almost nothing else. Some hi-fi amps also have a phono input: it is made for a turntable cartridge, a signal about a hundred times weaker and equalised. Plug a mixer into it and you clip the input from the very first settings.
If your mixer has phono inputs, it works the other way round: the mixer receives the turntable, then sends out line level.
The amp mode: stereo, parallel or bridge
- Stereo: each channel amplifies its own input. This is the normal setting for two speakers.
- Parallel: input A feeds both channels. Useful when both channels serve the same way, for example two subwoofers in mono.
- Bridge: both channels combine to drive a single speaker with more power. The minimum load impedance usually doubles: a 4 ohm speaker can make the amp shut down, or damage it. Read the manual first.
The most common mistake: gain structure
The reflex is to keep the amp low “to be safe” and push the mixer until it sounds loud. Result: the mixer clips, and the amp faithfully amplifies an already clipped signal. It sounds harsh, and that square-wave signal is what overheats tweeters.
The right method:
- Set each mixer channel’s gain so the peaks land around 0 VU, without lighting the red.
- Put the mixer’s master at its nominal mark, often 0 dB or two thirds of the travel.
- Then raise the amp gains to the volume you want. If you are short of volume with the amp gains at maximum and a clean mixer, the amp or the speakers are too small, not the mixer.
Also watch the amp’s clip or limit LED: if it lights up often, back off. It means the amp has reached the end of its power.
It hums: the ground loop
A low, constant hum, present even without music, almost always comes from a ground loop: the mixer and the amp are connected to earth through two different paths, the audio cable and the mains.
- Plug the mixer and the amp into the same socket or the same power strip.
- Switch to a balanced link (XLR or TRS jack) if you were on RCA.
- Use the amp’s ground lift switch if it has one: it lifts the audio ground, not the safety earth.
- Never disconnect the mains earth, neither with an adapter nor by breaking the pin. It is what protects you if something fails.
The choice between balanced and unbalanced is covered in balanced or unbalanced.
And in a sound system?
In a sound system, the master does not go straight to an amp: a preamp or an active crossover first splits the signal into ways, sub, bass, mid and top, and each way has its own amp. The connection between the mixer and that preamp follows exactly the rules above. The full chain is in the mixer wiring diagram, and you can hear what that split does with the online dub preamp.
If your speakers are powered, there is no separate amp: the master output goes straight into each speaker’s input.
Frequently asked questions
Can I connect a DJ mixer to a hi-fi amp?
Yes, into a line input (AUX, CD, LINE), with an RCA cable or an adapter. Never into the phono input. Keep the volume reasonable: a hi-fi amp is not made to run at full power for long.
Why does it distort when the amp is low?
Because the mixer is clipping. Lower the channel gains and the master until the red is gone, then raise the amp.
Which cable between mixer and amp?
Two XLR cables, or two TRS jacks, for a balanced link. An RCA cable or an RCA to jack adapter if the mixer only has RCA, over a short distance.
Do I need one amp per speaker?
No. A stereo amp drives two speakers, one per channel. In a multi-way sound system, however, each way has its own amp or amp channel.