AE-252

Week-8:  The Vari-Fi jfet preamp contruction is progressing (click to see). 

Download the Audio Wiring Diagram

AE-252 Final Exam Requirements (click for PDF version)

  1. Draw JFET schematic from memory. 
  • Label input, output and power connections.
  1. Draw block diagram from xlr input to xlr output. The hit list should include:
  • Phantom power distribution
    • Switch
    • LED and its resistor 
    • RC slow ramp-up time constant (Google R/C time constant and provide a summary)
    • 6k8 resistors
  • Input pad (primary side of Input xfrmr)
    • Three position switch plus trim pot
  • Output Load (secondary side of Input xfrmr)
    • Include Flat, Warm and Air positions 
  • Direct Input "Hi-Z" Jack
    • With Normal
    • Feed to and include Input Sensitivity Pot
  • First Stage Preamp (triangle)
    • Feed to and include Output Level Pot
  • Second Stage Preamp (triangle)
    • Feed to primary side of output transformer 
    • Optional unbalanced output on 1/4-inch connector
    • Wire Output xfrmr secondary to XLR output (male) connector 
    • Include polarity reverse and optional Load / Termination switches
    • Optional balanced output on 1/4-inch connector


The power supply and the two preamp stages are done, the later have to be tested.  The front panels and additonal parts have arrived.  So we should hear audio this week.