Summary of 3W STEREO DIFFERENTIAL INPUT CLASS-D AUDIO AMPLIFIER WITH UP DOWN VOLUME
Summary: A compact 3W stereo class-D amplifier using the PAM8408 IC provides differential inputs, 32-step UP/DOWN memory volume control, 2.5–6V operation, built-in short-circuit and thermal protection, and ~87% efficiency—suitable for portable battery-powered devices. Two tactile switches control volume; shutdown via jumper J3 preserves the volume setting.
Parts used in the 3W STEREO DIFFERENTIAL INPUT CLASS-D AUDIO AMPLIFIER WITH UP DOWN VOLUME:
- PAM8408 IC
- Power connector CN1
- Audio input connector CN2
- Speaker connectors CN3 and CN4
- Jumper J3 (Shutdown)
- Solder jumpers J1 and J2 (optional)
- Power LED D1
- Tactile switch Switch 1 (Volume UP)
- Tactile switch Switch 2 (Volume DOWN)
- PCB and supporting passive components (resistors, capacitors as required by the PAM8408 application)
The circuit presented here is a 3W stereo audio amplifier with memory UP/DOWN volume control. The project is based on PAM8408 IC from Diode Incorp which is a filter-less class-D amplifier with high SNR and Differential input which helps eliminate noise. Two tactile switches are provided to control the UP/DOWN volume in 32-steps and it will hold the setting when the chip is in shutdown mode. The operating supply is 2.5V to 6V DC and this supply range helps to operate it with batteries like the use of 4 x Alkaline batteries. The small PCB size, 87% efficiency, low cost, minimum external components make this project ideal for portable applications. The PAM8408 also has built-in auto-recovery SCP (Short Circuit Protection) and thermal shutdown. The circuit works with differential audio signal input. It is advisable to use shielded wire for the audio input signals. Jumper J3 is open in normal operation, and if you close it puts the amplifier into shutdown mode and the audio volume will memorize when shutdown mode is recovered. Solder jumpers J1 and J2 are optional and of no use, it is advisable to keep these jumpers open. Connector CN1 is for power supply, CN2 is for audio signal input, CN3, and CN4 are for the speaker, Jumper J3 is for Shutdown, D1 is the power LED, Switch 1 increased volume, and Switch 2 decreases volume.
Volume changes are affected by toggling either the UP or DOWN tactile switches. After a period of 1 cycle pulses with either the UP or DOWN switch press, the volume will change to the next specified step, either UP or DOWN, and followed by a short delay. This delay decreases the longer the line is held low, eventually reaching a delay of zero. The delay allows the user to pull the UP or DOWN terminal low once for one volume change, or hold down to ramp several volume changes. The delay is optimally configured for push-button volume control. If either the UP or DOWN pin remains low after the first volume transition the volume will change again, but this time after 10 cycles. The followed transition occurs at 4 cycles for each volume transition. This is intended to provide the user with volume control that pauses briefly after initial application, and then slowly increases the rate of volume change as it is continuously applied. There are 32 discrete gain settings ranging from +24dB as maximum to -80dB as a minimum. Upon device power on, the amplifier’s gain is set to a default value of 12dB, and the gain will remain when Shutdown Jumper J3 is closed.
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- What IC is used in this amplifier?
The amplifier uses the PAM8408 IC from Diode Incorp. - What supply voltage range does the circuit require?
The operating supply is 2.5V to 6V DC. - How many volume steps are available?
There are 32 discrete gain settings. - Does the amplifier remember the volume after shutdown?
Yes, closing the shutdown jumper J3 preserves the volume setting when recovered from shutdown. - What are the maximum and minimum gain values?
Maximum gain is +24dB and minimum is -80dB. - What input type does the circuit use?
The circuit works with differential audio signal input and shielded wire is recommended for audio inputs. - How is volume controlled?
Two tactile switches toggle UP or DOWN to change volume in steps, with a delay pattern that speeds up if a switch is held. - What protections does the PAM8408 provide?
The PAM8408 includes auto-recovery short circuit protection and thermal shutdown. - What connectors are provided for speakers?
Speaker outputs are provided on connectors CN3 and CN4. - Are J1 and J2 required?
J1 and J2 are optional and not used; it is advisable to keep them open.
