[Davey]

A linear "regulated" supply would take some doing, but a simple unregulated raw supply is easy.
You get a big transformer, some big reservoir capacitors, some diodes that don't make much noise and connect it all with a good grounding scheme.  It's a project for a first year electronics student.

Cheers,

Dave.

[Julf]

All of the specs I have seen indicate that well-made linear power supplies outperform switching supplies.

I'd be very interested in seeing any specs you might have that show that a linear PS outperforms a well-designed switching supply when powering a class D amp. So far my experiences have been exactly the opposite.

[jult52]

Hi julf,

Here's a basic to-do that has some comparative specs under "Noise and Ripple":

http://www.power-supply-designer.com/2011/03/linear-ps/

The Wikipedia entry on switched ps is instructive:

http://en.wikipedia.org/wiki/Switched-mode_power_supply#SMPS_and_linear_power_supply_comparison

This unsourced engineering mini-paper has a graph on p 2 showing a wide disparity in noise & ripple between the two types of supplies:

http://digital.ni.com/public.nsf/ad0f282819902a1986256f79005462b1/7438e77138bddf1b86256f660008e9cc/$FILE/linear_versus_switching.pdf

Thanks for making me look this up.  It seems to be conventional wisdom among engineers that regulated linear have superior noise & ripple stats compared to switched mode supplies, which in turn are more efficient, smaller and handle input voltage swings better.

[Julf]

Hi, Jult,

Thanks for making me look this up.  It seems to be conventional wisdom among engineers that regulated linear have superior noise & ripple stats compared to switched mode supplies, which in turn are more efficient, smaller and handle input voltage swings better.

Thanks for the links!

That is indeed the conventional wisdom. In the specific case of nc400/smps600, there are a couple of specific things - one is the synchronous operation, and the other is the superior current capability (as linear regulators use a virtual shunt resistance that limits peak current). The ripple of the smps is of course at much higher frequency than the linear one, and as a class D amp needs a low pass filter in any case, the HF ripple gets dealt with anyway.

Now, all this is assuming a *regulated* linear supply - not just your bog standard rectifier-plus-large-caps unregulated supply. Regulated linear supplies in the 400-600 W range are not trivial undertakings.

I am in no way against linear supplies for class D amps - but it should be an informed choice based on facts rather than superstition and audiophile folklore.

[Active-6way]

Does anybody know what kind of cable i should use between an minidsp with rca female out and an XLR female connector build in a chassis with smps600 and nc400.

Would somethg like this http://www.proaudiola.com/product-p/1-m2549-rca-xlrm-1.htm be ok ? Because i can't seem to find an wiring scheme for these cables

[FloridaBear]

Does anybody know what kind of cable i should use between an minidsp with rca female out and an XLR female connector build in a chassis with smps600 and nc400.

Would somethg like this http://www.proaudiola.com/product-p/1-m2549-rca-xlrm-1.htm be ok ? Because i can't seem to find an wiring scheme for these cables

That should work just fine. The other option would be to purchase standard interconnects and get a female RCA to male XLR adapter.

[a.wayne]

Can the operating voltage be changed on the nc400 kits, I dont need 500 watts at 4 ohm , 1 ohm is where i live, is this possible and are the modules safe at 1 ohm ...

Regards ...

[Julf]

Can the operating voltage be changed on the nc400 kits, I dont need 500 watts at 4 ohm , 1 ohm is where i live, is this possible and are the modules safe at 1 ohm ...

Hypex specifies the minimum load impedance as 1 ohm in "Recommended Operating Conditions", so you are safe down to 1 ohm (but not below).

Power supply voltage can be dropped down (to the undervoltage cutoff limit  of 35 V), but you might just want to limit input voltage instead - lowering the supply voltage probably doesn't bring much benefit.

[a.wayne]

Thanks for the response , lowering the voltage will/should improve the low Z performance ....

[Julf]

Thanks for the response , lowering the voltage will/should improve the low Z performance ....

Why?

[a.wayne]

Speaker loads below 4 ohm are current driven as oppose to voltage driven , by lowering the psu voltage , the output stage will have better SOA and less current limiting. Also looking at the published specs it appears the output impedance is between .5-1ohm , seems it might be too high to drive a 1ohm load...

Regards

[Julf]

Speaker loads below 4 ohm are current driven as oppose to voltage driven , by lowering the psu voltage , the output stage will have better SOA and less current limiting.

I don' t think the current capability is SOA-limited (or supply voltage dependent). It seems to be hard limited by the overcurrent protection at 24 A.

