Understanding the Audio Power Meter Concept
The term ‘Audio Power Meter’ encompasses a wide range of devices utilized for measuring amplifier output, covering various types of equipment within this category. This project aims to construct a straightforward circuit capable of measuring the output of any amplifier device effectively.
Power Indication through Dual-Colour LED
This uncomplicated circuit serves the purpose of indicating the power sent to a loudspeaker. The dual-colour LED exhibits a green light at approximately 1 watt, shifts to orange at 1.5 watts, and turns bright red beyond 3 watts. Connected parallelly with the loudspeaker connections, the circuit derives its power from the audio signal. The added load, represented by the 470 Ohm resistance (R1//R3), poses no challenge for any amplifier.
Operational Dynamics of the Dual-Colour LED
During the positive half cycle of the output signal, the green LED illuminates, provided the voltage reaches a sufficient level. As the output voltages increase, T1 conducts (based on the voltage divider R2/R1), causing the green LED to dim. In the negative half cycle, the red LED is activated through R3, lighting up when the voltage surpasses a specific threshold. In the transitional phase, where T1 regulates the green LED’s brightness. The combination of red and green produces the dual-LED’s orange hue.
By selecting appropriate resistor values, the power levels can be customized to match specific requirements. The chosen values in this context are tailored for typical usage in a living room setting. It might surprise you how loudly you need to increase your amplifier volume before the LEDs light up! These resistors can be 0.25 W types, as long as the amplifier doesn’t exceed a continuous output of 40 W. Beyond this power threshold, the transistor might not function optimally, so it’s crucial to be cautious. Since T1 operates in saturation, the transistor gain (Hfe) is not critical, and similar types can be interchanged. The mentioned power levels apply to 4-Ohm speakers. For 8-Ohm speakers, all resistor values need to be halved.