Hum over ADAT?

[dgatwood]

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.

You can build a pigtail like I described for XLR just the same way as you would for 1/4". You wire a normal XLR cable and add the extra wire on the ground. The only difference for XLR is that you should also add a heavy gauge ground jumper wire between the ground pin on the XLR connector and the shield lug so that you ground both the signal ground and the chassis ground on the problematic piece of gear. Probably not required, but a good idea, anwyay.

 

[dgatwood]

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.
?

In this case, that definitely will not work. There is no gear with an electrical connection to the Behringer. Thus, the Behringer's power supply design is the source of noise on the ground bus, but the ground on its inputs is also probably coupled to the signal ground (which apparently is the same as its chassis ground) through a resistor. Therefore, the Behringer is noisy because the ground is already floating.

Note that I can't imagine why this would be an issue for a 3-prong piece of gear unless they did something really wrong, but....

Edit: lifting the mains ground on the Behringer -might- work -if- you don't have a valid mains ground on your outlet at all. If so, they you're getting back current from the floating ground on your power strip and another device is generating the noise. That would be a bizarre fluke, though, and would indicate something wrong with your building wiring.

 

[dgatwood]

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...

The funny thing is this: now that I think about it, the BNC cable might make things somewhat better---not because the hum is clock-related, but because it will provide a grounding path out of the unit through the BNC cable. In fact, it will probably make things better even without switching the sync source.

That said, I'd be surprised if the problem went away completely as a result of doing this---unless the noise level is relatively small....

 

[jabulani jonny]

I do have a ground lift that I can try this evening after work if you think I should. dgatwood I've read many of your comments advising not to lift the ground on equipment like this so I don't want to do anything that would cause any problems. I'm gonna try to look around town a little more, I've looked at our music store, conveniently named "Everything Musical" that never seems to have what I'm looking for. They had a 12ft BNC cable for $35. Only place I haven't checked is Radio Shack in the mall and to see if there were any video survielance or video supply stores in town.

The only thing I didn't do the other night was to see if I actually got an audio signal through the Behri to the MOTU after changing the clock source. Based on your earlier comments it looks like I should not get an audio signal coming through the Behri since, without an ADAT cable connected to the Behri input from the Motu ADAT output for clock sake and without a BNC connection, it has nothing to clock to being set as the slave.

Unfortunately I don't have another ADAT cable to test that theory, so I'm stuck til I get the BNC cable.

So...dgatwood, should I try lifting? Again, both the Behri ADA and the Motu896hd are plugged, with 3 pronged plugs, into a Furman Pl-Plus Series II, which is the only thing plugged into an outlet of my house, which was built in 2003.

I don't think I'm up to creating an XLR pigtail for every input on the Behri so anything I can do to skirt that would be preferred. Thx!

Jonathan

 

[SonicAlbert]

Try the ground lift. You only have to do it for as long as it takes to see if it works. If it doesn't help, then go back to the way it was. If it does work, then you are at least part way toward solving the root cause of your hum problem.

And certainly gear can hum by itself without anything being connected to it. That happens all the time with amps.

There's a great little device you can buy from Radio Shack for around $5 that tests the continuity of your power receptacles. I'd suggest buying one and testing all outlets before you use them. It will tell you if there's a problem.

Just because a house is new does not necessarily mean it is wired 100% correctly. Someone could have goofed.

Also, sometimes hunting down and solving hums can involve as much "magic" as it does "science". So examine all possibilities, even those that might seem like they wouldn't matter. In this category you have to consider any electronic or electrical equipment in near proximity to your audio gear. This includes wall warts and power lines, especially wall warts or external power supplies of any kind. It also includes the internal power supplies of other gear that may be near your Behringer. I've often found it very helpful to physically move gear around to see if a hum is lessened.

 

[jabulani jonny]

Ok, another quick question guys. I've located a 6ft BNC cable at Radio Shack for $10. I can spring for that. There are 1ft varieties available on line. Will the additional length introduce any oddities since it will be in the rack along with lots of other cables, ie. power from the units and mic/instrument cables when recording. Does the length matter?

Jonathan

 

[RAK]

For what it's worth, I have a MOTU828mkII and the Behringer ADA8000 (in 1 handy 2-rack space travel case no less!!). Anywho, I got the Behringer ADAT output going to my MOTU ADAT IN, and achieve the clock sync through the Behringer BNC IN to the MOTU BNC OUT (MOTU acting as Master, Behringer acting as Slave). Then I'll usually use the MOTU ADAT Out in Toslink mode for backup to a HIMD or some such device.

