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Class D Switching Power Amplifiers and Power D/A conversion

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Old 8th May 2006, 02:19 PM   #11
Did it Himself
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My recommendation would be to use a single transformer, but separate rectifier and capacitor system for each amp. This gains you the better regulation and smaller size and lower cost of one bigger transformer, but minimised crosstalk to levels below worth bothering about.

As for rectifier and capacitor designs, I prefer to use the dual rectifier approach. This requires separate secondary windings. So you will need a total of 4 bridge rectifiers for a 2 channel system.

I prefer this way because it gives you better quality ground and loads the transformer better so you can get that little bit more out of it.

On those images you put up, the first one has too many snubbing caps used IMO. The one on the AC side makes the most difference.
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Old 8th May 2006, 02:39 PM   #12
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I must commend you on your level of thorough research. An example to be followed.

Secondly I think you have a pretty good plan there. It should let you learn alot along the way.

I pretty well agree with richie00boy, though I think I'd definately want the beefy transformer which will have better regulation in itself and will keep all those caps pumped up.

Bleeders also have the advantage of helping to maintain equal voltage off of "series" caps.

It seems like you've done more than enough to help you get started, everything else just comes one step at a time.

Oh, I like the fuse before the switch
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Old 8th May 2006, 06:20 PM   #13
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the big drawback of having a stereo amp. with 2 transformers is the weight it will have and the size of the cabinet in comparison with a 1 transformer setup. The advantage of having a bit more power out of it is marginal. Did a lot of testing with different ways of making PSU's for stereo amps. and it just is a choice of either having a heavy and big stereo amp. versus a smaller 1 with a tiny bit less power. And the difference in quality, well that's personal and for me not enough/marginal. For me soundstage is far more important than absolute power. And the size/power of the transformer is not so important as with an A/B amp. Class D is soooo efficient.
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Old 9th May 2006, 12:21 PM   #14
bck2diy is offline bck2diy  United States
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Thanks richie00boy, classd4sure and Bert for your input. I have attached an updated version which follows the design advocated by richie00boy. Also, I have included the circuit for isolating supply ground from audio ground (ref: adire audio) which I plan to use (for single ended input setup).

When I have to move to step 3 (mono amp setup for each channel), I would replicate the blue box contents and rewire T1 - T4 (see attached image) as in version 1 to each of the blue boxes (i.e., two rectifier bridges per channel)

Richie00boy, I assume you're talking about the snubbing capacitors C4 - C11 (both in version 1 and the attached image) and C17 - C24 (in the attached image). I don't plan on putting them on initially. I plan to add them to see if there is any measurable or audible (mostly the latter) difference and remove them if none is found.

Classd4sure or Bert, so a single transformer does provide good channel separation (soundstaging) if the bridge circuit is done correctly? Do I correctly understand what you're saying?

If so, I think I have my final design and I can proceed to the next steps. This helps me get started!!

Thanks all for your help!!
-bck2diy
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Old 9th May 2006, 12:36 PM   #15
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That looks good in principle. I would move C2 and C3 to be as close to the bridge though as it's only there where they will do any good. You know my thoughts on the individual diode caps.

It is unecessary to include two sets of bleeders, one resistor across each rail will suffice. Although personally I do not like bleeders as they just waste power and capacity, and are another thing to fail. The amp will drain the caps down perfectly well, and during testing when the PSU might be powered with no load all you need to do is bleed them manually by a resistor or light bulb.

All that's missing is a cap across the neutral switch. I would use Y-rated caps for these positions to ensure they fail safe (open) should the worst occur. I use 2.2nF or 4.7nF.

I assume you have an effective soft-start system for the transformer?
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Old 9th May 2006, 12:37 PM   #16
Bgt is offline Bgt  Netherlands
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the schematic you've drawn here does not allow you to connect the grounds together. Each supply should have their separate windings. So you'll need a transformer with 4 separate windings like this. Otherwise problems. If you want to use 2 bridges per amp. use 2 transformers so you'll have 4 windings.
I also do not prefer caps. across the rectifier diodes or bleeders.
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Old 9th May 2006, 01:29 PM   #17
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Default I like bleeders

http://www.rubycon.co.jp/en/notes/al...Connection.pdf
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Old 9th May 2006, 01:41 PM   #18
Bgt is offline Bgt  Netherlands
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Default Re: I like bleeders

Quote:
Originally posted by classd4sure
http://www.rubycon.co.jp/en/notes/al...Connection.pdf
Chris, here you'll need bleeders for the sake of protecting the caps. This situation does not apply to a stereo amp. There are no free running caps.
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Old 9th May 2006, 01:42 PM   #19
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Oh, I like bleeders too for series-connected caps. Like the app note says they are a wise choice. But in audio power supplies where series caps are not used in the vast majority of cases, they are simply a waste of energy and potential for hazard.

A split rail audio PSU is not akin to connecting caps in series, especially the twin bridge approach like what has been advocated in this thread.
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Old 9th May 2006, 01:45 PM   #20
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Because the amps load them? Not good enough to warrant not using them I think. There's really nothing wrong with using bleeders and obviously they have their purpose. Although, I didn't bother with them in my supply either, I wouldn't go say they're not a good thing.
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