Building the ultimate NOS DAC using TDA1541A

[tubee]

I find it amazing that one would come up with the audio equivalent of a Heath Robinson design when all one need do is change a tap or two.

Rfbrw: The added clock-pcb is only 68 by 95 cm, has a lot of (charcoal-heated) iron coils on it, and it was a good thing i live nearby a cable-manufacturer. (lol)

[Terry Demol]

Originally posted by -ecdesigns-
Hi all,

Still catching up answering posts,


Terry Demol [post#505]

I must admit I was sceptical about these clock upgrades, just like I was about using tubes. But now I heared what difference only a simple external clock module can make, I fully agree with you

I read about the slaved transport on the internet, some time ago. Very interesting, indeed it's logical to have the master clock as close to the DAC as possible to reclock the I2S signals. So basically, correct me if I'm wrong, you will have to feed the 16 MHz master clock back to the transport for it's internal servo mechanism and I2S timing. If so, won't this affect servo stability / servo noise? Transporting a 16 MHz clock across a interlink seems quite critical. But I am still very interested in how it improves sound quality.

EC,

If you use the master clock in DAC and send it back to transport,
you can use std 8414 receiver chip and simply reclock right at the
DAC chip with a D flip flop.

Theoretically, with this setup there is no need to go to I2S because
the whole system is synchronous. Any jitter introduced by the SPDIF
I/face will be eliminated when reclocked by master XO at DAC chip.

It's really pretty simple, you just have to get the timing right for
D flip flop.

If I remember correctly, Guido T reclocked all the lines coming
into DAC but we just did the LE on PCM63.

The best, ie; lowest jitter setup has the master clock right at the
DAC and a very low noise separate power supply for it. I
recommend a small discrete shunt reg fed with it's own split bobbin
transformer.

Also I think you need to be careful how clock is sent back to
transport to prevent noise coupling.

Cheers,

Terry

[ErikdeBest]

The added clock-pcb is only 68 by 95 cm

Have you made it with valves that it is so big? Sure it was hard to fit it into the CD cabinet

[tubee]

My home itself is the cabinet of cdp. Pathway to kitchen is righthand along CDM-1. I have to beware of the H-F cables with the hot coffee...

[rfbrw]

Originally posted by tubee


Rfbrw: The added clock-pcb is only 68 by 95 cm,

Should be able to fit the entire dac in that space.

[a333bt]

Originally posted by rfbrw



Should be able to fit the entire dac in that space.

I agree with that. http://www.diyaudio.com/forums/images/icons/icon10.gif
Talking

[-ecdesigns-]

Hi Terry Demol,

thanks for your reply [post#512]


I finally received the 26LS31 and 26LS32, they seem to work fine, I also did experiments using 2 differential drivers in parallell to increase output current. Since a network cable has 4 twisted pairs, I decided to add the master clock to the differential interface as well. Had some doubts if it would work (16MHz) but it did. So now we have MCK, BCK, WS and DATA on one single computer network cable.

Measurements and listening tests showed I2S also had jitter, at least on my sony transport, I already reclocked the I2S signals from the CS8412 on the transport side using 2 cascaded D-flipflops. I buffered the master clock very close to the crystal oscillator (74HC132 SMD), then I used this buffered signal for clocking the transport, D-flipflops and the differential interface. I used a thin coax cable of approx. 2.5mm diameter for making the connection from the buffer to the reclock circuit,

I also added a separate power supply for the mini crystal update based on a bandgap reference diode and a separate 12V external battery supply (only for the oscillator) as it draws little current, this should reduce master clock jitter a bit. Oscillograms show that reclocking works. I have noticed sound quality always benefits from a clean signal leaving the transport, that's why I don't like to use the SPDIF signal on the interlink anymore, even when it's reclocked in the DAC.

On the receiving side it's a different story, some jitter appears again (I now used 2.5 meters of computer network cable). Remarkable was that MCK (16 MHz) was relatively clean, I have no explanation for this yet. Using the I2S signals as they are, already greatly improved sound.

