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Audiophonics RASPDAC MINI LCD KIT Review (Streamer)

PeteL

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What is the display actually showing? Are album covers and titles showing?
 

danadam

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What is the display actually showing? Are album covers and titles showing?
From the product page:
raspdac.01.jpg

raspdac.02.jpg

raspdac.03.jpg
 

Lambda

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Ground loops only occur when there are differing potentials between grounds.

In the illustration above, the cables will all be terminated at the same ground on each device - therefore no ground loop will exist, at audio frequencies.

If this was RF - then it would be a different situation - but at audio frequencies this is of no consequence.
Ground loop currents can be induced by stray AC magnetic fields[4][6] (B, green) which are always present around AC electrical wiring. The ground loop constitutes a conductive wire loop which may have a large area of several square meters. By Faraday's law of induction, any time-varying magnetic flux passing through the loop induces an electromotive force (EMF) in the loop, causing a time varying current to flow. The loop acts like a short circuited single-turn "transformer winding"; any AC magnetic flux from nearby transformers, electric motors, or just adjacent power wiring, will induce AC currents in the loop by induction. In general, the larger the area spanned by the loop, the larger the magnetic flux through it, and the larger the induced currents will be.

The power supply provided with this product is of the two pin variety - and hence there is no path to ground (unless in some countries where neutral is connected to ground - in which case there could be a ground path under certain circumstances).
in almost all country's neutral is connected to ground.
power-supply-system-TN-C-TN-C-S-TN-S-TT-IT-.gif

The Question is only where...
It is this capacitor that causes noise (it is *not* a ground loop) - it is mains noise injected into the device it is powering - which also creates a small potential between the device it's powering and other equipment.
it is creating a small current between the device it's powering and other equipment's ground. the return part for this current is ground...
so the loop is closed trough ground. therefore you can call it ground loop.
The current introduces a voltage drop over the cable impedance...
330px-Signal_cable_with_ground_current.svg.png

These are leakage currents - which although akin to earth loops, are not quite the same thing, as mains earth is not directly involved.
Mains earth do not have to be involved to have a ground loop. (although it is in this case) you can have ground in Airplane.
 

audio_tony

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in almost all country's neutral is connected to ground.
power-supply-system-TN-C-TN-C-S-TN-S-TT-IT-.gif

The Question is only where...

it is creating a small current between the device it's powering and other equipment's ground. the return part for this current is ground...
so the loop is closed trough ground. therefore you can call it ground loop.
The current introduces a voltage drop over the cable impedance...
330px-Signal_cable_with_ground_current.svg.png


Mains earth do not have to be involved to have a ground loop. (although it is in this case) you can have ground in Airplane.

I was (trying to) draw a comparison between direct ground loops - e.g. two separate pieces of equipment connected to mains earth on the same socket (and the differing potentials that exist between those grounds at the equipment) vs. capacitor leakage inducing mains currents into the chassis of connected equipment.

I'm clearly not very good at explaining this, but I don't view induced currents from a mains PSU (which creates noise in the device it's powering) as being a ground loop, particularly when the 'other' end is not grounded in any way.

Ultimately, they are just leakage currents. (that's the way I view it anyway)
 

kchap

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I've been collecting RPi4Bs! It's interesting. Just going through my concerns/thoughts:

  • No heat sink (or fan) so it will run hotter than the NanoSound One.
  • Does it need a linear 5V supply? Would the standard RPi PSU work ok?
  • The specs on the DAC is acceptable; 6 months ago it would have just crept into the top quartile.
  • Balanced output are nice but not mandatory. The NanoSound One and the Khadas Tone card (I used it with another RPi4B) have unbalanced outputs. I do not personally have earth loop issues.
  • I'm happy with Volumio or MoOde, I have swung back towards Volumio at the momement. To be fair I am not a big user of high end streaming services so do run into issues with Tidal or qobuz that plague some users.
  • I would like an integrated on/off switch.
  • I wish I could borrow one so I could check if my concerns are warranted.
  • I do like the case.

