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Old 16th December 2012, 07:57 PM   #401
DF96 is online now DF96  England
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Class D needs a DAC, as it is an analogue architecture. Whether the A is a voltage which then gets converted to a pulse width (which then finally gets converted to a voltage), or A is just a pulse width, it is still analogue because the voltage or the pulse width are both analogues of the original sound pressure signal.
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Old 17th December 2012, 08:15 AM   #402
marce is offline marce  United Kingdom
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Doing it this way would keep it all digital to the output filters, and thus make noise controll less of an issue, (I did propose a 1 box version myself earlier, one protective earth connection), and for the output you could use planar inductors or a planar transformer with capacitive screening to further stop any digital noise coupling to the analogue outputs (even if they are speaker level outputs, help with EMC when you add them long antennas). Seen a similar thing with an ADC input, to digital, transported, pulse width out with cap inductor to recreate the analogue signal, this was Bell Labs telephone bandwidth though, not high end audio.
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Old 17th December 2012, 10:21 AM   #403
Julf is offline Julf  Europe
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Originally Posted by marce View Post
Doing it this way would keep it all digital to the output filters
I guess it depends on your definition of "digital". I don't consider pulse width modulation or pulse density modulation "digital" as such, it is still an analog domain, albeit a switched one. To me "digital" really involves encoding the signal as discrete symbols and/or numerical values. A conversion from PCM to PWM/PDM is a digital-to-analog conversion.

Of course, that conversion can happen in one step that is powerful enough to drive a speaker, but that involves a feedback loop all the way back from the "amp" output to the pulse modulator in the DAC, and I am not sure that doing it in "one step" really buys you anything - is noise control really such an issue, and how do you prevent the noise from affecting the (analog) feedback loop?
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Old 17th December 2012, 01:10 PM   #404
marce is offline marce  United Kingdom
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True,
We are switching between two sates so you have high dI/dt, there is no real analogue content until after the filters, so you have to use layout rules for SMPS/Class D, not analogue layout.
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Old 17th December 2012, 09:39 PM   #405
TNT is offline TNT  Sweden
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Quote:
Originally Posted by DF96 View Post
Class D needs a DAC, as it is an analogue architecture. Whether the A is a voltage which then gets converted to a pulse width (which then finally gets converted to a voltage), or A is just a pulse width, it is still analogue because the voltage or the pulse width are both analogues of the original sound pressure signal.
Roger that - it has to be de-quantizised but maybe not by the recreation stage as in sinx/x but exchanged for something else... is there some gains to be made here? The "filter point" could be a single one and moved to the edge of the system. I'm really out fishing here competence wise so please correct me if I'm wrong in my reasoning.

Also, I would like to use the ESS (32 bit) digi level control. No pots - it's so 19xx...

All inside is synchronous except for a USB / spdif input which should be protected by a fifo buffer which downstream side is clocked by the master clock(s) which in turn is located very close to the critical point where the payload (music) leaves the digital domain and going analogue.
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Old 18th December 2012, 04:19 AM   #406
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Also, I would like to use the ESS (48 bit) digi level control. No pots - it's so 19xx...
fixed =)
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Old 18th December 2012, 10:58 AM   #407
DF96 is online now DF96  England
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Quote:
Originally Posted by TNT
Roger that - it has to be de-quantizised but maybe not by the recreation stage as in sinx/x but exchanged for something else... is there some gains to be made here? The "filter point" could be a single one and moved to the edge of the system. I'm really out fishing here competence wise so please correct me if I'm wrong in my reasoning.
Sorry, I can't comment because I don't understand what you are saying.
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Old 18th December 2012, 12:19 PM   #408
qusp is offline qusp  Australia
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I thought it was just me...
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Old 24th December 2012, 07:55 AM   #409
TNT is offline TNT  Sweden
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Originally Posted by Julf View Post
I guess it depends on your definition of "digital". I don't consider pulse width modulation or pulse density modulation "digital" as such, it is still an analog domain, albeit a switched one. To me "digital" really involves encoding the signal as discrete symbols and/or numerical values. A conversion from PCM to PWM/PDM is a digital-to-analog conversion.

Of course, that conversion can happen in one step that is powerful enough to drive a speaker, but that involves a feedback loop all the way back from the "amp" output to the pulse modulator in the DAC, and I am not sure that doing it in "one step" really buys you anything - is noise control really such an issue, and how do you prevent the noise from affecting the (analog) feedback loop?
OK 48 bit. I did not mean anything else really than what Julf wrote previously.

Merry C!

/
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Old 27th April 2013, 03:20 AM   #410
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Originally Posted by abraxalito View Post
Here's something one or two of you guys might be interested in - a passive filter designed for NOS DACs. I've read a few reports and agree that NOS sounds a bit rough at the top end - I've wondered if this is due to amps or tweeters creating intermod products with the ultrasonics. So here's a design which I'm currently building to test my hypothesis - a 50dB stop-band passive anti-imaging filter. Ignore the 0.001 resistors, they're just there to see the effects of lossy inductors in running the sim.
Hello

Any new developments on your 7th order filter ?

Thank

Bye

Gaetan
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