Keep in mind that a transformer’s voltage rating only tells you it’s AC voltage output. Find the Maximum Supply Voltage Output by a Transformer The next step is finding a transformer voltage rating that can deliver this maximum supply voltage. The ± symbol indicates that the voltage is +30.2 V on the positive rail and -30.2 V on the negative rail. So my power supply will need to deliver a peak voltage of ☓0.2 V for my amplifier to output 40 Watts into 6 Ω speakers. Use this formula to calculate the maximum supply voltage required by your amplifier:įor my 40 Watt amplifier, the maximum supply voltage it needs is: It usually peaks late at night when people are asleep and drops in the daytime when more people are awake and drawing current from the power grid. Mains voltages can vary up to 10% depending on your location. Regulation values can usually be found in the transformer’s datasheet, but if you don’t know your transformer’s regulation, a safe value to use is 15%. The regulation of the transformer I’ll be using is 6%. Regulation is the increase in output voltage of a transformer when the load isn’t drawing current (i.e. Then factor in your transformer’s regulation and the variation in your mains voltage. To find the maximum supply voltage, take the peak output voltage and add the voltage drop (V od) of the LM3886 (4 V). This is the voltage the amplifier needs from the power supply to get the desired output power. Now that you’ve found the peak output voltage of your amplifier, you can calculate the maximum supply voltage (V max supply). The amplifier I’m building will be 40 Watts with 6 Ω speakers, so my peak output voltage is:įind the Maximum Supply Voltage Needed by the Amplifier Your amplifier’s peak output voltage will depend on your desired output power (P o) and speaker impedance, according to this formula: Peak output voltage (V opeak) is the maximum voltage measured across the amplifier’s speaker terminals. Required Power Supply Voltageīefore you can find the required power supply voltage, you need to calculate the amplifier’s peak output voltage. If the transformer’s VA rating is too small, the amplifier might clip or distort the audio at higher volumes. This step is important because if the transformer’s voltage is too low, the output power of the amplifier will be less than what you expected. These calculations will tell you the correct voltage and VA ratings for the transformer you’ll use to power your amp. Let’s start by figuring out how much voltage and power your amplifier will need from the power supply. BE SURE TO TAKE ALL NECESSARY SAFETY PRECAUTIONS, AND NEVER WORK ON A LIVE CIRCUIT!! Determine the Required Power Supply Voltage and Power WARNING: THIS PROJECT INVOLVES WORKING WITH MAINS SUPPLY VOLTAGES THAT CAN SERIOUSLY INJURE YOU OR KILL YOU.
#AUDIO POWER AMPLIFIER DESIGN FULL#
It may be in the device’s user manual, but if not, you can get a rough estimate by playing a 60 Hz pure sine wave (there are apps that will do this) at full volume and measuring the AC voltage between ground and the left or right channel with a multi-meter. You should be able to find your speaker’s impedance on the back of the speaker or in the user manual.įinally, you’ll need to know your input voltage. This is the output voltage of the audio source you’ll be amplifying. You’ll also need to know the impedance of your speakers. The maximum output power of the LM3886 is 68 Watts, but the actual power you get will depend on your power supply voltage and speaker impedance. Output power is what you’ll typically see stated as the Wattage rating of an amplifier. At the end I wire up the amp so you can hear what it sounds like:īefore starting to design your amplifier, you should have an idea about how much output power you want to get out of it. You can also check out this video to see a quick overview of the design process.
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