Why so little use of SMPS in commercial amps?

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Most commercial amps still seem to be using bigass transformers instead of SMPS designs. I'm a bit perplexed as to why - it seems that it's not all that hard to reduce noise down to inaudible levels with a bit of clever design, while the elimination of a big, expensive transformer can save a lot of cash.

So, where's the SMPS designs?
 
The simple answer is probably that regular transformers are extremely rugged and well understood. If you decide to go the SMPS route you need to design for the peak power draw or run the risk of the power supply going into protection or blowing up. A regular transformer can withstand momentaneous power draw several times above it's rated power, so you can get away with a nominaly under-sized transformer.

Sad, but true.
 
Development time costs as well, and to build a good, reliable and low EMI SMPS with good enough properties for audio is not that easy.
On the other hand, power transformers are not so expensive, so apart from weight there is not so much to win for powers of below 500W.
 
As stated EMC is one of the major concerns, design time, layout etc plus with high powered SMPS direct from mains you quite often have 300+ volts D.C floating about so isolation for the various low voltage standards becomes an issue. Even though the transformer is much smaller, you have the production costs of all the other components required for the SMPS. Even though the actual cost of these components is relatively low, they have to be placed, soldered inspected etc which can soon push costs up depending where the products is manufactuered (UK Electronic Assembly is approx £90-£120 per hour), plus EMC testing etc.
 
The price of copper and the metals used in the cores of toroids is rising, and at the same time the requirements for compact and light weight equipment are increasing, so the way in which audio amplifiers are designed is progressively changing.

For very high power applications, where output voltage is also high and dangerous like mains input voltage, the future is probably no transformer at all.

For lower powers, SMPS.
 
To have an SMPS, you have to engineer one, and the design skills for the high power SMPS are not the same as for audio circuits. There may be nuance to linear power supply design, but the process is familiar to most any engineer already on staff.


MAny consumers associate weight with quality.

This is not unlike the sound effects engineered into your American car doors. Car doors could safely and reliably simply click shut, but consumers are more comfortable with a big KA-Chunk sound.

Any number of the SMPS I find in professional audio gear will handle a dead short across the power rails. They just shut themselves down.
 
The simple answer is probably that regular transformers are extremely rugged and well understood. If you decide to go the SMPS route you need to design for the peak power draw or run the risk of the power supply going into protection or blowing up. A regular transformer can withstand momentaneous power draw several times above it's rated power, so you can get away with a nominaly under-sized transformer.

Sad, but true.

Actually, you have to design for both peak and minimum current -- it's like the old "dog food" linear programming problem where you had to learn how to optimize a design within some constraints. I've mentioned this before (search the "wayback machine" Rocky) -- Sanjaya Maniktala has done a really nice power point on SMPS magnetics which can be found on the Nat Semi website -- search under his name.
 
Coincidentally (or not?), people also expect a power PSU to have some mass, though some of the new 80 Plus PSUs are actually featherweight.

Why not with the same mass using the lighter-weight advantage of SMPS build a 1.5kW PSU to satisfy the desire of heavy weight and big numbers. :D
 
it's also an EMI issue on SMPS as well a safety issue. The EMI is a more difficult topic in designing and the power factors requested. Therefore, companies come up with the easier transformer design. especially in asia, where understanding how to make a good SMPS is not always given. a bad SMPS gives bad audio results and SMPS regulation and filtering for good audio ( S/N, ripple currents, overshot behavior etc.) may cause some problems.
 
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I cant imagine that there ever will be a SMPS as forgiving, reliable and simple to service as
a regular transformer based. The number of components involved in a SMPS is drastically higher and alone therefore the MTBF will be uncomparable higher. An other aspect is recycling. During the usable lifetime of a decent rated transformer you will have to recycle a pile of SMPS-junk that many times will exceed the weigth of a transformer based PS.
 
SMPS for audio

recently i tested a SMPS for response behaviour, and it was bad: overshots, recovery time, etc.most caused by EMC components on seconday side, and also due to poor regulation speed.
mostly, here in china, standard SMPS are designed for an unknown application, and the surprise will automatically come, when used for audio.

The relatively big noise, spikes, and others on the DC will cause undesireable effects.

Most SMPS today is specified ( calculated after temp. measurements!!) to 50000 hrs. at 40 centigrade ambient temperature, which will drastically drop, when temperature is higher.

Any (small) failure of a component of an SMPS will have a big effect on an audio device.
Fazit: SMPS isnt to be recommended.
 
one other problem for smps for audio is that say if it was a 600W peak power demand....

-well then you are likely to do a bridge or resonant smps etc.

-But then, these smps's use film capacitors in the power-path.

And that is the weak link in the chain.

The film capacitors are weak unless you buy extremely expensive ones.

-Consider a full-bridge smps......that has a film capacitor in series with the primary.......and it is there to prevent the primary saturating from flux-walking.

-considering resonant SMPS, well, they obviously have a film capacitor in the power-path, to give the resonance...

-and it is this dreaded film capacitor that is the glaring weakpoint of the smps.

-because capacitors are just not sturdy enough to carry large ripple currents....such as in the power-path of an smps.

Sure you can pay a fortune for film caps that are up to it...but then you really are out of pocket, and wish you'd done a 50Hz transformer.

Also, i'm sorry to say it, but i disagree that smps interferes with audio circuitry........good layout of all audio and smps circuitry will prevent interference.

-and now we have DSP audio which can filter out unwanted noise.

Also, there's nothing to stop you from just using a flyback for 500W offline.....and you simply beef up the heatsinks / components until it meets the spec.

-damp the switching transition until you pass through emc.

...it wont matter becuase its audio.......its going to be on , ath the very most, 1/3rd of its rated peak opower.

and the good thing about flyback is ...no film capacitor.

....however, above 1KW, a flyback will be so dissipative that the heetsink would make it heavier than a 50hz transformer....so then you have to use the types of smps with film capacitors.......
 
I don't think film caps are all that bad. I've taken apart lots of half bridge computer power supplies (must be close to 100 already), and in only one of them did i find the film cap with burn marks on it, but regardless of that it still worked. I did swap a new one in however.

I'm finishing a 650W halfbridge supply right now, uses a 2.2uF film cap in its primary. Doesn't have any problem. And besides the flyback, there's also the 2-transistor forward if you really wish to do without film caps.
 
Intersting you bring up the point of caps in half bridge.

the half bridge is where one must decide the value of the rail splitting caps..........they take a lot of ripple current......and end up being very expensive and large.

and must be rated to the Vin of the supply because in case of overload, cycle by cycle current limiting comes in, and the centre point drifts to a rail.

there is a lot of argument over the sizing of the series cap in the half bridge...and its necessary voltage rating
 
and must be rated to the Vin of the supply because in case of overload, cycle by cycle current limiting comes in, and the centre point drifts to a rail.

Never opened a halfbridge PSU up yet that has its caps rated to Vin. Heck, i've even seen some with 160 volt rated primary caps... That is perhaps because they don't use cycle by cycle current limiting because they are voltage mode, and the action of the overcurrent protection is to simply shut down the whole thing.

there is a lot of argument over the sizing of the series cap in the half bridge...and its necessary voltage rating

I can see its voltage rating being an argument. But its size is given simply by the current flowing thru the primary and the permitted voltage drop of the cap. If you allow for more voltage to drop then you have higher primary current and obviously higher current thru the cap itself, and you'll be running in circles till you do the right thing and that is sizing it properly.
 
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