[regal]

yes he is right.   Make sure you bleed the B+ caps before touching anything

[lpaudio2]

sounds good!

Question regal, for the filter mod can you describe that the same way markc did, ie. what parts go where on the board. Im assuming the inductors on there currently get replaced, but not clear if any other parts get removed or where the .01 and .1 mkp caps are added in? It also looks like there are two sets of inductors which are the ones that get replaced?

[regal]

I plan on photodocumenting everything this weekend when I upgrade the fake PCM1704K to real PCM1704K's.

BTW,  The 2nd inductor is removed and jumpered.   The first inductor is replaced with the TDK.

You have to solder the little film caps onto the legs of the thick film resistors and use these in place of the 220ohm resistor on one end and in place of the cap (C34&C33) on the other end.

[pbrstreetgang]

sorry regal you lost all credibility with the fake 1704K conspiracy theory. Tell me how that happens please? The may be black market authentic chips but they are most certainly 1704Ks. This isnt something you do in a back alley somewhere with photos and an exacto knife.

[regal]

Maybe you misunderstood,  I am not saying they pressed a PCM1704.

I am saying they hand marked PCM1704U's and "made" them K's.

Have you even seen a K version ? 


If you want to attack my credibility,  that's fine I'll just quit posting.
I came here to help people,  not be attacked.

I happen to be an engineer who knows more about the chip trade than
I am sure you ever will.  Its not GR or Sonicrafts fault that the chinese are
hand marking PCM1704 as  K versions.  I measured the stock lite DAC 60 PCM1704 "K"
and it is no where close what a "K" measure.  They are plain old PCM1704U's.

Later.

[markC]

Regal, don't go away because of one poster. I'm quite interested in what you have to say. I've been wondering why these chips have 2 little white dots on them instesd of actually saying 1704u-k.

[pbrstreetgang]

Sorry, I may have been too harsh. And since you are knowledgeable of the chip trade, do you happen to be in the audio industry? If so please let me know with and with what so I can put it in context. I have asked before but it wasnt clear.

Maybe you misunderstood,  I am not saying they pressed a PCM1704.

I am saying they hand marked PCM1704U's and "made" them K's.

Have you even seen a K version ? 


If you want to attack my credibility,  that's fine I'll just quit posting.
I came here to help people,  not be attacked.

I happen to be an engineer who knows more about the chip trade than
I am sure you ever will.  Its not GR or Sonicrafts fault that the chinese are
hand marking PCM1704 as  K versions.  I measured the stock lite DAC 60 PCM1704 "K"
and it is no where close what a "K" measure.  They are plain old PCM1704U's.

Later.

[Danny Richie]

I have looked into the chip type deal to some degree. I even called TI about it a couple of times.

Apparently these chips are made in China.

I was told by one guy that they were all printed with the part number during assembly then graded. If there was a white dot on the chip (painted on by hand) then that noted the K designation.

I have also heard that US made chips are graded then printed so the K series letter is clearly printed on them.

I have also been told that not all the chips made over there in China go out the front door of the plant. Some leave out the back door if you know what I mean.

Keep in mind this is not first hand information, just what I have been told.

The DAC-60 used to be advertised as having K series chips from the manufacturer, but they are advertised that way anymore.

Now, you guys keep the discussion on an honorable level and don't get or take this stuff personal.

[zware]

I am new on forum. I have done some hobby work on DAC60(stock version) modifying. Mainly cap's, tube rolling and similar.
Sound is .... advanced but always can be better 
I have tried with by-pass caps on cathode with 220uf oscon. This I have removed as sound was fuzzy to my ears. This change is out of my knowledge.
I was about to try change PCM1704 but I have put it on hold as action is not that simple and was strange to me that price for all 3 versions PCM1704U, PCM1704U-J and PCM1704U-K is same $30.7 looking on DigiKey site.
regal, would be interesting to see what change  will be after move to 'real' K version. 

[markC]

Did you also change the I/V resistors and cathode resistors when you added the cathode by-pass caps? If not you made things worse, not better, as this would create more gain and amplify any dac chip distortion even more than stock form.

[zware]

No I didn't change I/V resistors. This is probably why results ware nok.
Do you have any idea what values should be for this 2 resistors in case of using 220uf for by-pass (those I have in my hands right now)?

