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.
- 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!

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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