Hum over ADAT?

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jabulani jonny

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Hey guys, let me first say that I've got a Furman PL Plus on the way that I'm hoping will help filter any power noise, but here's the issue. I've got a Behringer ADA8000 that connects to a MOTU 896HD by an ADAT optical cable. Both units are plugged into the same halfway decent consumer power strip. My monitors are also plugged into this power strip. I'm getting what sounds like a ground hum, but I thought that if everything was plugged into the same power source that it shouldn't be doing that. I'm thinking the power source is the issue, but I'm wanting to trouble shoot any other possibilities. With only a few variables involved, does anyone have thoughts as to what might be causing the hum. Here's the equipment that I've run and still get the hum.

MOTU 896HD- plugged into power strip
Behringer ADA8000 hooked to 896 through optical- plugged into power strip
Computer- plugged into power strip
2 Wharfedale monitors running balanced cables from balanced output of 896- plugged into power strip


Thx for the help.

Jonathan
 
When do you experience the hum (is there a source on the input of the mixer)?
What other connections besides optial ADAT cables connect the gear?
Can you hear it on the headphone monitor of the board while you hear it on your monitors... how 'bout with the monitors powered down?... everything but the board powered down?

Isolate down to the point where you loose the hum... then reconnect pieces one at a time, carefully monitoring (through cans and monitors) what piece creates it...

You're not getting a ground loop through optical cables... it's just passing along a hum from one of the connected sources
 
Hey MOFO, no other connected sources. The only connections with the hum audible are those mentioned in the previous post. I'm gonna do some more 'sperimentin' tonight and see if I can nail it down. Thanks.

Jonathan
 
Your only analog cables are from the 896 to the monitors. Either the monitors are humming for some reason, or there is a some interference leaking into those audio lines. That's where I'd start looking for the hum anyway.

You should try disconnecting the Behringer to see if that reduces or eliminates the hum. Also check to make sure that the levels on your 896 are correct. For example, if you have the Behringer feeding the 896 and both of the units have their preamps turned up high, you will most likely get some noise.
 
K, got my power conditioner in and plugged it up. I had the Behringer ADA8000 connected to the MOTU896hd through ADAT optical with both plugged into the Furman PL Plus. All inputs were cut all the way down. The monitors were plugged into the MOTU896HD using Balanced XLR cables and not crossing any power cables. These were the only things plugged in and hooked together. I still had the hum.

I then had an idea about the clock source since the ADA8000 was set as the master since it was running into the ADAT in on the MOTU896HD. The last I checked, I had the MOTU set as the slave. Well I powered down and changed the ADA8000 to the slave and the hum disappeared. So....is it alright to run the ADA8000 using it's internal clock and the MOTU896hd using its internal clock, since I don't have an ADAT cable running out from the MOTU 896hd to the in on the ADA8000. Will this degrade signal somehow? T

Thanks for the help!!

Jonathan
 
jabulani jonny said:
K, got my power conditioner in and plugged it up. I had the Behringer ADA8000 connected to the MOTU896hd through ADAT optical with both plugged into the Furman PL Plus. All inputs were cut all the way down. The monitors were plugged into the MOTU896HD using Balanced XLR cables and not crossing any power cables. These were the only things plugged in and hooked together. I still had the hum.

I then had an idea about the clock source since the ADA8000 was set as the master since it was running into the ADAT in on the MOTU896HD. The last I checked, I had the MOTU set as the slave. Well I powered down and changed the ADA8000 to the slave and the hum disappeared. So....is it alright to run the ADA8000 using it's internal clock and the MOTU896hd using its internal clock, since I don't have an ADAT cable running out from the MOTU 896hd to the in on the ADA8000. Will this degrade signal somehow? T

Thanks for the help!!

Jonathan
Click to expand...

Go buy a 75ohm BNC cable and connect the MOTU wordclock out to the Behringer clock input. They are only a couple of bucks at an electronics shop (note: they are 3-4x more expensive at places like Sam Ash though!)

You are better off using the MOTU's clock as opposed to the Behringer's.

In any digital system you should always have a single master clock (in this case it should be the MOTU).
 
Hey tnj, yeah that's what i was thinking. I appreciate you confirming that though. I'll swing by and pick one up. Thanks for the help ya'll.
 
tnjazz said:
You are better off using the MOTU's clock as opposed to the Behringer's.