BTW I saw a news item that some RPi4B models are going up in price due to the global chip shortage Arstechnica RPi shortage

Edited
 
Last edited:

Martinvb

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  • No heat sink (or fan) so it will run hotter than the NanoSound One.
  • Does it need a linear 5V supply? Would the standard RPi PSU work ok?
- Yes, this may be an issue with this type of compact enclosure, which is not optimal for use with the power hungry Pi4. Last summer, the processor of my unit went up to 70 degrees (Celsius), resulting in on screen warnings for overheating (blinking thermometer). I therefore fitted a small, silent (switched) fan in the enclosure, which brings down the core temperature 15-20 degrees when needed.
- Use of LPS is highly debated in the audio/Pi community. As demonstrated in this review, even an OEM switch-mode p.s. will produce satisfactory results. Lps should be measurably better, although I doubt that you will hear this, even with high end gear.
 

garbz

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the return part for this current is ground...
so the loop is closed trough ground. therefore you can call it ground loop.
This is not helpful. The capacitor would not be doing this anywhere near an audible frequency so the "loops" are not at all what we are classically calling a "ground loop" in the audio world. Indeed capacitors linking signal / mains to earth are present in every piece of electronics, but it's disingenuous to say every audio system has a ground loop.

The current introduces a voltage drop over the cable impedance...
Equally not helpful. The potential difference created is related to the current and the voltage drop across the interconnect. This would be the equivalent of someone farting in Paris and you smelling it in London. The currents involved over an interconnect are waaaaaaaaaaaaaaay to minuscule to generate a potential difference in anything other than a dangerous fault condition. The overwhelming majority of audio ground loops are induced magnetic field loops or faulty ground connection forcing current to return over the chassis safety wiring. Any other form of ground loop is vanishingly rare, not only audibly but measurably too.
 

Madjalapeno

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octavius

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Hi guys, I have Raspdack mini LCD half year now and I have to say it is small and clever box :) I have standard switching supply and I would like to buy better linear PSU. I have tested just xiaomi power bank and I instantly got better sound.

I´m thinking about :
AUDIOPHONICS LPSU25

or I don't know If I will able to listen differences with more expensive
ALLO SHANTI

What do you think about this two linear psu? :)
 

garbz

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What problem are you trying to resolve? Do you have audible noise issues? Just asking if your money may not be better spent elsewhere. The problem is that when equipment is designed to run from a single supply 5V then the benefits of a low-noise linear supply are somewhat moot. This stuff is more relevant when there are dedicated analogue and digital supplies with independent power paths around components on the board. These devices have powersupplies which have shared digital / analogue components so if noise is an issue it will still be an issue as digital devices do their thing.

Also your supply may be a switching PSU but most components on the board will actually be powered by whatever is on the circuit. e.g. nothing in the raspberry pi runs on 5V, so the very first thing your powersupply connects to is almost universally.... a voltage regulator which may be linear or switching.
 

octavius

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Thanks for the feedback. But why Iisten better sound with Xiaomi power bank when I compare to ordinary mobile phone charger? And many other people "swear" they listen some improvements with a linear psu? Just thinking...
 

Lambda

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I instantly got better sound.
How "better"
Less Noise?

Your run of the mill phone charger PSU maybe has high leakage current "a ground loop" and therefore introduces noise.
A power bank would fix this because its has way higher impedance to ground and mains.

A linear PSU is not the solution (although it might be a solution). What you are looking for is a Low leakage PSU.
Can be switching one as long as there is low capacitance between primary and secondary and ideally a grounded shield.

But if you don't have a noise issue a power supply is unlikely to improve it.

And the money anyways better spend on a external DAC ideally with balanced output and isolated input.
 

octavius

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I though better bass, nicer sound and let's say cleaner sound. There is also Nirvana psu. It is better switching power supply.
 

octavius

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I try to swap it again if it was only dream or reality :) I still in doubt why many people use linear psu?
 

Lambda

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I still in doubt why many people use linear psu?
Well i could make a long list of stupid thinks people do because they believe...

Linear Powersupplys have (sometimes) lower leakage compered to some Switch mode Powersupplys.
And the leakage is only of low main frequency and harmonics.

This can theoretically some times help if you have "ground loop" noise.
Have you?
If you don’t hear noise if no music is playing its unlikely you would have or hear some if music is playing...

The other advantage is linear psu has lower noise or lower frequency noise. but this in invalid in your cases because you have a computer (pi) on the same power supply generating switch mode noise anyways.
 

octavius

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Thanks for explanation. No I don't have any "ground loop" noise. So I will use my phone psu adapter and save some money.
 
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