I HATE GROUND LOOPS!!!
I've been fighting this issue for weeks now! I'll get it resolved, but it's sure driving me nuts... :? :? :? :? :? :? :? :? :?
The sad thing is, the electrical is fine. It's an issue between a "balanced" Hard Disc Recorder, and this "unbalanced" console.
I've done everything in terms of electrical. So now it's time to dive in further into the harnesses and HDR. (I've already dived into the belly of the console). I've lifted the grounds on the harness. Didn't change anything. If anything, it might be louder.
This loop has thown me for a loop!
That's my update. The sessions have been going well, but I can't mix until I resolve the grounding issue.
Anyone here had any experiences w/ troubleshooting or a resolution to a similar issue? (Without spending 4 digits).
Floating floor over basement concrete. (Artifact Recording)
Originally posted at johnlsayers.com, topic 839.
A couple things to try...
1. Connect the HDR to the same outlet as the console
2. Float the cold pin on the HDR output...some active balanced outputs cannot handle having this pin connected to ground.
Cheers
Kris
Very nice job on the plumbing, there, Aaron! I agree with Marc: if I ever have to do any such thing, consider me inspired. :) (Of course, my house was built in 2000, so I doubt I'll need to do that anytime soon! :lol:)
Burying the cleanout under concrete... Brilliant. :x
--Keith :mrgreen:
Aaron,
you can definately have a buzzing that takes place because of unruly gear coming together.
If thatt's the case - unhook everything and begin - very slowly and methodically putting together your system, testing with each and every piece you add into the chain. Eventually you'll find the offendingpiece or cable.
BUT - if it's a ground loop (as you seem to think) then the only cause can be multiple grounding points in your electrical / grounding service.
That would not be related to the gear - just to grounding points................
Chek to make certain that the everything you have (cable, telephone, etc.) is bonded to the same ground........ that's the only way you'll fix a true ground loop............
If you really want to know for sure - unhook everything from power sources and use an oscilloscope to test your ground circuit - if it has a ground loop you will get a dirty 60 Hz signal.......... if it's clean you don't have a ground loop.........
Rod
Already tried.1. Connect the HDR to the same outlet as the console
Also have tried (and is still currently wired this way). I lifted all ground pins between the console and the HDR.2. Float the cold pin on the HDR output...some active balanced outputs cannot handle having this pin connected to ground.
I have also done this. The only components at "that" point was...Console, Monitors, HDR, and LCD Screen. Here's a little more detail of what I have done and tried...grab a cup of coffee, you'll be reading this for awhile... I have lifted all grounds on every piece of equipment in the studio. I have pulled the modules out of the console and retightened all grounding points to the central star point of the console. I have tried running a separate ground wire from the console star ground to the star point at the panel. I have completely lifted the ground all together. I have tied neutral and ground together at the panel. I have run 2 new grounding rods. Tying the ground to one, and the neutral to the other. I have changed the console from 120VAC to 240VAC. (BTW...the console sounds better @ 240VAC). I have changed the HDR to run @ 240VAC as well. No change. I have lifted the ground points on the Elco connector in the console (made it worse). I have pulled the power supplies away from all audio cables, conduits, etc. Brought them in the control room. Isolated away from the rack. I have disconnected all cable connections from the studio system. I have disconnected all outboard gear, 2 track machines, amplifiers, and all other equipment (with the exception of the basic list above to make it work (console, monitors, LCD and HDR). I have lifted the Neutral/Ground connection at the main panel. I have measure the voltage between Neutral and Ground. There is about 0.2 volts if I remember correctly off the top of my head. And there are a few more, just can't think of them at the moment. Anything else??? :? :?If thatt's the case - unhook everything and begin - very slowly and methodically putting together your system, testing with each and every piece you add into the chain. Eventually you'll find the offendingpiece or cable.
Holy Moly! :shock: :mrgreen:
Looks like over the weekend or last few days, we've crossed over the 200k mark on views.
