MHZS - Mystery of the DAC Chip

Dear KiKo,

I took my CD 33 PCB back to Mainland China, to the dealer which me and my friends got our CD 33. The sales there said he will try to get me a replacement board at the minimum charge. He said a brand new PCB cost around GBP 50, which is around HALF the price of the original CD player.

The sales is trying to get me a PCB without the capacitors installed as he knows that I am going to replace all the caps anyway. He hasn't tell me how much it is going to cost me .... but should be less than GBP 50. Have my fingers crossed.

I just feel upset with myself wrecking the CD 33. It is soooo stupid of me trying to rush everything and I lost my temper on doing it. Anyway, it is a good lesson and reminder for me.

One thing for sure, I won't quit DIY .... ha..ha... Will continue after I got my new PCB back hopefully the end of this week.

Thanks for your information.  :wink:

Hey Alfcat and Kikko,

Been a little while. I've not changed anythig in my 33 for a while since I got it fixed. I may be not seeing the entire picture here, but from what I see of your damaged board, there is nothing that a bit of wire will not fix. My recommendation is to glue the cap you wish to use where it belongs on the board upside down, and run 28ga leads to the correct locations in the circuit. There should be no harm in this and you should not suffer at all performance wise.

Since my DAC ship solder job, I've been a bit reluctant to try any other mods to my CD player. I've been building a new preamp instead. Good luck guys!

Blair

Hi Blair,

I am still waiting for the return of my CD 33 PCB. Time comes to a standstill like .... This is indeed a very "long" week for me as I need to wait ....

I will continue to modify the CD 33 once it gets back. I still haven't got the chance to test out the large LED I got from Hi Fi Fever. Also considering adding another power supply to the OPAMP ... but this has to be done at a later stage.

Keep in touch and good luck with your Pre-Amp project as well!

I'm finished with the preamp. It sounds great! I've been working with tube gear for a while now.

I'm working on some PP monoblocks using 6SL7GTB, and 6SN7GTB driver tubes with a line stage using the 6922 tube. The PP circuit is going to be a quad of SED KT88s.

You can take it with a grain of salt (pardon the american phrase) , but putting a separate power supply on the OP amp may be a moot point. There is plenty of reserve power in that toroid for the opamp, and if the circuit has fast enough diodes, you are going to get about as much out of it as you can. I recommend using your CD 33 as a transport, and begin to mod a DAC for better resolution and soundstage. Plus if it is a DIY DAC, you get plenty of room to play around. I want to build a DAC, but they are really expensive to build here in the US. I can buy a good DAC for about the same as building one.

Hope this advise helps.

Blair

My colleague is persuading me to DIY an Audio Note Pre-Amp. He said it is easy and simple and won't cost me too much even with good components.

I started playing with these toys say somewhat around May this year. Still got a long way to go, learning as I proceed. The first thing I have to learn is Basic Electronics, ha..ha... as I am an Economist, not a pure scientist.

I agree with what you've said. There is plenty of room for improvement with the OPAMP and perhaps even the DAC. I just wish I know more about these gadgets ... ha..ha..

Your suggestion on using the CD 33 as a transport is also a good one. Yet, I have to save up some money before I can go ahead with this DAC project.  I guess the LITE ones maybe my choice.

Actually I lived in N. America for almost 5 years; mainly in Canada. I can manage some of the slang and I like watching movies all the time. That helps me a bit in keeping up with the American phrase. Blair, where are you located?

CAT

I'm in Dallas Texas.

I have not seen the audionote kits, but if they are the same ones as here in the US, they are a bit expensive compared to simple DIY designs. Your prices and mine are a bit different though.


The LITE audio DAC is a good choice if you are into mods, but there are plenty of kits for full DIY DACs out there. They are about $1,000 USD so a bit out of my price range.

Actually, even as a transport, the 33 is not a great choice. A mid line Toshiba uses a better laser pickup. The DAC chip in the 33 is very difficult to work with also, so you really need to use an external DAC if you are going to tweak the DAC circuit.

Good luck, and if you want to play around with preamps, let me know. There are a bunch of circuits out there I think are very nice and cheap to build. What are you using for amplification? There is a very nice zero gain line stage kit, I really love. It is the first line amp I built, but I still love it.




