The Mini³ portable stereo headphone amplifier


  • Oct 21, 2011: A LiPo (lithium-ion polymer) battery option is now available when used with the χ1 battery management board. Please read the χ1 website for details.
  • Mini³ circuit boards are available.
  • Precision CNC-machined and engraved Mini³ front and rear panels are now available from AMB audio shop.
  • Custom-built, ready-to-use Mini³ amplifiers are available from some professional builders.


Mini³ ("Mini cubed") is a high-quality DIY portable stereo amplifier for dynamic headphones. Designed to be a small battery-powered unit with built-in charging circuit, Mini³ provides high performance and excellent sound that belies its size and cost. Its footprint is almost exactly the size of a credit card, and about 0.9" (23mm) thick.

A perfect companion with portable media players such as the Apple iPod, iPad or smartphones and tablets, Mini³ offers dramatically improved sound when driven from the player's line output, and used with high quality headphones. The performance of Mini³ is so good, it could also serve as a headphone amplifier with dedicated home CD players and other sources without taking up much desk or shelf space. In conjunction with an off-the-shelf enclosure solution and wire-free board mounting of all components, Mini³ is easy and inexpensive to build. The only surface-mount parts are the two opamps, all other parts are through-hole. See the Tech highlights section for details.

Some photos of the Mini³ (click to enlarge)

Mini³ version 1 was never released. Version 2 is the current offering, featuring a smaller, sturdier and more attractive aluminum case. The technical difficulties with version 1 were solved in version 2, and the battery run-time has been greatly increased. See the History section for details. Unless otherwise noted, all information in these pages pertain to Mini³ version 2.

There are two variants of Mini³, the "high performance" and the "extended runtime" editions. The high performance edition has higher output current capability and offers superior measured benchmarks especially with low impedance headphones. The extended runtime edition provides decent output current capability while giving much longer run-times between battery charges. Both editions offer excellent sound. The only parts difference between the two editions is the choice of opamps. See the Parts list section for details.

There are also two choices of batteries. The standard Mini³ uses a 9V NiMH rechargeable battery, and is charged by Mini³'s onboard charging circuit. The optional χ1 battery management board may be added to use specified LiPo battery packs with much longer runtimes and short charge time.

To obtain the blank printed circuit board and some related parts, visit the AMB audio shop. Other parts are available from online vendors. See the Parts list section.

Please be sure to read every section of this site carefully before attempting to build the Mini³ amplifier. If you don't thoroughly understand everything, please consider having someone more experienced to build the amplifier for you.

The scope of the Mini³ project

The Mini³ project is primarily centered around the main headphone amplifier board, which incorporates a battery-charging circuit. To make a working amplifier, you will also need a 9V NiMH rechargeable battery, an AC adapter (for battery charging), and a Hammond 1455C801 or 1455C802 enclosure. The Mini³ circuit board was designed to slide into these cases without additional mounting hardware.

What skills and tools are needed

You should know how to read a schematic diagram and correlate it to the circuit board layout, identify electronic parts and their pin-outs, have decent soldering skill, and be proficient with a multimeter. You need at least a basic set of tools for electronics work, such as a good soldering iron (with a fine tip) and accessories, screw drivers, needle nose plier, diagonal cutter, a sharp tweezer (for positioning the SOIC-8 opamps), etc. For the front and rear panels, you will also need to be able to accurately drill the holes needed for the input, output and DC power jacks, volume control, and indicator LEDs (unless you opted for the AMB CNC-machined and engraved panel set).

Why not offer a full kit

AMB is not prepared to stock all the needed parts and offer them as a full kit. This amplifier is AMB's contribution to the DIY community rather than a for-profit product, AMB cannot assume the commercial support role that might be implicit with a full kit.

Why not offer the finished product

This is intended to be a project for DIYers, and AMB is not set up to manufacture completed units.

Professional builders

Inquire with the following list of professional builders if they would build you a completed Mini³ amplifier, in case you cannot build one yourself.

Where to get help

Be sure you read all the information at this site. If you cannot find an answer to a question, or encounter a problem you cannot solve, the best place to get support is the AMB DIY audio forum. Search the forums for an answer before asking a question. Your question may have already been asked and answered.

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