[HairyMerkin]

I've got a hum when my CMOY is silent.
 
I'm fairly certain it's a ground thing because I can eliminate it entirely if I touch the 3.5mm jack and the outside of the case.
 
nb. I have a cable that ends in a gold connector (metal) and that's what I'm touching.
 

It's a ground loop right?
 
I've tried it with a cord that ends in a plastic connector but it's still the same.

 

[Yoga Flame]

How is your CMoy powered? And what is the source feeding it?
 
(The picture doesn't show up for me.)
 

 

[wdahm519]

Need some more information.  Did you use insulated input and output connectors or is the ground shielding of the in/out connectors touching the metal case?  
 
Its usually not a good idea to ground the input and output to the same ground.  Try an insulated output connector.

 

[DefQon]

Background hums are GND and power related issues.
 
Sounds like you might have a GND loop here or if your Cmoy is using 9v batteries, one of the batteries are on low power. If your using a power supply via transformer, you need a regulated PSU.

 

[HairyMerkin]

The battery wasn't flat
The PSU is regulated
 
 
http://parts.digikey.com/1/parts/103376-conn-rca-jack-r-a-black-pcb-rcj-041.html are the two coaxial SPDIF connectors

 

[wdahm519]

 
Quote:

The battery wasn't flat
The PSU is regulated
 
 
http://parts.digikey.com/1/parts/103376-conn-rca-jack-r-a-black-pcb-rcj-041.html are the two coaxial SPDIF connectors

 
Erm... those are not S/PDIF connectors.  Those are just standard mono RCA jacks.  I think that's what you meant though.  Also, those are not the connectors I'm talking about.  I'm talking about the 3.5mm stereo audio jacks on the CMoy.  
 
 

 

[HairyMerkin]

 
Quote:

 
Quote:

The battery wasn't flat
The PSU is regulated
 
 
http://parts.digikey.com/1/parts/103376-conn-rca-jack-r-a-black-pcb-rcj-041.html are the two coaxial SPDIF connectors

 
Erm... those are not S/PDIF connectors.  Those are just standard mono RCA jacks.  I think that's what you meant though.  Also, those are not the connectors I'm talking about.  I'm talking about the 3.5mm stereo audio jacks on the CMoy.  
 
 

 
 
Isn't that what S/PDIF connectors are? RCA jacks for coaxial S/PDIF, and toslink for optical?
 
How do I tell if they are insulated on the cmoy?
 
They look identical to these; http://au.mouser.com/ProductDetail/ADAM-TECH/ASJ-6-4A/?qs=ogqIPVdloe%252bUizPi9ZU1ImlMhigygBB9RCjPw0SWK4E%3d

 

[wdahm519]

 
Quote:

 
 
 
Isn't that what S/PDIF connectors are? RCA jacks for coaxial S/PDIF, and toslink for optical?
 
How do I tell if they are insulated on the cmoy?
 
They look identical to these; http://au.mouser.com/ProductDetail/ADAM-TECH/ASJ-6-4A/?qs=ogqIPVdloe%252bUizPi9ZU1ImlMhigygBB9RCjPw0SWK4E%3d

 
Uhh, sure.  If you want to think about it that way.  But S/PDIF is Sony/Phillips DIGITAL Interface Format, and you're passing analog.  So, it doesn't really make sense to talk about S/PDIF.  Its an RCA, and more people will understand what you're talking about if you say that.
 
Well, if the ground shield is tied to ground on the 3.5mm jack and is touching the metal of the case then its unshielded.  You'd need a multimeter to figure this out.  But, its probably your problem.  When you touch the input/output, you become ground and it silences the hum.

 

[HairyMerkin]

I've got a multimeter, what do I need to check?
 
If that was the case, and it was the CMOY wouldn't it also have a hum when I'm running off USB on the dac? It doesn't

 

[wdahm519]

Check for continuity between the ground pin on the 3.5mm jack and the case, and also for continuity between ground on the board and the case.
 
It doesn't have hum when you're running the DAC?  I mean, you still have a 3.5mm connector being plugged into the CMoy.  It should be the same.  You're sure this isn't just a noisy signal problem?  Have you omitted all other possibilities other than the Cmoy itself? 
 
If not, start there.

 

[HairyMerkin]

If there is continuity between the altoids tin and the CMOY I need to put something inbetween where they touch, right?

 

[HairyMerkin]

 
Quote:

If there is continuity between the altoids tin and the CMOY I need to put something inbetween where they touch, right?

I used masking tape just to check. And it worked.
 
The CMOY grounding against the case (from the pot) caused a hum while using coaxial input to the y1 DAC > amp, that is now gone.
 
 

 

[DefQon]

As I stated earlier, background hums are always a GND and/or power related issue. It's good that you found your problem and rectified it.
 
Def