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Salas PS board to power a Mac Mini...
Salas PS board to power a Mac Mini...
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Old 1st September 2018, 03:07 PM   #1
Manolo47 is offline Manolo47  Puerto Rico
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Default Salas PS board to power a Mac Mini...

Got a 2009 vintage Mac Mini server from a friend. It has an outboard ps, and is being used in conjunction w/Audirvana, and it is a very musical combo. I optimized it according to suggestions in the web that deal with transforming Macs into "music servers" . One aspect that seems to make a big difference is the power supply. Supposedly implementing a linear ps makes a big difference in audio quality in these applications. So, I wonder if the Salas positive ps board, or any other linear ps board such as TPA, etc, both of which I which I have, once connected to suitable transformer and dialed for 18.5v could be used.... I am asking because I don't know about what would be the wattage or current needed for this application. Thanks
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Old 1st September 2018, 03:45 PM   #2
Salas is online now Salas  Greece
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Salas PS board to power a Mac Mini...
You better choose a series type linear PSU for that application because computers vary widely their current consumption regarding the tasks they perform. A CCS biased shunt regulator like my designs would have to stay biased for top consumption at all times thus eating the excess and becoming extremely hot. To know the peak current needed you can impose a 0.1 Ohm resistor in series with its feed by making some female to male connector (not sure if you can find such when its Apple thus surely custom type) or by cannibalizing the brick's DC cable and measure voltage drop on a resistor put in it to extract the information with Ohm's law. Use the min max DMM's function to register fast peaks. Should be at max peaks during boot time.
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Old 1st September 2018, 04:00 PM   #3
Salas is online now Salas  Greece
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Salas PS board to power a Mac Mini...
You could also roughly estimate from the wall consumption of its SMPS brick using a KILL A WATT style meter or by simply duplicating the brick's DC amperage capability if written somewhere. I wouldn't expect less than 6A peak for 100W max consumption class computers.
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Old 1st September 2018, 06:42 PM   #4
Manolo47 is offline Manolo47  Puerto Rico
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Read that it is 4-6 amps. depending on processes going on.
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Old 1st September 2018, 08:00 PM   #5
Salas is online now Salas  Greece
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Salas PS board to power a Mac Mini...
Maybe in this case a high current linear chip like this one could do the job decently:

MIC29752WWT | MIC29752 Series ADJ 1.25 to 25 Vout 7.5 A LDO Voltage Regulator - TO-247-5 | MICROCHIP
- Future Electronics
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Old 2nd September 2018, 06:33 AM   #6
Salas is online now Salas  Greece
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Salas PS board to power a Mac Mini...
So a 15VAC 150VA transformer, 8A soft recovery diodes like MSRF860G (sinked), and a 22000uF 25V reservoir capacitor will be also needed. Dial the LDO chip for 18V DC output to allow breath space vs the raw DC at peaks. Give the chip a sink. It will also need a 22uF 25V Tantalum or normal ESR electrolytic capacitor right at its output for stability. Minimum load is 10mA that can be drawn by the Adj resistors when scaled properly. Read the application info in the datasheet.
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Old 2nd September 2018, 11:25 PM   #7
linuxfan is offline linuxfan  Australia
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There are many commercial linear power supplies for old Mac Minis; from Teradak, Sbooster, UpTone Audio, HDPLEX, etc.
I'm not aware of any equivalent DIY regulator boards.

But may I suggest a step back, and re-evaluate the situation?
This whole concept started back in the days when people were using internal PCI audio interfaces for computer audio.
Then high quality USB audio interfaces became available, and a neat idea was to leave the computer+power supply as-is, and just pay attention to providing clean power to the USB interface + DAC. Depending on the design of the interface/DAC, noise from computer side could either be mitigated/filtered, or completely isolated.

Nowadays the flavour-of-the-month computer audio device is an embedded computer - Raspberry Pi, Beaglebone Black, etc. Many, if not most, DAC's for these devices attach directly to the expansion bus, and share the same power rail - so once again there's interest (and potential merit) in providing clean power to the computer.

Back to the Mac Mini - you might not really need a linear power supply - what DAC are you using with it?
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Old 3rd September 2018, 11:40 AM   #8
Manolo47 is offline Manolo47  Puerto Rico
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Interesting Linuxfan! I use the Twisted Pear Audio Buffalo 3 SE dac with the JLSounds USB interface board. This board has two power supplies, independent of the USB 5v from the computer. One is for the USB portion 5v, and the other is 4v or something like that, for the clocks and generators. These two sections are galvanically isolated
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Old 3rd September 2018, 01:17 PM   #9
linuxfan is offline linuxfan  Australia
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Great. You have a high end DAC, and a high end USB interface.
Yes, the JLSounds fully isolates its I2S output, so the "dirty" GND on the computer side never touches GND on the DAC side - great. So I don't think you will obtain much benefit from a linear power supply for your playback computer.

But I see you have a very good system, and maybe want to squeeze the last ounce of SQ out of it.
Can you maybe borrow a linear power supply to audition? Or maybe a variable laboratory power supply from a technician?

But again, let's look at the big picture (not just the Mac Mini) - a secondary, and often unintended, benefit of using a linear power supply with a computer device is that it may prevent noise from being thrown back into the AC supply - which could otherwise negatively affect other components of your audio system - especially the DAC. And rather than spend $300 - $1,000 or so on a linear supply, there are other methods of achieving the same outcome;

i) use a heavily filtered SMPS to power your Mac Mini. Unfortunately there are very few commercial products of this type. iFi Audio springs to mind, but I see they only go up to 15V/1.2A.
Neurochrome has a filtered SMPS designed for their amplifier -
Switch-mode power supply for audio amplifiers.
but you would need to ask them if you can have a 19V version instead of 24V.

or ii) fit an AC filter to your DAC (and maybe also your amp). Something from Schurter or Schaffner, like this -
FN 9222
You might ask whether it's a good idea to fit such a filter to the standard Mac Mini SMPS - I would seek expert advice on this, because it's possible that such a filter is already incorporated within the SMPS.
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