Well, on another note...still trying to trace down the issue of buzz from HDR to console. This weekend I resoldered and depinned a few things. So now the shields are lifted on the receiving end of the snakes from console to HDR and HDR to console. NO CHANGE!
The buzz appears to be coming through the + or Hi side of the signal path, not the - or Lo side. Go figure?
Any more suggestions? This is a new one for me. Just trying to avoid buying $4k worth of transformers. Can't afford 'em. :evil: :? :?
A few more questions...
What is your HDR (brand/model)..and do you have a schematic of the output stage? Same for the console...except what's the input stage look like?
Is the HDR truly balanced, or is it impedance balanced. Do you have buzz issues with only the outputs connected to the console, or just the inputs, or both?
If possible do your experiments on one channel of HDR output connected to the console...no sense working on a whole snake when chasing down a connection issue.
Have you ruled out a possible problem with the HDR itself...can you conect it to some other peice of gear (maybe a compressor with balanced input) and not get buzz?
BTW, don't float the shields on the unbalanced signal...it won't work properly. The same holds for impedanec balanced gear...you can't truly float this stuff.
Cheers and good luck!
Kris
It's a Mackie HDR 24/96. It worked fine w/ the previous console. And yes, I tested just before everything was swapped (console). The console is: Soundcraft Series 2400. (36 channel, 24 bus). No problems w/ 2" tape machine.What is your HDR (brand/model)..and do you have a schematic of the output stage? Same for the console...except what's the input stage look like?
Hadn't had a chance to call Mackie and find out.Is the HDR truly balanced, or is it impedance balanced.
As far as I can tell, it's when the output is connected to the console. Signal appears to be farely clean to the machine.Do you have buzz issues with only the outputs connected to the console, or just the inputs, or both?
Difficult to do w/ DB25's and Elco/Edac connectors on each end. But not entirely impossible. Just a PITA.If possible do your experiments on one channel of HDR output connected to the console...no sense working on a whole snake when chasing down a connection issue.
As mentioned above, works fine on a balanced console.Have you ruled out a possible problem with the HDR itself...can you conect it to some other peice of gear (maybe a compressor with balanced input) and not get buzz?
Are you referring to the console input or the HDR input? The shield is lifted at the input to the console, and at the input to the HDR. Originally, all were connected. According to several references, including the Soundcraft Manual, it mentions lifting the shield @ the receiving end of the snake.BTW, don't float the shields on the unbalanced signal...it won't work properly. The same holds for impedanec balanced gear...you can't truly float this stuff.
I'd suggest ordering some Dsub25 and Elco connectors from Digikey and making a dedicated test cable. One channel only, and perhaps include a Male/female XLR pair in the middle of the cable to let you play with different configuration options. Might be a good idea to wire up a second channel to an XLR so you can see if the noise is at the HDR side or at the console side (probably at the console. Does the noise affect all channels, or only the ones that are connected?Difficult to do w/ DB25's and Elco/Edac connectors on each end. But not entirely impossible. Just a PITA.
I'm refering to the console input...whichever signal is unbalanced (I think it's your console ins that are unbalanced, right?). By 'lifiting the shield' are you refering to a sheild going around an entire snake (which is okay to lift in an unbalanced connection), or the shield of twisted pairs within the snake (which would normally be carrying the ground reference)? without having a wiring diagrm it's kind of hard to know what your installation looks like. From your description of the symptom it sounds like it could be the cold (-) output from the HDR has been tied to ground,and it's trying to actively drive it. The usual way to connect active balanced outputs to unbalanced inputs is Balanced Ouput -> Unbalanced Input 1. Ground -> Ground 2. Hot (+) -> Input + 3. Cold (-) -> No connection I'd do a continuity test on your snake to make sure that the colds aren't conencted to ground. Oh, and does the buzz problem only occur on the return channels connected to the HDR, or does it afflict the whole console? BTW, you can use an active balanced receiver to get balanced inputs into your console. Would be way cheaper than 24 channels of good transformers. Cheers Kris[/list]Are you referring to the console input or the HDR input? The shield is lifted at the input to the console, and at the input to the HDR. Originally, all were connected. According to several references, including the Soundcraft Manual, it mentions lifting the shield @ the receiving end of the snake.
