Linear power supply for Mac Mini circa 2009

If you are using an external DAC that means you are sending a digital stream to the external DAC and the external DAC is then converting it to analogue sound waves. A digital signal would not sufffer interfence and often has error correction built-in, therefore I would say this is a load of smelly brown stuff from a bovine animal and you should not worry about this.

Furthermore the Mac mini in question uses a proprietary connector, is long discontinued and you are therefore unlikely to find such a beast.

An upgraded power supply on a Mac Mini does make a substantial audible difference. The 2009 Mac Mini is a bit easier to upgrade if you can get a hold of the power brick, which may be a challenge. It was plug and play, at least when I ordered the supply from Core Audio Technology. But this was a few years ago and I use a 2011 Mini now with a different power supply. Both were very nice upgrades to my audio system.

Regardless of whether you have an external DAC, your system is only as good as your source. Computers process audio in real time as a square wave. As I understand it, any noise in the power supply creates timing and amplitude distortion in the square wave. So upgrading the power supply reduces that noise and distortion. All I can say is the difference is substantial and a definite increase in resolution and performance.

I'm not sure if Core still upgrades the 2009 Minis, you should ask them.

You are missing a very critical element here.

An audio signal on a computer is a square wave, not ones and zeros. A square wave is an analog representation of a digital signal and has both an amplitude and timing component to it.

Applications are not real time, the data they are processing is. Applications are buffered and their data are sent in packets which are checked for errors. If an error occurs the data is resent or a crash occurs. Audio data, however, is being processed in real time. Each piece of software, every algorithm, and every background process creates a duplicate version of the audio square wave using voltage from the power supply. The resulting versions of the audio square wave IS the square wave that is sent to the DAC as no correction can be done to "guesswork."

Voltage is used at the output to convert the data from a PWM signal to a PCM signal and again from a PCM voltage to an optical signal, which is then converted back to a voltage at the receiving end.

A cable is sending voltages just like the computer. A square wave may be called a digital signal, but it's technically an analog wave form. It is a voltage and no DAC can correct for amplitude distortion that comes from noisy voltage -- that amplitude becomes the signal that the DAC receives, it's not signal plus noise, just a dirty signal that we hear.

The Mac does not send the original digital data. If you are using itunes, there are several layers of processing that ocurr within itunes, each of which creates duplicate version of the original data based on mathematical algorithms. i.e. new versions are created each time a process is done. Once a file leaves the hard drive and hits the first piece of software it is processed in real time.

Some audiophile applications attempt to buffer this real time process by loading it into memory for processing and hijacking system resources, but this does not negate everything outside of this software and the fact that it is still processed in real time where format conversion and duplication occurs.

You can control the volume on the Mac using optical. It just depends on whether it's a dithered volume control or not and what piece of software you are using. Bit perfect audio is a misnomer and does not exist in digital audio. Just because a device says its bit perfect is irrelevant, it only means a signal is within a certain range. But a digital square wave contains tremendous amounts of frequency, timing, amplitude and harmonic information. That information gets masked and distortion by noise that introduces harmonic content that doesn't exist in the orginal file.

1. The Mac and OSX IS processing the digital audio signal. Thousands of times. How can you possibly say the audio signal is not being processed in the computer? This train of thought is over 2 years old, if you have been following the progression and research regarding computer audio you would know this is not even remotely true.

2. A digital signal IS a voltage. It is a square wave. There is no such thing as ones and zeros when it comes to an audio signal on a computer. The only time it is ones and zeros is when it is a file sitting on a hard drive. As soon as that file travels down a cable it becomes a voltage created by the power supply.

A digital signal is a square wave. Which means it's an ANALOG representation of a digital signal. This signal is either 0V or 3.3V -- regardless of whether it's in a DAC or a computer. These voltage pulses use an optical chip and are converted to light pulses, which have both timing and intensity characteristics.

