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Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
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Old 13th January 2021, 11:23 AM   #1291
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
Location: Haarlem, the Netherlands
Have a look here Downloads | Linear Audio and scroll down to "Design data package for Marcel van de Gevel's Valve DAC from Vol 13". Version 2.1 of the configuration file (the one programmed into the FPGA module that's on its way to Australia) uses the extension header as an I2S input.
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Old 13th January 2021, 03:24 PM   #1292
SonnyMarrow is offline SonnyMarrow  United States
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Wound all the inductors while I wait for other parts. I think my thumbs have arthritis now...
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Old 13th January 2021, 07:28 PM   #1293
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
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Getting back to the question about how to connect a Raspberry Pi to the I2S input of the original valve DAC (with configuration file version 2.1): I don't see the point of fancy reclocking boards with ultralow jitter/phase noise oscillators when the DAC has an asynchronous sample rate converter with a slow sample-rate-ratio estimator, like the original valve DAC has. The jitter of the signals driving the DAC core will in any case be determined by the simple balanced TPTG oscillator built around an ECC81.

I would therefore just connect the Raspberry Pi's I2S outputs straight to the valve DAC. Assuming a Raspberry Pi model 3B running Volumio, you can simply connect it like this:

Pi's pin 35 (GPIO19) to DAC's lrcki2sin (P9 pin 11)
Pi's pin 40 (GPIO21) to DAC's datai2sin (P9 pin 5)
Pi's pin 12 (GPIO18) to DAC's bcki2sin (P9 pin 9)
Pi's pins 14, 34 and 39 (subset of its GND pins) to DAC's ground (P9 pins 2, 4, 6, 8, 10, 12, 14 and 16)

and indicate to Volumio that it is driving a generic I2S DAC. The DAC's mutei2sin (P9 pin 3) has to be grounded. The DAC's sel4192in (P9 pin 1) can either be grounded permanently when only the I2S input is used, or be connected to an extra contact of the source selection switch so it only gets grounded when the I2S input is selected. The other pins of P9 need not be connected to anything as long as you don't require the raw DSD interface or the deemphasis.

Connecting more than one I2S source requires some kind of multiplexer or switch to funnel it through the single I2S input.
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Old 13th January 2021, 07:31 PM   #1294
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
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Quote:
Originally Posted by SonnyMarrow View Post
Wound all the inductors while I wait for other parts. I think my thumbs have arthritis now...
They look good! I hope your thumbs recover...
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Old 13th January 2021, 07:57 PM   #1295
Tix88 is offline Tix88  Italy
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Join Date: Jan 2015
I Marcel

How many meters of wire does it take approximately to wind the inductors? I have a 0.6mm silver wire coated with Teflon, could I also use it?
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Old 13th January 2021, 08:09 PM   #1296
SonnyMarrow is offline SonnyMarrow  United States
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Join Date: Dec 2016
It takes a lot. Not even accounting for the added thickness each time you add a layer of wire around the former, you would need at least 20 meters for the default number of turns. The center of the coil former is about 12mm in diameter, so circumference ~38mm, 130 turns for a set of inductors = about 5 meters. There are 4 sets of inductors, so 20 meters without even accounting for wire thickness. Probably going to be more like 30-35 meters.

Last edited by SonnyMarrow; 13th January 2021 at 08:12 PM.
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Old 13th January 2021, 11:21 PM   #1297
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
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Quote:
Originally Posted by Tix88 View Post
I have a 0.6mm silver wire coated with Teflon, could I also use it?
Definitely, if you have enough of it and if it fits on the coil formers. See SonnyMarrow's answer for the length.
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Old 13th January 2021, 11:29 PM   #1298
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by acg View Post
...to enable USB/HDMI/Optical inputs for the original ValveDac as well as the Rpi for streaming.
Assuming the optical input is a TOSLINK-input, that can go via one of the four DIX4192 inputs, you just need to add an optical receiver module and a decoupling capacitor for its supply (few euros).

How many signals do you want to multiplex/switch to the I2S input? Three, one from a USB interface, one from an HDMI interface and one from a Raspberry Pi? Do you need the mute, de-emphasis and raw DSD functions for any of those?
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Old 14th January 2021, 01:50 AM   #1299
acg is offline acg  Australia
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My SACD player outputs digital via HDMI, coax spdif or optical. I've not listened to any of those outputs to figure which is best and I am not even sure the DSD layers will be put out over anything but HDMI...actually pretty sure they are not. This digital stuff is all new to me...my mind has been in the analog realm building amplifiers, preamps and phonostages...this is my first digital project and my knowledge is a little short in terms of protocols (and other areas as well!). Apparently the DSD "signal" is available to be extracted from HDMI video signal, and something like this little board can do it. Well it has I2S, coax and optical out, so turns out would even be suitable for routing via an optical input. Would like to find a more 'single use' solution because this board has lots of unnecessary things, but it would certainly do to initially test things.

Something like this optical receiver?


USB input: perhaps this one

I2S switching would be nice for the USB interface, the HDMI interface and streaming from the Rpi. No idea on mute, de-emphasis or raw DSD functions...I will have to research just what they are.
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Old 14th January 2021, 05:12 AM   #1300
acg is offline acg  Australia
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Join Date: Oct 2013
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See attached for two things: a comparison of the Linear Phase vs Gaussian 6th order filters for Fc = 82kHz, and the spreadsheet used to calculate the component values.

Note that this spreadsheet is useful only for current sources like the ValveDac and the DSDOnly variant...voltage source output stages need not apply. Both the 0.05deg Equiripple Linear Phase and Gaussian to 6dB filters are in the spreadsheet for all orders from 3rd to 6th and Marcels LC Interpolation method is used which means that filters can be calculated for different termination impedances (I am lowering the load impedance to improve the noise performance a little).

You enter your parameters in the yellow boxes and the green boxes give you the component values...it's that easy.

Standard source and termination impedances are 5600 and 375ohm differential respectively.


Anthony
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File Type: png Linear Phase vs Gaussian (Custom).png (183.8 KB, 59 views)
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File Type: zip ValveDac Custom Reconstruction Filters.zip (13.8 KB, 4 views)
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