Blair

Another view:



And an amplifier:



Blair

Dear Blair,

Interesting work you have there. I haven't make up my mind on the Pre-Amp thing yet as it depends a lot on time available and $$$. I don't want to go into anything that needs US $ 1K or more .... hard to find that spare money.

My CD 33 PCB is back. They charged me US$ 40 for putting everything back on a new PCB. Yet, they also put the burned 2.2/ 2W dead resistor back without knowing about it.

I put the board back and turned it on. It seems okay ... I haven't connect the RCA sockets back so I have no idea how it sounds. Have my fingers crossed.

Since they put all the caps back, I have to go through the process of de-soldering them out and put back my Jensens ... painful.

CAT

CAT,

Good news u can get your new board so soon....and with usd40 is very acceptable price.....

Dear WINDWSS,

Yeah, thank God.

I managed to put back most of the capacitors yesterday. Spent almost 2 hours in doing so. Now, I am glad to hear the sound I am used to; though may not be everybody's cup of tea.

Will try to see if I have time to continue with the LED modification next to the laser to reduce reflection later this week or next.

Keep in touch

dear vash,

can you give me some info on cheap & nice pre-amp?  (schematic & part list)....especially your zero gain line stage...
Thank you.

Dear cat,
If u plan to buy a DAC then save the money don't mod too much on your DAC part of CD33. Mod the power section enough....
after you had mod with the led teach me how to do it... is the effect is good?

Yes, I can, but I need to find the schematic. I really do like this line stage because it can be used with a SS amplifier as well. I'm currently working on a different, less expensive power supply, so hang on and I'll send it to you.

Vash

Dear Vash,

U can send it to my email: sswong@healthtronics.com.my which will be easier & faster.....

what kind of less expensive power supply u studying now?
tube rectifier? i understand that got people use 300B as tube rectifier in China.... so i will try out to use 6N3/2C51 as tube rectifier later.....

ss

One think I don't understand. I put back all my previous parts back on the new PCB. However, the S/N ratio dropped to 65db ... which is 10 db less than before ... :

Hi,

does anybody know where new PCBs from the MHZS Players were sold for changing?

Dear KiKo,

I got mine from China. The sales I got my CD 33 said it cost RMB$ 900 to get a new PCB for the Analog Section with everything on.

In Hong Kong, never heard of any place doing this.

CAT

Dear CAT ,

thank you very much!

Can you give me the adress or email or homepage of the place you have got it?

And another question I have to you. All manufacturers in HIFI and Audio have their own homepage. Only MHZS has nothing. I have tried everything.... www.mhzs.com, www.mhzs.hk, www.mhzs.cn and and and.....and all metacrawlers I know, but without result.

Who is the mysterious manufacturer? Is it the Bada company? I think it must be possible to order directly from the factory or not?

KiKo

Dear KiKo,

I did the same, NOTHING related with MHZS whatsoever found. This CD comes not from a well known company nor there is a big firm behind its production.

Another active member here, Viewer, had just purchased and modified a second hand CAYIN CDT-15A or so. That one has some support, I think. You can check out what Viewer did in my other thread "Interesting S/N Ratio for the CD 33".

The shop I got the CD 33 has NO web page or so. It is not a big store at all. Kind of like the Variety Store next to our neighbourhood (I mean the scale & way of operation). Some said the Bada CDs are very similar to the MHZS but there is no proof that they came from the same source.

I only have the Chinese Address of the company. Unlike firms in Western Countries, this address may also be a FAKE. If you need anything, you may drop me a note and see if I can ask the sales I know to arrange for you. Last time he told me that he did this as a favour for me (to get a new PCB). Yet, each time we go there, we bring him a lot of business ... ha.ha.. and I think he doesn't mind to continue giving us favour.

CAT

Hi

I have finished the CD66 , but there is no clock modification yet. This will come later.

At first take a look at the high resolution pics of the PCBs. I have studied them and investigated some weakness of MHZS Players.

Here they are:

Dear KiKo,

Long time no see. Glad to see you back.

The photos are missing. Hi Fi Fever allows upload to 1M only. I think your Hi Res photos have to be in different sections of the PCB.

Awaiting for your report.

