NOS Burr-Brown PCM56 DAC with Tubes!!!

[L0rdGwyn]

I have no problem believing PCM56 sounds better than 1541A, it is a better DAC chip. And implementation is very important - more than the chip itself, I think.

P. S. I'm curious, have you tried adding negative feedback to your tube output stage? Or 6E6P does not have enough gain to support that?
And another noob question: what is the input transformer for? Is it just for 5x gain (assuming that's what 1:5 means)?

The gain of the 6E6P as designed with the 1:5 step-up transformer is just right for a 2Vrms output, and as a triode it is very linear without any feedback. Feedback could be added if the transformer secondary I/V resistor were increased, but that would increase the reflected load to the Iout pin of the DAC on the primary, which is undesirable. The transformer could also be rewired for 1:10. But for a tube gain stage without feedback, the distortion performance is quite good. I don't feel strongly about experimenting with feedback, -87dB H2 is quite low in level and all other harmonics are down below -100dB and the output impedance by way of the hybrid mu follower is good for me at ~120ohm.

The step up transformer provides voltage gain and performs the I/V conversion for the DAC via the reflected load to the primary winding by the 510ohm secondary resistor.

 

[Alexium]

I agree, that harmonic is very low. Actually, I've only really taken a close look at your measurements after asking the question, otherwise I probably wouldn't have asked it. Sounds like you've done the best job possible with such simple circuitry, and it's actually amazing how much performance you've gotten out of it. Thanks for the explanation!

What's the advantage of having the I/V resistor on the secondary side rather than the primary?

 

[L0rdGwyn]

I agree, that harmonic is very low. Actually, I've only really taken a close look at your measurements after asking the question, otherwise I probably wouldn't have asked it. Sounds like you've done the best job possible with such simple circuitry, and it's actually amazing how much performance you've gotten out of it. Thanks for the explanation!

What's the advantage of having the I/V resistor on the secondary side rather than the primary?

Putting the I/V resistor on the secondary can help snub any ringing of the SUT while also providing the I/V conversion. Most say the sound is better this way as well.

 

[audio2design]

Nice work!

 

[AnalogSteph]

At the very least, it seems you've got this commercial $1500 monstrosity beat. And I assume the USB interface will accept at least 192 or even 384 kHz, so you can do oversampling in software with the trusty SoX resampler to your heart's content (which is likely to beat most every filter integrated into DAC ICs anyway). At that point you can also easily stay away from 0dBFS+ levels.

 

[L0rdGwyn]

At the very least, it seems you've got this commercial $1500 monstrosity beat. And I assume the USB interface will accept at least 192 or even 384 kHz, so you can do oversampling in software with the trusty SoX resampler to your heart's content (which is likely to beat most every filter integrated into DAC ICs anyway). At that point you can also easily stay away from 0dBFS+ levels.

Small victories something is wrong with that DAC, 1.4% THD at 2Vrms is horrendous!

Here is a link the the JLSounds USB module I am using, very flexible design for this application.

I2SoverUSB - I2S over USB Audio

 

[Alexium]

I assume the USB interface will accept at least 192 or even 384 kHz, so you can do oversampling in software with the trusty SoX resampler to your heart's content (which is likely to beat most every filter integrated into DAC ICs anyway)

That is a very interesting point. I've heard that hi-res music sounds better compared to 44/16 not because we can actually hear the improvement, but because the hi-res capable DACs, for example PCM1794, work better at high sampling rates. I can't back it up because I don't actually hear any difference, but the idea sounds very plausible.

 

[fcdvpds]

Thanks! You know I had originally set out to build something similar with the TDA1541A, but that chip is a little more finnicky and expensive, so I thought PCM56 is a better place to start experimenting.

But I was very curious to hear a good implementation of the TDA1541A - I ended up purchasing a TDA1541A-based DAC from a small Serbian company called Audial, the DAC is the S5, designed by Pedja Rogic. Also NOS R2R, however no tubes (transimpedance amplifier I/V stage) and transformer coupled outputs.

It is a kick ass DAC, and I am happy to say my PCM56 design compares very favorably to it! In fact, the noise floor of my own is a bit lower. Two different flavors, one goes in my two-channel system, the other for my headphone system

View attachment 158790

Hi! Which source you use with the Audial S5? I have an Audial S4 and it sounds really good connected via Coaxial to my CD player but the USB connected to my Macbook Pro sounds very "tense", not good at all. I suppose it is the computer noise.

 

[L0rdGwyn]

Hi! Which source you use with the Audial S5? I have an Audial S4 and it sounds really good connected via Coaxial to my CD player but the USB connected to my Macbook Pro sounds very "tense", not good at all. I suppose it is the computer noise.

Hey there - I run it either connected directly to my PC via USB or out of an Innuos ZENMini MK3 music server, also USB. Sounds great to me in either case! USB is preferred as it runs the TDA1541A in simultaneous data protocol. Maybe ask Pedja about it, he is the expert of course.