Then I decided to reclock the I2S signals again (DAC side), with MCK from the differential interface, sound again improved, and not just a bit. However, oscillograms still showed slight 2 phase jitter on BCK (similar to asynchronous reclocking). Then I only reclocked BCK (DAC side). Oscillograms now showed a stable BCK at the highest timebase setting (X10). Interference (within one chip) using these high frequencies shouldn't be underestimated. The signals surely not follow the neat diagrams drawn, they seem to have a mind of their own. So the only way to be sure is to keep measuring and listening.

The octal D-I DAC then started to show what it's capable off, seems it just needed a clean clock signal. If a setup (DAC) should be able to transmit the soul of music as maxlorenz described it [post#375], this one does, it comes over loud and clear. Sound is so smooth now, there is an abundance of crystal clear details, midrange sounds so beautiful. And I never heared bass reproduced so accurate on my set.

Problem now is, I keep pausing and scanning the same tracks to make sure wether a specific sound (that I didn't notice with the "old" setup) is actually on the CD or produced by ambient noises. Last night it seemed like a thunder storm was building-up (rumbling), so I already started to pull mains plugs (lightning strikes have destroyed equipment here twice already), then it turned out to be very deep bass sound from a CD recording (I left the CD changer playing all the time). Yes the the sound is scary realistic now.

I still have to try the setup you mentioned, putting the master clock in the DAC and feed MCK back to the transport.

But how to use multiple inputs? They might not use the same master clock frequency (sattelite receivers, USB devices). Maybe this is not clear to everybody, but I also want to use the octal D-I DAC to switch between a number of digital input sources (input selector), not only connect it to one dedicated transport. That is also the reason I don't want to change the timing chain with taps as rfbrw indicated, as the D-I system will then only be able to function correctly with either the sony or the philips format exclusively. Philips format needs all 8 taps at exactly 8BCK intervals (64), Sony format needs all 8 taps at exactly 6BCK intervals (48).

I plan to use I2S interfaces with master clock exclusively for the octal D-I DAC inputs. Devices connected to the octal D-I DAC must provide a I2S (philips format) signal together with the master clock. This can be done by using small converters close to the digital source. Screened twisted pair network cable with RJ45 connectors can be used for the interlink.

All this interface testing and clock tweaking seems to be a bit "off topic" but it's essential for the final octal D-I DAC circuitry setup, and the modules needed.

I will post schematic diagrams of the new I2S setup and the battery operated master clock soon.


cheers,

John

[philpoole]

Hi John,
(thanks for the reply on reclocking earlier)

I noticed that the foil screened cat5 cable I have is basically a bundle of twisted pairs within a shield. Might be overkill, but you could fabricate a cable (from several lengths of the above) so that each individual twisted pair is shielded. Might be useful, especially as you're running mclk next to data and bclk.
I guess your cable might already be like that.

I've almost finished the driver board (using 2x DS9638) and hope to mount it in the CDP one day soon, and my TDA1541As arrived in the post this morning

I've got all of the bits to build a basic DAC now, fed with this balanced I2S. Need to think about I/V conversion and some form of output filtering though.


Cheers,
Phil

[tubee]

it turned out to be very deep bass sound from a CD recording

Hi John:

This is a good sign, bass reproduction particular and mid-band also can profit a lot with a clean digital signal. I experienced this also on the first time i listened to my plastic non-os CD640, after installing a good clock with dividers. (some other members here think i am only elaborating the clock) But digitally OS systems can profit too, (304)

clock tweaking seems to be a bit "off topic

I don't think this is slight off-topic here, it still involves with improving your design, and to get it "ultimate''

Measurements and listening tests showed I2S also had jitter

How did you measure the jitter?

[Dutchman]

Hello EC designs,

I am very patient waiting, looking in my inbox email, for your invitation as you have posted earlier. Perhaps something went wrong?


->
Hi Dutchman,

Thanks for your reply [post#453]

Yes of course you can come over to listen to the DAC, I will send you an invitation by email.

When you decide to come over and listen to the octal D-I DAC and sonic resonators, you can bring your favorite CD's for comparison.

If you like the octal D-I DAC sound, you can build it of course. The octal D-I DAC core (analog mainboard), tube output stage and SPDIF audio interface could already be used."

....

I already have a CS 8412 waiting for a good job... I don't have the 1541's, but that is, I guess, no problem.