[TristranThorn]

Just bought a second hand Zero (upgraded version with OPA627, LT1364, pot) and notice a faint humming in headphones when connected to the headamp output. When I touch the chassis with my hand, the volume of the humming increases significantly. There is also an inconsistent crackle-like noise. The pot is noisy, but that was expected and is acceptable.

I have unsuccessfully tried a power cable with no ground pin and in other wall sockets as suggested in other threads. I have tried moving all other electrical equipment off of my desk as well. I opened it up and inspected the ground wire on the pot and that looks OK.

The signal is coming from a Macbook via optical output. The noise is present even when no signal is connected to the DAC. When the Zero's output is connected to an iBasso D2 amp, all noise described above is eliminated.

I would greatly appreciate any suggestions.

 

[Aynjell]

I'm going to subscribe to this thread for learning purposes, but isn't this a ground failure?

 

[Pricklely Peete]

2 things to check...make sure the volume pot has a casing ground wire to the pcb.. see this pic (the pot is the Alps upgrade)

The second is to make sure the opamps are all seated fully in their DIP8 sockets and oriented properly.

If you still have some scratchy crackling sounds (after checking the 2 suggested options) when you turn the vol pot try a little shot of Caig Deoxit or contact cleaner on the pot (internals) and work it around a bit. The other possibility is some untrimmed leads or leftover solder on the underside of the pcb. Take the main board out and inspect it for such things.

Hope that helps....

Peete.

 

[TristranThorn]

Well, you guys were right. The connection between PCB ground wire and pot was loose. I did inspect it before but not closely enough (i.e. touch it!). Had my dad solder it and the hum and pot noise are gone. Thank you very much, gentlemen, and sorry to waste your time.

 

[Pricklely Peete]

Not a waste of time at all...glad to have helped you solve the problem

I'm trying to figure out what you mean by "you guys"

Peete.

 

[TristranThorn]

Heh, gotta give Aynjell a little credit. 95% Peete, 5% Aynjell. Thanks again sir.