'Analog Dinosaur' succumbs to the joys of FBA : enter Raspberry Pi 2/IQ-Audio DAC+!!

[Marco]

there are some nice looking ones on the eBay, maybe like this one ?
http://www.ebay.com/itm/Hifi-linear-...item20f80f7928

I'd be very careful using any 'off the shelf' linear PSU unless you know *exactly* what the Pi's electrical requirements are, not only in terms of getting it to function, but in achieving a worthwhile improvement over the supplied SMPS unit.

As I reported earlier, our resident PSU expert (Paul Hynes) is currently designing such a linear PSU for me, for the Pi, and have been exchanging some dialogue with him on the matter. As a point of note, for those interested and able to understand what he's written, this is some of what he had to say on the subject:

The Pi boards I have here both have three low cost regulator chips for power distribution. It should be possible to replace these with my high performance regulators once I have the set-up running.

Then after looking at the circuit of latest Pi model, he said this:

The latest Pi has a completely different on board regulation system to the ones I have here using switch mode voltage regulation to provide the lower voltage rails. I will have to do some investigation with this, as I have no clue how much current is required for each rail. The current rating of the regulators will dictate the physical requirements of this upgrade so I have a little R&D to do to deal with this solution. Also the high speed shunt regulators I use for digital circuitry cannot regulate down to 1.8v for one of the rails so I will have to develop a circuit that can provide the 1.8v at the required performance level.

He has since bought the latest Pi and an IQ-Audio DAC+, in order to facilitate his experiments, so I am awaiting the results of what he comes up with.

The conclusion I reached from what he wrote, however, is that if you want to do the job right, and obtain optimal results (which is all I'd ever be interested in), you *must* have an intrinsic understanding of what makes the Pi (and IQ-Audio DAC) 'tick', so to speak, and simply buying an 'off the shelf' linear PSU from ebay is unlikely to produce the desired effect.

Marco.

[mikmas]

Have you got no idea then why, when using my preamp, I'm getting proper sound levels through, when the Volume Control Mixer (on Volumio) is set at 'Hardware', but not when it's disabled?

I've heard my preamp, with the Pi, on a number of occasions with 'Hardware' enabled, and it sounds great, but not as good as it does with the preamp out of the equation, so if I can obtain the same proper sound levels by disabling 'Hardware', and using my preamp, then according to you, that should sound best of all.

Not a Pi user but having read the Qaudio PDF and based on experience of a raft of 'digital' an 'analogue' preamp stages I would guess that the reason is pretty straight forward. The Pi has it's own amp stage to provide a signal to the output. Either through a chip or the optional 'physical' rotary control outlined. If you use either of these 'hardware' options from the Pi input to a preamp (rather than direct) you are applying preamplification twice - with the resultant degradation. If you disable the Pi 'hardware' amp you are effectively cutting out the signal and will get nowt (or a very weak signal) to your preamp - which is what you experienced. Strikes me that if you want to get around this you would need to pick up the signal from pins on the board BEFORE it is delivered to the Pi 'hardware' section. Failing this, what you were doing before was fine - i.e using the amplified output from the Pi 'hardware' amp directly to your power amp.

Very similar to using Stan's early DACS where you had the option of using the onboard OPamps outputs or modifying them to pick up the signal directly from the DAC chip

[Marco]

Hi Mike,

Not a Pi user but having read the Qaudio and based on experience of a raft 'digital' an 'analogue' preamp stages I would guess that the reason is pretty straight forward.

The Pi has it's own amp stage to provide a signal to the output. Either through a chip or the optional 'physical' rotary control outlined. If you use either of these 'hardware' options from the Pi input to a preamp (rather than direct) you are applying preamplification twice - with the resultant degradation. If you disable the Pi 'hardware' amp you are effectively cutting out the signal and will get nowt (or a very weak signal) to your preamp - which is what you experienced.

At last - NOW we're actually getting somewhere. That's exactly the explanation I needed!!

At least I know now that I wasn't doing anything daft.... What's also interesting, from what you've stated, is the resultant sonic degradation of applying pre-amplification twice, which is proof positive that the Pi/DAC unquestionably performs best without the use of an active preamp, and with sound levels controlled instead, by a digital interface, such as Volumio - which is exactly what I've been doing all along.

Shows I'm not deaf then, so thanks for that!

Marco.

[tubehunter]

No Marco you use the Hardware option and control the volume (in the digital domain) via the web page.

I have the volume option set @95% (should be around = 0dB in the Dac) then disabled and control the volume via a Alps Black pot.
This is then connected to my Quad power amps.
I do it this way as I have need of another input which requires attenuation.

An example of the Pi digitally clipping is Otis Tayor's new album Hey Joe Opus Red Meat.
Track 06 - They Wore Blue, about half way through the sax on the right channel will distort if the Pi's volume is set at 100% ( = +4dB in Dac )
Sounds Ok set at 95%

I have built my Pi into a nice Aluminium case with a linear power supply with an encapsulated transformer double regulated.

