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Old 18th October 2009, 04:22 PM   #1
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Default What is evil about switching PS?

I'm new here and new to the DIY side of audio for that instance. I am on my way to mod the Behringer DCX, and it appears it is the consensus that switching PS is the first thing that any equipment can be improved upon. So what is evil about them, and what sort of benefits do we normally get when using a better supply like WJ or shunt regulator? Would appreciate all your inputs.
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Old 18th October 2009, 10:04 PM   #2
bountyh is offline bountyh  United States
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Switchers normally don't have as much stored energy so they can't deliver high peak currents for sudden transients. That's mainly because they don't use the massive output capacitors the older 60 Hz power supplies did.
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Old 18th October 2009, 11:20 PM   #3
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I'm merely an amateur myself, so take this with copious salt...

The DCX isn't a power amp, so the transient demands are probably not huge. Not to say that Behringer wouldn't underbuild the PSU anyway -- they are remarkably.. uh.. inexpensive devices.* But, as I've been told, switching PSUs tend to be electrically noisy. If the switching frequency is high enough, the noise can be taken out of the audio band, and should not affect the sound... but power supply design for audio seems to be somewhat of a black art, and it is necessary to italicize "should" when referring to the possibility of audible consequences to things which, on paper, don't matter.

For what it's worth, switching PSUs create interference like transformers create hum. Just about any well-engineered and well-built power supply will work beautifully. Similarly, any poorly-executed PSU will suck. Regardless of operational mode. As I understand it, the complexity of SMPSs makes them an easier target for poor design.

This is where someone with actual experience comes in to verify or refute the above.

* PS: I have several pieces of Behringer gear. They are to me the duct-tape of pro audio. There are few manufacturers out there whom produce quite the array of problem-solving devices that Behringer does, especially at anywhere near the price. A cheap piece of gear that works well enough and is affordable enough to have "just in case" trumps an expensive, better-performing piece of gear you can't justify. That said, I tend to use them in places where the sonic penalties are less important, and when their untimely demise won't ruin my day.
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Old 20th October 2009, 03:15 AM   #4
Enzo is offline Enzo  United States
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Consensus where? A switching PS COULD be a source of noise, and COULD be a problem source, but IS it in your unit? SOlving problems you don;t have is not solving anything. The garlic I wear around my neck to keep elephants away from me seems to be working.

If your unit is noisy or shows signs of audio artifacts that could be due to aliasing at high frequencies, then maybe a little extra filtering mught be a good idea.

I operate an authorized Behringer service station, and while the stuff is indeed inexpensive and not bulletproof, I have not encountered any real power supply issues. Sometimes a shorted out power amp can take a SMPS down with it, but that is not the case here.

Switchers can generate a lot of high freq noise that linear supplies do not. Then again, linear supplies make a lot of 60Hz or 120Hz ripple and hum that switchers do not. (50Hz/100Hz in other parts of the world.) As Sir said just above, a poorly designed supply of any sort will add noise to the system. And a well designed supply won;t.


Switchers do not have large caps to hold up against large transients like linear supplies do, that is true, but unlike linear supplies, the switcher recharges its caps 100,000 times a second instead of just 60 or 120 times. The SMPS doesn't HAVE to hold up for an entire transient. And as also said above, your little processor is a DSP with a little analog I/O, so transients are not an issue.


You want to know the biggest problem we have with those little SMPSs in the Behringers? The connectors. There is a service bulleting telling us to look for the connector - about 7 pins I think - on the SMPS that runs to the main board. We are instructed to unsolder and remove the connector parts from each end and hard wire the individual wires to the two boards. This eliminates intermittqant connections that can cause trouble. That same situation can of course occur in linear power supply connections.

Personally, I think if you want to fiddle with the thing to "improve" it, the SMPS isn;t where I would start. probably a focus on the analog circuits would pay off better. The op amps are generic general purpose types. I don;t think these units are especially noisy, but you might get a couple db lower noise floor with other parts.