In any digital system you should always have a single master clock (in this case it should be the MOTU).
Click to expand...

Agreed. That said, there's not a snowball's chance in you-know-where that an unstable clock will cause hum. In the unlikely event that the clock is even unstable enough to produce any audible artifacts (doubtful), you'll just hear a small loss in high frequency clarity. If it gets farther out still, the other end will start ignoring it and you'll get stuttering and dropouts, but still no hum.

The reason your hum disappeared when you switched the Behringer to slave is that ADAT cables only pass a signal in one direction. With only a single cable from its output to the 896's input, the Behringer didn't have any input signal to slave to. Thus, its converters stopped processing audio and stopped generating a signal. What this tells us is that the Behringer has a hum problem even with all the inputs turned down. Does the Behringer have a three-prong power cord? I'm guessing the answer is "no", but....
 
It's actually not alright to have different digital devices running on their own clocks. You'll get other artifacts besides the hum, like pops and clicks. A clocking problem wouldn't cause the hum anyway.

As said earlier, you should get a BNC cable and slave the Behringer unit to the MOTU. However, the good news is that you seem to have isolated the Behringer as the culprit. Now it's just a matter of seeing if you can figure out the real cause of the hum and find a way to eliminate it for good.
 
gatwood, when I had the hum I had the Behringer set as the Master and the 896hd set as the slave. I could get mic/line signals through the Behringer, but with the hum. The hum went away when I switched the Behri to slave. The Behri should not have been looking for something to slave to as it was set to master and, as you state, I only had an ADAT cable from its output to the 896hd input. Both the Behri and the 896hd have three pronged power cords and were both in the same power source. Not sure that all this means anything as switching it to slave seemed to fix the issue. I'm ordering a BNC today from here: https://www.digitalwatchguard.com/securitycameras/pc/viewPrd.asp?idcategory=247&idproduct=2280

That looks like it should do the trick, any caveats? Thx for the help!

Jonathan
 
jabulani jonny said:
gatwood, when I had the hum I had the Behringer set as the Master and the 896hd set as the slave. I could get mic/line signals through the Behringer, but with the hum. The hum went away when I switched the Behri to slave. The Behri should not have been looking for something to slave to as it was set to master and, as you state, I only had an ADAT cable from its output to the 896hd input. Both the Behri and the 896hd have three pronged power cords and were both in the same power source. Not sure that all this means anything as switching it to slave seemed to fix the issue. I'm ordering a BNC today from here: https://www.digitalwatchguard.com/securitycameras/pc/viewPrd.asp?idcategory=247&idproduct=2280

That looks like it should do the trick, any caveats? Thx for the help!

Jonathan
Click to expand...

Does the Behringer Hum when nothing is connected (except a monitoring point) and the Clock is set to master

No... but if you sing a few bars :D
 
Hey MoFo, was that a real question? If so, the answer was "yes". Nothing but monitors and ADAT connected, set to Master=hum, set to slave with no BNC or ADAT input= no hum.
 
I think you need to confirm that it is indeed passing signal in it's current state as the slave device. It's useless unless it is clocked to a master device. So you need to hook up an ADAT cable from the MOTU to the Behringer so the Behringer has something to clock to. If it is still quiet, then you've solved your problem. But I really don't believe it is fully sorted out yet.
 
jabulani jonny said:
Hey MoFo, was that a real question? If so, the answer was "yes". Nothing but monitors and ADAT connected, set to Master=hum, set to slave with no BNC or ADAT input= no hum.
Click to expand...
Yup... real question... but I was suggesting you test with nothing connected to the Behringer... no adat, no powered monitors... isolate the ADA8000 as the only device under test... though I'm not sure of the monitoring capabilties of the 8000 without connecting the line outs to you monitors...

And Albert's correct, you haven't fixed the problem you've only masked it... If you ever want to use the digital I/O on the 8000 you'll wish you had resolved this early in the game
 
To make things more complicated...

Just an added bonus, tho I don't own the ADA8K, I was looking into one some time ago. I remember reading that the Berry produced a much lesser quality sound when it was slaved to another clock. Conversely, I've discovered the same was true when using my Motu 828mkII. I'd slave the Motu to the clock coming off my MAudio 24/96, (i.e.), and sound quality wasn't nearly as strong.
 
jabulani jonny said:
The hum went away when I switched the Behri to slave. The Behri should not have been looking for something to slave to as it was set to master and, as you state, I only had an ADAT cable from its output to the 896hd input.
Click to expand...

