Toroidal Linear vs Switch Mode Power Supply

[Nightlyraider]

Learned a few things before 9am. I could go back to bed and my day would still be successful!

 

[Bob Lee (QSC)]

The energy storage capacity deal is true, but in reality it may be that the energy is not AVAILABLE in the same way as with a traditional supply.

it is not uncommon to hear that "my SMPS amp just does not sound right in the lows".

We are not talking here about "sine wave power", most amplifiers will satisfy their paper specifications. But most of us have noticed that even with virtually identical specs, different amps can have drastically different "feel". This is due to performance that is "not documented" in the specs. (we tried to document that low freqency transient performance with our 40 Hz single cycle power spec, but then lots of people yelled at us for having "fake peak-power specs")

The reason for the difference is often that the SMPS comes with a "current limit"..... A traditional supply has no such thing.

if your big lead-sled power amp wants a very large current for a low frequency transient, it just draws that current, as much as wanted, from the power supply capacitors. How much it can draw is simply a function of how big the capacitors are. "Good" amps had large capacitors. And capacitors have no current limit, they can supply pretty much whatever you want, limited only by their "capacity".

Notice that this is NOT affected by the fuse, or the allowable line current, etc.... it is a short term pulse, and pretty much all the power comes from the "local storage".

Now, with that SAME total energy storage at high voltage in an SMPS, it is "on the wrong side of" a solid-state device or devices.....the SMPS switching IGBTs are between it and the amplifier. Often the amount of storage on the "amplifier side" of the SMPS is much lower than normal for a traditional power supply

ALL the power that the amp wants must come through those solid state switching parts. But those parts have a maximum current that they can conduct. if that is exceeded they will be overheated or even instantly destroyed.

The SMPS control circuit always has a maximum current limit. SMPS parts are expensive, and it is not usual to drastically oversize them. So the current limit may be set to protect the parts, while allowing the sine wave power.

BUT, with that current limit BETWEEN the "energy storage" and the "energy consumer", it is like a 'throttle valve", set low enough that the transient power may be choked off so that it is little more than the sine wave power.

Inherently this is different from a traditional amp, which as mentioned has NO such "throttle valve"...

You will hear the result in the low end, and I think that is one big reason for complaints about the low end on some SMPS amplifiers.

Many manufacturers, but not necessarily all, have found ways to avoid this problem. It is inherent with an SMPS unless the SMPS is designed specifically for an amplifier application, and not just made like any other standard SMPS.

True, but I'll add that the way power supply current limiting manifests itself is in premature clipping, because it will cause the supply rail voltages to sag. Current-limiting circuits seldom, if ever, involve direct gain reduction. If the amp isn't clipping, then it's generally safe to say that the audio signal isn't being unduly compromised.

While it's not uncommon to hear that "my SMPS amp just does not sound right in the lows," it's also not uncommon for people to not be able to tell an SMPS amp from a LFPS amp by sound alone.

Not all amps with conventional, line-frequency power supplies handle heavy-duty bass frequencies adequately; in some, when the audio signal's period becomes significantly longer than the reservoir recharge period, the reservoir being drawn down will sag significantly, even as the reservoir of its opposite polarity gets replenished.

In the end, what matters more than whether the power supply is line-frequency or high-frequency is how it and the amplifier design are implemented. A good, solid design and implementation is always better than a poor one.

 

["Q"]

Actually, I'm going to defend the "stores current" idea....... if you can stand a bit of techie-talk

BOTH a transformer (and definitely a purpose-made inductor) and a capacitor store energy..... but they do it in different ways.

A 'current" is moving electrical charge.... electrons on the move.

An inductor DOES store current....... you "charge it up" by applying a voltage to it, and current through it increases.....If you then disconnect from teh voltage, and connect it to a load, the current continues to flow. Initially the same current flows, then it decreases with time as the energy is depleted by the load. The inductance "stores current" in that rather direct sense.

Would it be fair to say that both the transformer and a capacitor store "voltage" as a magnetic field in the transformer and an electric field in the capacitor but, that they manifest outputting that "voltage" in different ways due to the mechanic of their storage?

Also, is the lesser PF of a traditional supply due to it having big capacitors but not enough inductance in the transformer? Maybe another argument for big transformers?

 

[seamonkey]

Besides some SMPS being universal on line voltage, and regulated, we forgot to mention active Power Factor Correction (PFC). Making SMPS even more efficient and another buzz word for the marketing ads. PFC is becoming mandatory for some things in Europe. All the dongles in the world are switching over to SMPS, those little loads add up.

