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Class D Switching Power Amplifiers and Power D/A conversion

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Old 2nd May 2015, 09:02 PM   #1
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Default full digital class d amplifier - hifimediyDDX320

i would like to realize a total digital installation in my car, like this:

- player HD like raspberry PI (or platform like this that support volumio) + volumio.
- DSP processor to realize filtering + eq + ambient correction, connected digitally (i2s if is realizable, or spdif / toslink) to the player; i'm thinking about the minidsp product (minishark) instead the commercial product like mosconi, audison and so on.
- digital amplifier (power dac); i would like to use this type of amplifier instead the classic analogic amplifier, in order to avoid to use a DAC, digitally connected to the processor.

until now, the only class D amplifier with digital input that i found, is the DDX320.
all the other class D amplifier that i have seen (hypex, anaview, icepower) have the analog input.

someone have already utilized it ? with wich result ?
someone have already utilized other model of class D amplifier with digital input ?

for the digital amplifier i'm searching a product with the same performance to a traditional good class a/b amplifier.
the most important characteristic that i search in the sound is clear and open & wide stage, with a sound no cold or metallic.

do you have any suggestion for other product other the hifimeDIY ?

thanks to all.
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Old 2nd May 2015, 10:04 PM   #2
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Quote:
Originally Posted by maxbruz68 View Post
- digital amplifier (power dac); i would like to use this type of amplifier instead the classic analogic amplifier, in order to avoid to use a DAC, digitally connected to the processor.
Why? It's a fair bit more easy and cheaper to design and build a low noise DAC that feeds an amplifier output stage with an analog signal. There are several class D chips on the market already that has a digital input, a high quality DAC and an output stage built into a single chip. Many of these also have a built-in programmable DSP that you also seek.

For example the relatively low cost TAS5756M. It might not be in your power range, the DSP might not be as versatile as you want, or the differential 18 bit Burr-Brown DAC might not be the quality you're looking for but it'll give you an idea of what is available on the market in the low cost section.

But given your requirements are only for car audio and you only seek the quality to be on par with a good quality class ab amp, the above chip will far exceed your needs.

Last edited by Saturnus; 2nd May 2015 at 10:16 PM.
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Old 3rd May 2015, 01:39 PM   #3
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Hi Max,
I'm using it that way, and it works well :
Cubietruck/Volumio ---> Nanodigi (from Minidsp) ---> (2x) DDX320
I use Nanodigi only as a DSP crossover; nice gear.
As Nanodigi is SPDIF input AND output, it makes sense having only one digital to analog conversion in the whole process. Souncheck's paper about it.
Other products I've heard about : NAD D7050 and Denon PMA-50 (non DIY).
Soundcheck's tweaks made a clear upgrade in sound quality

@ Saturnus : please consider the benefit of DDX320 (#2)
1) SPDIF ---> DAC ---> PWM ---> Class D output stage filter ---> speaker
2) SPDIF --------------> PWM ---> Class D output stage filter ---> speaker

Alain
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Old 3rd May 2015, 02:12 PM   #4
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Quote:
Originally Posted by alain_online View Post
@ Saturnus : please consider the benefit of DDX320 (#2)
1) SPDIF ---> DAC ---> PWM ---> Class D output stage filter ---> speaker
2) SPDIF --------------> PWM ---> Class D output stage filter ---> speaker

Alain
It's been discussed to death before on these boards.

There is no real or theoretical benefits. Only drawbacks of direct digital amplification stages.

And even then. It is "true digital"? If it has feedback like the STA320 chip it's not really "true digital" anyways.

It really comes down to the simple fact that since digital to analogue conversion has to take place somewhere in the chain from source to speaker, it's all about finding the best place to do it, and the amplifier output filter is not it. And we're not even talking about a true digital amplifier here as it has analog feedback that has to be converted to a digital signal.

Last edited by Saturnus; 3rd May 2015 at 02:15 PM.
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Old 4th May 2015, 10:32 AM   #5
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Hi Saturnus,
Sorry, I had missed that discussions.
Any recommendations about good/better designs ?
Alain
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Old 11th May 2015, 07:52 PM   #6
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reading the convention paper taken into the Hypex website (here attached) i understand that (on par.3 history) is possible to obtain (only ideally ?) a conversion PCM (digital signal) ---> PWM (analog signal).

i don't remember how exactly works the DAC but i don't believe that is based to PWM modulation
Attached Files
File Type: pdf AES120BP - ultralow distorsion digital pwm.pdf (199.9 KB, 24 views)
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