Hum over ADAT?

[dgatwood]

dgatwood- I'd love to get your insight on the fact that lifting the ground on the Behri didn't change anything as far as the hum goes. I'm wondering if a pigtail would work, if lifting the ground didn't do anything. This is partly due to my ignorance of the issue though.

You'll recall that I said it shouldn't do anything....

There are three causes of hum that I'm aware of:

1. A device whose power supply isn't properly filtered. This device will hum even in isolation.

2. A device whose input is connected through a resistor to ground, but whose ground is floating. This occurs because in the absence of a true ground, the path of least resistance from the shield to ground is through the resistor into the input. NOTE: This requires another device electrically connected to this one (not through an optical cable). In this case, the device with a poor ground is the destination. This requires a second device with a poor ground to generate the noise.

3. A device whose shield is properly grounded, but which is attached to a device whose shield is not and which generates noise on the shield. The noise passes through the shield on the cable and induces noise on the signal line.

In case #1, the device will hum in isolation, and since it does not have a valid ground, disconnecting the ground (if there is one) won't do anything. In case #2, the device doesn't have a valid ground, so disconnecting the ground (if there is one) won't do anything. Only in case #3 will disconnecting the ground from the wall make the hum go away, because that's the only case in which the device actually had a valid ground to begin with.

Thus, if the hum went away in your case, it would mean that A. that device had a working ground, and B. the device is hooked up through a real metal cable (with a metal shield) to the device that is actually generating the hum. However, the Behringer hums in isolation, which won't occur with case #3, so lifting the ground couldn't reasonably have made the hum go away.

The problem is that the Behringer device was electrically designed for the case ground and signal ground to be grounded, but due to something wrong in the power supply, they aren't. Probably a manufacturing defect. Anyway, the pigtail should probably do the trick. It's a workaround, though. Ideally, somebody should look inside the thing and figure out what's wrong with the ground in the power supply.

Oh, just to rule out the obvious, have you tried using a different power cord?

 

[jabulani jonny]

That is really good info, It'll take me a few reads to absorb it, but very good info. I haven't tried a different cable. I'll do that and see. Question: Would opening up the power supply and looking at it provide anything? I mean, is there something that would be noticeable that could be fixed?

Well, before I do that, i'm gonna check the warranty and see if I can replace it.

 

[dgatwood]

That is really good info, It'll take me a few reads to absorb it, but very good info. I haven't tried a different cable. I'll do that and see. Question: Would opening up the power supply and looking at it provide anything? I mean, is there something that would be noticeable that could be fixed?

That would depend on what's wrong. I have no way of knowing that without opening it up myself and looking inside.

 

[RAK]

mkay, I'm stumped. I picked up a 6ft 75ohm BNC cable from Radio Shack and now the Behri is slaved to the MOTU at 44.1. Check.

You say the Behringer is slaved to the MOTU at 44.1? Did you mean you selected 44.1 as clock source on the Behringer? If you did that means you set the behringer as Master. The two clock settings on the Behringer to act as Master are 44.1 & 48. The other two settings set the Berhinger to act as Slave. If you want to Slave the Behringer to the MOTU via BNC, make sure you have selected "WC IN" on the Behringer, and that you're connected to the BNC Out on the MOTU. Also, make sure the Optical IN on the MOTU is set to ADAT and not TosLink.

Just trying to clarify.

 

[RAK]

Here's an interesting point. The level of the hum is different between channels and one channel has none at all, zero, clean as a whistle. What's up with that?

Any other ideas besides trying a different ADAT cable?

Jonathan

Well, here's something I just thought of, but I'm not really sure if would/could be a cause of the problem.

Do you have the Phantom Power on on the Behringer? (point of information for those who don't know the ADA8000's phantom power is universal across all 8 channels). My question (that I've never really explored) is could the phantom power being on with no mics plugged in be creating noise? Does that make sense to anyone (I'm not sure it does to me) Or maybe it's just a failure of the phantom power in the behringer.
But if you've got it off, then I guess it's not the issue.

I've not had problems with my ADA8000, but I certainly wouldn't be surprised to hear it had a bad power supply.

 

[jabulani jonny]

Hey Rak, yeah I've got the correct setup as far as Master/Slave going on. I prolly just mispoke. Also, I've got the phantom off so it's not that. I just think it's a faulty unit and unfortunately I didn't catch this when I was still in warranty. Crap. So now I need to sell this unit to get the Digimax, but I'm not sure if you can sell it with a faulty power supply. That just sucks.

Jonathan

 

[RAK]

Maybe you can sell it to someone who wants an electronics project to play with. I hope it works out for you.

 

[SonicAlbert]

First, you don't know that it has a faulty power supply. At this point that is still speculation from people that have neither seen, heard, or tested the unit. For all we know it could be within spec, but you have higher standards than can be met by the cheapest 8 channel converter on the planet. Or, it could some other flaw, something else out of spec within the unit.

I certainly don't feel right about pawning off broken gear on unsuspecting eBay-ites. I've had people do that to me a number of times, and it is unfair to say the least.

The unit is most likely not worth the time/expense/shipping cost of fixing, so maybe just write it off and figure out how to pay for a better converter from scratch.

There have been many times where I've had to learn a lesson the hard way, or the expensive way. Buying cheap gear and then being stuck with subpar performance is one of those lessons that one usually learns the hard way.

 

[RAK]

First, you don't know that it has a faulty power supply. At this point that is still speculation from people that have neither seen, heard, or tested the unit. For all we know it could be within spec, but you have higher standards than can be met by the cheapest 8 channel converter on the planet. Or, it could some other flaw, something else out of spec within the unit.

Well that's true, but I was taking his word that the noise he was hearing was more than the "normal" amount. I have the ADA8000 and it's certainly not quiet, but I've never had an issue with it, or felt the noise floor was too great.

I certainly don't feel right about pawning off broken gear on unsuspecting eBay-ites. I've had people do that to me a number of times, and it is unfair to say the least.

Unless I missed a post, who said anything about doing this?

 

[SonicAlbert]

Unless I missed a post, who said anything about doing this?

I was just agreeing with and amplifying what he said in post #46.

 

[jabulani jonny]

Hey Sonic, I hear you. If I do sell it, I'll fully disclose what I've run into, along with the fact that it is still undetermined what it is. I'm not into hoodwinking anyone, but any little bit that I can get to go towards the Digimax will certainly help.

I think what makes me think it's the unit the most is the different volume levels between channels. To me that's the biggest indicator. If it were the cable or anything external I would expect the level of hum to be consistent between channels. However the fact that there are a couple of louder channels and one that has no hum at all makes me suspicious.

Jonathan