Digital.

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pre65
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#46 Re: Digital.

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Ray P wrote: Sat Sep 14, 2019 9:32 pm
I know of one valve DAC but there may be others.
Would it be possible to divulge the identity of this remarkable piece of kit ?
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#47 Re: Digital.

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pre65 wrote: Sat Sep 14, 2019 9:46 pm Would it be possible to divulge the identity of this remarkable piece of kit ?
Of course, though it's not a piece of kit but a design for DIY building. It has a valve-based delta-sigma (or sigma-delta) core. There's a thread about it on DIY Audio;

https://www.diyaudio.com/forums/digital ... -13-a.html

As far as I can tell the designer is the only person to have actually built one but it seems to have been well received at a Dutch audio meet. That may be changing though as a couple of us are working on projects to build a revised version. The original used an FPGA for upsampling and deriving (from PCM)the SDM data stream needed for the cores but HQ Player can take care of all that so the designer has produced a revised design that just accepts SDM (DSD) data. We've recently taken delivery of some custom-made 4 layer (and large and expensive) PCBs and I hope to get the surface mounted stuff (clock and data handling) soldered shortly.

Another guy is doing some new PCB designs using a modular approach that should make for an easier build.
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#48 Re: Digital.

Post by Ray P »

The designer of the valve DAC has also been experimenting with an unconventional silicon based decoder;

https://www.diyaudio.com/forums/digital ... range.html

as is another chap;

https://www.diyaudio.com/forums/digital ... stors.html
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#49 Re: Digital.

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I have read that article in Linear Audio and its impressive. But call me cynical that any design that includes a FPGA could really be called a valve dac, more of a dac with valves.
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#50 Re: Digital.

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Nick wrote: Sun Sep 15, 2019 10:49 am I have read that article in Linear Audio and its impressive. But call me cynical that any design that includes a FPGA could really be called a valve dac, more of a dac with valves.
Semantics to some extent but the FPGA operates solely in the digital domain and you could choose to send the data from it to a decoder or do something else with it so I don't really see it as a core element of the actual decoder - it essentially just doing ASRC. In the design, the derivation of an analogue signal happens with the valve-based DS cores.

In fact, the project I'm embarking on dispenses with the FPGA module completely but of course it still uses silicon in the clock and data management elements.

Still, in my book it is truer to the term valve DAC than a conventional IC based DAC that just happens to have some sort of valve-based circuit attached to its outputs - in that scenario the valves only ever see an analogue signal and have no part in the 'conversion' from digital to analogue.

Anyway, it'll be interesting to see how it turns out and, depending on that, might make an interesting exhibit at next year's Owston event.
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#51 Re: Digital.

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I guess that as the cat is out of the bag I'll start a project thread for the valve DAC.
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#52 Re: Digital.

Post by Greg »

Sorry, forgot another thing. After raspberry Pi I use a microRendu. It was a great improvement but not as good as the Devialet built in stage I now use. microRendu remains a good bit of kit. The guy I sold it to is chuffed to bits with it.
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#53 Re: Digital.

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Ray P wrote: Sun Sep 15, 2019 11:27 am
Nick wrote: Sun Sep 15, 2019 10:49 am I have read that article in Linear Audio and its impressive. But call me cynical that any design that includes a FPGA could really be called a valve dac, more of a dac with valves.
Semantics to some extent but the FPGA operates solely in the digital domain and you could choose to send the data from it to a decoder or do something else with it so I don't really see it as a core element of the actual decoder - it essentially just doing ASRC. In the design, the derivation of an analogue signal happens with the valve-based DS cores.

In fact, the project I'm embarking on dispenses with the FPGA module completely but of course it still uses silicon in the clock and data management elements.

Still, in my book it is truer to the term valve DAC than a conventional IC based DAC that just happens to have some sort of valve-based circuit attached to its outputs - in that scenario the valves only ever see an analogue signal and have no part in the 'conversion' from digital to analogue.

Anyway, it'll be interesting to see how it turns out and, depending on that, might make an interesting exhibit at next year's Owston event.
I too will be interested in how it sounds and look forward to reading how you get on, BUT the pedant in me still thinks that calling a sigma-delta decoder a DAC, while true in the sense that it converts a digital signal into an analogue one is rater misleading in the sense of the original question "Just out of interest Ray, is there a valve DAC without any DAC chips ?". You can decode SD with a resistor and a cap because all the hard work is done up stream converting a multibit signal into a possibly noise shaped single bit stream. To me in the context of the question you would expect a black box with i2s on one side and analogue on the other to be the DAC. Correct me if I am wrong, but that's not what you have here.
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#54 Re: Digital.

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Nick wrote: Mon Sep 16, 2019 3:03 pm I too will be interested in how it sounds and look forward to reading how you get on...
Yes and thanks, it'll be an interesting journey. I'm starting with an open mind rather than an assumption that valves will automatically be better but it'll be fun to do something other than the usual modern ESS/AKM or NOS legacy chip type projects that seem to be everywhere. I enjoy this hobby as much for the building as the listening.

BTW, we had to order a minimum of 5 PCBs so we have two spare boards should anyone be tempted at any time...
Nick wrote: Mon Sep 16, 2019 3:03 pm ...BUT the pedant in me still thinks that calling a sigma-delta decoder a DAC, while true in the sense that it converts a digital signal into an analogue one is rater misleading in the sense of the original question "Just out of interest Ray, is there a valve DAC without any DAC chips ?". You can decode SD with a resistor and a cap because all the hard work is done up stream converting a multibit signal into a possibly noise shaped single bit stream. To me in the context of the question you would expect a black box with i2s on one side and analogue on the other to be the DAC. Correct me if I am wrong, but that's not what you have here.
Like I said we're talking semantics and ultimately the points aren't that important but this is a 'valve DAC without any DAC chips', you just have to feed it the correct digital data, which in this case is SDM/DSD as it won't decode i2s/PCM - AFAIK there's nothing that defines a DAC as having to be suitable for PCM data? Whether you feed it with 'native' SDM or you choose to derive it from some other format, whether an FPGA ASRC type function on the front -end or something upstream like HQ Player doing a similar function is, to me, a separate issue.

While we're in the general vicinity of delta-sigma processing its maybe worth thinking about how a mainstream delta-sigma DAC chip functions with PCM data.

Anyway, the Valve DAC project is what it is so from my perspective the most important thing is to try and build it, get it debugged/tested and see what comes out of it.
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#55 Re: Digital.

Post by Nick »

While we're in the general vicinity of delta-sigma processing its maybe worth thinking about how a mainstream delta-sigma DAC chip functions with PCM data.
That's sort of my point, DSD and DS DAC's convert the PCM into a bit stream that allows simple conversion to analogue. In your case, you are doing all the PCM to bit stream conversion "elsewhere" so I regard the majority of the DAC in this case as being "elsewhere".
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#56 Re: Digital.

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Nick wrote: Mon Sep 16, 2019 8:21 pm That's sort of my point, DSD and DS DAC's convert the PCM into a bit stream that allows simple conversion to analogue. In your case, you are doing all the PCM to bit stream conversion "elsewhere" so I regard the majority of the DAC in this case as being "elsewhere".
Whereas I consider that those DACs have a load of other stuff added to them so they can accomodate other data types - the 'DAC' is where the conversion takes place.

Six of one and half a dozen of another...

Shall we leave it there?
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