Never had any problems in terms of grounding noise with this setup.
I would also suggest trying the ground lift.

I think I have a 6 ft BNC cable or something like that (it was all they had at radio shack when I was there). I just leave it coiled with a velcro tie in my rack case connected between the two interfaces.

 

[jabulani jonny]

Bingo, that's what I'll do then instead of waiting on one to be shipped. Are you saying you run your ADA with a ground lift? I've got an 8 space Gator roller rack that houses a Furman Pl-plus, the Motu896, the Behringer ADA8000, a couple 2 channel compressors and a headphone amp. Gonna stick an outboard effects unit in there as well. A perfect mobile recording setup. Love it...except for the hum I was getting.

I'll report back with findings. Thx. guys

 

[tnjazz]

Ok, another quick question guys. I've located a 6ft BNC cable at Radio Shack for $10. I can spring for that. There are 1ft varieties available on line. Will the additional length introduce any oddities since it will be in the rack along with lots of other cables, ie. power from the units and mic/instrument cables when recording. Does the length matter?

Jonathan

No. Make sure it's 75 ohm cable though. There are also 50 ohm cables with BNC connectors, for other uses...

 

[RAK]

Are you saying you run your ADA with a ground lift?

No. I haven't run across any hum issues (other than bad TS cables when doing recording, but that's something different). I was just saying you might try the ground lift idea to see if that helps.

 

[jabulani jonny]

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. With only my monitors hooked up, no inputs into either the ADA nor the MOTU, no other devices hooked to the Furman, other than one monitor. I get the hum with or without a ground lift. Yes, with the ground lift in there's still a hum and I don't think there's an audible difference, other than the fact that it's a different volume between channels!!! So I'm stumped. I can get audio through the Behri, but there's a faint bit of hum at decent listening levels. 8 channels of that won't do. Again, the ground lift doesn't help. When I check the MOTU channels, they're dead quiet.


So...what's the freakin deal with this thing?

 

[Brooks]

Cut the Shield on your monitor cables.

 

[MOFO Pro]

You said one monitor powered by the furman?? You're powering your monitors from two different outlets??

 

[dgatwood]

I don't think I'm up to creating an XLR pigtail for every input on the Behri so anything I can do to skirt that would be preferred. Thx!

You only need to add a pigtail for one input per device. It is same to assume that the ground contacts on all of the input jacks are connected together internally.

 

[dgatwood]

Ok, another quick question guys. I've located a 6ft BNC cable at Radio Shack for $10. I can spring for that. There are 1ft varieties available on line. Will the additional length introduce any oddities since it will be in the rack along with lots of other cables, ie. power from the units and mic/instrument cables when recording. Does the length matter?

If it is long enough to connect between the devices, you're fine. I wouldn't go over about 20 feet. I think that's the suggested maximum.

I usually use a standard coaxial cable (for cable TV) with an adaptor on each end. I have a few standard adaptors I use when I need some obscure 75 ohm connection---some F-to-RCA adaptors, F-to-BNC adaptors, etc.

 

[jabulani jonny]

Mofo- no the Motu, the Behri and one monitor are all plugged into the Furman which is plugged into the wall. There are no other devices plugged into the Furman and not other sources connected either to the Behri or the Motu.

Brooks- ummm....no, now where's my Staples button?

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.

Jonathan

I promise I didn't think it was going to turn into this. I appreciate you guys stickin' with me to help me work it out. I'm stuck at this point.

 

[SonicAlbert]

Where is the other monitor plugged into? Is the hum coming out of both speakers?

Since the ground lift didn't work, I'll suggest again that you take your gear out of the rack (one by one) and move it around to see if that makes a difference. Start with the Behringer. Also move around the routing of the power cords.

You need to eliminate all variables, and you've hardly started to do that. Also try plugging both monitors into the same place. What else is on the Furman power strip besides those units you've mentioned?

Also, some gear is more sensitive to power issues or interference than others. What else is on the breaker that is powering the Furman? Are there dimmers anywhere in that circuit?

I'm going to start repeating myself, but I really think you should spend the 5 bucks at Radio Shack and get their continuity tester.

You should also different ADAT cables, and if at all possible try a different ADA8000 unit in place of the one you are using now. There may just be a problem with unit itself.