 

[L0rdGwyn]

I received today some new Burr-Brown chips, the famous PCM63P-K. Getting quite hard to find, I am planning to build a new NOS DAC using a pair of these in parallel per channel with fully passive output using transformer I/V conversion, which is a battle of compromises between DAC load, output voltage, and output impedance.

 

[JimmyBuckets]

There is only one way to listen to the tube'd DAC, using more tubes obviously. Listening to the classic HD650 with my 6A5G SET amplifier.

View attachment 158765

Holy cow beautiful! I bet it sounds amazing

 

[restorer-john]

I received today some new Burr-Brown chips, the famous PCM63P-K. Getting quite hard to find

That's because they are likely, unfortunately 100% fake.

Why do people keep falling for this? The selection K stamp was always in line and the fab was not PHL, it was Japan. And the date, they killed the '63 before 2000, not after. Your date code is showing 40th week 2000.

It's likely just a normal PCM-63, re-silk screened..

 

[JimmyBuckets]

That's because they are likely, unfortunately 100% fake.

Why do people keep falling for this? The selection K stamp was always in line and the fab was not PHL, it was Japan. And the date, they killed the '63 before 2000, not after. Your date code is showing 40th week 2000.

It's likely just a normal PCM-63, re-silk screened..

Aren't you full of cheer this morning . It's crazy how much people know on this forum.

 

[restorer-john]

Aren't you full of cheer this morning . It's crazy how much people know on this forum.

The selection stamp is way out of line. Like too far out for BB. It looks fully fake, like the single and double crown TDA-1541 stamps you see.

 

[L0rdGwyn]

That's because they are likely, unfortunately 100% fake.

Why do people keep falling for this? The selection K stamp was always in line and the fab was not PHL, it was Japan. And the date, they killed the '63 before 2000, not after. Your date code is showing 40th week 2000.

It's likely just a normal PCM-63, re-silk screened..

I'm not concerned about it. More important to me was to have four chips from the same batch. Of course if they were re silk screened, I have no way of knowing that they are, so I'll just have to live in blissful ignorance. I've seen measurements have shown the batch designations are not all that reliable anyway.

 

[L0rdGwyn]

Aren't you full of cheer this morning . It's crazy how much people know on this forum.

Being full of cheer is antithetical to being an audio forum member, you learn this over time.

 

[JimmyBuckets]

The selection stamp is way out of line. Like too far out for BB. It looks fully fake, like the single and double crown TDA-1541 stamps you see.

I was just busting balls. I have no idea. I was in the cigar business for a long time, and people would come in all excited about the "Cuban" cigars they had just bought. It was a similar process of showing them unfortunately that 99% of the time they were fakes.

 

[JimmyBuckets]

Being full of cheer is antithetical to being an audio forum member, you learn this over time.

For sure. I was telling someone the other day that to be a true audiophile, you spend more time trying to hear what is wrong with your system, than listening to music. As a younger guy I spent lots of money chasing the perfect system. This will date me, but at the height of my madness I took out a small loan to buy some Von Schweikert VR-4's. I think I was running them off the First Watt Aleph 30 for the mids and highs while running the bottom half off an Adcom 5800 (also designed by Nelson Pass if memory serves). I was running a Benchmark DAC-1 as my pre and dac. I used a Pioneer stable platform player as my cd transport. I spent a few more years swapping components around trying to find what I was looking for. Eventually I cancelled my subscription to all the audio mags and dropped out of the forums for the most part, and sold my rig without replacing it. High end audio ruined music for me. When I am on this forum...it's the old "when in Rome..." Some I agree with, some I don't, it's not important enough to fight about. The only "rig" I have now is for headphones. RME DAC with some DT1990s. I have a few other sets of headphones, but I bought them because I think they are cool, not so much to reach audio Nirvana. Maybe this makes no sense, but now if I buy something, it's for what is more so than what it does. This was an over share, but oh well Rock on!

 

[L0rdGwyn]

For sure. I was telling someone the other day that to be a true audiophile, you spend more time trying to hear what is wrong with your system, than listening to music. As a younger guy I spent lots of money chasing the perfect system. This will date me, but at the height of my madness I took out a small loan to buy some Von Schweikert VR-4's. I think I was running them off the First Watt Aleph 30 for the mids and highs while running the bottom half off an Adcom 5800 (also designed by Nelson Pass if memory serves). I was running a Benchmark DAC-1 as my pre and dac. I used a Pioneer stable platform player as my cd transport. I spent a few more years swapping components around trying to find what I was looking for. Eventually I cancelled my subscription to all the audio mags and dropped out of the forums for the most part, and sold my rig without replacing it. High end audio ruined music for me. When I am on this forum...it's the old "when in Rome..." Some I agree with, some I don't, it's not important enough to fight about. The only "rig" I have now is for headphones. RME DAC with some DT1990s. I have a few other sets of headphones, but I bought them because I think they are cool, not so much to reach audio Nirvana. Maybe this makes no sense, but now if I buy something, it's for what is more so than what it does. This was an over share, but oh well Rock on!

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.

 

[TCD333]

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