AudioAmp380

Design Features

• Pre-amp plus power amp
• 50 Ohm input impedance matches Product Detector outputs
• 0-10x Gain trimmer potentiometer on preamp
• External mount gain potentiometer
• NE5534 Pre-amplifier
• LM380 2.5W Audio Power Amplifier
• 12V nominal power
  • 10-22V
• Fits into standard 80x50x20mm extruded aluminum enclosure

Pre-Amplifier (NE5534)

• Low-Noise Operational Amplifiers
• Internally fixed gain of 50 (34 dB)
• 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 gain/bandwidth - Tune for best sound
• RV2 - volume control (after preamp and before LM380 Amp). 1x5 header wire to external pot

Jacks

J1 - Audio In

• 50 Ohms input impedance for radio applications
  • Output of Product Detector stage
  • R1 = 51 Ω
  • RV2 = 500 Ω pot
• Optional Line Level Input
  • The impedance of a line input is typically around 10 kΩ
  • R1 = 10 kΩ
  • RV2 = 50 kΩ pot
• RCA jack

J2 - Audio Out

• 8 Ohm speakers
• RCA

J3 - Power

• 10V-22VDC
• 5.5mmx2.5mm DC jack

Measurements

• MHS-5200A Signal Generator
  • 200 mV
  • 100-10KHz
  • Drives 50 Ohms
• Adjust Trimmer CCW for full gain
  • With adj screw to the right side
• Benchtop Power Supply DPS3005
  • 12V
  • 20mA with volume control fully down
  • 300mA with volume control fully up (3.6W)

Rev 2/3 Schematic

Revision History

Rev 1 Rework

Rev 1 Schematic

• (Before rework)

LM380 Equivalent Schematic

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

• Jumpers on rear side

Rev 2

• Schematic C5 was 100uF, should be 100nF
  • Fixed on prototype
• Footprint wrong on C2 (older rev 2 was ordered)
  • 10uF can be fit onto the card
• Didn't have any 100uF cap to use at C9
  • Used 47uF - power bypass = OK value

Rev 3

• Fixed C3 footprint already
• Fixed C5 footprint back to 0.1" small cap footprint
• Card works

Videos

• Charlie Morris ZL2CTM design

Panel Cutouts

• Panel cutout (PDF File)

Assembly Sheet

• LM380 Rev 1 Assembly Sheet
• LM380 Rev 2 Assembly Sheet
• LM380 Rev 3 Assembly Sheet