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Iron Pre

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Original price $ 150.00 - Original price $ 175.00
Original price
$ 175.00
$ 150.00 - $ 175.00
Current price $ 175.00
Out of stock
Out of stock

The Iron Pre Completion Kit is over here.

This is the Iron Pre from Zen Mod - limited quantities and hot off the press.

There are two versions of the project: 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:

PCB Specifications (Main Boards):

  • 2oz copper / ENIG, 2-Layer, 1.6mm thick
  • PCB dimensions - 228mm x 85mm
  • Mounting Hole Spacing – 220mm x 70mm

Parts Kit Specifications:

  • PCBs included for two channels (1x for SE and 2x for Balanced)
  • “Twister Board” PCB – Input Selection with LEDs and Mute x 1
  • Active Devices (QTY based on SE / Balanced)
    • Matched JFET Pairs (2x / 4x)
    • BD139 (1x / 2x)
    • BD140 (1x / 2x)
    • BC546 (7x / 14x)
    • BC556 (7x / 14x)
    • LM336 (2x / 4x)
    • IRF510 (1x / 2x)
    • IRF9510 (2x / 4x)
  • CineMag CMOQ-4HPC Signal Transformers x 2

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.


Customer Reviews

Based on 6 reviews
Christophe G.
Brilliant really

I built an SE version first, as I could get hand on an early kit from another DIYAudio member. The build is really easy to do, even more when using the dedicated case from Hifi2000.
The Iron Pre sounds so natural, and so airy, that I was totally happy when I tested it. So happy that I ordered the balanced kit, which is yet waiting for me to build.
It's probably the best pre-amp I own. No, it is the best pre-amp I own.

So Great!

I couldn't be happier. The kit is awesome. The support is great. And the sound? Fantastic.

Greg P.
Not too early

Even though I am not done building this unit, I have good things to share about the build in general. First off, the quality of this kit is very good and I wouldn't hesitate to recommend it based on just that. Many of the parts chosen are to be by the builder and that is where it gets to be truly yours when it is finished.
There are parts on the way, and this will soon be assembled as prescribed. Likely, I will make a unique choice by utilizing a stacked volume control for the input and know from experience that such a choice allows for not just volume adjustment, but balance as well with no disadvantages of the usual implementation.
Probably around Christmas this will be complete. Pictures promised then.

Mike T.
Very nice kit

Still waiting for some parts (relays and rotary switch) on backorder till Feb. Can't wait to hear what it sounds like when finished. Hoping a chassis will be made available through the store so we all don't have to order individually from Italy. Very thankful that all the hard to find semiconductors came with the kit.

A lovely sounding preamp

I built the balanced version of the Iron Pre and finished it a month or so ago.

I've built a lot of really good sounding preamps over the years - tube, solid state and buffers. I still have most of them. However, I wonder if I will listen to them again. This one sounds soooooooo good. I would guess that it's just synergy with the Papa amps I've built, but it sounds amazing with my non-Papa amps as well.

I was going to take a picture of the inside, but didn't want to pull it out of the system to do so. So I'll describe the build instead.

- I used two Antek AN-0218 transformers, and covered them with the Antek CA-002 steel covers.

- I used two EIZZ 10K stereo attenuators. They sound great, but the volume steps are a tad too large at the louder end of the range (around 3 dB), so at some point I will try a balanced chip based control.

- I used a shielded quad microphone cable between the volume controls and the boards. I didn't use any extensions to bring the volume controls back to the board inputs (mainly because my chassis didn't have adequate layout to do so), so thought it best to use shielded cable. I have no noise when I stick my ear up to the driver at full volume.

- I used thin gauge solid silver coated copper wire between the boards and the inputs and outputs.

From a build perspective, I love how easy it is to implement both balanced and single ended inputs and outputs in this design.

From a sound perspective, I am incredibly happy. It is hard to describe how good this preamp is. The music is detailed but never synthetic. It is warm but the midrange and treble shine through beautifully. Stereo width and depth is equal to the best I've heard in my system, if not better. It sounds great with all the genres of music that I like to listen to (jazz, jazz, jazz, classical, electronic, pop, rock and jazz).

In my experience, there are a number of exceptional sounding DIY and commercial amps, but it is really hard to find an exceptional sounding preamps. This s an exceptional sounding preamp.

Dennis R.
Nothing wrong with the KISS

From the mind of Zen Mod and through the diligence of ItsAllinMyHead and the efforts of heroes unsung and un-named in the DiyAudioStore, you have the opportunity to build a pre-amp that incorporates a number of technologies and a number of options for extending to your own tastes and delights.

At the heart of it all is a pair of transformers-configured-as-autoformers in the gain stage (input-> attenuator-> buffer-> gain-> out) instead of traditional active devices (tube, BJT, FET) which to my ears brings instant linearity without the stretching and warm-up pre-game shoot-around while pulling with honesty the best it can extract from your sources. Speaking of which, you can have up to five sources, switched via relays, and, if you opt for the balanced version, your choice of single or balanced inputs for each source. It also provides for balanced and single ended output.

The build skill level is moderate. There are some choices to be made, some concepts to be understood, and some thinking and assembly planning to be done. But that's what we're all here for: helping each other along the path. If you've done a few amps and a few linear power supplies and dealt with pre-amps and buffers, this will be a fun challenge, and not just a paint by numbers. If you want to start extending with remote controls, powered volumes, MUSE type interfaces, threads are popping up where these approaches are being worked out. It's a platform. I think there will be many implemented variations with this transformer's heart. The boards themselves host the linear progression from source to switchery to gain, and on the other half, from PSU transformer connections through the rectification into the regulated rails with biasing pots and test-points and jumpers. The kit itself provides some of the key components, including the transformers, matched buffer FETs, and various PSU active devices. Your job is to find the rest of the BOM from your favorite suppliers. The kit has forced me up my chassis-drilling machinist game, and that's good for me, though the forthcoming specialized chassis in the works perfectly captures the fun and whimsy of this serious piece of audio. I went with a store-sourced Slimline 2U (350 depth) and am working on my own front and rear panel layouts.

How does it sound? The first thing you notice is silence. It's a black hole through balanced outputs, and barely a whisper single-ended. Not a hint of hum in spite of mine sitting open-faced on the stereo-rack, sunny-side up, surrounded by amplifiers, streaming and gaming devices and DACs CD players and the LCD TV too. And then you press play. Sonically it is honest. It brought bass control to the M2X, and revealed heretofore unknown micro-dynamics in many a favorite listen of mine. It's not colored; it's not dry or sharp nor is it dark and moody. It just *is* and it gets out of the way and lets your sources and amps speak. Especially the Aleph 60s. It brought back those feelings of being able to follow any musical thread in any material from Metallica to Monk, especially revealing of recording-engineer decisions, or of the dynamics of the performer and the reflectiveness of the room.