How to fix 60 cycle hum in a DAC?

[barleyguy]

Quote:

I'm starting to get confused about your set up, you say you're connecting the profire and tango through an optical cable, so how are you measuring the analog outputs of the tango?  Are you looping them into it's own inputs?  Can I see a picture of your setup?

I only temporarily connected them analog in order to discern which ports had the hum on them (because the ProFire doesn't have any hum).  Normally I run the ProFire 2626 with two Tangos connected via optical.
 
Computer->Firewire->ProFire 2626->Tango In and Out Optical
 
when measuring, it was either:
 
Tango Out->ProFire In or ProFire Out->Tango In.  (I also tried Tango loopback, but looks just like the output.)
 
The power input section is a combination of Voltage Regulators and Electrolytic capacitors.  I'm pondering whether I should re-cap them and see if it helps.  I'll try to post a picture soon (been working too much).
 
Thanks,
 
Harley.

 

[samsquanch]

I think you're just having ground loop issues, get a ground lift, or modify a cable so that the shield on the connector plugging into the output of the tango is not connected. 
 
This appears to be the answer since when you loop the out to the in, you aren't having the 60hz issue.  (1 ground plane instead of 2)

 

[barleyguy]

Quote:

I think you're just having ground loop issues, get a ground lift, or modify a cable so that the shield on the connector plugging into the output of the tango is not connected. 
 
This appears to be the answer since when you loop the out to the in, you aren't having the 60hz issue.  (1 ground plane instead of 2)

The power supply plug going into the Tango isn't grounded.  It's a two prong.
 
The 60 hz does appear looping the out to the in.  It just doesn't appear when I go out of the ProFire.  The outputs of the Tangos always have it.

 

[samsquanch]

Quote:

The power supply plug going into the Tango isn't grounded.  It's a two prong.
 
The 60 hz does appear looping the out to the in.  It just doesn't appear when I go out of the ProFire.  The outputs of the Tangos always have it.

 
The issue might be that the tango is trying to ground itself through your computers dac, which is where it could be picking up the 60hz signal.  Ground issues are insanely complicated, and don't always make sense, even after you cure the problem.
 
I highly suggest using a ground lift if you're using balanced cables, or a 1:1 isolation transformer if you're using unbalanced connections.  This might not be the cure, but it's absolutely the first thing I would do if I were encountering this issue.
 
 
Edit:  When I posted this, I didn't appear to read correctly that the 60Hz appears when looping the out to the in.

 

[barleyguy]

Quote:

 
The issue might be that the tango is trying to ground itself through your computers dac, which is where it could be picking up the 60hz signal.  Ground issues are insanely complicated, and don't always make sense, even after you cure the problem.
 
I highly suggest using a ground lift if you're using balanced cables, or a 1:1 isolation transformer if you're using unbalanced connections.  This might not be the cure, but it's absolutely the first thing I would do if I were encountering this issue.

I seriously doubt that it's a ground loop, because it's consistent even when connected to the computer only over optical.  Optical cables can't have ground loops.

 

[samsquanch]

Quote:

I seriously doubt that it's a ground loop, because it's consistent even when connected to the computer only over optical.  Optical cables can't have ground loops.

 
OH FOR REAL?
 
 
Even when looping from the out to the in on the same piece of gear, I would lift the ground.  Reason:  I don't know how they have designed their ground plane.
 
It's a simple test to perform, you can hack up an old cable, or go buy a ground lift from guitar center or the likes, they're great things to have on hand if you're doing recording or live sound.  I'm being aggressive on this issue because it's the absolute second thing I would check if this were my rig and I was having this issue, first would be to check my cable management, which doesn't seem to be an issue in your case.  
 
As stated earlier in this thread ~-100db is well past inaudible.  Also, you won't be recording from the outputs, so in the end any hum on them shouldn't matter, as long as your inputs are clean.
 
If you're hungry to rip open your case and jab at the board with a soldering iron, then have at it, your gear, your time, your money.  Enjoy.

 

[barleyguy]

Quote:

 
OH FOR REAL?
 
