Chasing out Hum

[alexdingley]

Hey there,

I've got some 60-cycle hum when I connect my DAW to the console. I've swapped snakes out, checked for proper ground, ensured common ground, and this subtle hum persists

I recently went over my whole home studio & rewired a lot of it. I've got a Toft ATB-16, hooked in/out of a set of Apogee AD-16x & DA-16x... A thing of beauty... but, if I'm being honest, there's a noticeable 60Hz hum just above the noise-floor... I've been un-plugging gear and re-plugging unit-by-unit to find the issues. Turns out, as soon as I connect the snakes from the apogees to the console's Direct-outs & Monitor Ins... I get the hum. If I unplug all of the gear from the console, there's no hum and I can open up the CR knob to a hush of the faintest white noise... like it should be...

I have all of that gear plugged into a Furman PL-Plus power conditioner. I've disconnect all other gear (for the testing), and the DAW & Console are connected to one conditioner, which hits one outlet on the wall... the hum is there. I've tried other outlets in the house, by using a heavy extension cord,... same deal. Has anyone got thoughts of whether or not a (never thought I'd ask this) Monster Power racked power conditioner would help?

Here's some perspective on how noticeable: When I'm monitoring at an average 85db-90db in the control room, and I pause a track, I can definitely hear the hum - just a little louder than the electrical noise of the noise floor.

Here is a link - this is a file recorded from my external master recorder... directly off of the console. it's a 24bit 44.1 file, with no normalization or alteration. Take a peak at it in any DAW


So, am I asking too much of my system to not have that much inherent noise in the mixes? Would you tolerate that level of noise? If not, what would my next steps be in trying to eliminate the hum?

[wren]

Have you tried different cables between the Toft and the Apogees? I don't know what kind of snakes you're using, but what I'd try to do would be to unplug everything, then slowly start plugging things back it and see when/where the hum reappears. From there, assuming the hum appears with just one or two cables, try different TRS cables instead of the snake you're currently using and see if that changes anything.

But I'm a little confused about exactly what your setup is, as well as what kind of troubleshooting you've done. Is the hum just in the lines from the Toft outs into the Apogee A/D, or is there hum if you take "clean" tracks and play them back through the Apogee D/A, to the Toft, and to your monitors? I'm assuming you're using the Toft as a monitor controller of sorts as well too. When you hook up the Apogee D/A to the Toft in the most minimal way (just to play a CD, say), is there hum? Do you have another monitor controller you can swap for the Toft to see if that makes a difference?

I don't think a real power conditioner would necessarily fix the issue (though your Furman is nothing but a glorified, expensive rackmount power strip - it doesn't do any kind of conditioning). I'd try an Ebtech Hum Eliminator and/or HumX before a power conditioner, but I'd definitely try a bunch of other stuff before I spent money on gear that *might* fix it.

[Randyman...]

Don't you love ground loops! You should try tracking down a multi-room grounding issue that happens over DirecTV wiring! That's some fun stuff there...

You can try to lift the sleeve (shields) at one end (generally the rx end) and see if that helps.

Try with a single channel and a single cable (or a complementary pair of I/O) if you can.

Since I believe the AD16/DA16 must use DB25's, you can likely "make-shift" a TRS Female-to-TRS Male as an extender for one channel of your DB25 snake, and lift the shield on this one connection (with the remaining 15 channels unhooked). If you need a DA/AD I/O loop, do this for both the input and output sides with all other channels disconnected. Same deal if you are using DB25-to-XLR snakes - make an XLR-F to XLR-M cable and lift the shield on this adapter cable.

I had to use three Radial J+4's (-10 to +4 with galvanic isolation) to kill the aforementioned DirecTV issues to my home theater setup (a $600 fix!). Was hoping to avoid transformers, but true galvanic isolation seemed to be the only way in my situation.

I used an Ebtech as well (also solved the galvanic isolation requirement), but it did not perform well enough as a -10 to +4 level converter (it's passive, so relys on transformer voltage step-up tor gain, and adds some coloration in the process). The line-level Ebtech hum-isolator (with a 1:1 transformer - not a level shifter) is probably more transparent IMO...

[wren]

Oh, damn, they are DB25's! I didn't even think about that. Forget my swapping-cables advice. Listen to Randyman - his shield lifting idea is a good one. And like he said: isolation transformers will probably solve your problem. They ain't cheap, though, so I'd suggest trying other stuff first.