The quality of the optical signal will have to do with the optical receiving chip and the power supply used to convert to and from a voltage before and after voltage. In addition, the optical signal has a huge reflection issue within the cable. When the light reflects off of the walls of the cable you end up having the same signal showing up at the receiving end twice, this results in harmonic distortion because content is introduced into the audio signal that shouldn't exist.

3. USB cables contain Data+/Data-, 5V, and Ground. The Data +/- are voltages and the 5V rail is used to control the USB Bus or USB powered devices. A Cable cannot transfer ones and zeros, it can ONLY transfer a voltage. In the case of optical, the signal is a voltage that is converted to light and back to a voltage... which incidentally creates 3 extra stages of signal conversion.

4. The audio signal must be taken from it's format on the hard drive. A version is created using voltage from the power supply to send it through the SATA cable. The piece of software runs mathematical algorithms based on the content of the file. Any algorithm creates an absolutely new version of the original signal that is created by voltage from the power supply. If you change the volume, convert the file format, play a different file type, use a different piece of software, have background DSP processes running... everything runs in real time and makes copies of copies of copies of the original audio file BEFORE it ever leaves the computer.

5. The above is why applications like Amarra, Pure Music and Audirvana were created. They understand that every process in the computer not only slows down how quickly the computer can process the audio signal in real time, but every process creates copies of copies in real time.

6. The resulting output is quite substantially different from the file that comes from the hard drive. Once the file is processed by software it must go through the operating system audio Kernel to be output in the proper path and format. As you said, there are both optical (a PCM SPDIF Format) and USB (usually PCM, but can also be PDM if outputting to a DSD-capable DAC). The digital signals in a computer are a pulse width modulation that gets converted to a pulse code modulation. This final version is sent as a voltage down to the DAC. The clocking information is built into the square wave. It is not an i2S signal and so the data and clocking information are not separate entities.

If streaming audio to a DAC via ethernet the data is buffered and sent in packets. These packets are re-sent if there are errors. The only thing this eliminates is the length of cable carrying a voltage between components. It does not negate any processing up to the point of airplay, or where the file is converted from the original format to a format the computer can send in packets over ethernet/wifi. I guarantee a piece of software is running and doing math to complete this process.

7. It has been fairly common knowledge for the past two years that power supplies make a substantial difference on a computer's audio performance as well as its video. The signal to noise ratio requirements for video are not as steep given the clocking frequencies used in video compared to audio.

I personally have used a power supply on a 2009 Mac Mini as the OP asked and I can attest to a significant sonic improvement by doing so. I have also done more recent mods to my 2011 Mac Mini by removing the internal power supply and using and external supply, which was an even greater improvement. So much so that my wife even commented on the difference. A fine lady, but not one to so much as listen to my audio system, let alone notice a change I've made.

I'm not sure if you are debating that digital is just ones and zeros or if you are debating the effectiveness of a power supply on a computer. A DAC cannot correct for a bad source. Whether you are using a computer or you are using a CD Transport (a transport has no DAC built in) the concept is 100% the same. Both are generating a digital square wave that gets sent as a voltage down to a DAC. Both are voltages, both are digital signals, both are processed in real time, both are susceptible to the quality of power supply. Or are you arguing that the quality of CD Transport doesn't matter either because it's digital?

An audio system is only as good as its source. If you haven't tested an upgraded power supply or even a battery on a Mac Mini I encourage you to do so before saying it doesn't work. It does not help the OP to have people say it makes no difference when they themselves have not tried the upgrade and are guessing.

Ok-- And what products would those be for what company? No offense, but forums are an easy place for someone to hop on to say "I'm so much smarter than you I'm not going to even respond except to announce that I'm too smart to even spend time responding to what you have said."

If you are so ultimately knowledgeable about digital audio, then you should also be able to make an argument for why a power supply WOULD make a difference on the computer being that the signal is "just ones and zeros". All you have said is that it doesn't make a difference -- let's say it does... how about telling us why?

If people hear a significant sonic difference adding a better power supply to the computer then what is happening that is caused by this power supply change that results in improved -- or even changed -- audio quality?