Here is whats on the console...
Qty. of (3) 56 pin Elco's.
Configuration is: 8 channels tape send and return on each Elco. The other end is broken out to (2) DB25 connectors for "Send" & "Return".
Using 16 pair Mogami. The first 8 channels are Tape Send. 9-16 are Tape Return.
With no Elco's attached, the console is quiet (with the exception of it's own noise floor...which whispers just a little).
Attaching the Elco's...it's...BZZZZZZZZZZZZZZZZZZZZZZZZZZZ
When I went through connectors the other night, I verified the pinouts.
Does this also happen when connecting 1 Elco and leaving the Return Dsub unconnected? How about when connecting the return and leaving the send unconnected? What are the levels on the Tape returns when you hear the buzzing? If you mute those channels does the buzz go away? I'm trying to see if connecting the HDR in this manner sends the whole console's noise floor to hell, or if the problem is limited to just the returns that are connected. If you solo some other input, is is quiet or buzzy? Cheers KrisWith no Elco's attached, the console is quiet (with the exception of it's own noise floor...which whispers just a little). Attaching the Elco's...it's...BZZZZZZZZZZZZZZZZZZZZZZZZZZZ
When I connect just the cables, (without being connected to the HDR) I get some buzz & hum. Once I connect the HDR (powered on or off) it really goes to hell. I've tried connecting only one Elco w/ just send or just return. I've tried all 3 Elco's w/ returns unplugged, and have some noise, but not as bad. I've unplugged the sends w/ returns plugged in...Bzzzzz.Does this also happen when connecting 1 Elco and leaving the Return Dsub unconnected? How about when connecting the return and leaving the send unconnected?
Master Fader @ 0 (unity gain) Individual channels, pushing up the fader one at a time it comes through the 2 mix.What are the levels on the Tape returns when you hear the buzzing?
Yes. Although there is some leakage that still comes through just a little.If you mute those channels does the buzz go away?
Quiet. Unless I turn the control room volume wide open, Master Fader @ +10 & Channel fader @ +10. Then there's some, but it's not nearly as bad, and somewhat manageable, unless I solo every channel. If it's a channel with nothing plugged in, no problem. Other info...The mogami cables are approx. 30 ft. (Longer than I prefer), but I needed the slack for two reasons. 1) if I end up w/ a console w/ a left had patchbay, I'll need. 2) the slack to pull the rack out of the room for access, soldering, etc. Cables are away from power cables, supplies, etc.If you solo some other input, is is quiet or buzzy?
Aaron, not much to add this time, but I wanted to give you a heads up to a Soundcraft 2400 mod that a guy on another forum has done. Basically he's added THAT corp balanced receivers to all his inputs on the board...a big patchbay mod. If you can't get this problem sorted out, perhaps you can consider something like this, but on a smaller scale, limited to just the tape return part of the patch bay.
