Hi,

Been lurking for a few weeks since I decided to take the plunge and purchase a Squeezebox 3 (wireless) to feed my Meridian DSP5000 speakers.

First impressions are good using the digital ouput, even though this is only using MP3's. I've now dowloaded EAC and FLAC, ordered a 250Gb HDD and need to start EAC'ing my CDs so I can really appreciate the sound.

I've read no end of threads that suggest dumping the PS that is supplied with the unit and replacing it with a non-switching variety. Can anybody point me to a UK supplier (weblink would be great).

Many thanks

I don´t know for sure where you can get one in UK. Here i found mine on ebay. You can try if you find a cheap spare PS for the Atari X800XL. When i remember right the old external Iomega ZIP drives also had a strong Linear 5V PS.
Good luck!

Thanks for the 'heads up' on the Iomega... I have an old 100Mb external drive in a draw at home gathering dust, I'll check it out when I get home at the weekend...

Assuming you're referring to the Slim Devices Forums, then if you read more carefully, you'll find that the enthusiastic supporters of replacing the switched mode power supply are those in the "audiophile" camp who refuse to do a blind test to verify their claims. They would be roasted alive here on HA.

You'll also find that Sean Adams of Slim Devices has posted an in depth technical explanation of why changing the external power supply will make diddly squat difference - basically because the external wall wart is only there to provide the basic 5V feed, which is then used by the multiple linear supplies that are inside the SB3.

By all means try a different supply, but be prepared to discover that it makes no difference. And therefore don't pay too much for one.

If you're concerned, just add a lowpass filter to the supply.

hehe, I believe all switching power supplies already have chokes and capacitors in them to perfectly filter out the switching frequency

I haven't tested the supply in question, so I can't say.

If you read further you´ll find other reasons. I don´t know what tese supplys do to the analog out. I never connected it this way.
Fact is i get a slight humming on my power amplifiers when connecting the coaxial output to my DAC. This degrades sound a bit here. I tried the switching supply delivered with my box, a 5V switching supply of a Lexmark printer box and a 5V Lindy switchbox switching supply. All generate humming.
I bought a 6.90€ linear supply with a simple 7805 regulator and all humming is gone.
Looks like these switching supplies still power out some garbage that interacts with my monoblocks.

I'll just have to let my ears judge whether the change is for the better or not... but I take your point about not spending too much money (which is a foregone conclusion for me - I live in Scotland!)

Thanks to everyone else for their responses...

You say you get a hum on the digital out? Are you plugging the DAC into the same supply?

Of cause not. Don´t tell me how to connect something. I have some experience doing such things. It is just that my Monoblocks have a bandwith of about 150KHz and are pretty sensitive about garbage over ground.
Edit: Ups! Yes, connecting via Coaxial and i should have a bandwith above 200kHz, not 150, sorry.

Then how could the quality of the power supply possibly matter? Its not like noise is going to change your FLAC files.

Well, assuming its at least good enough to keep the CPU from getting math errors.

When you get added noise in the audiochain it doesn´t change the sound!? From now on i can´t follow.

You haven't added noise to the sound chain though. All the Squeezebox is doing to the digital out is changeing one set of 1s and 0s into another set of 1s and 0s.

Thats why I asked if you had the DAC plugged into the same power supply. You seemed to be implying you could hear the power supply noise, and of course that would only be possible if the power supply were actually connected to some analog component. Since it wasn't connected to the DAC, theres no way the power supply could change anything.

?? If you connect the Squeezebox to a DAC and this DAC to Power Amplifiers you´ll get a connection over ground. Is it this so hard to understand?

I don't understand. What kind of connection between the power supply on the Squeezebox and amplifier are you thinking of?

The reason you're getting humming is because of ground loops. The linear supply you're using now probably doesn't have an earth connection, only a relative +- output. Let me guess, this one was 2-prong and the other ones were 3-prong? If you're connecting it to the amp and you know the amp is well grounded, you can cut the ground pin on the power supply. I don't recommend this though. Try putting the power supplies on the same power strip, or same outlet. This might help a little, but the root of the problem is poor component design. Can't really help with that.

