For modern Apple Mac minis (model years 2010, 2011, 2012, and 2014), our unique Mac mini DC-Conversion / Linear Fan Controller Kit (MMK) performs several functions important to elevating the audio performance of this compact computer.
The MMK converts a Mac mini to operate on external 12V DC power by replacing the computer's stock switch-mode power supply with a circuit board that fits perfectly in the space vacated by the SMPS. There is no soldering and no cutting of wires required, the procedure is completely reversible, and a toolkit with detailed instructions is provided. The MMK also provides a carefully chosen amount of filtering (a pile of filter caps after a regulated external supply is not good for performance).
Conversion of a Mac mini to accept DC power is not new, and pairing the computer with a high quality external linear power supply is one of the best upgrades you can perform on this popular computer. So why choose the UpTone MMK? Because it includes the world's first and only linear fan controller circuit for Macintosh computers.
A little background: 3 and 4-wire fan control circuits are used in many modern computers because the cost, size, and heat to include linear DC control (i.e. smoothly varying the voltage to adjust the speed of the fan based on internal temperature) is prohibitive. So the method used is called PWM (pulse width modulation), whereby the voltage sent to the fan is a train of DC pulses. (See the excellent and not hard to understand tech explanation of fan control circuits at: PWM Fan Control.
The trouble with PWM fan circuits is they operate at around 25kHz, and the pulses are high current (we measured them from a Mac mini fan at over 500mA)—not ideal in a computer being optimized for audio. Our unique circuit uses a power opamp, and while we utilize both the tachometer line from the fan and the signal from the motherboard, we completely eliminate the pulses—providing the fan with just smooth and variable DC.
The 12V input connector to the MMK is a high quality 5.5mm x 2.5mm DC barrel jack (center pin positive). To boot and operate a Mac mini that has been converted with an MMK requires a 12V power supply capable of delivering at least 4.5 amps.
The MMK also has a coaxial/SMA jack for connection of a cable to support the pseudo-Kelvin-sense feedback circuit of the UpTone Audio JS-2 choke-filtered LPS. That circuit eliminates the voltage drop of the DC supply cable and ensures instantaneous voltage regulation right at the computer end regardless of spikes in current demand. [Use of this feature is entirely optional, and the computer and board will function perfectly with a JS-2 or any other quality external DC supply even when nothing is connected to the SMA jack.]