Purifi Class D: Junk?

I will note one thing though- I've seen a number of SMPSs (Switch Mode Power Supplies) used in class D amps. I think its a bad practice. They work, sort of; the problem is that class D amps go from almost no current draw at idle to quite a lot at full power. SMPSs don't have a lot of capacitance at their output and so can be drained faster than they can replenish. A lot of them will shut down if you put a lot of capacitance at their output. So if you're not running an amp with a regular power transformer and a lot of capacitance available for the class D amp to feed on, you're probably not hearing what it can do.

I can't agree with this statement Atmasphere, it really depends on the power supply, how it was designed, and circuit limitations.

Most switch mode power supplies for power amps I see for audio are not power factor corrected. They tend to be single stage LLC, with a simple bulk capacitor arrangement on the front end. Poor design choice in my mind, but is what it Is.


They store most of their energy on the high voltage side, not the low voltage side. Let's say no PFC boost front end, so at 120V, say a bulk voltage with losses of 160. Pretty easy to put 1000uF, if not more on the front end. At 160V, that's 12.8 joules. That's the equivalent of 16,000uF at 40V. I would be more inclined to put a PFC boost front end with a link voltage of 400V. Now my 1000uF (450V capacitors) is like 100,000uF at 40V.


That 450V, 1000uF capacitor is lot smaller than the 100,000uF, 50V capacitor. All that is required is the LLC stage has high surge (added power capability), and suitable continuous capability.

JUNK? That’s kind harsh.. There are some good sounding class ds. NO they don’t float everyone's boat, but they get the job done for a lot of folks.. Is it my favorite amp? For some things, I think it is the absolute best.. I use 3 12k Behringer for SERIOUS bass duty.. I have 1300.00 invested. Come one come all, unless you have 4 of those things..:-) The best performance is 220 single phase. They can suck a PG&E pole dry, just like the rest of the welding machines can, too. Don't underestimate pro equipment EVER.. Couple of mods and some good cables. Can crumble a house...

It's how you got to hear it the first time. Live anyway..

NC500 I have a few, wonderful amp with buffer boards.. George has got them cooking along without, buffers. I didn’t like Ice or the Hypex 400 without buffers. Maybe he’s got something special there.

I use them in the hot summer months, with a tube front end. Valves in the cooler months..

Yea I don’t listen to junk. I never have. BUT then I like tone control, Mcintosh, Russco and VMPS speakers, too.

I like slower runnin' women too.. That's just me.. There is "too fast" ya know.. :-)

Regards

I can't agree with this statement Atmasphere, it really depends on the power supply, how it was designed, and circuit limitations.

Most switch mode power supplies for power amps I see for audio are not power factor corrected. They tend to be single stage LLC, with a simple bulk capacitor arrangement on the front end. Poor design choice in my mind, but is what it Is.

The problem I was getting at is for the most part you can't use an off-the-shelf SMPS and get top drawer results. I think you could if you had a supply custom built but IME that's a very pricey thing to do- and not something that most 'high end audio' manufacturers can pull off due to the quantities involved.


Obviously storing electrons at a higher voltage allows a lower capacitance, since voltage dominates the energy formula; I think the problem might come in when that conversion to the actual voltage being used has to occur and occur quickly. We were able to use SMPSs for prototyping, but continually ran into current limit shut down issues and the like. After a while (and also once we had sorted RFI issues) it got much easier to simply use a conventional power transformer. We still had to be careful about the power supply since it had to have a number of protection circuits built in.

Given the price of high end audio equipment, if you are doing 1K units a year, 3 year design, 3000 units, you could amortize the $100K design cost, at $33/unit additional.  Most audio companies would be best off contracting that out.  Hypex does their own, and I have seen some a company or two offering audio targeted switch mode supplies.