Not much you can do with the DSP section, and that doesn;t leave a lot else.
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Old 20th October 2009, 03:30 AM   #5
sandyK is offline sandyK  Australia
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Default What is evil about switching PS.

A typical SMPS as used in many CD/DVD players and wallwarts, has a 100nF capacitor between primary and secondary. If you rub your finger along the metal case of a SMPS unit, you can often feel a vibrating feeling. With a 230VAC system, and using a 10megohm input DMM, the reading to earth from the "earth" side of the output RCA connectors is often over 100VAC, albeit at low current. The effects of having several pieces of SMPS powered gear is additive, and will affect the S/N of an amplifier. You will often get a nasty little bite when plugging/unplugging input RCAs on an amplifier with a 3 pin power plug when SMPS sources are used.e.g. DVD player,STB etc.
SandyK
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Old 20th October 2009, 03:36 AM   #6
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I was going to ignore this thread until I noticed obvious disinformation. Anyone who knows what they are doing will not place a 100nF cap between primary and secondary circuits, as this will immediately violate leakage current standards dictated by safety agencies. A value of 1-2 nF is much more the case.
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Old 20th October 2009, 04:06 AM   #7
sandyK is offline sandyK  Australia
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wrenchone
There may have been an error in the diagram I saw, however, these capacitors are clearly shown in the Service Manuals for the Pioneer DV 563As and variants, along with an exclamation mark.
Silicon Chip magazine also wrote an article on this subject, along with voltage measurements and waveform screen shots of the problems caused by these capacitors.
The comments about the "feeling" and "bites" are well documented elsewhere, and from personal experience I can assure you the "bites" when plugging/unplugging can be quite painful.
SandyK

Last edited by sandyK; 20th October 2009 at 04:09 AM.
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Old 20th October 2009, 05:37 AM   #8
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This sounds like criminal incompetence, or a bootleg product where people didn't care. Even in the crappiest switching supplies I've encountered lately (and I've seen some sorry examples from no-name makers), care was taken to meet safety standards regarding leakage current.

With recent manufacture DVD players, I'm accustomed to seeing a nice, clean multilayer board incorporating all the digital goodies, and a sorry-a**-looking hunk of sh** pushed off in the corner that is the power supply, purchased from the lowest-bid no-name supplier.
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Old 20th October 2009, 04:16 PM   #9
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I'd read a number of claims on various boards that the sound of my Squeezebox (played through a DAC) could be improved if I replaced the cheapo switching (it is switching?) power supply included with the SB in favor of a linear one.

Welborne Labs had a specifically recommended kit, and when it went on sale, I was curious enough just to try it.

I finished building it on Sunday, and I can tell you that the difference is noticeable. I don' t know about tighter buns and firmer abs... oh, sorry, wrong lingo script there... ;-)

I can't tell if the bass is "tighter" -- I don't know what that would sound like, but a pretty pronounced difference could be heard on strings. I'm sure the sound was just "fuller". More detail, I'm certain I heard, in the sound as well.

I suppose if the power supply has more... capacity to deliver current, then it can better respond to/with the changes in the signal, so it makes (logical) sense (to me), that more detail might be heard, instead of having the player act sluggishly, and, I imagine, rounding off the transient changes...

Who knows if my "logic" corresponds to reality. I can hear a diff, though, and I didn't really expect I would hear much if anything.

Brenton
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Old 20th October 2009, 04:22 PM   #10
h_a is offline h_a  Europe
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I had a good look at SMPS myself and to me it mainly comes down to the conclusion that it's much easier to build a good, high transient and low noise linear supply.

SMPS are fun, but need some real dedication to be low noise.

Well, technically they are certainly good enough for audio, so it's a personal decision. Practically, companies prefer the cost savings due to not having to buy large, expensive toroids, which make the product also heavy and expensive to ship.

Have fun, Hannes
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