[regal]

Marc is correct,  there is a report of someone adding cathode by-pass caps on Head-fi and it giving good results,  but I think he was holding back some info.   Of interest is that the Monarch NM24 uses cathode by-pass caps,  I don't know what their I/V resistor is though.

[regal]

Marc is correct,  there is a report of someone adding cathode by-pass caps on Head-fi and it giving good results,  but I think he was holding back some info.   Of interest is that the Monarch NM24 uses cathode by-pass caps,  I don't know what their I/V resistor is though.

Also use 1000 uF to avoid roll-off.

[regal]

Here is a picture of the completed mod,  You can see how I soldered the film caps to the legs of the TO-220 caddock thick film reistor.  Under the green bypass-caps you have to pull the little stock film cap.  You can use its ground pad for the bypass cap's neg leg.  You have to solder the + leg of the bypass cap to the + leg of the cathod resistor.  The inductors are on the underneath.

The old IV filter was :  resistor>inductor>cap>inductor>cap --tube
The new IV filter is:  resistor+cap>inductor>resistor+cap>jumper>empty--tube

We compared my brother's DAC-60 vs. mine with the mod,  and there is a whole lot more smoothness,  especially in complex passages.

I think I should try upgrading the CRC caps and the 47 uF's after the mofset, I could use douple pole Jensens for both.  I am still on the fence regarding the choke.   Any experienced tube PS designers thoughts,  or those who have done the choke mod?




Sorry my camera can't do macros.  Just for the heck of it we compared this to his Mark Levinson DAC,  I actually prefer the DAC-60,  the midrange is more liquid and life like.  Probably the absence of any opamps or silicon in the DAC60 signal path make it a special beast.

[regal]

[. I also changed the plate and cathode resistors to 300 ohm which actually makes less noticeable tube distortion than before the bypass caps,  it puts the tube bias in a better spot.

[lpaudio2]

regal... what actually went where with that filter mod? I follow about 10% of that, without part locations, or values im finding it hard to follow... I would really like to do this mod for the filter...

I think what im struggling with here, is the only schematic that I can find I cant blow up big enough to see where any parts are, and im not knowledgeable enough to just find the parts.

Are the cathode resistors the resistors right after the cathode of the tube? What is the RXX part number for them on the lite boards?

I think from your picture, you removed the inductors, and now have what looks like an inductor with a resistor, can you confirm the locations of these, one looks to be c40?

[zware]

I am also not clear about filter modification. Looks like like dac has been changed to K version - any comment how much this change did improvement in sound?

Picture of my Hi-Cap DAC60. most of cap's replaced with 'better' mostly doubled capacities. i.e. PS caps are 1000uF and all other  bypassed on bottom with  film caps.All rectifiers have bee changed. I agree it might be overdone but sound has been advanced and hobby work had no compromise

http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=0

You can see that digital part also improved to help job to CS receiver. All this modd's are not done with my knowledge. I'll ask friend that is father of ideas to join letter when he is back from holiday.

[regal]

The IV filter mod is pretty simple:

Stock:     IV Resistor (220 ohm) -> inductor -> cap -> inductor -> cap -> tube
Modified: 100ohm+cap -> inductor -> 100 ohm + cap -> jumper -> remove ->tube

Replace plate and cathode resistor with 300 ohm
Add bypass cap to cathode

Make 6 " leads to the inductors and put them to the side of the board to lessen EMI.

I could open the unit and get the numbers but I guess I feel that if you can't trace this path with a DMM and read the IV filter schematic I posted you should just wait for the Sonicraft Level 2 mod,  it will be better any way I am sure he is doing other upgrades with it.  Probably when you guys take out the PCB and trace the path from the 220 ohm IV resistor to the tube it will make more sense.

The K version from TI measured (on its own) better but it made NO difference in sound,  the THD of the SRPP is too high for it to matter in this DAC.

[pbrstreetgang]

despite my ugliness toward you, you are committed and with good intentions. This has legs and I for one would like a full rundown if possible. What you think is crucial and what is marginal. Thanks

[zware]

"
The K version from TI measured (on its own) better but it made NO difference in sound,  the THD of the SRPP is too high for it to matter in this DAC.
"
hmmm then this is why he is working on changing tube circuit to mu-follower.... still in work. on first try mid and heights ware absolutely great with some problems with deep basses. When this done probably last step would be change of dac's to 'K' version. soft/sharp switch on DF has been done as well. Do you expect tube circuit will reduce THD?