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Class D Switching Power Amplifiers and Power D/A conversion

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Old 27th September 2011, 08:26 AM   #411
Nevod is offline Nevod  Russian Federation
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I believe the "adapter", which schematics I'm attaching here does something like that.
I don't remember exactly though how it works, have to dig though 50+ pages of forum for that. IIRC, it mixes 200 kHz square wave with input signal, provided from a normal power amp, and then runs it through a small step up transformer. THD is 1% at 200Hz, not suitable for higher frequencies.

Could you please explain what would be that modulation method?
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Old 27th September 2011, 08:33 AM   #412
Bruno Putzeys is offline Bruno Putzeys  Europe
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What Ouroboros is talking about is to have a 50% duty cycle source and a 4-quadrant synchronous rectifier equally running at 50% where the phase between the two square waves is varied. On average, somewhere on the planet someone is trying this method about once a year in an attempt to build a "one stage class D amp and SMPS" only to realise the thing still contains the same number of active devices and the same amount of ferrite. But it would rid you of the step-up.

Now something that I have been wondering about is why so many people want a class D amp to drive headphones with. You can build a HV amp for electrostatic headphones using devices no bigger than a TO92. No magnetics needed. If you use circuit boards for the stators you can integrate the amp.
There's a time for everything, and this is not it.
Old 27th September 2011, 09:05 AM   #413
Ouroboros is offline Ouroboros  England
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Thanks Bruno, that's pretty much it.
The scheme I looked at basically takes the output of a normal PWM modulator and follows this with two async divide by two stages, one dividing on the rising edge of the PWM, and the other on the falling edge. The output from one of the dividers feeds the full-bridge output stage, while the output of the other divider controls the sync rectifiers. Both signals stay close to a 50% duty cycle, but have a varying phase shift between them.
Works well for a clocked open-loop system at 50Hz, but I'd like to see evidence that it could be made to work over the audio band. For 100V output class-D PA amplifiers it would be a useful technique.
Old 27th September 2011, 09:51 AM   #414
Bruno Putzeys is offline Bruno Putzeys  Europe
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I think the first useful class D amps with this techniques were designed by Brian Attwood and sold by Peavey. It's quite long ago. Specs weren't brilliant but it worked.
There's a time for everything, and this is not it.
Old 27th September 2011, 12:26 PM   #415
phase_accurate is offline phase_accurate
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Yes they were the DPC series (Digital Power Conversion). They were one of the first really powerful amps on the market using one rack space only.
At least in Switzerland they were not officially available. I am not sure wheter this was because of an EMC issue or maybe the lack of power factor correction.


Old 27th September 2011, 01:06 PM   #416
FloridaBear is offline FloridaBear
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Bruno, I would sure like to applaud your participation here in the DIY community. That seems to be a rare quality among professional audio designers.

The progress (e.g. input buffer) on the NC400 sounds fantastic. Are we rapidly approaching the "ultimate" amplifier in NCore? It sure seems to me that we are, at least in audible/measurable ways (i.e. what matters).

I'm planning for NCore to be my personal "ultimate" amplifier in any case
Old 27th September 2011, 03:13 PM   #417
mr_push_pull is offline mr_push_pull  Europe
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Bruno, I have to step in and tell you how anxious I am about this product. I started to think that you've dedicated yourself completely to Grimm Audio and left Hypex for good. Happy to find the contrary.

I've been using a UCD180-based amp for about 5 years now and recently started to consider purchasing a Hypex SMPS as I got myself some rather hard to drive loudspeakers which make the current PS sound like it's reaching its limits sometimes. But I'm only happy to have looked here because I found about the NC and decided to wait until it's released. BTW one more vote for the 400W version (if the vote is still open).

I was curious about the form-factor and heat sink requirements. I might even order in advance a nice case for it
Old 28th September 2011, 10:20 AM   #418
Bruno Putzeys is offline Bruno Putzeys  Europe
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@FloridaBear: One can always imagine designing fancier output stages using the latest newest hyperwonderful power devices etc but for practical purposes the NC400 is going to be "the best I can do" for a while.

@MrPP The module is mounted flat and cooled through the base like the OEM series UcD modules. If you just bolt them onto the bottom of a metal case you've got enough cooling. Mounting them in an angled position requires an L bracket which we'll probably supply as well. The module takes up roughly the same size as the UcD400OEM but it's not exactly the same shape. I'm now revising the layout so more details remain up in the air.
There's a time for everything, and this is not it.

Last edited by Bruno Putzeys; 28th September 2011 at 10:23 AM.
Old 28th September 2011, 11:40 AM   #419
ackcheng is offline ackcheng  Hong Kong
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Hi Bruno,

Can you NC400 be Bridged to get more power? 3 of them will make NC1200!
Old 28th September 2011, 01:56 PM   #420
Bruno Putzeys is offline Bruno Putzeys  Europe
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Yes you can bridge two modules just like UcD (and just like UcD it helps to strap a small cap across the load to insure the two amps synchronize). This would make a 1200W/4ohm amp (NC1200 is 1200W/2ohm).

But three of them?
There's a time for everything, and this is not it.

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