ADAT cables are not necessarily perfect, just because they are optical. Check the ends and make sure the end of the cable is clean and not damaged in any way. I've had the ends of the cables get messed up and then cause weird problems. Not sure how that would cause a hum, but worth a look anyway.

Like I said, there are so many variables and you've really eliminated very few at this point.

 

[jabulani jonny]

Hey Sonic, here's what I just did. I took the Behri completely out of the rack and set it 4 feet from the Motu on the floor. There is nothing, not a single unit plugged into the Furman except for the Motu and the Behri. I did not use my monitors, just headphones. I made sure nothing was crossing any power cables, BNC or ADAT. I did not have a mic or an instrument plugged in, just going off arming the track to monitor and hearing the hum. Literally, just the Motu and the Behri into the Furman and hooked together via BNC with the Behri slaved to the Motu and an ADAT out of the Behri into the Motu. There is nothing else plugged in anywhere, not into the Furman, not into the wall, not even in the room. The room receptacles are on their own breaker in the Fuse box. They do not share with any other room or any other appliance, no dimmers.

Just using headphones, I tried several different receptacles in the room, all gave the hum. In the phones the hum seemed lower in level than in the monitors. You may say, duh!, but I had the phones level maxed out. When I did plug a single monitor into the Furman to hear what it sounded like, it was as strong as it was last night. Now, it's not just crazy overbearing. I've got the volume cut up pretty good in Nuendo and on the MOTU. However, if I start stacking channels it's gonna get nasty quick.

I then tried several receptacles throughout the house and there was no change in the hum, still there. I tried different configurations of plugs on the back of the Furman, with no luck. I checked the ends of the ADAT cable and it looks fine to me, it's not that old either. The only thing I haven't done is try another ADAT, because I don't have another, but I'll pick one up today and try that. I don't have access to another ADA8000. I don't know anyone that own's one, or a set of preamps with ADAT output. I'll see if I can't do some more digging.

I looked at Testers yesterday at Radio Shack, but didn't really know what I was looking for. There was a little yellow plug looking thing with three lights on it. Is that what you're talking about? I have no electrical experience if you can't tell. Thanks a ton for the help.

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

 

[SonicAlbert]

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?

I'm really glad you tried moving the ADA around and isolated it, along with trying different outlets. I think that helps reveal what the problem is.

First, you are still getting the hum when the ADA is isolated, which pretty much proves that the ADA is the source of the hum.

Second, it is interesting that different channels of the Behringer are giving off different levels of hum. There's no real nice way of saying this, but that's kind of a characteristic of cheap gear. Cheap parts, flimsy construction, and the result is an inconsistent product and you tearing your hair out.

I noticed the same thing with some of my Mackie mixers (don't have them anymore by the way). The channels didn't sound the same. Some were louder than others, some brighter or darker than others, almost like they were eq'ed. Some noisier than others.

If that ADA8000 is still under warranty I would try to get the store to take it back or exchange it.

However, and this is a big however:

You mention that you have your headphones up all the way to hear this hum. That's really loud, and you'd blow your ears out if you actually sent audio through them at that volume. It is normal at those levels to hear hiss, because you are listening to an analog signal. Hum is bad at any volume level though. In a perfect world there should be no hum at all, but it can be very tought ot get rid of entirely.

If you turn your headphones down to normal listening levels, can you hear any hum at all? Or are you worried that the hum will stack up if you lay down multiple tracks over and over?

In that latter case, you might try using only the one or two quietest channels on the ADA8000. Definitely not a perfect solution.

You also might go up market a little bit and try out something like a Presonus DigiMax FS.

http://presonus.com/pr_digimaxfs.html

 

[jabulani jonny]

Sonic, the stacking of 8 tracks with the Behri is my concern. I primarily do live recording so I'd pretty much be using 8 tracks right then and there. It's funny that you mentiont the Digimax. That's exactly what I'm moving to. That's my next purchase, but I wanted to make sure before I tried to sell the Behri that it wasn't completely shot so I could atleast sell it with a clean conscience. I am going to try the warranty. I don't think I'm out, so I'll go that route. If I can get it replaced, I'll ebay it and spring for the Digimax LT, which is what I should've done in the first place. Oh well, live and learn.

Sonic, you and dgatwood have been a tremendous help. I greatly appreciate the patience ya'll took in going through this with me. I think as long as I keep the Behri low enough and use it sparingly I can get by until I spring for the Digimax. I think that's the ticket. Thanks a ton!!

Jonathan