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Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
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Old 17th November 2019, 03:59 PM   #361
MarcelvdG is offline MarcelvdG  Netherlands
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You could connect the raw DSD signal you want to test to an input of the filter board via a resistor (anything from 560 ohm to 2.2 kohm will do) and a DC blocking capacitor (preferably in the 10 uF to 100 uF range), leave the other input open and listen to the output signal. The output signal will be softer than line signals usually are and the filter will behave as an overdamped second-order filter, but that doesn't matter much for a simple functional test.
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Old 17th November 2019, 04:11 PM   #362
nautibuoy is online now nautibuoy  United Kingdom
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Marcel, have you picked up on this thread?

STAR Pure DSD DAC-Signalyst New

Maybe the CT7302PL gives you fresh options for a future Valve DAC (or discrete Silicon DAC)?

Ray
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Old 17th November 2019, 04:51 PM   #363
MarcelvdG is offline MarcelvdG  Netherlands
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Hi Ray,

Thanks for the link. I had heard about the existence of the CT7302 and other asynchronous sample rate converter chips with DSD outputs, such as the AK4137. In fact the CT7302 has an evaluation module that you could connect straight between any old S/PDIF source and the DSD-only version of the valve DAC (or any other DSD DAC):

http://www.comtrue-inc.com/images/CT...oard%20APN.pdf

For me, designing my own fifth- and seventh-order digital sigma-delta modulators and learning more about FIR filter design and FPGA configuration was part of the fun. If I ever make a new valve DAC, it will probably use a cheaper FPGA board and have the ASRC included in the FPGA.

Marcel
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Old 20th December 2019, 07:29 PM   #364
MarcelvdG is offline MarcelvdG  Netherlands
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Hi Ray, is there any news?
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Old 20th December 2019, 07:34 PM   #365
nautibuoy is online now nautibuoy  United Kingdom
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Quote:
Originally Posted by MarcelvdG View Post
Hi Ray, is there any news?
Hi Marcel, slow progress at the moment I'm afraid - too much else on my plate!

I have some leave over Christmas so I hope to make some more progress in the next week or two.

Sorry it's taking so long.
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Old 20th December 2019, 08:16 PM   #366
snax is offline snax  United Kingdom
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Hi Marcel / Ray.

The year has definitely been a hectic one.

I finished a contract recently and had time to populate some of the board.

Sorry for the amount of flux. I have read your warning, Marcel and it will be cleaned from the board before testing.

I have wound the pot cores and I am currently putting a KiCAD image together so I can do a home brew regeneration board.

Will post again when I have the regen board populated.
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Old 20th December 2019, 08:34 PM   #367
MarcelvdG is offline MarcelvdG  Netherlands
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It looks like it will be a challenge to mount those Russian 15 nF filter capacitors...
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Old 20th December 2019, 08:46 PM   #368
snax is offline snax  United Kingdom
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Hey Marcel,

They will stay on top of the board... its the 10uf under the board that I'm struggling with. I'm never one to shy away from a challenge and those SMD's were... satisfying!

I am using an AK4137 board that i picked up in Korea to convert PCM to DSD. It recognises the input correctly but I don't have any way of testing if the DSD256 output is working yet. It's on my bucket list of things to do.
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Old 20th December 2019, 09:06 PM   #369
MarcelvdG is offline MarcelvdG  Netherlands
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Ah, I didn't realize those were the output coupling capacitors. I thought my capacitors were big, but they are nothing compared to these!

You probably already know this, but you can functionally check a raw DSD output with an RC low-pass filter at 20 kHz or so, for example 820 ohm and 10 nF or 2.2 kohm and 3.9 nF. Connect the DSD output to the filter, AC couple the filter's output to an amplifier with volume control using a coupling capacitor of a few microfarads, make sure not to turn up the volume too high and check if you have sound. The reason for not turning up the volume too high is that at high volumes, the remaining ultrasonic quantization noise might damage your tweeters or your amplifier.
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Old 20th December 2019, 09:15 PM   #370
snax is offline snax  United Kingdom
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I didn't but I do now.
It been a bit of a steep learning curve with a few moment of sobriety to keep my interest.
Cheers.
Have a fabulous Christmas if I don't post before.
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