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So I'm listening to the Mac Mini on a linear power supply.....

Posted by AbeCollins (A) on December 27, 2014 at 00:15:46

More correctly, I tried a few linear power supplies.......... To skip the details, you can scroll toward the bottom to Listening Results

I modified my Mac Mini to accept +12VDC from any external power source by removing it's internal switching power supply and replacing it with an inline filter module from TeraDak. I also have the TeraDak +12VDC / 10-Amp linear power supply. I bought them off eBay for $300 USD.

One side of the filter module has a 2.5mm diameter power input jack and the other end connects to the logic board within the Mini. This module looks very similar to another one that I have by Core Audio Technology. Of course each power supply has their own internal filtering but these modules provide additional high frequency filtering right at the logic board. They are essentially LC filters with multiple LC sections. They are not absolutely necessary as at least a couple 'audiophile' power supply makers for the Mini provide only a straight through cable to the logic board from the 2.5mm power input jack.

I won't bore you with more oscilloscope screen shots showing power supply generated wide band ripple under 1-Amp load, and transient noise inflicted upon the power supply output from the computer. I will summarize by saying that all power supplies below vary in ripple from about 1.5mV Peak to Peak up to about 8mV P-P, measured w/o enabling the 20MHz BW limit on the scope. I've seen some 'audiophile' power supply makers spec measured ripple from 20Hz - 20,000Hz. How convenient to restrict the measurement bandwidth to such a narrow range. You can convert my Peak to Peak measurements to RMS if you wish to compare against other power supply manufacturers that spec RMS. The TeraDak measured 1.5mV P-P under 1-Amp load..... which is just over what my Mini draws while playing music.


The Mac Mini switching power supply (black) was removed from service. The white
TeraDak filter module is installed in it's place to accept 12VDC input via the 2.5mm jack.



$29 13.8VDC 6-Amp power supply I bought about a decade ago trimmed back to 12VDC.
This one uses the classic LM723 regulator chip and 2N3055 NPN series pass transistor. I
recall seeing this design from as far back as the 1970s supplying upwards of 50-Amps or
more, using a darlington stage and several heat sinked 2N3055s. A very common design.



General purpose bench linear power supply rated 0 - 30VDC / 10-Amps. I think I paid
about $175 for this one a few years ago.



No-name Chinese 12VDC 7-Ah AGM sealed lead acid battery. I use this for extra run time
power with my Moultrie game camera for photographing night critters in the backyard.
Fully charged the battery powers my Mac Mini for over 6 hours. Measured noise on this
battery was about 3mV P-P under 1-Amp load.



TeraDak 12VDC linear power supply bought new off eBay from HK.



Mac Mini i7 quad-core 2.6GHz 16GB RAM SSD & HDD. PS Audio NuWave DAC. TeraDaK linear power supply.
AIFF 24/96 music files. Audirvana Plus. iPad visual remote controller.



Listening Results:
While I heard, or thought I heard very slight differences between the Mac's built-in switching power supply and the external linear power supplies and battery, I cannot say with certainty that these differences were real or just differences in mood over the course of my listening sessions. In other words, none of the power supplies stood out as being a night and day improvement or disappointment. None were perceived as being 'better sounding' than another.

I gave it an honest try, and I'm sure some will say that my system is simply not resolving enough. That's a common response here so I expect it. However, I can say with certainty that I have heard very noticeable differences among $1000 Benz-Micro vs Dynavector cartridges, phono preamps ranging from $150 to $4000, interconnects, and 6 different USB DACs that I've had in my system. Even comparing iTunes alone or with Audirvana Plus, Pure Music, or BitPerfect were more noticeable to me than the Mac Mini power supplies summarized above.

------------------ One Additional Thought ------------------

There is one power supply that I wanted to try but I can't seem to find at the moment. It's buried somewhere in the basement in a box since our recent move this past summer. It is a general purpose adjustable switching power supply with a patent-pending Noise-Offset circuit to minimize the pulse-noise of the switching circuit relative to a received radio signal in a shortwave receiver. This power supply is intended for use with radio equipment like HF - UHF radio receivers and transmitters. The ability to 'shift' the noise may shift a switching harmonic from interfering with a desired radio signal. I thought it might be interesting to deliberately 'shift' this switching noise across it's range to determine if it's effect could be heard via the computer music server. Maybe next time.

Similar to my switcher that I can't find at the moment. Note #7 in the drawing.

• Installing TeraDak Filter Module in Mac Mini   (Open in New Window)

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Kimber Kable

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