Here's the link:
http://www.prodigy-pro.com/forum/viewto ... 391985856c
Cheers
Kris
http://www.kineticsnoise.com/arch/icw/index.htmlJohn, glad you like it so far, sticky is probably a good idea - Aaron - Actually, I'm not sure if anyone even makes RC1 anymore - it used to be made by US Gypsum, they discontinued it, another company started making it then changed it (spelled R-U-I-N-E-D-) - now, Auralex offers RC-8, which is probably named because it is 8 times as expensive :cry: - I think the auralex stuff is around $.73 per FOOT !!?! but it Will work for ceilings - I just found out about the Dietrich stuff not too long ago, and don't have pricing info on it yet - here's a link to what I'm talking about, if you beat me to a price and availability, please post it in the Materials forum - http://www.dietrichindustries.com/bigdp ... sories.htm The RC Deluxe is what you want - NOT the RC-2, it won't give nearly the isolation with double legs. Angled ceilings can get tricky, but you can do it. Just don't violate the 2-leaf rule, a third leaf is a no-no unless it's just absorption material. One way for a sloped ceiling is to mount 22 gauge steel studs on isolators which are fastened to the sides of the ceiling joists - one end is mounted so that the steel stud is almost touching the joist, the other end is down several inches, the intermediate ones are adjusted accordingly. Using these isolators with steel studs negates the need for RC completely. http://www.kineticsnoise.com/architectural/icw.html On your nails coming thru the subfloor - get a pair of heavy nippers and clip them off flush. This is your first, last, and ONLY chance to do this so you'll be happy with it later. The 4 PCF stuff will bias your walls away from good bass isolation slightly, but with increased high mid isolation. Not ideal, but probably workable. Another reason for the extra mass up against your subfloor... Been up all night on 12-hour graveyard shift, so that'll have to do for now - ... Steve
A couple years too late for me (except the tracking rooms), but good info. I don't recall seeing those on their site a couple years back though. If I did, I avoided due to budget constraints. On another note, thought I'd drop in and say hello to everyone. Been unavailable the past week. Had the ole B-Day last Wed. and took the rest of the week off from work just to clean the house and studio for my annual party. So my apologies for not posting recently. Well, things are coming along. About a week and a half ago I rebuilt the bathroom wall downstairs that I removed when I had to take out the sewer line. Leveled the bathroom floor and installed concrete backer board. Probably not necessary, but did it anyway. Bought some White Carrera Italian Marble to install for the studio bathroom. ($7 a SF) Good lookin' stuff. Still trying to resolve the buzz issue, but hadn't had time this past week to dive into it again. Will probably get into again (if not tonight) in the next couple days hopefully. That's the latest news. (Edit: BTW Kris, looks like some interesting info. Unfortunately though, this console doesn't belong to me, so making console mods is currently out of the question. If I do anything, it would have to be external.) :Dhttp://www.kineticsnoise.com/arch/icw/index.html
Aloha Aaron,
Congratulations and Happy Birthday to you! :D
May you have many more great and productive years ahead! :wink:
Aloha 8)
Thanks Kendale! :D
Well, I have some bad news regarding the buzz issue. I called Mackie, I called another tech, and we are officially at a consensus with this setup...
I'M F***ED! :cry:
Transformers are going to be the only solution.
(actually there is 1 other solution. A balanced console.)
Sadly, this is an issue with a number of new systems... Protools included. They don't interface well with unbalanced equipment. One solution is to build an unbalanced line driver, which would be cheaper than transformers, and wouldn't color the sound as much. I am dealing with a similar issue here with a Helios rebuild. The Helios is totally unbalanced and we are searching for ways to interface with active balanced outputs that won't impact the sound too much.
Check out this tread over on PSW:
http://recforums.prosoundweb.com/index.php/t/9030/0/
Best of luck! I feel your pain!
Dave.
Here you go, Aaron...Transformers are going to be the only solution.
