Podcast
145

MEP EP #145: The Vox in a Box Roxs

Podcast Notes

  • 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.

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Download: MP3
RSS Feed: Link
Twitter: @MacroFab

Runtime: (00:57:09)

Hosts:
Parker Dillmann
Stephen Kraig

Guest:
N/A


Vox in a Box Schematic - Page 1

Vox in a Box Schematic – Page 1

 

Vox in a Box Schematic - Page 2

Vox in a Box Schematic – Page 2

 

Vox in a Box Schematic - Page 3

Vox in a Box Schematic – Page 3

 

The Vox in a Box driving the VOX AC30 Tube preamp and speakers!

The Vox in a Box driving the VOX AC30 Tube preamp and speakers!

 

Stephen has also been modeling parts in electronics in Fusion 360!

Stephen has also been modeling parts in electronics in Fusion 360!

 


Special thanks to whixr over at Tymkrs for the intro and outro!