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TubeDAC from Sheldon Stokes with PCM63
TubeDAC from Sheldon Stokes with PCM63
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Old 12th February 2019, 11:57 AM   #11
samoloko is offline samoloko  Bulgaria
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Big thanks to Sheldon Stoke to share this project http://quadesl.com/pdf/tube_dac.pdf

I like to activate thread again as we have very well regarded R2R dac

from todays point of view I would like to upgrade:

1) change digital receiver CS8412 to AK4113 / AK4118 - that way It will accept every possible spdif resolution with lowest jitter and will output IIS
2) change digital filter to @ 3lite 16 x digital Interpolation filter 16x Digital interpolation filter - drive PCM56, PCM58, AD1865 and so on up to 768 kHz
3) change output stage to Patrick IV converter
4) play with power supply

Last edited by samoloko; 12th February 2019 at 12:00 PM.
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Old 12th February 2019, 12:47 PM   #12
samoloko is offline samoloko  Bulgaria
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here Is digital input selector Spdif input board on TAOBAO help, how can i buy???

or

AK4118 digital receiver board SPDIF input switch IIS with IIS support XMOS sampl | eBay

Last edited by samoloko; 12th February 2019 at 12:58 PM.
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Old 12th February 2019, 02:09 PM   #13
Ken Newton is online now Ken Newton  United States
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I suggest that you look into hearing this DAC with it's digital filter removed - NOS style. You will need a bit of glue logic to connect the 3-wire digital audio input bus to the PCM63s without the DF chip. A small glue logic board should fit conveniently in place of the now vacant DF's location.

With CD, there will be a slight (approx. 11uS) inter-channel flat time delay as a result of not having a demultiplexed left/right data stream, but this will be inaudible via loudspeakers. It is equivalent to about 4mm (if my recollection isn't faulty) of physical path length arrival difference between each loudspeaker and your ears. Certainly there is more than an 4mm path length difference between your speaker set-up right now. Also, unless you listen with your head in a vise and equidistant from each speaker, you are already experiencing more than an 4mm offset while in your listening chair.

Last edited by Ken Newton; 12th February 2019 at 02:21 PM. Reason: clarity and typos
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Old 12th February 2019, 10:06 PM   #14
jean-paul is offline jean-paul  Netherlands
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So effectively only the DAC chips remain?
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Old 13th February 2019, 01:19 AM   #15
Ken Newton is online now Ken Newton  United States
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The DIR chip and the DAC chips, yes. The glue logic connecting the two.
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Old 13th February 2019, 05:23 AM   #16
jean-paul is offline jean-paul  Netherlands
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Also the DIR will go for a AKM type and samoloko even wants to have other DAC chips....so it is about those tubes I think. CS8412 is old news compared to modern DIRs and no tube in this world can improve its jitter If it is just the PCM DAC chips that will be reused I can tell that is not going to happen unless you leave them on the original PCB. These PCM63 very often die when removed from a PCB. Even with pro gear I never succeeded in having them removed without damage. A few weeks ago I had the same issue with an old PCM63K DAC and decided to give it away as it really costs less time to build a better performing new DAC. A DAC nowadays does not need tubes so it will be cheaper, smaller, less power hungry and it will accept high res material and it will sound better too.

So I would suggest to leave this 1997 design alone and build something completely new as it already is mostly a new setup. Make it a compact one board solution too as old PCB's never are reused practically. Of course the new design can be compared with the old DAC and then let the ears decide. I think you can build a new DAC for 100$ without the casing.
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Last edited by jean-paul; 13th February 2019 at 05:40 AM.
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Old 13th February 2019, 08:28 AM   #17
samoloko is offline samoloko  Bulgaria
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Quote:
Originally Posted by jean-paul View Post
Also the DIR will go for a AKM type and samoloko even wants to have other DAC chips....so it is about those tubes I think. CS8412 is old news compared to modern DIRs and no tube in this world can improve its jitter If it is just the PCM DAC chips that will be reused I can tell that is not going to happen unless you leave them on the original PCB.
Hi jean paul,

having not so expensive digital selector based on AKM (I have shown In ubove post) Including all type sources like coax, fiber and usb and with LCD display as a bonus and getting IIS from front end and feeding 3lite 16 x digital filter which do as well Fifo reclocking Is what I think of ultimate solution for almost every R2R dac, not just this.
please anyone, feel free to correct me If that Is not the case
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Old 14th February 2019, 09:40 AM   #18
ihear21khz is offline ihear21khz  Malaysia
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We have done an extensive amount of experimentation with the SDS Dac and there are many little things you can do to make it sound better. We modified ours and several others to the point that we could no longer use the original PCB / PCB layout. What we use today is a very radical new layout for what is essentially the same signal circuit but optimized around the PCM1704, NOS and transformers instead of tubes for the output.

One of the simplest things that you can do to improve the performance of what you have right now is to fit a Tent Labs' XO Clock and matching power supply. The quality of the decoupling caps to the pcm63 chips is also critical and you can use good smds (COG was the rage then) soldered right on the appropriate pins of the dac chips.

On the digital input side you can bypass the small 0,22uf film cap as it is highly unlikely that there will be any DC at the SPDIF output of your CD transport.

You can also use very thin solid core wires to replace the clock and data lines between the DF and the Dacs. Note, that ALL of them must be EXACTLY the same length to connect the DF's BCK, WCKO, DOL and DOR pins to the PCM63 chips. Cut off the existing tracks on the PCB close to the pins of the DF and PCM63s. Some may say that it will be impossible to hear the difference.....well they can believe what the want.

I don't think changing the DIR chip to anything more than an CS8414 (you also have the change the cap and resistor for the filter time constant or whatever on pin 20) will improve the overall sound very much. There are many other little detail things you can do but go with the XO Dac from Tent Labs first.

Cheers,
David
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Old 14th February 2019, 09:52 AM   #19
samoloko is offline samoloko  Bulgaria
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and where will you put that XO clock
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Old 14th February 2019, 10:24 AM   #20
jean-paul is offline jean-paul  Netherlands
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Especially the old Crystal receivers are the weakest link in older DACs. Changing them to a lower jitter DIR is one of the basic things to do first. No tube or transformer can improve higher than necessary jitter.

Please leave the input cap where it is as the industry has chosen to use RCA connectors for both analog and digital audio. This means analog DC carrying Signal can be coupled to the input transformer. Of course the SPDIF RCA can be changed for a better 75 Ohm BNC (at both sides), then the cap is not necessary.
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