It is a fact that a power supply upgrade on the computer not only improves the sound, but it does so dramatically. Quite frankly, it was one of the single largest upgrades I ever made to my audio system and not something that required an A/B comparison. It was the equivalent of going from a $100 DVD player to a $10,000 transport -- and my previous transport was a nearly $12k Esoteric transport. If you do a little research you will see that there are thousands of other people who feel the same way about the merits of a better power supply on a computer.

While you yourself haven't experienced it and don't believe in it doesn't mean it's not true and that it doesn't happen. So for the sake of argument, and assuming that it DOES make a difference, how about telling us why. Proof that people on the web believe that it makes enough of a difference for the OP to bring up this thread should be enough reason for you to examine why it could possibly make a difference, if not for my reasons stated above.

Do share.

Digital signals are just as vulnerable to noise and degradation as any other analgue signal.

The effects of noise differ by nature of the duty of the signal.

I am sorry but I don't agree. If you are using an external DAC you are sending the unaltered digital data - digital means 1's and 0's. Therefore this is a waste of time and money. When you are using an external DAC the Mac will not be processing the audio, it will be a glorified file-transfer.

The link from the Mac to an external DAC is not even electrical, it is optical using a laser running over the mini TOS-link connection.

What you say may make a small difference if the Mac was being used as the DAC but not if you use an external DAC, if you use an external DAC it would be the external DAC power supply that would be the one you would need to look to.

When you are using the optical TOS-link, you cannot even control the volume on the Mac because it is sending the unaltered digital data. Altering the volume means altering the ampliptude of the sound waves i.e. the analogue wave-form and as the Mac is sending the original digital data it therefore cannot do this.

If you are using an external DAC the Mac is not processing the audio signal the external DAC is. As such the Mac is not altering the original digital data.

If the Mac was acting as the DAC then you would be right but I have clearly said I was talking about using an external DAC. When using an external DAC the data is never changed from its original digital form whilst in the Mac. The external DAC does that conversion and processing. When you are sending via an optical TOS-Link to an external DAC you are not sending a square wave, you are not sending an analogue signal you are sending a digital signal which is 1's and 0's.

At most one could argue the Mac takes the stored digital data, and decompresses it and then sends it out (digitally). This is 100% not going to alter it or lose anything if compared to the stored lossless audio file (AIFF, WAV, WMA Lossless, FLAC, Apple Lossless) and if you feel otherwise then while you may know a lot about analogue signals you don't know how digital works.

What you now appear to be moving on to is away from the original subject and are now talking about ripping from a CD in to a computer. This was not the original subject. In fact from the original post the music could equally have been downloaded over the Internet from the iTunes store or be direct copies from digital masters and there was no mention at all about CDs.

Note: It is increasingly common for AV receivers support computer network connections for receiving audio directly from a computer and this includes via Apple's AirPlay protocol. This of course is a digital process and it incorporates the normal computer error correction and buffering steps for transferring digital data. AirPlay uses Apple's Lossless format. So even if you want to try and say TOSLink is not 100% accurate this would be. Again this is nothing to do with CD ripping which was not mentioned in the original post. The AV receiver would then act as the DAC to convert the digital data back to audio.

I totally agree with John, since the DAC is external, it and it alone

will control the ultimate sound quality of the resulting analog output

that would be related to the power supply.

Date can be transfered to an external DAC from the Mini by 2 methods,

for a 2009 Mini at least.

One is via the optical interface which is an encoded bitstream. This is a

sequential series of ones and zeroes with 16 to 24 bit framing of the data.

This can be either a raw representation of the audio signal or it can be

in an encoded format.

The other is via USB which can only be in the form of digital data.

The only issue with quality in either case in the data transfer is

the quality of the clock signal. With USB, this is usually horrible and

most external DACs have digital clock recovery circuits to solve this

issue.

I was starting a lengthy piece to show you how you are either confused

or misled, but it seems it would be useless since I am simply an engineer

who has designed products for both commercial and military applications

in both analog and digital audio, video and RF and guess everything I have

done has just been an illusion.