Let me try this again. A digital converter requires a clock signal to function. When the Behringer is in "master" mode, it is generating its own clock signal. When you put it in "slave" mode, it has to get the clock signal from somewhere else.

In order for the Behringer to get a clock signal from somewhere else, you must either be feeding in an input via the ADAT port or via a clock connection. If nothing is hooked up to either of those inputs, the Behringer can't really go into slave mode because it can't slave to anything. Thus, when you do that, it just plain shuts off its output.

Thus, the hum didn't go away because you fixed the hum. The hum went away because the Behringer stopped sending out any signal at all. It is equivalent to simply disconnecting the ADAT connection between the two devices.

Here's my advice.... The Behringer obviously doesn't have a valid signal ground. Probably just bad design, since there's obviously a valid chassis ground (3-pin plug). Do a quick search for "pigtails" on the board and read my advice to any of a half dozen folks who have had similar problems with different pieces of gear. The first four search results (ignoring this message) are on this subject. The same technique should solve your problem unless the Behringer is just plain hosed. :D
 
AAaaaaaaaahhhhhh! :lightbulb: I see. I should've picked up on that. So the hum's not gone, I'm just not hearing it. Well dang. I've got a BNC cable coming in, had to order it because nobody in this town has one under $35. I'll do the search as you suggest and see what I can come up with. I greatly appreciate all the help and taking the time to walk me through this. I'm ready to get rid of the Behri anyway, my next purchase, besides a Macbook Pro, is to upgrade to a Digimax LT.

Jonathan
 
Here's the thread that you spoke at length about it: https://homerecording.com/bbs/showthread.php?t=207689&highlight=pigtails

The ADA has 8 XLR inputs and the ouput is ADAT to the Motu896hd, as we've discussed. So I'm a little confused as to where I would use a "pigtail", not to mention that I've never soldered, but have been meaning to learn cause I need more cables.

And is there a way to check to see if it indeed is the power supply on the Behri? It does have an internal power supply with a 3 prong cable, looks just like any other seemingly properly grounded piece of gear.

Jonathan

Edited: "i" before "e", except after "c"
 
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You could try lifting the ground to see if that's it. Go to the hardware store and get a small adapter that has the three prong input on one side, but only two coming out the other. No ground prong in other words. Then plug that in and see if it makes a difference.

That will tell you if you have a grounding problem, but it won't tell you what the problem is. It could be any of a number of things, one of which could be the Behringer.

Is the Behringer located near any strong magnetic fields?
 
NeoMagick said:
Just an added bonus, tho I don't own the ADA8K, I was looking into one some time ago. I remember reading that the Berry produced a much lesser quality sound when it was slaved to another clock. Conversely, I've discovered the same was true when using my Motu 828mkII. I'd slave the Motu to the clock coming off my MAudio 24/96, (i.e.), and sound quality wasn't nearly as strong.
Click to expand...

This is incorrect. The opposite has been found to be true. The Behringer units sounded noticeably better when slaved to a good clock (in the tests it was a Big Ben). Of course the key is to slave it to a GOOD clock, not just ANOTHER clock.

As far as the MOTU and the M-Audio clocking situation you're describing, MOTU clocks are known to suck badly in all of their units. However, I suspect M-Audio has an even worse clock. Hence your discovery.

jabulani jonny said:
AAaaaaaaaahhhhhh! :lightbulb: I see. I should've picked up on that. So the hum's not gone, I'm just not hearing it. Well dang. I've got a BNC cable coming in, had to order it because nobody in this town has one under $35. I'll do the search as you suggest and see what I can come up with. I greatly appreciate all the help and taking the time to walk me through this. I'm ready to get rid of the Behri anyway, my next purchase, besides a Macbook Pro, is to upgrade to a Digimax LT.

Jonathan
Click to expand...

You are on the right track here. This is a 75 ohm cable so when it comes in you should be ready to test properly. If I understand correctly you don't have another ADAT cable you can connect to do your testing, so until the BNC comes in there's not much you can do. You'll set the Behri to slave, set the MOTU to master and then connect lightpipe out from the Behri to the MOTU. If the hum returns there is a grounding issue, likely with the Behri as has already been suggested. HOWEVER, you have then established a good clocking environment so buying the $2 BNC cable is not a waste of money...
 
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