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Old 28th April 2015, 09:09 PM   #21
Pano is offline Pano  United States
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The Best DAC is no DAC
What does the DSD waveform look like? I've never looked at it. Class-D is usually a square wave with variable duty cycle.
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Old 28th April 2015, 09:36 PM   #22
nironiro is offline nironiro  Croatia
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Looks similar
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Old 28th April 2015, 10:20 PM   #23
supra is offline supra  Australia
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Originally Posted by giannettino View Post
We have discussed that in Italy for many weeks.....if you can..take a look to jlsounds usbi2s interface..with double proper power supply..(LT3080 based in most of our cases)..the results can be stunning (HQplayer as "engine")
Sorry for my english...
G
Can you tell us more about this, maybe a circuit?
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Old 28th April 2015, 11:07 PM   #24
Ken Newton is offline Ken Newton  United States
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Default DSD utilizes a DAC

In a 1-bit digital signal encoding/decoding system, such as DSD, the system only needs to represent two discrete amplitude states. Call those two states high and low, or 1 and 0, or positive going and negative going, or whatever, but only two states need be recorded, and later reproduced. Because of that, there isn't the need for most of the circuitry (resistor networks and such) required for multibit digital signal conversion. A simple logic gate or some other two-state driver circuit could form the DAC circuit for 1-bit decoding. One consequence of 1-bit encoding/decoding is that is creates a great deal of quantization noise, but that can be moved out of the audible band. In short, functionally, there is a DAC circuit even with bare bones DSD playback.

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Old 29th April 2015, 01:06 AM   #25
abraxalito is offline abraxalito  United Kingdom
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You still do have a DAC, just its not called a DAC, its your digital signal's buffer as Ken points out just above.

The downside of using just a digital chip for your DAC is that it has about 6dB PSRR on average - meaning your digital power supply's quality is the limitation. This could easily be the cause of your bass lightness. The other issue is jitter - a 'raw' DSD signal is inordinately sensitive to jitter. It can be ameliorated through using a transversal filter - like Miska has shown in one of his DSD DAC schematics.
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Old 29th April 2015, 01:28 AM   #26
hazard500 is offline hazard500  Australia
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Originally Posted by abraxalito View Post
You still do have a DAC, just its not called a DAC, its your digital signal's buffer as Ken points out just above.

The downside of using just a digital chip for your DAC is that it has about 6dB PSRR on average - meaning your digital power supply's quality is the limitation. This could easily be the cause of your bass lightness. The other issue is jitter - a 'raw' DSD signal is inordinately sensitive to jitter. It can be ameliorated through using a transversal filter - like Miska has shown in one of his DSD DAC schematics.
The digital buffer is a buffer. It's input is a digital signal and its output is the same digital signal. So where is the digital to analogue conversion that you are talking about?

The point is this - the digital output from the USB receiver is normally fed to a DAC. I am not feeding it to a DAC. I am trying something different, if it hasn't been tried before. As per Wikipedia (so it must be right!)

"The process of creating a DSD signal is conceptually similar to taking a one-bit delta-sigma analog-to-digital (A/D) converter and removing the decimator, which converts the 1-bit bitstream into multibit PCM. Instead, the 1-bit signal is recorded directly and in theory only requires a lowpass filter to reconstruct the original analog waveform. In reality it is a little more complex, and the analogy is incomplete in that 1-bit sigma-delta converters are these days rather unusual, one reason being that a one-bit signal cannot be dithered properly: most modern sigma-delta converters are multibit."

To re-iterate. I am not using a sigma-delta convertor. Or any other converter. I am feeding a digital signal (DSD, or PDM) into a band-width limited transformer (hence acting as a low pass filter) to reconstruct the original analog waveform. Any conversion (if you want to call it this) happens in the transformer. Same as Class D amp. PWM signal is fed to a low pass filter then to the speaker. Where is the DAC in a Class D amp?

Anyway let's not argue about semantics. Call it a DAC, or not a DAC. Whatever you like. But i am trying to minimise the signal path in my system. Because I feel like it. And I can (well if this works, I can). You point about about power supploies is valid, and I know I need a better p-s. WIll a better p-s improve the bass? That's an interesting point, I can hear noise at the moment that I need to deal with but I hadn't considered the impact of the p-s on bass response.

Also, I don't know what a transversal filter does. Do you have a link?
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Old 29th April 2015, 01:33 AM   #27
abraxalito is offline abraxalito  United Kingdom
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The D/A conversion occurs when you cease to interpret the signal as a digital one and begin to interpret it as an analog signal. So that happens at the output of your buffer because you're not feeding it into a digital circuit downstream, rather an analog one.

I'll have a hunt around and see where I found Miska's circuit - its an implementation of a 32 tap transversal filter.
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Old 29th April 2015, 01:43 AM   #28
maxlorenz is offline maxlorenz  Chile
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WIll a better p-s improve the bass?
A good PS will improve everything!

Good luck.
M.
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Old 29th April 2015, 02:27 AM   #29
counter culture is offline counter culture  United States
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The digital buffer is a buffer. It's input is a digital signal and its output is the same digital signal. So where is the digital to analogue conversion that you are talking about?
So if there's no digital to analog conversion, what are you going to listen to?
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Old 29th April 2015, 05:16 AM   #30
abraxalito is offline abraxalito  United Kingdom
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Here's the link to Miska's zipped design info for his transversal DAC : http://www.signalyst.com/doc/Dsc1-revA.zip

<edit> I'd missed your question about the classD amp. ClassD amps are purely analog so there's no need for a DAC, as they have nothing 'digital' in them.
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