Here is an interview done with Gordon Rankin, Charles Hansen, and Steve Silberman titled "there's no such thing as digital" about how digital is, in fact, not just ones and zeros.

http://www.audiostream.com/content/draft

If you aren't familiar with those names, they are some of the pioneers of digital technology from Ayre Acoustics, Wavelength Audio, and Audioquest.

First question and answer:

It's common for people to envision and represent a digital signal as a series of 1s and 0s. As such, there's really no room for error, at least according to this binary theory. Is a digital signal simply a series of 1s and 0s?

Charlie Hansen: Unfortunately not. The "1"s and "0"s are just abstractions that are easy to think about. But in the real world, something real needs to represent those two abstract states. In modern digital electronics, we have almost universally chosen a voltage above a specific level (that varies from one "family" of electronic parts to another) to represent a "1" and a voltage below a different specific level (that again can vary) to represent a "0".

In the real world, those two voltages are not the same, so there is a "grey" zone between the "black" of the "0" and the "white" of the "1". Also, it takes time for the signal to change levels, and the time required to do so can depend on dozens (or even thousands) of other external factors.

You are ignoring the fact that computers do practically nothing but manipulate 1's and 0's and when an external DAC is used that is all the computer is doing. When using an external DAC the computer is not processing any audio wave forms, just the 1's and 0's.

If a computer could not reliably and consistently and correctly do as such then it would not even be able to be relied on to do something as basic as -

2 + 2 = 4

(or 010 + 010 = 100 in binary 🙂)

When working in the digital realm, the computer will be using multiple means to ensure the digital data is processed correctly such as checksums, cyclic redundancy checks, hash values, forward error correction, retries, etc., etc.

In the real world where people do not wear tin foil hats the odds of errors is insigificant.

Hello,

I am writing to say that I agree with Mintzar

I build audio circuitry as a hobby.

He or she is correct in his or her assertions regarding the coversion of digital data to an analogue stream. The digital data is coverted to a fluctuating voltage (a square wave), much like how an amplifier works to convert one signal to another. This signal is superimposed on a rail voltage by transistors NPN or PNP type stacked within a chip. This line voltage is rarely perfectly linear, and fluctuates with the changes in load in the electricity gereating the dc current.. This analogue voltage carrying the digital signal is highly susceptible to distortion and degradation from environemntal concerns as well as quality of the underlying dc power it relies upon. If the vlotage sags or spikes too much, a failure is registered, or a gap is present.

There is also a timing aspect, as the process relies upon a physical, steady flow of electrons.

Computers do a lot more than just manipulate ones and zeros. The idea of a one and zero is simply a simplified ILLUSTRATION of a much more complex process that is occuring between the hard drive and a DAC. Ones and zeros illustrate the the underlying principle, but do not explain the complex methods required to transmit data as an electrical signal from one component to another, to another, to another etc.... there are countless opportunites for error, which is caused by signal degradation, noise, dc voltage integrity, component noise, etc..

In computers, errors in data are created frequently however, like dna replication, there is a series of checks and balances that allows the correction of MOST but not all errors in digital signals travelling within the computer system. Read and write errors are just one type of error, and often the quality of power supplied, as well as environemntal distortions are the cause of these errors. This system of checks and balances requires a sophisticated process to occur in real time, and the extent of errors needed to be addressed affects TIMING within the constant output of signal voltage.

A high quality DC power supply reduces the source of voltage-based and electromagnetic-radiation-based errors, and there by affects the timing of the signal.

Asynchronous connections attempt to address this problem by making use of a usb data-type connection that is capable of buffering, and retiming at the recipient end, however, across a digital audio connection this is not possible and timing errors are inherent in the signal. This type of error presents itself as jitter.

ALSO there is the problem of gain in digital signal transfer. Low gain digital signals have poorer quality and can sound thin, show lack of depth and at worst, have drop outs.

The DAC chip is only one part of a great number of critical components, but the result is only as good as the integrity of the source. Upstream integrity is critcal to all signal transfer.

