AudioAmp380

Design

• Pre-amp plus power amp
• 50 Ohm input impedance
• Gain trimmer potentiometer on preamp
• External mount gain potentiometer
• [1] Pre-amplifier
• LM380 2.5W Audio Power Amplifier
• 12V nominal power
  • 10-22V
• Fits into 80x50x20mm extruded aluminum enclosure

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Pre-Amplifier (NE5534)

• Low-Noise Operational Amplifiers
• Equivalent Input Noise Voltage 3.5 nV/√Hz Typ
• Unity-Gain Bandwidth 10 MHz Typ
• Common-Mode Rejection Ratio 100 dB Typ
• Wide Supply-Voltage Range ±3 V to ±20 V
• Used as single supply

Audio Power Amplifier (LM380)

• Wide Supply Voltage Range: 10V-22V
• Low Quiescent Power Drain: 0.13W (VS= 18V)
• Voltage Gain Fixed at 50 (34 dB)
• High Peak Current Capability: 1.3A
• Input Referenced to GND
• High Input Impedance: 150kΩ
• Low Distortion
• Quiescent Output Voltage is at One-Half of the Supply Voltage

Controls

• RV1 - trade-off book gain/bandwidth - Tune for best sound
• RV2 - volume control (after preamp and before LM380 Amp. 1x5 header wired to external pot
• J1 - Audio In, 50 Ohms input impedance
• J2 - Audio Out, 8 Ohm speakers
• J3 - Power, 10V-22VDC

Rev 2 Schematic

Rev 1 Rework

• Issues
  • Front end opamp has + and - reversed
  • Also hooked up the feedback to the wrong input
• Replace R1 with jumper
• Replace C9 with jumper
• Remove C2
• 5 Cuts
  • 4 on front
  • 1 on back
• 5 jumper segments on back
  • 2 nodes

Videos

Assembly Sheet

LM380 Rev 1 Assembly Sheet