Reclocking - part 2

After more detailed study of reclocking, I found out it is not so easy - well, it is much easier if DAC and transport share the same master clock (#5 works much better, #3 is possible to have - it does not work if you have different clocks, soon or later buffer overrun/underrun will happen). #2 is a way to go. See XO-DAC or its implementation.

The week-end is over, have to work now... and wait for the AN DAC Kit to arrive ;)

Matej

Reclocking

Searching the forums I found someone has nicely put how reclocling should be done.
My opinion is that #3 is the only clean way to go, but #5 is best price/value performance (how it is usualy done) - also Mr Kusunoki described this method (comment on his article: since this method is not 100%, transports sound differently).

1.) Get rid of the problem right at the source, e.g. the player. The player and the DACs would be fed from the same local low-jitter clock. PSU design and clock distribution scheme would be optimized to have the lowest jitter possible at the DAC, while the jitter at the rest of the circuit isn't that important.

For external DACs, we either have to isolate the timing of incoming signal from the timing of the DAC chip, or recover the original clock better than usual.

2.) Design a high quality PLL which recovers the original clock better than a simple CS841x receiver chip. The Pass Labs D1 (service manual available from their site) is a nice example of a good implementation of this technique.

3.) Let the input data stream fill a FIFO buffer. The DAC is fed from a local low-jitter clock and the data comes from the buffer. Due to the separate transport and DAC clocks, the buffer will empty or fill up slowly, depending on which clock is faster. Thus, we must provide some means to slightly "tune" the local clock source to keep the buffer about half filled.

4.) Use an ASRC to complete isolate the timing of input data stream and DAC chip. This approach is cheap and easy, but there are some caveats.

5.) Asynchronous reclocking right before the DAC. A nice idea, cheap to implement and it works good.

DAC part improvements

A good sounding DAC requires:

• low jitter


• clean, low noise power supply for analog part (and for clock)

Audio Note digital board (signature version) is my DAC board base. It is really well good designed, but still not perfect. Audio Note completely ignores the jitter issue. I take low jitter as important component of DAC design - reclocking must be done just before DAC. This is the thing I will have to do on my own.
Secondly, I will investigate analog voltage regulator design for the DAC chip analog voltage supply - this has to be clean as possible. AN board does not use classic LM317/TL471 regulators (they are good, but not good enough), but LF351/pass transistor/LED combination. I hope it does its work good or I will provide it myself.
I also consider using battery power supply (SLA/VRLA) as they provide low-noise DC (yet to be measured under load).

I also have to provide low-noise DC voltages of 6.3V and 230V for the 6DJ8 tubes.
Any suggestions?

Matej

My CD player DIY project

I decided to upgrate my CD player, but good (audiophile) CD players cost a lot (> 2000EUR). I digged a little but into the CD player construction and found out that its implementation does not justify the price. Moreover, there a design flaws all over...
So said - "I'll do it myself. A very gode one".

As many of you already know CD plater consists of 2 parts:

1. transport (a mechanism that reads CD and outputs data - usually SPDIF or even I2S) and


2. DAC (digital-to-analog converter) w/ output stage (2Vrms output is required, for unbalanced RCA).

Transport

Choosing a transport was an easy thing - CD-PRO2LF. Great transport, no clumsy tray, very turntable alike.

A great DIY (including controller board, remote, PSUs) can be purchased here.
Quite a straight-forward implementation. The only think-about thing is: should I inject DAC clock (and reclock SPDIF) or not. Tentlabs X03 is what I have in mind.
By-the-way, CD-PRO2LF has an I2S output (advantage over SPDIF of avoiding additional jitter), but there are many different I2S standards. CD-PRO2LF can be configured to output a specific standard, but this would require additional work (to sent DSA commant to the control unit). But I want to have transport DAC independed and I will most likely use SPDIF output.

DAC

DAC part is trickier.
I will not write an essay here. I agree with the Kusunoki's "Non-oversampling Digital filter-less DAC Concept".

This left me the following DAC chip choices: PCM1704 (new vesion of PCM 63), TDA1541 (and its economy versions: TDA1543, TDA1545), AD1865.
TDA1541 is very nice (also accepts I2C outputed by CD-PRO2LF), but requires 15V (and lots of decoupling caps).
PCM1704 is also great, but requires additional filter to convert 16-bit to 20-bit.
I found AD1865 most appropriate (all over 5V), very good specs and nice sounding (Audio Note preffered DAC chip).
Simpler is better.

By-the-way, there is quite good CD player available - fully differential (4x PCM1704-K), non-oversampling - Primare CD31. Worth listening, if you do not want to DIY.

I found these three DAC implementations to be really good one (my reference):

• "Tentlabs" DIY DAC


• Extremist DAC


• Audio Note DAC2.1 Kit

At the end, I ordered Audio Note 2.1 Kit w/o M2 PSU (that was to expensive for me). It shoud arrive in a few days. Weeeee :)
But I have some improvements in my mind, keep on reading...

TerraFolk, N'taka (2004)

This is a CD thay I really enjoy (lately).
For all folk lovers, this is a must hear.




More info at: http://www.terrafolk.org/

Blog created

Hi, all!

I decided to create a blog where I will "blog" things I do regarding audio.
I hope you'll find this page useful.
Comments are more than welcome.

Take care,
Matej