[audioneophyte]

Hi guys,

It appears I spoke positively way too soon on the Zhaolu D2 unit. I have the CS4398 unit with the "upgraded" headphone amp.

Everything was going good until I noticed a slight buzzing/static noise on the left channel with my headphones. Well, I ignored it for a few hours but it got worse, and then I noticed touching or tapping the volume control would cause the static/noise to get a lot worse. I opened it up but couldn't really notice anything visibly wrong ... the static is still there, and I also hear a pretty nasty hum whenever I turn the volume pot past 1/4 maybe. Also touching it or having your hand near it (the pot) causes the buzzing to increase.

I'm stumped on this. Did I just get a lemon? I sent an email to iFi about this but I'm hoping I wont have to send it back, because I really liked the sound quality, but these issues are killing it.

 

[bizkid]

Could be a groundloop issue. I got that once when i had a groundloop between my active speakers and the zhaolu connected to the pc.

 

[audioneophyte]

How would I check?

I am using optical cable for the Zhaolu, I was using coax before but I thought maybe isolating the PC from the Zhaolu electrically would fix the issue.

I also noticed this:



Notice how the leftmost blue whatever it is (sorry guys, not an electronics person myself) is soldered backwards compared to the others? Could that be it?

EDIT: Nevermind, the picture here: http://www6.head-fi.org/forums/showt...181056&page=12
Looks the same, back to square one

This is quite annoying because I don't have the skills/tools to investigate properly.

EDIT 2:

It MUST be some sort of ground issue. I put it back together exactly the way it was at first and noticed that if I lift the unit off the table and put it on an anti static bag and move it around I can get static in the right channel, and then the left one too. This is really messed up. Anyone have any clue how I can begin to fix this?

 

[audioneophyte]

After writing the first message I tried to troubleshoot the unit best as I could.

1) The issue is not related at all to input, it will occur with coax, toslink, analog (RCA) or NO input.
2) It will occur after "idling" the unit for a few minutes (less than 5) or after playing music through it for a few minutes (less than 5).
3) It is manifested by static/humming noises, especially in left channel. They vary in amplitude but will get worse the longer the unit is on. Physicaly moving the unit from a table to a different surface, such as an anti-static mat will cause the static noises to also occur in the right channel or both.
4) The headphone output and RCA (analog) volume controlled outputs are both affected.
5) The RCA non-volume controlled output is NOT affected.
6) I can not test the XLR jacks because I have no XLR equipment.
7) The L channel humming occurs regardless of volume level. Beyond 1/2 volume there is also a buzzing noise in both channels but I assume this is normal due to very high volume at that setting?

I have tried different power cables, and different sockets throughout my house. The issue occurs regardless.

It appears to be a grounding problem with the headphone amp/volume control, especially after hearing static in both channels when moving the case to a different surface.

I reseated the headphone amp with absolutely no effect.

I don't know what else to do at this point.

I noticed the actual power plug inside doesn't use the ground (it has nothing connected to it) even though it is uses a three pronged adapter. Is this normal?
EDIT: This post seems to be talking about the lack of chassis ground: http://www.world-designs.co.uk/forum...3&postcount=15
Does this make sense?

 

[global]

Quote:

Originally Posted by audioneophyte EDIT: This post seems to be talking about the lack of chassis ground: http://www.world-designs.co.uk/forum...3&postcount=15 Does this make sense?

Hi

I am that same Global!

In the World Design post I was referring to a safety issue WRT the rules re electical safety in the UK. Your country and others may differ.

Basically, in the UK, an electical device may be ungrounded (mains earth/ground) only if there are two unbroken layers of insulation between all high voltage points and any conductive material which may be touched. The Zhaolu breaks this rule as there is only one insulating layer. EG there is only a layer of PVC insulation between the incoming 240v live cable and the chassis ( an air space does not count in this instance). In order to meet regulations in such a case, the chassis must be earthed/grounded to mains earth which can be done per my WD posting.

I would not expect this to be significant in your particular problem which I am currently investigating on my own DAC since I now have the same problem having fitted the upgraded CS board!

I will be re-flowing the solder joints on the DAC board tomorrow. I'll post back if I have any results.

 

[audioneophyte]

Ok thank you very much for the clarification.

I tried grounding it just for kicks and (as expected) without any positive results.

The noise is still there.

At this point I'm gonna leave it be and see what the dealer (Wei / iFi) has to say.

It appears to me that there is a serious issue with the upgraded headphone amp.

 

[Labtek]

Quote:

Originally Posted by audioneophyte Ok thank you very much for the clarification. I tried grounding it just for kicks and (as expected) without any positive results. The noise is still there. At this point I'm gonna leave it be and see what the dealer (Wei / iFi) has to say. It appears to me that there is a serious issue with the upgraded headphone amp.

I have a feeling that one or more of your transistors is blown in the amplifier stage. They are easy to change and easy to test. They only cost a few quid. They are the black things screwed to the heat sink at the top of your picture. There is something you can do in the meantime which is to make sure they are screwed tightly to the heat sink. If not then you get a similar problem. It may just be a build quality issue. If your feelin brave just swap the transistors one by one from one channel to the other and see if it makes a difference. Have fun.

Advice:
-Practice soldering
-careful what you solder
-screw them in nice and tight
-don't worry about the goo on the backs of the transistors
-If their is a fuse for each channel use them. If not make sure all the transistors are installed in both channels before you switch it on.

You may want to wait for verification of this course of action and advice from other headfier's before proceeding.

 

[bizkid]

i had EXACTLY the same problem! Just the headphone amp and its outputs were affected. It was definately a ground loop issue in my case. Maybe theres some wrong soldering or other problem on your PCB causing it? I have no idea. But i had exactly the same symptoms which were caused by a groundloop between the Zhaolu and my active speakers.

 

[audioneophyte]

Quote:

Originally Posted by Labtek I have a feeling that one or more of your transistors is blown in the amplifier stage.

Would that also manifest the noise/humming/static on the REAR RCA (volume controlled) as well, or just the front headphone output? Because I get the issues on both.

I'm wondering if it could be as simple as the potentiometer?

Edit:

I tried to isolate the headphone amp from the chassis by placing little standoffs from my PC toolkit on the spacers and the screws that it attaches to the case with.

Not only does it not help, it makes things worse. If I isolate it like that, just touching the volume knob increases buzzing noises in both channels.

I'm at a complete loss, this thing is broken.

 

[Labtek]

Quote:

Originally Posted by audioneophyte Would that also manifest the noise/humming/static on the REAR RCA (volume controlled) as well, or just the front headphone output? Because I get the issues on both. I'm wondering if it could be as simple as the potentiometer?

Yep it'll happen on both as the transistors are the main amplification stage and they are set in three's in your amp I presume and each transistor deals with a different frequency range so the headphones are also affected.
Firstly you need to identify whether its a hum or a buzz a hum will mean a grounding issue and is harder to diagnose and treat but a buzz is easier.

My first port of call is the grounding issue as above check everything. Don't be afraid the PCB's are quite sturdy as long as your not rough. Check for cracks and any poor solder joints. You'll know it when you see it. After a while all you'll see when you close your eyes is circuitry and you'll probably have dreams about routing the circuits from one resistor to the next. Its a small board so it shouldn't take long.

With a Buzz try swapping the transistors and check for any changes. It really is a question of trial and error. It really could be anything but if you get stuck in you'll have it fixed in no time and if you don't at least you'll know more than when you started. It really is as simple as that. I would however check the screws on the transistors as when they are loose they ground loop and it could be as simple as a cross tread. Even simply check earthing or make an earth to the chassis from the heat sink. I do find it odd that its in both channels but you could easily have blown two transistors. Theres not alot to go wrong and even with a few parts not working properly the amp will still function correctly. If all else fails get a multimeter and Isolate the different stages and work your way through the components checking the components one by one against themselves for large inconsistencies.
and replace accordingly. Or just get the thing repaced. Good Luck!

 

[dhp]

how can such an amazing DAC have such problems!! I am confused

 

[audioneophyte]

Ok.

I used imprecise language, so I'll try to make it clear.

The issue at hand is a static like noise that occurs in LEFT channel only. It is the exact same noise that occured at first when changing volume with the pot, if any of you own a PA2V2 it is the same noise the pot on that made as well.

It wouldn't be a problem if it was just during volume changes, but after a day of use it is now permanent. It fluctuates in intensity. I tried to isolate the PCB of the headphone amp from the case using the standoffs on the 4 screws attaching it to the case. This made things worse. Not only is the static like noise there, but it also introduces both humming AND buzzing in BOTH channels. It hums past 1/2 of max volume (with nothing playing) and it buzzes if I touch the volume control (the pot). I took off the standoffs and just put it back together exacty as I received it.

I checked the transistors and they are very tightly secured to the heatsink.

I visually inspected the headphone amp board and can't notice anything wrong, other than this:



Could that be the cause?

 

[audioneophyte]

Quote:

Originally Posted by DieInAFire how can such an amazing DAC have such problems!! I am confused

The DAC part works fine it would seem, the headphone amp part doesn't.

 

[Labtek]

Quote:

Originally Posted by audioneophyte Would that also manifest the noise/humming/static on the REAR RCA (volume controlled) as well, or just the front headphone output? Because I get the issues on both. I'm wondering if it could be as simple as the potentiometer? Edit: I tried to isolate the headphone amp from the chassis by placing little standoffs from my PC toolkit on the spacers and the screws that it attaches to the case with. Not only does it not help, it makes things worse. If I isolate it like that, just touching the volume knob increases buzzing noises in both channels. I'm at a complete loss, this thing is broken.

Calm down take a deep breath and think it through. If the buzzing increases when you unearth it by isolating it then you should do the opposite and earth it. The chassis will only give you so much earth. So you need a better earth. somegthing big and metal. Try that. Is the amp very close to the computer if so move it away and check again. Then if no good follow the other post.

 

[Labtek]

Quote:

Originally Posted by audioneophyte Ok. I used imprecise language, so I'll try to make it clear. The issue at hand is a static like noise that occurs in LEFT channel only. It is the exact same noise that occured at first when changing volume with the pot, if any of you own a PA2V2 it is the same noise the pot on that made as well. It wouldn't be a problem if it was just during volume changes, but after a day of use it is now permanent. It fluctuates in intensity. I tried to isolate the PCB of the headphone amp from the case using the standoffs on the 4 screws attaching it to the case. This made things worse. Not only is the static like noise there, but it also introduces both humming AND buzzing in BOTH channels. It hums past 1/2 of max volume (with nothing playing) and it buzzes if I touch the volume control (the pot). I took off the standoffs and just put it back together exacty as I received it. I checked the transistors and they are very tightly secured to the heatsink. I visually inspected the headphone amp board and can't notice anything wrong, other than this: Could that be the cause?

Could quite easily be because it is overlapping other tracks on the board. ease the overspill of with a sharp knife. Dont worry about the green stuff but try not to cut the track or you'll have to solder it.

Can you show me a picture of the Headphone amp stage? i.e. is it acting as a pre amp for the RCA as I really don't have clear picture of this amp in my head.