Also looking at the published specs it appears the output impedance is between .5-1ohm , seems it might be too high to drive a 1ohm load...

Not sure where you are reading that - the Hypex NC400 datasheet specifies Zout as 0.0006 ohm typical, 0.0025 max, so from that point 1 ohm is not a problem.

[Folsom]

How many output voltages does the smps600 have? One?

I bet it's possible to make an at least competitive linear PSU. But I would ask how the ncore modules do with voltage variance (unregulated) before I'd really believe it. But also a good PSU might be immense in size depending on how many output voltages are needed.

[Julf]

How many output voltages does the smps600 have? One?

There is the main supply vltages (+ and -) and the auxiliary supply voltages (+ and -), so 2 or 4, depending on how you count.

I bet it's possible to make an at least competitive linear PSU.

I guess it depends on your definition of "competitive". Sound quality-wise equivalent? Maybe. In most other aspecs (size, efficiency, heat dissipation, cost etc.) - no way.

But I would ask how the ncore modules do with voltage variance (unregulated) before I'd really believe it.

I  agree.

But also a good PSU might be immense in size depending on how many output voltages are needed.

Indeed - mostly negating all the non-SQ-related benefits of a class D amp.

[Folsom]

Even if it was better, it'd unpractical to make how I'd do it for anyone that has something called a budget.

But I'd like to note that in the pictures it appears to have a CMC in the PSU along with some filter caps. It has some built in noise reduction. You'd have to compete with that as well. That's part of the cost that probably wouldn't have a point worth it.

[Julf]

Speaker loads below 4 ohm are current driven as oppose to voltage driven

I am not quite sure what you mean by that. As far as I know, The nc400 is pretty much the equivalent of a voltage amplifier, so the speaker load is voltage driven, no matter what the load impedance (as in the amp controls the output voltage, and the current is depends on the voltage and the load impedance.

[a.wayne]

I don' t think the current capability is SOA-limited (or supply voltage dependent). It seems to be hard limited by the overcurrent protection at 24 A.

Not sure where you are reading that - the Hypex NC400 datasheet specifies Zout as 0.0006 ohm typical, 0.0025 max, so from that point 1 ohm is not a problem.

It seriously current limits going from 4-2 ohm at standard voltage, so yes i would like to lower operating voltage, much better for sonics and SOA and Yes correct on the output impedance , i had missed the unit used (iphone, old eyes) ..

http://www.hypex.nl/docs/NC400_datasheet.pdf


Regards

[a.wayne]

I am not quite sure what you mean by that. As far as I know, The nc400 is pretty much the equivalent of a voltage amplifier, so the speaker load is voltage driven, no matter what the load impedance (as in the amp controls the output voltage, and the current is depends on the voltage and the load impedance.

Low Z speakers require and amp to sink current  not voltage, calculate the amps needed for 500 watts @ 1ohm and see what i mean , the amp capability is assisted if we lower the PSU voltage , optimizing its output at 1 ohm , not 8 as is standard ...

Currently there is significant current limiting going from 4-2 ohms with standard supply voltage..


Regards ,

[Julf]

It seriously current limits going from 4-2 ohm at standard voltage

How do you know that?

i would like to lower operating voltage, much better for sonics and SOA

I still don't see how lowering the voltage would increase the current driving capacity. Have you actually done a SOA analysis on the nc400?

Any effects on sonics is of course speculation until verified.

[Julf]

Low Z speakers require and amp to sink current  not voltage

Ohm's law doesn't suddenly change at some magic impedance value.

The lower the impedance, the more current and less voltage are required to reach a specific power value, but what the nc400 controls is the voltage, not the current. The current is a result of the voltage, and lowering the supply voltage does not increase the current capability of the amp.

"Current-dumping" and current-control amplifier designs are another matter, but as far as I know, the nc400 isn't one of them.

calculate the amps needed for 500 watts @ 1ohm and see what i mean

22 A, something the nc400 can drive into 1 ohm by outputting a 22 V - independent of the supply voltage. You still need 22 V on the output to cause 22 A in a 1 ohm load, and it doesn't matter if the supply voltage is 30 V or 299.5 V.
 

the amp capability is assisted if we lower the PSU voltage , optimizing its output at 1 ohm , not 8 as is standard ...

No. If you know your load impedance is low, you *can* lower your supply voltage if you change component values, but just changing the supply voltage without changing anything else won't increase the current capability.

Currently there is significant current limiting going from 4-2 ohms with standard supply voltage..

What makes you think that?