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The Millett Hybrid MiniMAX

Technical Highlights

The Millet MiniMAX is the latest refinement in the fine tradition of the Do It Yourself (DIY) Millett Hybrid MAXed series of headphone amplifiers. All Millett Hybrids incorporate a hybrid single-ended vacuum tube gain stage combined with a solid state output stage. The Colin Toole-designed, Millett MAX family of amplifiers is no different, but includes many other features and refinements such as an onboard, linear-regulated power supply, relay-delay headphone protection, and a close integration with case design that bring the Millett MAX family to a level of performance and convenience heretofore unattained.

The MiniMAX also adds a highly-tested very-low-noise linear-regulated power supply that exceeds previous MAX designs by an order of magnitude. In addition, the integration of the MiniMAX with a custom-machined case design is un-paralleled in the DIY community. The case design for the Lansing Enclosures MicroPak "DT1" model case brings potential commercial quality appearance and features within reach of every DIY-er.

The Millett MiniMAX incorporates all of the following features and more:
  1. The basic Millett Hybrid circuit,
  2. onboard, very-low-noise linear-regulated Power Supply (~0.045mVAC),
  3. BJT-input/output totally discrete Diamond Buffer output stage,
  4. onboard, relay-delay circuit for headphone protection, and
  5. un-paralleled integration with a custom-machined case design from Lansing-Enclosures.
  • extruded TO-220 heat sink footprint for power supply,
  • extruded TO-220 heat sink footprints for all four BJT (Bipolar Junction Transistor) output transistors,
  • cooling holes beneath all heat sink positions,
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  • CCS based on a feedback transistor pair with selectable resistor sizes for different currents and superior B+ regulation,
  • power resistor option for heater circuit, allowing higher voltage supplies without damage to tube heaters,
  • 16mm minimum cap diameter pads throughout, 18mm for the PS,
  • extended lead spacing for the output film cap positions,
  • signal input/output terminal block pads with 5mm lead spacing, and
  • a 5 x 20mm buss fuse for walwart/power supply protection and a polyfuse for protecting the buffer and the tube circuit.

(production prototype)

(custom case rendering)

(early production prototype - Lansing CT1 case)


  • Alps RK27 pot positions
  • onboard Neutrik output jack pads
  • tube LED and panel LED pads included
  • axial Schottky rectifier diodes, axial ceramic snubber caps
  • board sized for Lansing DT1 (6 inches long) case, center post for stability around tubes
  • board dimensions: 5.25" wide x 5.82" (134mm x 148mm), 2oz copper on an 0.062" (1.6mm) FR4 dielectric

Like other MAXes, MiniMAX's Power Supply allows the use of a simple, inexpensive "Class II" 24VAC walwart supply (750ma minimum recommended). These supplies are plentiful and can be found powering security and CCTV systems all over. However, the MiniMAX uses a highly-developed, very-low-noise, linear-regulated onboard power supply to provide unparalleled audio-quality power never available before on a board-mounted power supply. Capacitor pads allow use of very large boutique electrolytics and film caps. The CCS is superior to the old current-limiting diode, resulting in improved current and B+ regulation for superior tube performance.

The DB's use one set of complementary output transistors for each channel. The board mounted heat sinks allow biasing up to 50ma each (recommended) and beyond. This allows for a very high level of "Class A" amplifier operation, meaning that switching noise is eliminated for the best sound possible. The idea of Class A configuration amplifiers is to bias to a current level that is higher than the load. This means that the transistors never have to "switch on," which can often result in audible distortion or other bad effects. At 50ma, the MiniMAX output buffer will well exceed the current draw of most readily available headphones.

For the ultimate in convenience and protection of your headphones, a relay-delay circuit has been incorporated into the headphone output circuit.

Finally, the MiniMAX - for the first time in a DIY-headphone amp design - brings an uprecedented level of design integration to the table with the option of the custom-machined Lansing "DT1" enclosure. The enclosure is pre-prunched for all plate-mounted components - volume control, headphone jack, RCA input jacks, power switch, power jack, and even three tip jacks, allowing one ot bias the tubes without ever dis-assembling the amp. The case body is machined for cooling slots on top, bottom and sides and includes machined tube hole openings, holes to access bias adjustment, and for the center post on bottom.
Join us in constructing the the Millett Hybrid MiniMAX. We believe you will find that it offers the most integrated DIY, headphone amp design yet available.

file last changed:Saturday, May 23, 2009 7:00:00 AM
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