 

[illusha]

in a round-about way, this thread started some interesting discussions... guess there isn't one good answer as to which technology to pick - there are many factors to consider and many designs to test out

btw, while reading around today, I found another excellent collection of audio-related articles here: Link Removed

 

[Jerrold Tiers]

[QUOTE="Q";10388492]Would it be fair to say that both the transformer and a capacitor store "voltage" as a magnetic field in the transformer and an electric field in the capacitor but, that they manifest outputting that "voltage" in different ways due to the mechanic of their storage?

Also, is the lesser PF of a traditional supply due to it having big capacitors but not enough inductance in the transformer? Maybe another argument for big transformers?[/QUOTE]

Nope......

Inductors (but not usually transformers) and capacitors store ENERGY, really, but the FORM they store it in differs.
Inductors directly "store" current, or moving electrons..... capacitors "store" charge, or electrons "packed into them" by a voltage.

Whichever, they store "energy". "Voltage" is not stored, voltage is a property, not an "item".

The low power factor is due to a number of things, but prime among them is the way current is drawn in short pulses with lots of distortion/harmonics.

An inductor in series would smooth the flow of current, improving the power factor. But you will lose output voltage, and voltage will depend much more on current.

Inductors have a lousy power factor also. It just happens to be lousy in the opposite way from the way a capacitor's power factor is bad.... in some situations you can use one to offset the other. The power company does this.

A resistor has a perfect 1.0 power factor. The electronic "PFC" (power factor corrector) draws power in such a way as to "appear" to the mains as if it were a resistor.

The Ampeg SVT-8PRO for instance has a PFC. Testing revealed that at high power, the power factor was around 0.999. Almost perfect. Only a few milliamperes of "reactive current" was drawn.

Another advantage of a PFC, as with the 8PRO, is that usually, the PFC makes the SMPS "universal", it can accept any mains voltage from 100VAC to 240VAC with no switches. all you need is a plug to match the wall outlet.

 

[seamonkey]

...
The Ampeg SVT-8PRO for instance has a PFC. Testing revealed that at high power, the power factor was around 0.999. Almost perfect. Only a few milliamperes of "reactive current" was drawn.

Another advantage of a PFC, as with the 8PRO, is that usually, the PFC makes the SMPS "universal", it can accept any mains voltage from 100VAC to 240VAC with no switches. all you need is a plug to match the wall outlet.

That's truly amazing. I don't think SVT-8PRO gets the credit it deserves in both Sound and technology wise. It boils down to nobody really wanting new tech out of Ampeg - just the same old stuff from some long ago era.

The new Ampeg mini heads will probably do good. They have a great price point. I hope they're reliable.

 

[tombowlus]

That's truly amazing. I don't think SVT-8PRO gets the credit it deserves in both Sound and technology wise.

+1 That SVT-8Pro is an amazing head, and so far, on the bench, it has proven to be the best-performing class-D head which we have tested to date.

 

[Calaverasgrande]

We are not talking here about "sine wave power", most amplifiers will satisfy their paper specifications. But most of us have noticed that even with virtually identical specs, different amps can have drastically different "feel". This is due to performance that is "not documented" in the specs. (we tried to document that low freqency transient performance with our 40 Hz single cycle power spec, but then lots of people yelled at us for having "fake peak-power specs")

I am one of those guys that was jumping up and down about that single cycle spec. Not just with you guys. My favorite amp company, Mesa Boogie, gives out no real specs on its tube bass heads, other than to say the 400+ does 50 "peak" watts.
To my way of thinking, I could give a damn about peak power for bass. I am not a thumb popping, slapping guy that wants instantaneous transient attack. I like big round slabs of tone with definition. I know kind of contradictory. If I am speccing a power amp for a sub on a PA I might be interested in the single cycle spec or peak power capability. It's gonn abe reproducing kick drum thumps. A meek amp will blur two kick drum pops into one indistinct thump. A good one will put out the same power for both. But a bass amp, in my world, is always going to be shaking that paper cone. It isnt going to have much time to rest and replenish it's reserves. So I am interested in sine wave output.
I also kind of think that the "feel" we talk about has to do with running an mpa near its rails and getting some compression in that manner. Lord knows its what us tube amp guys like. But before I got all tube ampy I was all about the GK 400rb/800rb "on the rails".

 

["Q"]

Nope......

Inductors (but not usually transformers) and capacitors store ENERGY, really, but the FORM they store it in differs.
Inductors directly "store" current, or moving electrons..... capacitors "store" charge, or electrons "packed into them" by a voltage.

Whichever, they store "energy". "Voltage" is not stored, voltage is a property, not an "item".

Ok maybe we both should have been more clear.

As I think Bob Lee stated here already, inductors can't technically store current because current is a flow electrons and if the electrons aren't flowing then there is no current.

