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NOS Burr-Brown PCM56 DAC with Tubes!!!

TCD333

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I don't identify with the term audiophile any more, I am in this thing for the music, and I like to build shit. If the shit I build makes the music more fun and engaging to listen to, that's a plus. But obsessing over "the timbre of a violin" or the "stridency of the highs" is not my thing. When I finish prototyping something, I listen to it and it is categorized as "good" or "bad" based on whether or not it has me vibing with the music. I don't listen to audiophile recordings, I listen to the music I like, even if the quality is crap. If you can break the cycle of audio nervosa and instead focus on the music, the enjoyment of this hobby goes up substantially and you can reach contentment, you might even be suddenly blown away by the quality of the gear you own, in my experience anyway.
You've done a really nice job on that DAC and it actually measures quite respectably for what it is. Well done.
WRT not identifying with audiophiles, 100% agree.
WRT PCM63, those DAC's can sound *really* good. I think I actually have at least 2 x original K grade floating around used in old projects here.
WRT best I-V for PCM63, my recommendation is run DAC into a grounded base stage BJT with collector cascoded into cathode of a tube. Run *lots* of current
and it can sound staggeringly good.
Lastly, if you are using Jlsounds III for PCM63, this may be a slight compromise because LE is reclocked inside CPLD. Might be worth trying to re clock LE OP
directly from master clock but I have not done this or looked into it, don't use PCM63 anymore.

Terry
 
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L0rdGwyn

L0rdGwyn

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You've done a really nice job on that DAC and it actually measures quite respectably for what it is. Well done.
WRT not identifying with audiophiles, 100% agree.
WRT PCM63, those DAC's can sound *really* good. I think I actually have at least 2 x original K grade floating around used in old projects here.
WRT best I-V for PCM63, my recommendation is run DAC into a grounded base stage BJT with collector cascoded into cathode of a tube. Run *lots* of current
and it can sound staggeringly good.
Lastly, if you are using Jlsounds III for PCM63, this may be a slight compromise because LE is reclocked inside CPLD. Might be worth trying to re clock LE OP
directly from master clock but I have not done this or looked into it, don't use PCM63 anymore.

Terry

Thanks, I appreciate it. I'll give your I/V stage some thought. What chip are you using these days?
 

TCD333

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DAC's -> a/ Moon 430HA for it's flexibility of multiple IP's (sounds OK) b/ Whatever is coming through for repair or upgrades c/ Current project PCM1794 for a 'musical that measures' project d/ Sabaj A20D 2022 will be here shortly for a 'blameless measuring' constant or yardstick.
The PCM63 can sound really good, there are many little tricks to help it. I just wanted to move on to DS or native DSD type converter.
TCD
 
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L0rdGwyn

L0rdGwyn

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I finished designing and assembling the boards for my NOS PCM63 DAC. Running two PCM63 in parallel per channel, output of each is the parallel Iout pin of the two chips. Planning to again use Sowter SUT I/V with some sort of tube output stage, likely a buffer with the SUT wired 1:10. Put the Talema transformers on the boards this time around to save space.

PXL_20221126_210241733-2.jpg
 

Doodski

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I finished designing and assembling the boards for my NOS PCM63 DAC. Running two PCM63 in parallel per channel, output of each is the parallel Iout pin of the two chips. Planning to again use Sowter SUT I/V with some sort of tube output stage, likely a buffer with the SUT wired 1:10. Put the Talema transformers on the boards this time around to save space.

View attachment 246273
Wonderful. I like! Very pretty layout. (If a layout can be pretty...lol. geeking out on your stuff.)
 

Alexium

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That is indeed a very pretty layout, as well as a very pretty mask.
May I ask what software you're using for designing the PCB layout?
 
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L0rdGwyn

L0rdGwyn

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Did some testing of my parallel PCM63 DAC.

I configured the JLSounds I2SoverUSB module for PCM63, made connectors from the module to its power supply PCB and the left and right channel DAC boards.

Then I connected everything up in a janky way for the sake of testing. Since these PCM63 chips are pretty old, I put them in one at a time and tested along the way to ensure I would know if one was bad. Thankfully, they are all good to go.

Here is my sloppy test setup on a box. My desk is a disaster from so many simultaneous projects, but it is what it is.

PXL_20221129_232251875-2.jpg


I dialed in all of the 5V supplies, everything is working as intended.

For the sake of initial testing, rather than rigging up the Sowter I/V transformers, I just soldered in 68ohm I/V resistor dummy load. This would represent the primary impedance of the transformer in theory.

Here is a 1kHz FFT at -6dBFS output from the DAC at 96kHz sample rate.

PCM63 DAC 68ohm IV -6dBFS Right Channel.jpg


Pretty happy with that result.

So with all of that tested, I am going to move forward with ordering parts for my tube buffer stage. I have a healthy stock of NOS E182CC, planning to use them in a circuit like the below.

Tube buffer.png


The output is a transformer coupled cathode follower. Both sections wired in parallel and biased by the DCR of the transformer. Each triode has a 15mA/V transconductance, so it should perform well. I am planning to use Lundahl's LL2753 interstage transformer wired 1:1. It has a primary and secondary DCR of 150ohms, so I am looking at around a 350ohm output impedance from the DAC with this setup.
 
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