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Preamplifier project by Zen Mod

Iron Pre

The Iron Pre is Zen Mod's first diyAudio store offering. His basis for the design is Keep It Simple, Stupid (KISS). It's a wonderful pre-amplifier that has been enjoyed by 100s of happy builders and listeners from around the world.

Iron Pre

Iron Pre

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Key Information

  • Preamplifier Project
  • Designed by Zen Mod
  • Intermediate to Advanced Difficulty
  • Only Essentials Kit Available
  • Comprehensive Build Guide


  • SE has user adjustable gain: 6dB and 12dB
  • Balanced will allow SE input and provide true differential output
  • 5 (configurable for balanced) selectable inputs
  • Power supply circuit included on the main PCBs



There are two versions of the Iron Pre: Balanced / Differential and Single-Ended.  Builders of the balanced version can select balanced or single-ended for each input.  The boards include not only the “iron-based” gain stage, but also a shunt-regulated PSU section, and a relay-based input switching section.  A total of 5 inputs are supported.  Each kit also includes a “Twister” board for input selection.  The balanced version is intended to be built as a dual-mono project.

You can read more about it here:


What Will You Need To Complete The Project?

This is not a “completion kit”.  It includes the parts that are generally more difficult to source and/or may have longer lead times. 

Below is not intended to be a complete parts list or Bill of Materials (BoM).  Many people customize their builds.  However, you’ll likely need:

  • Additional passive components per schematic
  • Power transformer(s) – 20VA minimum, 36VAC CT or 18VAC Dual
  • Wiring, Various I/O Hardware, Small Heatsinks
  • Input Selection Rotary Switch Compatible with “Twister Board” – Lorlin CK1060.
    Mouser Part Number (10SM160) is recommended.
  • Input switching relays. 12V or 24V Non-Latching Relays are supported.
    Fujitsu RY-24W-K come highly recommended.
  • Input attenuation – Potentiometer(s) / Muses / Autoformer Volume Control (AVC) Note – If an AVC is chosen, it is used in place of the signal transformer.  You can find details in the KISS thread.

What if I have questions?

This project is intended for intermediate to advanced DIYers.  However, many novice builders have achieved success.  This kit, along with yet another sensational pictorial build guide from 6L6, makes this project more accessible to a variety of builders.  If you need additional support, members have posted a number of BoMs, shopping carts, and parts lists in the forum thread.  The Mighty Zen Mod is ever-present and kindly offers support and a quick wit.  Other forum members are available to lend a hand and provide ideas for the never-ending list of options to customize your project to fit personal tastes and needs.  And yes, it will drive an F4.