AudioAmp380

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AudioAmp380-3D.png

Design Features[edit]

  • 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)[edit]

  • 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)[edit]

  • 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[edit]

  • 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[edit]

J1 - Audio In[edit]

  • 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[edit]

  • 8 Ohm speakers
  • RCA

J3 - Power[edit]

  • 10V-22VDC
  • 5.5mmx2.5mm DC jack

Measurements[edit]

  • 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[edit]

AudioAmp380-Rev3 Schematic.png

Revision History[edit]

Rev 1 Rework[edit]

Rev 1 Schematic[edit]

  • (Before rework)

AudioAmp380-Rev1 Schematic.png

LM380 Equivalent Schematic[edit]

LM380 Equiv Schematic.PNG

  • 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

U2-2 3 Rev1 Rev2 Cuts Jumpers.png

  • Jumpers on rear side

AudioAmp380 Back Jumpers.PNG

Rev 2[edit]

  • 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[edit]

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

Videos[edit]

  • Charlie Morris ZL2CTM design

ZL2CTM Schematic.PNG

Panel Cutouts[edit]

AudioAmp380 Panel Cutouts Rev3.PNG

Assembly Sheet[edit]