Quick Answer / Summary: Four numbers per amplifier: output power per channel, minimum load impedance, peak output current, and connector type. From them: gauge from current and length, connector from current (speakON above 100 W), and ventilation from class (AB needs more clearance than D). Class does not change cable sizing; it changes heat, weight and power-supply demands.
Class A, AB and D differ in efficiency, heat and size – not in what the cable has to do. Four numbers describe any amplifier’s cabling need, and they are the same four across every class. This guide lists them.
What Class Changes
Class A: low efficiency (20-30%), constant current draw, heavy heatsinks. Class AB: 50-70% efficiency, the traditional pro-audio workhorse, heat that needs 1U clearance. Class D: 85-95% efficiency, small and light, switching supply that can inject noise if poorly filtered. Cable consequences: none directly – current is current. Indirect consequences: class D’s higher efficiency allows more power in a smaller box, which raises current per connector; class AB’s heat demands ventilation that cable routing must not block.
Efficiency Is a Heat Number
A 500 W class AB amplifier dissipates roughly 250 W of heat at full output; class D dissipates 50 W or less. The rack plan changes, the cable does not.
Switching Noise
Poorly filtered class D supplies can inject noise into nearby signal cable. Separation rules matter more, not less.
The Four Numbers
Power per channel: tells you the current at a given impedance. Minimum impedance: tells you how many speakers can parallel. Peak current: sets the connector rating – a 30 A speakON versus a 5 A binding post. Connector type: what the chassis provides and what the cable must mate with. Write these four on the rack schedule; every cable decision follows from them, and every future technician can re-derive the plan from the label.
Current From Power
I = sqrt(P/R). 500 W at 8 ohm is 7.9 A; at 4 ohm, 11.2 A. The formula turns the first two numbers into the third.
Connector Rating
Match the connector to peak current, not to the amplifier’s appearance. A 5 A connector on an 11 A circuit is a hot spot.
Installation Checklist
Before power-up: gauge sized for current and length, terminations inspected for stray strands, polarity verified on every channel, ventilation clearance confirmed, and the rack schedule filled in. During commissioning: measure the load at the cable end, run at moderate level and check connector temperature, then document the settings. The checklist is short because the physics is simple – most failures are procedural, not electrical.
Measure the Load
A meter at the cable end confirms the impedance the amplifier will see. Surprises are cheaper before power-up.
Temperature Check
Warm connectors are normal; hot ones indicate resistance. Ten minutes at performance level finds it.
Class Comparison
| Class | Efficiency | Heat | Cable Impact |
|---|---|---|---|
| A | 20-30% | Very high | None – gauge by current |
| AB | 50-70% | High | Ventilation clearance |
| D | 85-95% | Low | Noise separation |
| H | 60-70% | Moderate | None |
Real-World Application Scenarios
A venue’s class AB rack needs 1U clearance per amplifier and speaker cable routed away from the heatsink exhaust. A class D install fits four channels in 1U and uses the same 14 AWG as the AB rig. A home class A amplifier heats the cabinet, so the speaker cable routes outside it.
Recommended Internal Resources
(1) Product cluster – https://zh-zong.com/productlist/ (anchor: speaker cable for all amplifier classes); (2) FAQ – https://zh-zong.com/faq/ (anchor: class and current questions); (3) Contact – https://zh-zong.com/contact/ (anchor: request a rack schedule template).
Related Reading in This Series
- Stereo Amp Setup: Cables, Balance and the First Power-Up
- Hi-Fi Audio Amplifier: Cable Specs That Matter and Myths That Don’t
- Audio Power Amplifier: Matching the Cable to the Load
Frequently Asked Questions (FAQ)
Q: Does amplifier class change the cable I need?
A: No – gauge follows current and length. Class changes heat and ventilation, which affects cable routing but not sizing.
Q: Which four numbers should I record?
A: Power per channel, minimum impedance, peak current and connector type. Every cable decision derives from them.
Q: Is class D noisier for cable runs?
A: Its switching supply can radiate if poorly filtered. Keep signal cable separated and use balanced connections where possible.