CAT

Hi Alf,

fine to hear from you!

Thank you for the tip.
Now I will start to arrange and to resize the pics.  Awaiting your comment after upping them.

At first some pics of not assembled PCBs. If you look for a circuit path it will be very helpful. Please ignore the marking.

Dear KiKo,

These photos are very useful. Although I am just an amateur, these photos give me / us a better understanding of the layout of the whole thing.

As I scan through the photos, your CD 66 uses 12AX7 instead of the 6N3?

Vash, t, WINDWSS and I are looking at the readings we got from the tubes. Please also check out our other thread"

http://www.hififever.com/forum/viewtopic.php?t=952&postdays=0&postorder=asc&start=700

Got to pick up my wife now ... ttyl

CAT

Hi Alf,

thats right. The CD 66 uses 12AX7 instead of the 6N3. The rest of the circuit is nearly the same. Espetially the Digital board with heater PSU.

Hi everybody,
This is my first msg on this board, i'm from France and we (mhzs french owners) are reading your posts with great interest. Firstable, thank you all for all your posts about mhzs players tweaks. We (french mhzs community ;-) ) are working on some tweaks too. If we find something new, i will post it on this forum. So Kiko, thank you so much for your pcb pictures (very usefull !), and could you please tell us more about your findings about mhzs weakness ?

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?

First greettings from the Netherlands in Europa.

Use this one.



Connect DAC output to the tubes analog input and you have a perfect DAC in your MHZS player.

Tube input are on right side from C7 en C8. Desolder this side and connect to new DAC board output.

Hallo,

nice to see how much guys from different countries are interested in this CDP and forum. I want to thank you for your response!

Here my point of view:

The Digital board is ok, you can increase the performance on classic ways.

I changed some elCaps to Panasonic FC, added some film Cs above the diodes and changed the input Cs of the filter for PSU. Just nothing in particular. After finishing you can add some damping material; here I used a rubber mat from a store which is selling sport articles. In earlier times I used tar-bitumen roof sheeting, but it makes a lot of dirt. Certainly bitumen is better and more heavy, can be well performed on the chassis, but the sand falls out of the bitumen and after a while it doesnt look. The free positions between the small film caps amazed me, so I studied the circuit paths for checking their functions. The conclusion is very easy - there is one high frequence filtering film cap in a line with 2 free places for other small film caps. Finance seems to be the reason for omitting them. Dont worry about that, I have seen it also on other very expensive equipment! The price doesnt matter, the manufacturers seem to produce the first prototypes fully assembled in best quality and on mass production they save their money. MHZS is doing the same........


Of course there is to paint the lens of the laser, you can read it on earlier pages of this thread. On this board there is not so much to do.

Now, the DAC board is a little bit harder. The most intersting things I found out after taking a look on the bare board.

1. The circuit paths are a totally chaos. For example:

You surely remember the 4 elCaps in a row, in front of them the 4 voltage regulators and in front of them the other 4 elCaps? At first it seemed to be so: 1 elCap to 1 volt. reg. and following is the next one elCap. If you believe it you are wrong. This is absolutely different. I will try to write the paths in some pics with an image editing prog.

2. The heater run very hot. The mounted voltage regulators run inexactly.

3. Read: http://focus.ti.com/lit/ds/symlink/pcm1742.pdf, the DAC needs Dual-Supply Operation: 5-V Analog, 3.3-V Digital. You have a cheap 2 Zener solution here, but TI says, you need a separate supply for the Digital input if you want to have a good sound.

You can see the connection diagram on page 25. The important facts here as copy:


"The PCM1742 requires a 5-V analog supply (VCC) and a 3.3-V digital supply (VDD). The 5-V supply is used to power the DAC analog and output-filter circuitry, while the 3.3-V supply is used to power the digital filter and serial interface circuitry. For best performance, the 3.3-V supply should be derived from the 5-V supply using a linear regulator, as shown in Figure 28."

There is no "clean" 3,3 V supply. The 2 Zener near the DAC produce 3,3 V but in a very noisy way. So I redesigned the complete PSU on this board.

