In exclusive partnership with top-tier modification house Parts ConneXion, Underwood HiFi is proud to offer the following carefully tested, factory-authorized performance enhancement packages for the Quad QC-24 preamplifier.


By virtue of selling consumer-direct, we can offer these super-charged, brand-new models for a better price than the same modifications would cost retro-fitted - though we offer that, too.

The Quad QC-24 is a wonderful $1000.00 tube preamplifier from one of longest-lived, most famous names in High-End audio. It is a Golden Ear Award winner in The Absolute Sound. Our mod takes it to the next level and allows it to compete with anything under $2500.00

QC-24 Level-1 mod - $1,490 + shipping ($600 retro-fit)

Our Level-1 mod installs:

  • Four small EAR brand Sorbothane isolation feet
  • Two sheets of SoundCoat chassis damping material cut & applied where applicable
  • Three pairs of Vampire CM-1F/CB copper body, direct gold-plated RCA input jacks
  • Four Auricap signal path, metallized polypropylene coupling capacitors
  • Four MultiCap RTX Series polystyrene and tin-foil coupling bypass capacitors
  • Four Film Cap power-supply bypass caps
  • Four Black Gate coupling bypass and power-supply capacitors
  • Eight Riken Ohm ½ and one watt signal path 1% carbon comp. resistors (gold-plated leads)
  • DH Labs Revelation Series pure 99.99% silver Teflon-insulated input/output wire
  • Four IR Hexfred ultra-fast soft recovery diodes
  • TRT WonderSolder used throughout

Sonic changes of our Level-1 mod

  • Lower S/N ratio with blacker silences, better low-level detail and 3D ambiance retrieval
  • Smoother yet more detailed presentation, better macro dynamics
  • It seems to play louder, with improved microdynamic contrasts
  • Tonal balance is more coherent from top to bottom
  • In addition, the midrange is a little more liquid than the stock machine's
  • Imaging is more defined, soundstage depth is enhanced
  • Bass extension and impact are dramatically improved, weight and authority built out, sounding more like solid-state in this area

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