Digital transformer

[Elso Kwak]

Originally posted by Elso Kwak

Wel in real world it does not work!

Hi all,
I feel deeply ashamed as a broken ground lead to the comparator board lead to the wrong conclusion!
The interface <B>does</B> work with the standard SPDIF output from the Sony CDP.
It also does work with the TORX173 receiver provided that a 10nF coupling cap is installed and a 100k resistor to ground from the comparator input to ground, having a path for the input bias current.
Sidenote:
It should almost go without saying that for a 75 coax cable connectors and chassis parts of 75 Ohm characteristic impedance should be used. The RCA connectors as prescribed by the AES/EBU are a completely wrong set standard!. They deteriorate the sound! 75 Ohm BNC or F-connector parts can be used. Or the quite expensive Lemo [Size 1 part# 275; suitable for the RG-59 coaxcable] I will not elaborate further on this as on the AudioAsylum hundreds of posts can be found on the subject.
Hint:
Replace the 74HCU04 by 74<B>V</B>HC04. I have idea why it makes such a big difference but VHC logic sounds a awfull lot better than HC (and AC).

[Elso Kwak]

Hi,
Yesterday I made my latest move by bypassing the digital interface pictured above and the digital input receiver (CS8412) and directly connecting DATA, WCK and BCK from the DSP (SAA7210) in the CDP to the Asynchronous Reclocker in my DAC. I just acquired a Philips CD-650 with that purpose in mind.
Sound is improved tremendously. Much more smooth and less digital. All arguments for a one box player!!!
Later I will place the ASR and the TDA1543 in the player and take out only the current outputs of the DAC-chip.
More depth and analog like! I like the sound very much.
Simplified schematic:
[SAA7210]->[ASR]->[TDA1543]->[IV-converter]->[Outputbuffer]

[massimo]

Originally posted by Elso Kwak
Hi,
.... Later I will place the ASR and the TDA1543 in the player and take out only the current outputs of the DAC-chip.

Iout from TDA 1543???

From TDA 1545A maybe.....

[Elso Kwak]

Originally posted by massimo


Iout from TDA 1543???

From TDA 1545A maybe.....

Hi massimo,
I am a bit puzzled by your post. I don't see any difference between the TDA1543 and the TDA1545A regarding the IV-converter. Both use a opamp and connect the non-inverting input to Vref. I-out of the DAC connected to the inverting input.

[massimo]

Yes, Elso, I was wrong.
I double checked both DACs Data Sheet....
I thought the older one had in built in integrator....

My memory...... I'm getting older....

[Elso Kwak]

Hi,
Forced by circumstances, both my Philips CD-650's broke down, I had to use the SPDIF interface again now with a Philips CD931. I did not find the I2S signals yet, waiting for the manual.
I followed Freds suggestion removing the inputcoupling caps to the DIR.
Now I have much more bass and much less glare! How is this possible? Thanks for the hint Fred!
I added some 1N4148 diodes to the digital input limiting the voltage between +3 and -0.6V, hopefully protecting the comparator.
I also experimented with a Scientific Conversions transformer in the CD-output and also with 74VHC86 directly driven by the opamp. The opamp was configured for a gain of 2x for this configuration producing 5V at the 74VHC86 's inputs. The transformer did not improve the sound, nor did detoriate it. I noted less slam with the 74VHC86 but did not get one of the outputs right....

[Elso Kwak]

Hi,
Jocko let me know he dislikes the diodes, as they are conducting and he wants a 0.5V p-p out as SPDIF norm prescribes.
Well I can't plaese everyone Hopefully I have learnt to count to 5 now
Sonically this circuit is not different from the previous one.....

[hifi]

This circuit is taken from Digital One V. 1.1 documentation. Digital One is from NET-Labs and is designed by by Enland Unruh.

S/PDIF output

IC1 0.1 uF 0.1 uF
|\ || ||
---| +-750R--+-- ||--+ +--||--- pin
|/ | || | | ||
| )||(
| )||(
| )||(
| )||(
499R | |
| | +------- ground
+----+----+ T1
|
---


T1 is a HF-transformer which has 2:1 turns ratio. Transformer type used in example circuit is SC944-05. IC1 in this circuit consists of 8 parallel connected buffer ports from 74ACQ244 IC.



So anybody tested this circuit?... I think I will put it to the test in a Nec 6xE player, while it does not requier -12v witch makes things easier

/ Micke

[CraigBuckingham]

Originally posted by HarryHaller
In theory......? I'm sorry I actually measure and listen to things. Digital is as tweaky as analog to do right. Bandwidth of interface is usually a funtion of the output drivers used, usally HC CMOS, rise time about 3nS. Schmitt-Trigger receivers cause reflections. A Schmitt-Trigger dumps some of it's output back into the input to make it switch faster. The positive feedback signal gets in the interface as reflections. Das ist Verbotten! Reflections in the digital interface cause R.F. noise and jitter in the data stream. Partial grounding is a small impedance between CD transport and DAC grounds.

Sorry, heven't got time to read to the end of the thread.

So has anyone measured the detrimental affect of the schmitt trigger input of the CS8412? Maybe it is already buffered internally. Even if it dumps energy back into the transmision line will this effect the switching transitions? Will there be reflections if the transmission line is properly termintated?