Quick Answer / Summary: Use a 3.5mm stereo cable for an amp’s 3.5mm aux input, or a short RCA pair for RCA aux inputs; a 3.5mm to RCA cable bridges the two. The source must output line level, which phones, players and computers do. If the amp has no sound, the usual causes are the wrong input selected, a mono or charge-only cable, or a mic-level source being fed into a line input.
An amp aux cord is the cable that feeds a music source, a phone, a player, a computer, into an amplifier’s auxiliary input. In most home and pro amps that input is a 3.5mm jack or a pair of RCA jacks, both expecting a line-level signal. Getting the level and the input selection right is the whole game; the cable itself is a simple stereo line interconnect.
What the Aux Input Expects
An amplifier’s aux input is a line-level input. It expects a small, steady voltage from a finished source, a phone, a streamer, a computer’s headphone out, not the tiny signal from a microphone and not the high voltage of speaker output. The input may be labelled Aux, Line In, CD or Input 1, and it may be a 3.5mm jack, an RCA pair, or both.
Line Level Defined
Line level is the standard voltage between audio components, roughly a fraction of a volt from a consumer source. It is high enough that a short cable introduces no meaningful loss, and low enough that the amp’s gain structure is designed around it. Microphone level is tens of times lower and will sound barely audible in a line input.
Finding the Input
Check the amp’s input list: Aux, Line, CD, Aux RCA, or a headphone out being used as a source. A 3.5mm aux jack and an RCA aux pair on the same amp often feed the same internal input, so either cable works if the source has the matching plug.
3.5mm vs RCA as the Aux Cord
The two common aux cords are the 3.5mm stereo cable and the RCA pair. Electrically both carry the same stereo line signal; the difference is the connector and where it is used. 3.5mm is compact and common on portable and modern amps; RCA is the classic home audio connection with its red and white plugs.
3.5mm Aux Cord
A 3.5mm TRS stereo cable from a phone or laptop to the amp’s aux jack is the simplest connection. Use a cable with a proper stereo, TRS, plug; a mono, TS, plug carries one channel only and the amp will hear half the sound.
RCA Aux Cord
For RCA aux inputs use a short screened pair, red for right, white or black for left, or a 3.5mm to RCA cable from a device without RCA outputs. RCA cables are cheap, and at line level the quality differences are negligible at normal lengths.
When There Is No Sound
The aux connection fails in a handful of predictable ways: the amp is set to the wrong input, the cable is mono or damaged, the source output is turned down or routed elsewhere, or a mic-level source is being used where line level is expected. Work through the list from the amp backward to the source.
Input Selection
The most common fault. The cable is fine, the source is fine, but the amp is tuned to a different input. Select the Aux or Line input, then confirm the source is playing with its own volume up.
Cable and Level Faults
A mono cable, a reversed or broken pair, or a source with no line output, a raw microphone for example, are the cable-side causes. Test the same cable to a known-good input, and test another source into the aux, to separate the two.
Choosing the Right Cord
Match the plug to the input, keep the run short, and screen the cable. A one to two meter screened 3.5mm TRS cable or RCA pair is the standard aux cord. If the run is longer or crosses power cables, a balanced connection or better screening reduces hum; for most home setups a short screened cable is all that is needed.
Length and Screening
At line level, cable length matters little up to a few meters. Screening matters more, because an unshielded aux cable lying near a power cable will pick up hum. Keep the aux cord separated from the power run.
Plug Quality
The plug is the part that wears: a 3.5mm plug in a small amp jack is cycled often. Gold or tin-plated contacts, a smooth plug barrel and molded strain relief make the aux cord last. The conductor inside can be simple; the connection at the ends is what matters.
Amp Aux Connection Options
| Amp input | Cable from phone or PC | Cable from CD player | Notes |
|---|
| 3.5mm aux jack | 3.5mm TRS cable | 3.5mm to RCA cable | Most portable and modern amps |
| RCA aux pair | 3.5mm to RCA cable | RCA pair, red and white | Classic home audio |
| Both on same amp | Either | Either | Often the same internal input |
| XLR line input | XLR or TRS to XLR | RCA to XLR | Balanced pro gear |
| Mic input, wrong choice | Do not use | Do not use | Mic level needs a mic preamp |
Practical Applications
Typical uses: feeding a phone or streaming player into a hi-fi amplifier’s aux input, connecting a laptop to a practice amp or a small powered PA, sending a CD player’s output to a receiver’s aux, bridging a portable player to a home amp with a 3.5mm to RCA cord, and running a music source to a small room amplifier for background listening. In every case the cord is a short screened stereo line cable matched to the input.
Frequently Asked Questions
What cable do I need for an amp’s aux input?
A 3.5mm stereo, TRS, cable for a 3.5mm aux jack, or a short RCA pair, or a 3.5mm to RCA cable, for RCA aux inputs. The signal is line level in all cases.
Can I use a headphone cable as an amp aux cord?
Yes, if it is a stereo, TRS, 3.5mm cable. Headphone cables are line-level capable, but a mono or speaker cable will not work. Check the plug has two insulator bands.
My amp has no sound from the aux input. What do I check?
Select the aux or line input on the amp, confirm the source is playing with its volume up, test the cable on another input, and make sure the cable is stereo, not mono.
Can I plug a microphone into the aux input?
No. A microphone produces a much lower signal than line level and will be barely audible in an aux input. Use the mic input, which has the preamp gain it needs.
Does an aux cord need to be expensive?
No. At line level and short lengths, a screened cable with good plugs performs the same as a premium cable. Spend on plug quality and screening, not on exotic conductors.
