EP#145: The Vox in a Box Roxs
Circuit Break - A MacroFab Podcast6 Nov 2018

EP#145: The Vox in a Box Roxs

  • Stephen's Vox in a Box
    • Preamp Design
      • Vox AC30 preamp - 3 gain stages with a cathode follower and a phase inverter
      • Phase inverter - create differential signals for the power amp input
      • Drop signal using voltage dividers and mosfet buffers
      • 320V phase inverter to 18V buffer drive
      • Built point to point on an aluminum plate for easy modification and testing
    • Power Amp Design
      • TPA3116 Class D amplifier
      • LM311 comparator mute circuit for start up mute ~5 to 10 Seconds
      • Runs at 400KHz - Left open pads for boosting this up to 1.2MHz
        • Is there an advantage at running at higher frequencies?
    • Power Supply Design
      • TPS40210 Switching controller into a diode/cap ladder voltage multiplier
      • 7 stages of multiplication leads to ~50V per stage
      • Variable Switching from 35KHz to 1000KHz
      • PMP8621 Appnote
    • Testing the Vox in a Box
      • Been going nonstop for weeks now
      • Have taken it up to nearly 60 Watts without problems
    • Layout of the PCB
      • Multiple ground system with master start
      • Each sub circuit has its own ground return
      • 8 Master star ground returns
      • 4 layers
    • Issues with the current design
      • High Voltage SMPS does not like high capacitive load
      • Ground for signal input is very important - Nearly all noise is dominated by this single point
        • Alligator clips for signal patching are not low noise…
      • Cold Heater impedance
    • Current Schematic for the Vox in a Box
    • Fusion 360
      • New amp design
        • Learning by building a virtual amp
      • Vox in a box
        • Going to model the whole design to ensure proper fit
  • R.F.O.

Tags: Chris Gammel, electronics podcast, Fusion 360, Hackaday, LM311, MacroFab, macrofab engineering podcast, MEP, PMP8621, Preamp, SuperCon, TPA3116, TPS40210, Vox AC30, Vox in a Box

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