 
Even when looping from the out to the in on the same piece of gear, I would lift the ground.  Reason:  I don't know how they have designed their ground plane.
 
It's a simple test to perform, you can hack up an old cable, or go buy a ground lift from guitar center or the likes, they're great things to have on hand if you're doing recording or live sound.  I'm being aggressive on this issue because it's the absolute second thing I would check if this were my rig and I was having this issue, first would be to check my cable management, which doesn't seem to be an issue in your case.  
 
As stated earlier in this thread ~-100db is well past inaudible.  Also, you won't be recording from the outputs, so in the end any hum on them shouldn't matter, as long as your inputs are clean.
 
If you're hungry to rip open your case and jab at the board with a soldering iron, then have at it, your gear, your time, your money.  Enjoy.

There's no ground to lift, because the power supply uses a two prong cable.
 
I am planning to use analog summing along with analog outboard gear, so I will be recording the outputs.  If I wasn't planning to record the outputs, I wouldn't have bothered with this thread in the first place.
 
But at -100 dB, it's likely the ambient room noise of anything coming in a microphone will greatly drown out the hum when it's played back, so I agree that it's unlikely to be a problem.

 

[KimLaroux]

In Canada, the neutral wire in AC is actually earthed. I don't know how it is elsewhere, but it's probably similar. So it may be possible that your gear still is grounded trough one of the wires. The AC cable that goes to the wall, can it be plugged either ways, or only one way?
 
And by "ground" we have to include reference. For example, the shield of an RCA cable. You need to connect it to something, somewhere. It may be connected to a floating signal ground on the DAC but connected to chassis ground on the other end. This is a common cause of ground hums. That the DAC is earthed or not is not really saying anything. The PSU still needs a 0V reference. It's still a matter of debate how this should be connected to chassis ground, or if it should be left floating. Because there are no standards, connecting different gears designed with different philosophy can ruin ground schemes. For example, by connecting the floating signal ground of a gear to the chassis of another.
 
If your DAC is not earthed, then it has a floating ground. By connecting it to other gear, you may be earthing this floating ground trough the audio cable's ground wire. This has the potential for ground issues.

 

[samsquanch]

Quote:

There's no ground to lift, because the power supply uses a two prong cable.
 
I am planning to use analog summing along with analog outboard gear, so I will be recording the outputs.  If I wasn't planning to record the outputs, I wouldn't have bothered with this thread in the first place.
 
But at -100 dB, it's likely the ambient room noise of anything coming in a microphone will greatly drown out the hum when it's played back, so I agree that it's unlikely to be a problem.

 
There is a ground lift because I'm not talking about earth ground, ground lift is referring to lifting the shield/ground wire on your audio interconnect.  Pin 1 on an XLR or the S of a TRS.  This is where the confusion is stemming from.  I am not talking about altering the ground on your power cable.
 
Plenty of people in this forum hyper obsess over things that don't matter, and not knowing you were planning on using outboard gear, this seemed to be on of them.
 
 
Addendum:
 
Ground lift:  http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/specialty-interface-solutions/lifter

 

[samsquanch]

Quote:

In Canada, the neutral wire in AC is actually earthed. I don't know how it is elsewhere, but it's probably similar. So it may be possible that your gear still is grounded trough one of the wires. The AC cable that goes to the wall, can it be plugged either ways, or only one way?
 
And by "ground" we have to include reference. For example, the shield of an RCA cable. You need to connect it to something, somewhere. It may be connected to a floating signal ground on the DAC but connected to chassis ground on the other end. This is a common cause of ground hums. That the DAC is earthed or not is not really saying anything. The PSU still needs a 0V reference. It's still a matter of debate how this should be connected to chassis ground, or if it should be left floating. Because there are no standards, connecting different gears designed with different philosophy can ruin ground schemes. For example, by connecting the floating signal ground of a gear to the chassis of another.
 
If your DAC is not earthed, then it has a floating ground. By connecting it to other gear, you may be earthing this floating ground trough the audio cable's ground wire. This has the potential for ground issues.

 
Good description on ground potential between gear.
 
In the USA the neutral and ground wires are bused together in the breaker panel, this is typical (99.99%), but not always.