Member Avatar for vinodvinu

Hithere,
I need to take 12v DC from my computer to feed an amplifier. I know there is some red and black wires . But my question is 1.) is there enough current to feed my amplifier( may be 2 or 3 A). 2.) is there any problem to my smps or pc by doing this ?.
Please help.
Vinod chandran

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asked about pulling 12 V from a PC SMPS to feed an amp, and raised concerns about noise and capacity. A concise, practical checklist follows so the thread's suggestions can be tested safely and reliably.

A few quick facts and checks

  • 12 V × 3 A = 36 W, so the important spec is the PSU’s +12 V rail current, not the PSU’s total wattage. Inspect the label on the PSU for “+12V” and the amperage (A) or combined 12 V wattage. If the label comfortably exceeds the amp’s steady and peak needs, the PSU can usually supply 2–3 A.
  • Use the correct power pins: peripheral Molex yellow = +12 V, black = ground (red is +5 V). Tap a spare Molex or SATA-power plug; do not repurpose CPU/EPS or PCIe connectors unless the connector/rail is intended for general loads.

Practical wiring and protection

  • Put an inline fuse on the +12 V lead close to the PSU (pick a fuse slightly above expected continuous current; e.g. 4–6 A for a 3 A load; slow‑blow if the amp has big input caps/inrush).
  • Use stout wiring (18 AWG recommended for margin and low voltage drop) and good crimp/soldered joints.
  • Measure with a multimeter under load before connecting the amp: confirm ~12 V and no rail sag. If the PSU is multi‑rail, ensure the connector used isn’t limited by a low per‑rail OCP.

Noise, grounding and audio quality

  • Switching PSUs have ripple and high‑frequency noise. Add local decoupling (large electrolytic, e.g. 470–1000 µF across 12 V→GND and a 0.1 µF ceramic for HF), and consider a ferrite bead or simple LC/power‑filter if hum or hash appears.
  • Ground loops between PC audio outputs and the amp are a common source of hum; an audio ground‑loop isolator or isolating transformer on the signal path is often simpler than trying to “clean” the 12 V rail.

Recommendation
For casual/low‑power use a 300 W PSU will usually be fine for 2–3 A if the +12 V rating checks out and the wiring/fuse are correct. For high‑fidelity audio, heavy peaks, or noiseless operation, a dedicated low‑noise 12 V adapter or bench supply is the better choice.

Recommended Answers

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Member Avatar for Rik_

There is not enough amperage for what you want to do unless you have a very high output PSU. Also your computer will put out some noise on the 12 volt rail which you will have to correct.

I tried this a few years ago and the result was very unsatisfactory.

Member Avatar for vinodvinu

Hi Rik,
Thank you for your reply. I have a 300w smps in my PC. Does this work ?

Member Avatar for Rik_

Nope, you'd need atleast a 500 watt.

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