Regulation of SMPS in power amps

[TomJ]

There’s an interesting difference in measured power between the Purifi 1ET400A EVAL1 amp with a Hypex SMPS 1200A400 (131/257W pre-clip, 205/380 at 1%, ASR) and the same amp with the NAD SMPS in the C298 (180/415 pre-clip, 269/528 at 1%, SSN). As I understand it, this is due to differences in their PS regulation.

Is there a downside to NAD’s approach? Is that likely to be used in future products from other vendors, eg a Purifi SMPS? In comparison to NAD and Hypex, how are the equivalent Pascal and ICEpower SMPS regulated?

 

[solderdude]

Looks like the power supply of the NAD is about 6V higher in output voltage and maybe even output current.

 

[boXem]

Technically, none of them is regulated: the higher the load, the lower the rails voltage.
Where did you get the C298 data from?

 

[solderdude]

Why would an SMPS not be considered regulated ?
The output voltage of those PS is pretty constant regardless of the load because of the feedback loop in there or is the power supply in these types of amps fundamentally different ?

 

[TomJ]

Where did you get the C298 data from?

SSN, https://www.soundstagenetwork.com/i...ts&catid=97:amplifier-measurements&Itemid=154

 

[wwenze]

Technically, none of them is regulated: the higher the load, the lower the rails voltage.
Where did you get the C298 data from?

Well technically that is called regulation too... Like a transformer voltage regulation is "the percentage change in the output voltage from no-load to full-load"

 

[KSTR]

The Hypex supplies, last time I looked, are all unregulated and their output voltage scales with mains voltage. This alone will give different readings. The difference, when expressed in Watts (which is a squared measure), may seem to be significant on paper but they are not. Twice the power is just 1.41 times (3dB) the output voltage and SPL, and a 3dB SPL increase only perceived as "a bit louder".

 

[boXem]

Why would an SMPS not be considered regulated ?
The output voltage of those PS is pretty constant regardless of the load because of the feedback loop in there or is the power supply in these types of amps fundamentally different ?

As @KSTR wrote, Hypex SMPS are unregulated. TBH I don't know for the one from NAD, but I would be surprised if it was.

Well technically that is called regulation too... Like a transformer voltage regulation is "the percentage change in the output voltage from no-load to full-load"

Then we don't have the same definition for "regulation"

 

[Lambda]

The Hypex supplies, last time I looked, are all unregulated and their output voltage scales with mains voltage.

Any idea why?
whats the advantage of this?

 

[solderdude]

Spoke to Hypex and indeed the output is not regulated.
Instead the output voltage is proportional to the mains voltage so a ratio determined by the DC input voltage after rectifying the mains.
So akin to a transformer with rectifier and smoothing cap.

 

[wwenze]

Any idea why?
whats the advantage of this?

Unregulated SMPS allows the concept of peak power. Some people like that sort of thing. Continuous power is bottlenecked by your transformer and switching elements, but if you put enough capacitors at the back, you can say that the amp can produce xxxx watts peak power for 100ms.

 

[boXem]

Unregulated SMPS allows the concept of peak power. Some people like that sort of thing. Continuous power is bottlenecked by your transformer and switching elements, but if you put enough capacitors at the back, you can say that the amp can produce xxxx watts peak power for 100ms.

Transients are a real thing.
Regulated SMPS are not perfect, they have a response time which potentially causes stability issues. So integrating an unregulated SMPS is simpler.
The power reserve is on the input side, not the output side, so more energy is stored with lower capacitance.

 

[TomJ]

So Hypex has taken a different approach from the active regulation that Benchmark uses in the AHB2 SMPS.
And NAD? Unregulated (like Hypex) with a higher output voltage, or a more extensive redesign?

 

[KSTR]

Any idea why?
whats the advantage of this?

I'm guessing here, but without a full feedback loop with the common opto-coupler + TL431 it's probably easier to make the supply resistant to short-term overload which is a key feature of any audio supply, output current should be thermally limited only.