There is a complicated process involved in translating the coded analague signal carrying the digital information, into an analogue audio signal between 20-20khz.

SMPS (switched mode powersupplies) are well documented to be extremely noisey power supply sources both audibly, and in their power delivery, and it is otten the introduction of this noise that results in component failure and electronic degradation over time. also the degradation of data. A smoother, more linear regulated power supply protects delicate circuitry better than smps. Each component in the electronic path operates within a set or parameters which varies signifantly in its attrbutes upon changing environments.

In addition to being audibly noisy, SMPS also emit radiation that introduces noise to a digital line. They are also UNGROUNDED, which prevents the dumping of stray volltage and is a source of of noise.

digital is a much more complicated process than simply being one or zero. The transfer of digital information is not "distortion free" however, certain types of harmonic distortion are reduced in digital playback because of the interpretation and conversion of the digital signal (which is actually a coded analgue signal) into a musical wave, which relies upon translation. Digital distortion is masked below a specific threshold, and evident as an error above the threshold. It is because of distortion and signal degraddation that one cannot use a usb cable that is 50ft long, or a digital PCM coaxal much longer than the same. Higher gain balanced professional standard connections such as AES/EBU and fixed impedance BNC are professional standards to address some of the limitations of sending digital data through an analogue signal down a cable. These increased standards are required to ensure integrity in the signal. As connection/transmission standards they are still however reliant upon signal integrity from the source.

Almost 100% of all DIGITAL and ANALOGUE audio equipment of hi-fidelity quality uses DC voltage that is NOT from a SMPS because smps are not ideal for hi-fidelity audio.

The "ONE" and the "ZERO" are not absolute. There are a variety of fluctuating values in the signal present, which are categoricaly placed into either the "probably one", or "proabably zero" category based on hardware response to the signal voltage, which triggers switching in the recipient. Degradation in the sent signal can impact the switching on the recieving end to create a similarly THD distortion-less output, but an incorrect one flawwed.

I appreciate that you may work in design teams to produce audio and video circuitry.

May i respond to your comment with a question?

What is the source of some of the problems you face when designing circuitry if it is not issues in accomidating voltage and current demands of componentry (all of which comes from a power supply) and ultimately signal to noise. Various power supplies produce variable levels of quality.

What is the problem with a noisey power supply, and how does this noise affect circuitry, data and component life?

-- the argument that improving a power supply to improve the systems integrity is not a dismisable argument.

Subjective and objective improvements to audio production are realized in power delivery and how it is managed through the entire chain as a signal carrier and before. Techniques are used to reject certain kinds of noise all over a given circuit, and are necessary - but ulitmately, DC rail stability is required to be as steady and noise free as possible to achieve the best possible results. this is the underlying base quality of the null signal.

SMPS are not the greatest. Sure, transformers are noisey too, but in a different way. And different types can be selected to avoid certain kinds of noise in the voltage, right? Noise from RFI, EMI, Static charge, Interwinding capacitance etc..

When power is smoothed and regulated it attenuates much of the noise.. but this always is relative. IF the power supply is noisey, there is going to be all kinds of problems in the circuit. Digital or not. Obvious or not.

It all affects how hard the countermeasures are at work, and how effective they are.

If someone has a noisey SMPS, it is reasonable that they would percieve an improvement in sound quality by changing or upgrading the noisey power supply.

Thats the guys point.

a noisey powersupply can interfere with quality of signal and resulting sound by various mechanisms.

The mac is not simpy transfering files to a dac.

It is creating an analogue PCM signal from a digital file. The PCM signal's integrity and quality and gain level are critical to the recipient device.

The dac converts the PCM signal to an audible signal.

Opitcal connections suffer some of the most sever forms of Jitter-based distortion posible. the mac-mini's optical toslink connection is known to be of terrible quality. Computers produce significant amounts of jitter due to the mutiple and varied processes computed by the cpu at a given time. Data is sent in packets.

all said. audio companies charge WAY too much for power supplies... you can build one just as nice for less than a hundred bucks.