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PostPosted: Sun Sep 24, 2017 12:34 am 
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Does anyone know what type of conversion technique is used in the Chord Hugo 2 (Multibit, Delta Sigma. or a combo of both?). A reviewer friend said to me, he interviewed the designer, and what he understands what was told to him, that it has none, and it's all done in the FPGA??? if so what other use this??

Cheers George

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PostPosted: Sun Sep 24, 2017 6:12 pm 
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Hi,

georgehifi wrote:
Does anyone know what type of conversion technique is used in the Chord Hugo 2 (Multibit, Delta Sigma. or a combo of both?). A reviewer friend said to me, he interviewed the designer, and what he understands what was told to him, that it has none, and it's all done in the FPGA??? if so what other use this??


I think I'll let Chord explain it:

Image

This shows the Chord Hugo 1/TT, but one has little reason to doubt Hugo 2 will be relatively similar.

Detailed PCB pictures here make it very clear what is happening:

http://www.qobuz.com/be-fr/info/Hi-Fi-Guide%2FIn-English%2FDAC-Chord-Hugo-a-candy-coloured175851

Note that this system uses a single fixed 104.7542MHz clock, without additional clocks, except for te two USB interfaces.

An FPGA is basically just a assembly of uncommitted logic blocks that can be made into anything. In the DP-777 we use a small FPGA to implement the memory buffer and a lot of other housekeeping logic.

The XILINX Spartan and Artix FPGA's have very strong build in DSP blocks, which one can use for digital filters and delta sigma modulators.

Ciao T

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PostPosted: Sun Sep 24, 2017 8:14 pm 
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Ok, I can see a dac for each channel (4E Pluse Array) a "code" name for whatever that is????

Cheers George

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PostPosted: Mon Sep 25, 2017 4:39 am 
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Hi,

georgehifi wrote:
Ok, I can see a dac for each channel (4E Pluse Array) a "code" name for whatever that is????


You can see it clearly in the closeup of the FPGA in the qbuz article.

The IC's have Z75 written on them (they look like Fairchild "Tinylogic" to me, in fact I use ones that look identical) and are accompanied by a resistor and capacitor each. Drawing a suitable schematic is left as homework exercise for the interested.

Ciao T

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PostPosted: Mon Sep 25, 2017 6:23 am 
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Delta Sigma
http://www.ti.com/lit/ds/sles081f/sles081f.pdf

Cheers George

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PostPosted: Mon Sep 25, 2017 8:41 am 
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Hi,

georgehifi wrote:


Well, the DAC in this is not used, only the USB to I2S functionality.

The 4-Element DAC is bottom right, four identical circuits, tiny chips, a small voltage regulator chip off to the side.

Image

Ciao T

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PostPosted: Mon Sep 25, 2017 8:23 pm 
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So are they doing a secrete men's business thing then, can you shed any more light on it?

Cheers George

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PostPosted: Tue Sep 26, 2017 10:37 am 
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Hi,

georgehifi wrote:
So are they doing a secrete men's business thing then, can you shed any more light on it?


It should be crystal clear from what has been shown.

Ciao T

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PostPosted: Tue Sep 26, 2017 11:05 am 
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Crystal??? (hint??) Cirrus???

I can't read that, and I've got a high rez monitor.


You do not have the required permissions to view the files attached to this post.

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PostPosted: Tue Sep 26, 2017 12:57 pm 
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Hi,

georgehifi wrote:
Crystal??? (hint??) Cirrus???

I can't read that, and I've got a high rez monitor.


NC7SZ175 - in other words a Flip-Flop, followed by R & C forming a lowpass.

Ciao T

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PostPosted: Tue Sep 26, 2017 1:37 pm 
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'cmon, what year is it?
Discrete implementations of D-S are reality, already done several times in DIY. The problem is they are closed-source, as they use FPGA proprietary software (internal cores and blocks implementation, as well as filter code generators), so you both can do it in a few clicks for basic D-S DAC and unable to publish it anyhow.

Ah, and beyond that simple D-S modulator you could play with multilevel D-S, "ring dac" et cetera.
Yet, some prefer the really basic in structure D-S modulator running at very high speed. Pure 1-bit at 100MHz modulation should be very nice.
Throw additional output gates, shift the phase between 'em and... you've got yourself something more than a 1-bit DAC :) you might want to see it in a bit of finite impulse response filter if you guess the coefficients :)

D-S design is a lot of fun!

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