But what they can do is store the potential for current flow. That potential is stored in the magnetic field around the inductor (please correct me if I'm wrong here). I misused the word voltage to refer to the potential of an inductor to "store" current.

The problem is, current is kinetic energy. If it is being stored or not in motion, it is , by definition, potential energy.

So really, instead of voltage we have a "magnetic potential" I'm not really sure what the term for that is. Gauss? Flux?

And I would say that really, current is an attribute of voltage not the other way 'round. Only because, there can be voltage without current but not current without voltage. (I know no textbooks will agree with me on this).

 

[Jerrold Tiers]

OK, this is a place to discuss amps, and not physics..... I'll put in a bit more for fun, but lets leave it pretty soon after this, OK?

[QUOTE="Q";10394289]
As I think Bob Lee stated here already, inductors can't technically store current because current is a flow electrons and if the electrons aren't flowing then there is no current.[/quote]

And then there is no energy content..... yes, the energy is in the magnetic field, BUT how did that field get established? ONLY THE CURRENT can normally store energy in an inductor, because the magnetic field is LINKED to current.

if you "externally" establish a field in the core of an inductor, you will induce a current in a conductor wound around it. A magneto such as is used in many small gasoline engines works that way. And electrical generation rather depends on that fact.........

if the conductor is open, you will generate a voltage across the open ends. if you have a current flowing, and you open the conductor, a voltage will be established across the break. That is how the magneto works.

There are details, since you can put IN energy in a small current in a large number of turns of wire, and later take it out as a large current in a separate winding of few turns. many SMPS work that way.

I did not intend my comment to be an exhaustive discussion of the physics..... it was a more-or-less humorous but also quite truthful but slightly different slant on the point......

And I would say that really, current is an attribute of voltage not the other way 'round. Only because, there can be voltage without current but not current without voltage. (I know no textbooks will agree with me on this).

Ah, but current ESTABLISHES a voltage.....in a resistor.... and you can have current flow in a "superconductive" material (generally at extremely cold temperatures) with essentially no voltage driving it. That's because a "superconductive" material has essentially zero resistance.

When you have a voltage with no current, you have stored energy, in an amount depending on the "capacitance" and the voltage.

When you have current flow but no voltage, you also have stored energy, in an amount depending on the inductance and the current.

When you have BOTH voltage AND current, then you have "losses".

 

[walterw]

isn't this entire argument becoming moot when that switch-mode power supply is attached to a new generation of class-D amps putting out twice, three times, five times the wattage of the linear amp?

and doing it with already ridiculously light weight and increasingly low cost?

 

[Calaverasgrande]

isn't this entire argument becoming moot when that switch-mode power supply is attached to a new generation of class-D amps putting out twice, three times, five times the wattage of the linear amp?

and doing it with already ridiculously light weight and increasingly low cost?

No it isnt moot if there is a negative effect on the audio quality. Not saying there IS a negative, but sheer amount of wattage is not an end in itself. Nor is light weight. At least for me and some other bassists, the tone and feel is more important than weight or efficiency.

 

[12bass]

What about adding a moderate capacitor bank to the output of a SMPS? Wouldn't that offer the benefits of both?

 

[Jerrold Tiers]

What about adding a moderate capacitor bank to the output of a SMPS? Wouldn't that offer the benefits of both?

it can.... SOME types of SMPS do not like the cap changed. Others have no problem with that. The higher the power and the less the regulation, the less it should be a problem, in general.

Larger capacitors can reduce "supply pumping" in a class-D amp.

 

[Growly Lytes]

What about Class H amps ?
Im quessing they are in the same boat as the rest ?

 

[ACB0015]

It is a great discussion. But can anyone step up and say who is making the good SMPS designs and who the good traditional designs? Or is mention of specific manufacturers not allowed in this thread?

 

[majortoby]

I will say that the Ampeg PF 350/500 and SVT-7 are all class D amps I have played. And they all sounded amazing.

 

[Growly Lytes]

By the sounds of things Poweramps are great till they break down, which isnt as long as a bass amp.I keep seeing people having all kinds of problems with Poweramps much more then dedicated bass amps.
Why is it so hard to make a 2 channel amp that works properly for more then a couple of years.
Fender BXR200 head i had & pumped it like nothing else & it kept a going.Never in 10 years did it get serviced.
First Poweramp i bought had loose screws inside & one of the fans was split apart......
Oh, then the bias had to be adjusted a month later because channel 2 was buzzing & distorting at low levels.The tech said we bassists have good hearing !

 

[chucko58]

What about Class H amps ?
Im quessing they are in the same boat as the rest ?

Class H is a variant of Class B (some say AB).