4. All electrolytics in signal path have to be removed (4 pieces , see above) with anything you want - or can pay.

5. A new clock is a good thing.

6. Except the elCaps I changed all resistors in signal path and the tube area for better ones. Some of them are non-magnetic Vishay-Dale Mil Spec  CMF-55, but not all, because they are hard to find here and the most powerful are 1/10 W. Furthermore not all needed values have been available. The other resistors are some of 1, 2 or 3 W metalloxide film from Yageo. The empirical formula is not to take lower power rating but the same value. Minimum power is the power of the old resistor.

7. I had one greater problem in redesigning that you maybe will have too. Please read this now very carefully and avoid this problem:

For the DAC I used a Linear Technology LT1584CT-3.3 / 7A linear regulator. This one has a stability of 0.05 %, is very fast and has a constant voltage of 5 %. Costs are 20 USD.

7 A is absolutely to much for the PCM1742, but it was the only one I could get without lead time. Then I made a great mistake. I connected him where the other linear regulator is connected , the LM 317 - on the big resistor 2,2 Ohms 2W near the two cooler. I have done it because I wanted a single path for the 3,3 V. And I thought, that a 5V regulator can share the same input as a 3,3V. After this procedure it got curious. Player has no  more signal! The solder joints seemed to be all right, so I have searched the error for weeks!

.............and then I found it. It was the expensive regulator. It had not 3,3 V on output, it had 3,85 V! But why?

At the end of the big resistor (where the LM317 is connected) there is an input voltage of more than 20V! So the 3.3V regulator and the LM317 share a 20V input? I couldnt believe. At first I thought the 2W 2,2 Ohms resistor is broken and I had a short-circuit. But it was not so. What was the reason?

The reason is that a Linear Technology LT1584CT-3.3 should not be connected on such high input. I found the answer here:

http://www.farnell.com/datasheets/84158.pdf........"input below 7V".

But why has a single 5V regulator (LM317) an input of 20V?

The answer is on the other side of the PCB. The bigger elCap is not only connected to this 2 voltage regulators, no, this cap is also connected to the 7812 regulator on the other side. This regulator produces this voltage only for the delay at the output.

Again studying the datasheet of the PCM1742 I found the answer on page 2:

" ABSOLUTE MAXIMUM RATINGS: Power supply voltage, VDD –0.3 V to 4 V,

and RECOMMENDED OPERATING CONDITIONS:

Digital supply voltage, VDD = 3 MIN, 3.3 NOM,  3.6 MAX. Here is the problem! This DAC dies at 3.85 V input!

The next problem is - by pulling up (slowly and carefully) the cover of the broken DAC the circuits paths were demolished. Between the cover and the chip is epoxy and the chip, the epoxy and the cover are stucked together.

After a longer time I got a new DAC, a new SMD adapter and a new regulator (for 20 USD again :shock: ).

This time I made no more experiments: the 3.3 V regulator I connected directly on the output of the 5 V regulator (on the same cooler of the LM317). The changing of the DAC is really a hard thing and I dont recommend that if it is absolutely not necessary.

The new high precision 5V regulator is a 1,5 A one instead of the old LM317 with 1 A. The heater runned very hot with 1 A, so I searched a solution for it, because I expected now overheat on the 5V regulator. This is a simply 20 W resistor. Pulling out the 2,2R I build in an 6,8R. Now the heater is a little bit cooler, the resistor a little bit warmer. I wanted that the heater is only handwarm, but he isnt yet. At least I added a second 6,8R in serial and an approx. 5R on the other regulator, the 7808 at the top of the pic.

It is a little bit better, but I will take greater values and conduct some experiments. For the 7808 10V input is enough, for the 5V regulator 8V. Its a simple thing to increase the resistors. Better a hot resistor than a hot regulator.

Its ready now! Now its a really good thing! I will try to explain that all with the pics tomorrow.

Have a nice day


Greetings to our new friends, coming to us from Holland and France. I am your neighbour. Coming from Germany. Pics will come tomorrow......

Alf, Blair? What are you doing now?

Dear Friends,

It is so nice to see people coming from all parts of Europe and our friend Blair from USA. I guess it is really hard to find a chance for people of different parts of the world to come together like this.

Although I am not the operator, I sincerely welcome you all to share your interesting experience.

