MHZS - Mystery of the DAC Chip

There are lots of weakness on the standard MHZS players    the implemented regulation and decoupling of the supply rails is poor,  the op-amp after the dac section is a waste of time, the standard clock circuit is noisy,  the SPDIF output is not very good etc etc

BUT  these cdp's are cheap  and fun to tweak :wink:     with some careful thought and added improvements the MHZS cdp's can be made to sound very good

Any idea's to add a better quality internal dac chip instead of the supplied PCM1742?

I have built some discrete regulators to try for the dac :wink:

[quote:67d1b01e5d="arnaudb"]I would be very interested by the results you get with your regulator...  
Question : Is it a 5 ou 3.3v reg ? Do you get 3.3 from the 5v reg as BB suggests in their 1742 documentation ?[/quote]

That one in the picture is set for 5v output but I can build another and adjust it to other voltages

You may have noticed I currently use modified super regs in my CD33, it will be interesting to see how these cheap easy diy ones compare.

If anybody wants to wire in another dac simply tap into the I2S  lines , of course the dac you use should be I2S compatible

[quote:d2ec9dd10a="arnaudb"]So t. what about your home made regulator, is it better with them ?
And what about the sound difference with them (more detail, focus,...) ?
Thx ![/quote]

I like it, its much better than a standard 3pin regulator.
I set the CRD to 4.7mA in the discrete regulator to lower impedance, the type of capacitor on the output has quite a big influence,  I'm using Sanyo SEP polymer,  the discrete regulator likes low ESR unlike standard 3pin regulators :wink:

Anyway sound is more focused with better separation of instruments, improved background details

Hi alfcat, the best way to connect that sort of separate dac pcb would be I2S  instead of spdif so it bypasses the CS8412/4  input receiver which would result in a much better performance, unfortunately this way is harder and unless you know exactly how to do it I seriously would not attempt  it :wink:    it can result in a damaged board.
I do not have a LITE dac  but judging by the picture it seems that two top right hand connectors are for the PSU/transformer  and the top left connector looks like its for another psu/transformer using a centre tap secondary

The sockets on the bottom right are the spdif input

The bottom left connector looks like its the signal Left,Right and ground output

[quote:bf0e3f0b1b="arnaudb"]Excellent t. !
Could you please post schematics and pictures of your regulator ?
It would be great ! ;-)[/quote]

I will try and find the schematic, there is no other pictures so it needs to be built on a piece of matrix board

[quote:ed5529b577="alfcat"]Dear t.,

So I need a separate PSU to supply power to this unit and connect the power output to the connectors on the top.

For the lower LEFT connectors, where should I connect the L.R and the Gnd to? Any idea which point on the CD 33 PCB?

I can get hold of the board but I need to know where should I connect the wires to the PCB. Please advise. Many thanks.

CAT[/quote]

I will need to find a good clear picture of your Cd33 so I need to have a search through the posts,  we need to be 100% you understand before fitting :wink:
Also as I do not know the Lite dac circuit we need a clear picture showing the layout.

There is several different ways to implement that dac board, you will need to compare them to see which you like best,  we will go the easy way as I think the I2S input for the digital section may be a little hard for me to explain how to do it,  I only recommend and help to do mods if I feel you are 100% confident in doing it
SPDIF will NOT be as good as the I2S  but is easier

We need schematic for this http://eshop.diyclub.biz/product_info.php?cPath=23_135&products_id=266
The one posted there is too small

We need to find a suitable output signal from that Lite dac,  lift ONE side of the 0.33uf coupling capacitors inside the CD33 (side nearest the CD33 op-amps) and run the left signal to one of those lifted 0.33uf capacitors and the Right signal to the other lifted 0.33uf  capacitor, this will then bypass the CD33's internal dac and op-amps.
With the Lite dac you should be able use the Left and Right signals from before the Lite dacs op-amps or after the op-amps,  both ways will work and both ways will sound a lot different

A schematic makes things much easier to explain :?

Koifarm, did you run the TDA1543 signal output from the I/V resistors to the MHZS 0.33uf  caps?
If you run the signal from the diygenie op-amps output to the MHSZ it may be overloading the tubes  (too high signal)

The strange noises you heard using the MHZS psu may be oscillation caused by instability

If I was to try a separate dac this is how I'd connect it

Other problem with these cdp's is that the I2S lines are run from long unshielded wires.
The dac chip and clock circuit in mine is now run from a small transformers and discrete regulators.
I may use mini shielded co-ax for the digital i2S lines feeding the dac, the chip is too far away being on a separate board

[quote:ea3c928d95="Kiko"]

The MHZS costs as 15 of this DVD Players and plays only music. Why isnt it possible that the manufacturer builds in some better devices, at least some Pan Fcs or MKP-WIMAs in signal path for example at that price?[/quote]

Good question Kiko!  and also why do MHZS use a cheap dac chip which is also used in cheap DVD's  and they advertise they fit their own designed dac chip which is lies :wink:

Bypassing the op-amp is a good mod :wink:

[quote:eebc4c06d2="alfcat"]Dear t.,

From you photo, I can see that you removed two of those caps, replaced the OPAM by putting in some caps, resistors ... and you have at least THREE? boards instead. One for the clock, what are the others for?

Do you think you can draw us a schematic too for your modification?

CAT[/quote]

The op-amp bypass mod is basically the same as the schematic Kiko posted.

The smallest board is a diy discrete regulator supplying the dac,  the one with the row of red caps at the side is for the pre regulation feeding the small discrete etc.
The other board is for the XO (clock circuit)

I'm currently building the AYA dac designed by Pedja Rogic ,  just waiting for some parts on order