My own experience with the stock switching supply on the SB2 (which I believe is identical to the SB3 supply) shows that there is indeed some minor mains frequency ripple on the nominally 0V side, and this does appear on the ground side of the outputs (both analogue and digital). This is because the SB2 supply is not grounded, and hence does not shunt the ripple to earth. Within the context of Wombat's DAC, I can conceive that this ripple might cause a hum if the ripple on the ground somehow worms its way through to the analogue output. But in the context of a properly grounded system, the ripple really ought to be shunted to earth somewhere and be rendered harmless.

I think Mike's question is how do you get a hum from anything related to the squeezebox when the signal over the coax is s/pdif, a digital signal, a square wave (technically biphase mark code)? noise would have to be so bad (like really really bad) that it would affect the clocking or actually be flipping bits, in which case it would be way more audible that a slight hum.

Josh

Here's one possible mechanism. There is a slight mains frequency (ie. 50 or 60Hz, depending on the country) ripple on the power supply "0V" rail, because the SB is not grounded. This ripple appears on the SB's ground plane, and hence on the screen on the SPDIF output. It's low enough in amplitude that it does not interfere woth the DAC's ability to decode the incoming digital signal.

Now, if the DAC has a shared ground plane between its digital input and analogue output circuitry AND the DAC is not grounded, then the ripple will appear on the ground of the DAC's analogue output, and it is conceivable that it *might* get through to the output of the power amp.

In fact, if the power amp has balanced inputs and is fed in the "standard" way from an unbalanced output (ie. signal to hot, ground to cold, screen connected only at power amp end), then the ripple will be treated as signal and amplified - in this case you'd get quite a loud hum.

All that said, I reiterate that if you properly ground the system, the ripple is shunted to earth and no hum will be present.

I guess that's possible, but any high-end standalone DAC that does that should be outed for bad circuit design. for the kind of money people spend on this stuff, the s/pdif should be optically isolated! though wombat didn't say what kind of DAC he has...

This kind of claim could be verified by hooking up the output of te DAC to an oscilloscope or spectrum analyser, and looking for the low frequency noise on its output, switching the supply should remove mains freqency if this is whats happening.

Now I have neither the test equipment, nor a squeezebox, but perhaps someone has who can perform this test and verify?

Kristian

Yes, the DAC is not "real" grounded, only two pins on the plug and also it is not electrically isolated on the coaxial side. I had a Pulse isolation transformer of an old 3Com 10base2 card in front of my DAC and all humming was gone. So does the cheap linear supply.

This is the exit of my Sony SDP-EP90ES DAC and still sounding good compared to others. I already had many devices connected but the Squeezebox was the first giving me that trouble.
http://www.diyaudio.com/forums/showthread....3275#post183275
I replaced all capacitors that are somehow related to the soundchain against Wima MP and some Black Gates for decoupling. The output OPs are LM6172. I only use it for simple stereo so i only modified the front exit.

Heres what I don't get then. Isn't the one of the advantages of a switching power supply that it does not produce 50/60Hz noise, but rather higher frequency noise based around whatever frequency it's switching at? It seems to me that switching to a linear supply would actually have made the problem you're describing worse, unless the switching supply was so terrible that it somehow had worse 50/60 Hz ripple.

To make it more complicated. Putting the switching supply to other plugs or changing direction makes the noise a bit different. It doesn´t sound like the typycal 50Hz humming. It sounds like a low noise plus added harmonics up very high.
It may have something to do with the high bandwith like mentioned before. Is it possible some parts get HF noise and shift it down to the audible range?

That does sound like a ground issue if moving plugs changes the problem. What happens if you connect the 0v coming out of the DAC to ground (and the same one on the amp if its grounded)? If I'm understanding the issue, that should get rid of most of the noise if its actually passing through the DAC.

This brings up a question I've had. I always plug the neutral line from my instruments into one ground at one point. So when I build stuff, I have no ground on anything, except for one device (usually the an amp or filter) which has the reference line connected to ground. Then everything else on the chain passes that ground on along with the signal. Is this the correct way to deal with this? Usually I put lowpass filters on my power supplies just to be safe, so I'm wondering if I've actually been miss-wiring my equipment, and just never noticed it.

