Join Date: Jun 2006
Originally Posted by Nisbeth
Thank you for that vote of confidence in my abilities Alan
As you probably know, normal "commercial" audio testing is done with sinewaves/noise at 1/8th power for consumer level equipment to simulate that you are normally playing music with a high PAR(peak-average ratio)/crest factor. For PA-use, you would normally go to 1/3rd power to simulate heavy use but that it is - the DIY'ers massively oversized PSUs with 1000VA for a 2*100W class AB amp isn't required here.
For a linear PSU, that means the "real" power requirement is then between ((2*250W)/0,93)/8 = 67W and ((2*250W)/0,93)/3 = 179W not counting transformer losses. For normal home use you could therefore go to 160VA with a bit of safety margin and even a 225VA transformer should be adequately sized. The key thing to remember is that while the average power may only be what is described above, the peak power/peak current requirements are still corresponding to (2*250W)/0,93) = 537W. For a linear supply this isn't much of a problem, the transformer will just be a little bit hotter. What you have to remember in this that the catch with an industrial SMPS is that it is not designed for audio, meaning that once you get to 100% load it will current limit to protect it, but on the other hand an industrial 300W PSU is designed to run at 300W output throughout its entire lifetime. Here, you would normally have to look at the peak current requirements of the amp instead of average power to ensure that you do not hit current clipping (which sounds really bad).
This is why I wrote that the PSU in the 250ASP is sized with a thermal limitation - it will deliver the peak power you need but if you try to run it continuously at that level it will overheat after a fairly short time because it is not required. Many DIY'ers will say that this is lying/cheating/misrepresentation of the product, but what it actually is is good engineering because 99+% of all real-world requirements are met!
I am not saying there is no benefit to oversizing the PSU in an amplifier, I am just saying that calculating how much you really need can be a useful reality check to avoid paying more that you actually need. Now if you think that any transformer under 2kVA is unsuitable for powering anything bigger than a three-tone doorbell then by all means go ahead and spend your money, but for the rest of us with limited means for this hobby I think it is very useful to check before spending the money.
I hope this helps explain my thinking
PS: Oh and by the way, not only am I actually from Denmark, I also used to work for ICEpower...
Our amp modules tested at real RMS power conditions and pass 5-30 minutes burning-in, we sure it is one power convertor first, it should have enough power capacitor to drive the loader, or not it will like Japanese car, small engine and light car body.underpowered and unsafe.
Here some link for chip class D amp measurement.
Guidelines for Measuring Audio Power Amplifier Performance, sloa068 - TI.com.cn
Audio Power describle link
Audio power - Wikipedia, the free encyclopedia
Proamp measurement DOC files come from AP website:
AP High Performance Audio Analyzer & Audio Test Instruments : Home
Last edited by authlxl; 7th November 2013 at 09:36 AM.