BROADCASTS.com

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.
  • Improve your circuit toolbox – Simple designs that will save your next product
    • Chris Gammel gave a talk at the recent SuperCon about circuits you should add to your mental filing cabinet
    • Speaking of the Super Con all the videos for the talks are live on Youtube so go give those a listen to!

Visit our Slack Channel and join the conversation in between episodes and please review us, wherever you listen (PodcastAddict, iTunes). It helps this show stay visible and helps new listeners find us.

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