ILoveHiFi wrote:
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=1044&start=110
Good, I was wondering how do you do it in a Tupperware.
I am for using SMPS, problem is I cannot find anything that fits. 24V is too low power, assume you swing +/-21V( 3V to rail), you get 1/2 X V^2/R = 27W max. That's too low. I need at least 30V. I even looked into Meanwell power supply that is 28V and it can be cranked to about 31V. BUT, it's too big to fit in the chassis. I did use it earlier on in a wood board proto amp.
Attachment:
SMPS supply.JPG
This is one with only 5 pairs of transistors with two 24V SMPS that are 10A each and cranked to 27V. It did at least as good as the Nakamichi PA-7. But as I said, it's too big to fit in a real amp chassis.
Also, remember, those SMPS are NOT designed to have 30,000uF hanging at the output, they oscillate. They are closed loop feedback inside, they always have an upper limit of how much capacitance it can drive. Without the cap, you can run into shutdown when you draw peak current.
I don't have experience designing SMPS, when I was working, I consider those are easy stuff and had my engineer designing SMPS and I designed the more challenging things. I regret this. I should have done it myself at least once. The off the shelf SMPS are not very good, too noisy, they don't know signal integrity. That's the reason people that work on high precision analog and low noise analog system avoid SMPS.
In the early 90s when I got promoted as manage of engineering, I pushed to switch all power supplies to SMPS. We reduced two rack mountful of analog supplies to just one small rack. We design very high precision and low noise electronics, I even have SMPS right in the heart of an electrometer amp that measure current down to pA. I used noise cancellation to get rid of the noise and it worked like a champ.
Audio power amp is nothing close to the sensitivity of the the Mass Spectrometers we design, SMPS will work perfect. Just have to know their limit. Know signal integrity design. I just need to learn the transformer part of it.
BTW, you run 2.5A/ch, that's way too low. You can run into shutdown. I remember they talked a lot about this problem in DIYAudio. I used at least 10A supply to give 5A per ch and still use a lot of caps to prevent current spike. that's when it gets too big.