V-PRE - Vox Top Boost Preamp


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V-PRE is the famous Vox "Top Boost" channel of their classic AC-30 amp from the 1960s

  • 3-way EQ
  • dual-triode all-tube circuitry
  • classic Vox AC-30 "bright" channel
  • 12V or 6V heater wiring
  • decoupled stages for low noise

V-PRE produces the classic preamp-portion of the "Top Boost" sound; brighter and clearer than the other channels on the AC-30. Run V-PRE through a cathode-biased amplifier for the complete tone. The original had only 2-way EQ but we have expanded this with a miodrange control - so 3-way EQ.

Assembly is simple with London Power's high quality printed circuit board, which assures stability and consistent unit-to-unit performance. V-PRE is much quieterr than the original Vox assembvly because we have added heavy filtering for each gain stage.

V-PRE can be combined with other preamp types for a multi-channel system, and the PCB has easy tie in points for whatever switching method you choose.

Components are our standard high-quality metal-film resistors, polypropylene and ceramic caps, and long-life electrolytic filters. These can be mounted on either side of the board depending on the tube orientation desired, as internal or external tube access. Both sides of the board are silk-screened for easy component placement. Pots have their own small PCBs to make wire connections simpler. The jacks and pots are chassis mounted.

Any 12A_7 can be used, but a 12AX7 will provide a tone and gain most like the original circuit. The tube is not included.Assembly is required. Allow for tube insertion space and ventilation when mounting tubes inside a chassis.

PCB size: 3.75 x 1.5" 95 x 38mm

Power requirements:
Heater: 6V at 300mA or 12V at 150mA, AC or DC
Plate: 160-450Vdc at 2mA
Use PSU-PRE or similar to build a stand-alone preamp.
Combine with AMP-10, AMP-25 or AMP-50 to build an integrated amp.

Would you like to receive this kit pre-assembled? Add PRE1-BLT to your order.


About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

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(807) 473-0952
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PO Box 10012, Thunder Bay, ON P7B 6T6 CANADA