I measure the voltage across the ground of the outputs or inputs and earth. Then i change polarity of the plug. I let it plugged the way the resulting voltage measures lower. Somewhere i read about this to connect the units "In Phase"

That may be so in theory. I'm simply reporting the evidence of my own SB2's power supply. But it seems to me that any device which is powered by the mains and which does not ground its 0V rail must in principle be a potential source of 50/60Hz noise.

Just to be clear, you're thinking that there could be variations in the neutral voltage at 60Hz from other devices in the house that would show up as noise?

I think you could avoid that if you included a lowpass filter between the outputs of the supply to attenuate 60Hz noise, in which case the lack of grounding wouldn't really matter. Though grounding might be easier still.

This is definitely a ground loop. It has nothing to do with voltage differences on the + pin, but only to do with your earth potential. Basically, because current is flowing through the earth wire which is not 0-ohms, it creates a voltage potential in that wire. If you hook up the ground for another device anywhere along that wire, you will create a ground loop. This ground loop acts as an antenna, picking up ANY stray EMI/RFI and line frequency hum.

The proper way to avoid this is to always use star grounding, connecting the grounds in a component to a common point, thus providing a low-impedance path for ground currents, but we can't all design our own equipment, can we? To work around this if you always maintain one component well-grounded, you can lift the grounds of your other components. This means, in plain english, to cut the earth wire on the mains to every component besides the one you decide should be earthed directly. This makes the components float to whatever voltage they want to be at, eliminating ground currents through the interconnects. You usually want to ground the power amp directly. Preamps, tuners and cd players are usually low-power, so they can get away with not getting grounded directly.

In other words, because your components are not designed perfectly, you must compensate by doing something a bit illegal.

Actually, the best idea for you would be to use an optical TOSLINK connection. This doesn't deal with electrical potential, as it uses light.

Also, I don't think that reversing the polarity to a plug should matter, unless the power supply is very poorly designed. It's all getting rectified and filtered to DC somewhere in the power supply.

More information can be found on google, or DIYAudio.com. Hope this helps.

I'm not proposing anything about the source of the noise, as I don't know how switched mode power supplies work. All I'm reporting is the clear evidence that there *is* a slight hum on the 0V rail of my SB2 supply, which proper grounding eliminates. If anyone who knows how switched mode supplies work could explain the possible source of this noise, I'd be interested.

Nice you all are looking for an explanation but kicking the standard Squeezebox switching supply in the dirt already did solve the problem for me for a while now.
If i really should be bored or others have real interest i can dig out the switching supply and worry about humming again.

I'm not so sure that this is the case in Wombat's setup. It certainly isn't in mine. I wasn't reporting anything about the + pin, but ripple on the 0V pin. (I'm sure there is also ripple on the +5V pin, but that doesn't seem relevant here).

As I recall, Wombat has an ungrounded DAC, and a (presumably) grounded power amp. When the DAC is fed from a SB3 powered with the stock supply (in which case the SB3 isn't grounded), he gets slight hum. I see only one grounding point in that setup (at the power amp), so I don't see where the ground loop is formed.

In my own setup, I have an ungrounded SB2 with the stock supply connected to grounded power amps. Left just like that, I get massive hum. Again, only one grounding point (at the power amps), so this is not a ground loop. I know for sure the cause of this hum: the 50Hz ripple on the 0V rail of the SB2 being interpreted as signal and amplified, because my power amps have balanced inputs. The hum was eliminated by strapping the SB2 ground plane to the power amps' ground.

Absolutely correct.

Perhaps test continuity using a DMM on the crappy PS from the -pin on the DC side to the neutral pin on the AC side. It might be hard-connected, which would be stupid, but very possible. That would be an ugly sound. I've actually done that, tied in the ground on my amp to the minus pin. Works when it's the only thing grounded, but sounds horrible when it's hooked up to another grounded component. This may be the case, which would dumb as hell.

The only other thing I can think of is poor output design. But I don't know how that would work. Have to think about it more.

Or, just hit it a couple times, and maybe it'll go away. This usually works for printers, audio equipment, copiers, fans, computers, monitors, cars, uh... everything.