Why are Switching power supplies so uncommon ? - diyAudio
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Old 10th March 2013, 05:31 PM   #1
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Default Why are Switching power supplies so uncommon in power amps?

Hello !
please excuse my trivial question
But SPS have a lot of benefits
if we do not want to talk about efficiency at least the weight
And still power amps powered by SPS are a very small part of the totality
I thought that only very expensive SPS were good enough to be used in a audio hifi power amp
I knew of Halcro, Linn Klimax range, Lab Gruppen ... all extremely good but also not precisely cheap
Now I read that Mackie has a line of amps with SPS that are not expensive and sound good. They are traditional class AB amps but with SPS.
To end all the ramblings why these SPS are so rare in amps ?
Do they have any drawback sound wise ?
Actually I am asking because I would like to try one of these products

https://www.coldamp.com/store/produc...power-supplies

in an old amp I have at hand. Just for curiosity
Thanks a lot for any info
Kind regards,
gino

Last edited by ginetto61; 15th March 2013 at 08:13 AM. Reason: To specify better the issue
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Old 11th March 2013, 03:44 AM   #2
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Looked at the SPS30 datasheet but it doesn't have a schematic or mention a topology, so here's a general answer.

I'm aware of three basic issues, though those more familiar than I with SMPS designs may have some corrections. 1) Typical home audio listening levels are on the order of 10mW output power, at which an SMPS is not cost effective, 2) an SMPS sized for the 100W or so most class AB amplifiers target will typically be in DCM for the few watts or milliwants an amp draws at quiescence, and 3) filtering switching noise off of the rails of a class B or D load requires the filter corner above the load bandwidth but sufficiently far below the switching frequency that meaningful rejection occurs. Since either switching frequency or pulse width goes to zero in most topologies and feedback implementations as the load goes to zero effective passive filtering of the supply becomes impossible since the switching fundamental and its harmoncs collapse into the audio band. The usual solution is to follow the switcher with an LDO but this is difficult at power due to limited LDO availability, need to maintain headroom on the linear regulator for good performance, and restores a fair bit of the cost and thermal complexity one hoped to avoid with a switchmode supply. With an amp appropriately sized for home audio SPLs it's often cheaper to pay for linear heatsinks than switchmode parts and magnetics though design inertia plays a part in this as well.

I'm aware of two classes of solutions to the above. One is a self oscillating supply---which is just applying Hypex/Philip's UCD class D amplifier topology or similar to output a DC rail rather than a audio signal---and has the rather useful property that the switching frequency varies with the output voltage rather than the load, making it considerably easier to keep the switching frequency above the audio band. Being a UCD patent licensee this is probably how Hypex implements their SMPS modules but I'm not aware of other implementations. The other is quasiresonant or resonant (mainly series LLC) topologies, wherein the magnetics remain in continuous conduction and switching noise/EMI is reduced. These topologies have only recently seen much adoption (my impression mainly in the past couple years) and implementations such as Connextronics' supplies still have CLC pi filters on their outputs.
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Old 11th March 2013, 03:52 AM   #3
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Big trafo + Diode + cap more robust than SMPS (waranty/reliability issues).

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Old 11th March 2013, 06:04 AM   #4
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I'm inclining to agree with @didiet78, it is probably more of a marketting choice, a good and stable SMPS is not easy to design, especially regulated ones witch for audio aplications must have a verry good EA compensation, so a verry good transient response where it would be the most needed, another reason could be the popular believe that switchers with theyr noise have real bad effects on audio amplification, more complex filterring solutions have to be considered and it would probably in all, cost maybe more than a simple 50-60Hz power transformer.

Evidently what i sayd is a subjective personal ideea, you all are in title to dissagree
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Old 11th March 2013, 09:29 AM   #5
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Hi to All !
thank you very much indeed for your kind and very valuable advice
I am not an expert at all but I have the feeling that real drawbacks are what limits their diffusion in audio power amps.
I like them because their are light above all
Thanks a lot and kind regards,
gino
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Old 11th March 2013, 10:07 AM   #6
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If you try to transport, setup and use 5kWatt power amplifiers, as Sound Engineers do when producing music shows in large dance halls etc, a 5kWatt power amplifier with a SMPS is less than 1/4 of the weight compared to a standard transformer coupled power supply weighing in at almost 1cwt, (50kG in new money). Most of us old timers have back pain issues!
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Old 11th March 2013, 03:30 PM   #7
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Quote:
Originally Posted by Harleyjon View Post
If you try to transport, setup and use 5kWatt power amplifiers, as Sound Engineers do when producing music shows in large dance halls etc, a 5kWatt power amplifier with a SMPS is less than 1/4 of the weight compared to a standard transformer coupled power supply weighing in at almost 1cwt, (50kG in new money). Most of us old timers have back pain issues!
Thank you very much ! I understand
actually i got my back pain already just we much less power
But ok ... i understand that if a system is not so common there must be drawbacks
Clearly when the amps are a lot and must be moved from one location to another the weight is really an issue for the professionals
no more doubt on SPS amps for home purposes
Kindest regards,
gino
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Old 11th March 2013, 04:39 PM   #8
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I agree in general terms with twest, but also I would add a hard misconcept about SMPS“s As I said in other posts, I have made one of them without trouble from about 12 years ago,

The problem expressed by this guy is true, but it is easily (almost for me) to compensate the loop for a too low current, and also I added some fixed loads for the supply not to enter in "hiccup mode" (Quickly start/stop switching as the load current becomes negligible). In my case, not only 6 power amplifiers are powered from a UC3842+STP7N60+TL431+BYT80 +-14V +12V +5V total 80W flyback topology, also the radio receiver (TDA7211+TDA1220B) and some TL082's in the audio path, and two early (very old) CD players and the control logic are powered from it, maintaining the minimum load necessary to not enter in hiccup mode. It is fixed 50KHz. This is the aluminium box at the last photo. No AM radio interference of appreciable high levels.
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Old 11th March 2013, 06:08 PM   #9
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Osvaldo, do you have a write up on your compensation scheme and minimal load levels you could link? Generally I find a base load of 5 to 10% of max load is required and making the control loop more sophisticated to more gracefully support lighter loads still leads to switching frequenies close enough to audio band they're difficult to LC filter effectively. I've managed higher than 50kHz at minimum load in buckers, though not by a whole lot---60kHz or so.
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Old 13th March 2013, 11:28 PM   #10
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Having a quick look at ebay or elsewhere online SMPS tend to be expensive.
It seems only top end amps have SMPS at the moment.

SMPS can be disasterous when they go wrong. I have seen mine blow up both mosfets, the SMPS chip and the SMPS power supply components. And there is much more to go wrong in a SMPS.

Behringer do a £140 1000w amplifier with SMPS for about £140.
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