[Marco]

I should also point out at this stage that the whole reason why I'm championing the Pi from the rooftops, as it were, is not because it is the simplest 'plug & play' FBA solution on the market (it isn't that at all), but rather because it ably fulfils the AoS 'SPPV mantra', i.e. it provides astonishing levels of 'bang for your buck', and is a veritable 'giant-killer' right now on the computer audio front.

*That* is why I have been rather 'verbose' on this subject!

I consider it my duty to inform AoS members of such products, so that they too can reap the same musical enjoyment from using this device as me. Informing each other of superb products, and discussing them in detail TOGETHER, and helping each other out along the way with any problems that occur, is exactly what a good hi-fi forum and audio community is for.

I am also determined to remove the 'mystique', attached to FBA, done well and cheaply, and to try and open it up to a much wider audience: folk who are music lovers, not necassarily 'computer geeks', and if we amass enough users of Pi, on AoS, we will create a dedicated section of the forum for members to discuss it, as we have done with the Beresford DAC and Technics T/T.

Crucially, that is where we will then be able to LEARN FROM EACH OTHER, through obtaining practical knowledge from the sharing of our combined experiences of using the Pi, expressed in layman's terms (as opposed from having to decipher and utilise the 'tech-speak' of those with in-depth knowledge of computer software/terminology and an interest in such), so that's why this thread has been specifically designed to attract as many people into the 'Pi fold', as it were, as possible.

Therefore, if you are reasonably technically proficient and have some relevant computer software knowledge, and/or know a friend who can help that does, and don't want to spend a fortune on an 'audiophile badged FBA product', which simply looks nicer but will unlikely produce superior sonic results, then the Pi/IQ-Audio DAC, for me, is the way to go.

Quite simply, it DESERVES to be shouted about, because it is *that* good!!

Hopefully that clear matters up, in that respect

Marco.

[Marco]

Hi Dunc,

No Marco you use the Hardware option and control the volume (in the digital domain) via the web page.

I have the volume option set @95% (should be around = 0dB in the Dac) then disabled and control the volume via a Alps Black pot.
This is then connected to my Quad power amps.
I do it this way as I have need of another input which requires attenuation.

I get exactly where you're coming from and why that doesn't really apply so much in my system.

Have you tried using the Pi, the same as me, minus the Alps pot, by just using Volumio on its own. If so, was it worse? Do you think there would be mileage in me using a similar passive pot, simply when I want to use the Pi? I'm not fussed on having the convenience of using Volumio to control sound levels if a passive pot would sound better.

I have built my Pi into a nice Aluminium case with a linear power supply with an encapsulated transformer double regulated.

Nice one, mate. Showz da shexy case!

What sonic improvements did you perceive with the addition of your linear PSU? Oh, and has Ian got one yet?

Marco.

[r100]

So do you know why I'm getting no volume (with my preamp in the equation) when I disable the 'Hardware' setting in Volumio? Is it because what you were telling me to do before doesn't work with the IQ-Audio DAC?

Marco.

no, sorry. I don't. It's a mystery to me at the moment. Probably, by "disabling" the mixer setting in Volumio, it cut's out an essential part that the IQ DAC needs to work. But I'm just guessing.

[r100]

I have built my Pi into a nice Aluminium case with a linear power supply with an encapsulated transformer double regulated.

Yes ! Please show us some pics my PiDAC is still "hung" from its Ethernet cable .

[Marco]

no, sorry. I don't. It's a mystery to me at the moment. Probably, by "disabling" the mixer setting in Volumio, it cut's out an essential part that the IQ DAC needs to work. But I'm just guessing.

See post #442. Mike explains all!

Marco.

[Krisbee]

no, sorry. I don't. It's a mystery to me at the moment. Probably, by "disabling" the mixer setting in Volumio, it cut's out an essential part that the IQ DAC needs to work. But I'm just guessing.

Under the hood Volumio is using MPD (Music Player Daemon - http://www.musicpd.org/). MPD interacts with ALSA (http://www.alsa-project.org/main/index.php/Main_Page), and its ALSA that interacts with the IQaudio DAC.

Volumio is designed to be a self-contained system with a web interface for user interaction. Trying to configure the system via the command line can break things as volumio stores settings in an internal database. But you can connect to your RPi in a way that allows you to use the command line and inspect how ALSA is working with the DAC and without breaking Volumio.

Page 25 of http://www.iqaudio.com/downloads/IQaudIO.pdf shows how "alsamixer" can be used to check things.

When you make configuration changes to Volumio which effect MPD, such as changing the mixer settings, you need to restart MPD for these changes to come into effect. Again, it's possible to examine the relevant MPD configuration file via the command line to see how various Voumio settings alter settings in the underlying MPD configuaration file. The relevant part looks something like this:

audio_output {

type "alsa"
name "Output"
device "hw:0,0"
mixer_control "PCM"
mixer_device "hw:0"
mixer_index "0"
dop "no"

}

I would expect that mixer control line will change as you change settings in MPD.

I thought the IQaudio DAC is connected via i2s, does Mike's #442 comment still apply? I suspect it's just a case of using the wrong mixer control setting in MPD which results in no audio.