Hi Dave, Yeah, that's been the unfortunate discovery of this headache. I was told by another tech about this a couple months back when I first started having this issue, but wanted to try all possibilities. And what a bummer!!!!!!! And I thought modern technology was suppose to make our lives easier. Whoever said that...well, I'll refrain from posting my thoughts on that. Hey Sharward, are those the "original" metal transformers, or newer plastic ones? On another note, I guess I'm going to have to do the alternative for now. Either run the signals through the tape machine in "Input" mode and use it as a buffer, OR transfer the tracks to tape and mixdown from tape. (Which is going to cost some $$$ since I need to get it fully up and running, aligned, and buy a new alignment tape.) Meanwhile, I guess it's time to start getting a biz plan together and talk w/ some banks, or finish out this construction, get a new appraisal on the house and get an equity loan. (This was my original plan anyways for getting a console). So in other words, I'm keeping my eyes open for my own console. Choices would be a Trident 80B or C, Neve, API, or something in that realm. But I really like Tridents after working on Roger Waters old console. That's my world at the moment. :roll:Sadly, this is an issue with a number of new systems... Protools included. They don't interface well with unbalanced equipment. One solution is to build an unbalanced line driver, which would be cheaper than transformers, and wouldn't color the sound as much. I am dealing with a similar issue here with a Helios rebuild. The Helios is totally unbalanced and we are searching for ways to interface with active balanced outputs that won't impact the sound too much.
Oh, man -- it looks like you're really in a pickle...
I wouldn't have been so silly had I known.
I'm totally clueless about recording equipment... Seems like a royal headache to me......
--Keith :mrgreen:
Yeah, at least I have a temporary work around so I can mix this album.
Aaron
I checked the SAE section on this site, but I need some clarification. I'm just curious to know when we say "unbalanced equipment" that causes the problem of "humming"are we referring to mixers and other outboard equipment only? In other words, if I understand the idea correctly, it's better to have a balanced system throughout your whole setup (balanced mixer, trs cables, xlr cables, compressors that use trs/xlr etc etc). If you plug in a keyboard that does not have a balanced signal or cable, is that signal unbalanced through the mixer and into any outboard equipment you use in processing that signal? Isn't a guitar connected to a mixer an unbalanced signal? Or, does it depend on if the cable you use in connecting the guitar is balanced or unbalanced? I'm also wondering where DI (direct boxes) come into this factor.
To sum it up...if you have a mixer that accepts a balanced signal, outputs a balanced signal and all your other equipment is balanced, if you plug in a guitar or keyboard using a trs cable, will the signal coming into the board be balanced or unbalanced?
Thanx!
In this case, it is the connection of the hard disc recorder output (with active balanced out) to the unbalanced input of the Soundcraft console that is causing the problem. In some cases, balanced output amps cause problems when they are "unbalanced" by the destination input... hum, buzz, loss of low end, loss of level etc. With more equipment coming with balanced connections, manufacturers are not taking unbalanced equipment into consideration when designing these output stages. Your example of a guitar is connecting an unbalanced *output* to a balanced *input*... this does not create a problem as you are not shorting out, or floating any part of the signal line. Using tranformers is the only "fool proof" method of connecting the gear because you can match the output and input impedances properly. You also have full electrical isolation between equipment that eliminates any noise. In older unblanced consoles, they would place transformers on the echo and FB send/returns due to the long cable runs involved. Mic inputs would typically have transformers on the inputs as well because of cable length, but the tape sends and returns would not. The close proximity of the tape decks to the consoles didn't generally warrant the cost of adding a full set of input and output transformers. In this case, Aaron has to either actively unbalance the system, install transformers on the HDR outputs (only), or (as he has suggested) buffer the signal through another device that has balanced inputs, and outputs that are not susceptable to unbalancing problems.
Dave.
Dave, that's the best summed up version of the problem in a nutshell. Thank You.
Yeah, I didn't have any problems going to the HDR. No buzz or ground loops recorded on the tracks. Just the return.
I hope to have the 2" machine up and running this afternoon. Randy Blevins was over this morning tweaking the machine. We blew a fuse on one of the power supplies, and he had to run off to another client to repair a master module for someone. He should be back this afternoon and hopefully we'll get the machine aligned. (had some bias card issues back in January when I was trying to align it.
So my work around for this will be one of two options. 1. Just put the 2" machine in "Input" mode and have the signal pass through it, or; 2. dump the tracks to tape and mix off tape (preferred for obvious sound reasons). I'm actually looking forward to mixing off tape again. Yippie!
Ahh...the sweet sound of analog! :mrgreen: