[Oublie]

Hi,

I received my new Zero Dac late last week but only got a chance to try it on tuesday as I was away for the weekend. Apart from an issue where the power cord arrived with a broken plug there is something far more troubleing wrong. This thing hums like crazy! i don't mean on the audio - the dac is crystal clear on the audio i tried it with my ultrasones on the headphone stage,mated to my nad amp using the headphone output, through two different stax energizer with a set of electrets and a set of lamdba's the sound is fantastic but the dac physically hums like mad - its actually louder than my music pc and it can be heard though the open headphones i own. The unit physically vibrates and you can feel it when you place your hand on it. Anyone got any ideas what would be causing this and how i would solve it. I emailed the seller - lawrence chan - he's sold a lot of these units to headfi member but i haven't had a reply yet. So while i wait for him to come back to me maybe some of you guys could tell me what would cause this.

BTW i tried two different power cables and plugged the unit into two different wall sockets, this made no difference the unit still hums loudly.

Thanks

 

[Heady]

Sounds like the transformer is humming to me. I think there's two possible causes, one the transformer is damaged and some part(s) is/are loose.

Second, you may had DC in your AC supply. Look up DC blocker schematics for a DIY fix although be warned, it is very dangerous to work with AC, if you don't know what you are doing.

 

[Oublie]

Thanks,

I thought it was possibly the transformer, it a pita and hopefully i can get lawrence to send me a replacement trafo for the unit as i hate the thought of shipping it back to hong kong when i could replace that myself.

I'll wait for him to get back to me and then see what can be done.

 

[looser101]

This may sound like a stupid question but...

Do you have a multispeed fan, multi brightness light, or dimmer near by?

R

 

[Oublie]

Quote:

Originally Posted by looser101 /img/forum/go_quote.gif This may sound like a stupid question but... Do you have a multispeed fan, multi brightness light, or dimmer near by? R

computer fans etc but i tested the unit without them switched on so its nothing to do with that. Also the humming is actually physical vibration and does not have an effect on the actual audio at least not that i can discern.

 

[looser101]

Toroidal transformers can be affected by DC on the AC (wall power). They will physically hum (vibrate), hence my question. The devices I mentioned are devices that may cause DC on the AC line. If the source is not readily apparent then physically move the DAC downstairs, basement, etc, plug it in, turn it on and listen for the mechanical hum.

Hope that helps you find the source.

 

[Oublie]

Quote:

Originally Posted by looser101 /img/forum/go_quote.gif Toroidal transformers can be affected by DC on the AC (wall power). They will physically hum (vibrate), hence my question. The devices I mentioned are devices that may cause DC on the AC line. If the source is not readily apparent then physically move the DAC downstairs, basement, etc, plug it in, turn it on and listen for the mechanical hum. Hope that helps you find the source.

Thank Looser101, tried that , made no difference i'm afraid - could it be caused by the trafo running out of spec. e.g. the trafo has a switch connected to swtich between 110v and 220v (here in the uk its 240v) obviously i checked to make sure it was set to 220 prior to it's first switch on i'm just thinking what if the switch has been wired in reverse?! would that possibly cause it or would the unit just fry? What would happen it i tried running the unit unplugged from the circuit board but switched to 110v would it break the transformer when running 240v throught it?

 

[Matias]

I'm having very high DC output at the RCAs: from 6.8V to 10V!
Phones output is OK though, and everything else (coaxial, optical, preamp) works OK.

In preamp mode, if I turn the volume up or down fast, the phones output has a big DC peak up to 7V!

What is wrong? Bad opamp (a pair of OPA627)?

 

[adamus]

try a cheap opamp, 2134 or even a $1 5532 or something. if the problem goes its your opamps. if not then i dont know.

 

[adamus]

you could also check the pins of the opamps for shorts etc, somewhere on this board i started a thread about fake 627's, find that thread and there are correct values of resistance between each pin.

 

[Matias]

Thank you VERY much, adamus.