I am a bit busy right now as this is the quarterly examination period at my college. I have to set a number of papers (not to mention marking them). For this week or two, I may not be able to contribute much but will continue the DIY thing by mid Nov.

For the time being, I will continue to read your posts and give some comments if possible.

Keep in touch guys and happy DIYing.

CAT

[quote:2761cc1bc4="Kiko"]Alf, Blair? What are you doing now?[/quote]

Hey guys,

I haven't done too much to my player since the DAC fix. That scares me to death :shock:

That little guy is a pain to resolder in place. There are a few leads that run through "dead end" traces as well which helps if you do have to change the chip though.

I have a few extras also. I wish I knew Kiko, I would have sent you one.

I still have the 213C, and plan to paint the lense and see if it is compatable, but again, I am just nervous about the swap because it works again . I have also been really busy with a few small projects I am generating to make some extra cash to support my habbit. I have a few regulated supplies a friend of mine and I are working on for a preamp using 12AU7s or 6SN7s.

I still plan to change out all diodes with UF diodes and all the caps on the PS board first. Typically PSs are the most important thing in sound quality. Clean in = clean output.

I also have a very nice looking open baffle hybrid I'm working on with aluminum bass drivers and a poly mid with a vifa XT25 tweeter. Should be very nice.

Good to hear from you guys.

Blair

Dear friends,

I have a plan to build an AudioNote 7 pre-amp before Christmas. My friend told me that the material cost will be around HK$ 2K (approx. US$ 230).

Just hope I can spare the time after the half yearly examination.

CAT

Dear Koifarm,

The DAC board you are using -- LITE AC-AH, I think it is no longer available at DIY Gene ... sigh

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

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 ?

Dear alfcat

I just have ordered one for another forum member to Modify his MHZS 66.

He had enough of the noise that the original DAC produced.

[quote:46f0c00836="Koifarm"]First greettings from the Netherlands in Europa.

Use this one.



Connect DAC output to the tubes analog input and you have a perfect DAC in your MHZS player.

Tube input are on right side from C7 en C8. Desolder this side and connect to new DAC board output.

[/quote]


Would the DAC in this link not be just as good? It is cheaper. How would this wire in?

http://cgi.ebay.com/CD-Player-DAC-Upgrade-Kit-BurrBrown-PCM67U-DAC-AE_W0QQitemZ250121862931QQihZ015QQcategoryZ14980QQcmdZViewItem

Thanks,

Blair

Dear Vash.

That DAC can you also fit in the MHZS players.

I do not know how it sounds. But the other DAC sounds musical. (very analog). No noise. I do not use the opamp output section of the DAC board. Less is better i expierenced.

The power supply for the two dacs you can take from the MHZS player. The analoge outputs from the dac connect as writen in the other reply.
The digital input is another story i must look inside my player to tell you where to connect.

[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

Dear Koifarm,

Strange, that board was NOT available yesterday at DIY Gene. Today, it is!

If I use that board, I will by-pass all the analog part, is that correct? In that case, it will be the same as having an External DAC connected through the coaxial out.

Please correct me if I am wrong as I don't know Electronics at all.  :

Alfcat,

If you connect the output from the DAC board to the cinch of the player then it is like a external DAC. But the trick is to use the good parts of the MHZS player.

The analoge buffer opamps on the DAC board you must not use ( like passive filter in the MHZS player ). The analoge outputs from the TDA chips you must directly connect with C7 and C8 as in the above reply from me. Then you do not use the bad opamps and you use the tube output of the MHZS player . The one we like.

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: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

Excellent t. !
Could you please post schematics and pictures of your regulator ?
It would be great ! ;-)

Dear Koifarm,

I understand your logic but I need further help from you as I am a dummy in this field.

The LITE DAC-AH board got several connectors which I highlighted in YELLOW circle in the photo that comes with this message. What and Where should I connect these to? I think one should be the INPUT source, one the OUTPUT and the next should be POWER. But there is still one left?

I used KiKo's CD 66 PCB as a reference as it has high resemblance with the CD 33 PCB. Can you point, by means of arrors or so, where should I connect those items mentioned above.

It would be better if I use a separate Power Supply for this board, is that right?

CAT

I've worked on kiko's pcb pictures ;-) I think that we can do better but if it can help a bit...

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