That said: I've solved so many different kinds of noise issues (yes, even ground loop hum) in so many different kinds of scenarios by replacing a few cables with better-quality ones.

[Gregg Juke]

Hoo-rah to that ^^^^.

We swapped out unbalanced cable for balanced in the CR quite awhile ago, and there is a noticeable diffrence in noise level, even though we have a hybrid/largely unbalanced system! You can shout "Radio Shack EQ territory!" at me if you want to, but it does work (at least it did for us)... And I would have been the guy to say "You don't need that!"...

GJ

[alexdingley]

Thanks for the input! (pun intended)

Even the Toft console manual recommends lifting ground on the receiving end of cables to eliminate unwanted hum... which I always found to be a strange idea, but I'm not above trying it.

I actually have a complete set of spare snakes that I can experiment with, so might do that. It would be great to eliminate that hum, but I would have thought that breaking ground on either end would actually allow MORE hum & interference into the system.

That said, I'll poke around and try it on a spare snake.

[alexdingley]

Okay... I just did a quick test with a few channels of I/O.

I star-grounded an 8-channel snake, and hooked it from my DAW into the console... and it was dead silent. Passed clean signal with NO HUM. WOW! I had no other gear plugged-in... but none of that is star-grounded, so i'm sure it would bring back the hum.


So... here's the question.

Before I ground-lift one end of every connection that hits my board (all told it's probably 60-70 connections) are there any major draw-backs that I'm going to run into?

Will this be more susceptible to EMF / RFI / Aliens? Just looking for all the info before I head down a path of much much snipping & de-soldering

[The Scum]

Connecting the shield at only one end is a fairly common practice, has been around for ages, and has been recommended by manufacturers in their official wiring diagrams.

As long as it's grounded at one end, the shield is still effective. Any noise picked up by the shield runs to ground, rather than trying to get into the signal cables inside.

Before you go and mutate a bunch of snakes, this might be a good juncture to apply a little more scientific thinking. Since your at the point where one connection can connect/disconnect the hum, you've got a good test bed for experimenting with the cause. There may be a more thorough solution than lifting shields. It would be terrible to have to go through the effort of snipping a bunch of connections, only to discover you had a miswired outlet somewhere. A "ground cheater" plug might help sort that out.

For the DB25 ends, you might be able to wire up some DB25 extenders that break the grounds - boxes like these:
http://www.l-com.com/d-sub-metal-diy-ki ... older-type

There are two pragmatic things that cause problems when you get into lifting shields.

The first is that you can't use it on microphones - phantom power needs the shield.

The second is that it's one more thing to have to keep track of if you're intermixing balanced and unbalanced gear. There will be some combinations that don't work

[alexdingley]

Thanks, The Scum, That seems like good stuff to keep in mind.

Yeah, I've done some testing with the power & everything is kosher there. Again, this isn't a major hum issue... so it's not like some outlet is causing major issues. Just a small background hum... If you listen to the clip, you'll see how subtle.

Obviously my mic lines will stay fully 3-pin intact, but I'll probably do this on the DAW lines & my balanced FX units that are patched into the aux sends/returns.

Out of curiosity, does this star-ground lifting work with send/return insert lines? I have single-TRS snd/rtn Inserts on the console... so going in/out of my couple DBX 160X units, I am running unbalanced connectors.

[alexdingley]

Wow... everyone, thanks for the insights. I posted this same question here and on an audio facebook group... similar advice in both spots. Did all the snips this morning. Just the balanced line-level devices that touch the Toft... huge difference!

Now, the signal chain from my synths & mics* all the way through to my Monitors & DSD 2-track recorder is quiet as can be.

* obviously, I didn't snip the grounding on any mic inputs.

Bummer though - My Roland JV-1080 seems to have a notable hum in it, regardless of the star-grounding. Not that it was crucial to my setup, but I enjoyed having some of those old sounds in the chain. Maybe I'll grab an ebtech hum-elim for that unit.

[Randyman...]

Wow... everyone, thanks for the insights. I posted this same question here and on an audio facebook group... similar advice in both spots. Did all the snips this morning. Just the balanced line-level devices that touch the Toft... huge difference!

Now, the signal chain from my synths & mics* all the way through to my Monitors & DSD 2-track recorder is quiet as can be.

* obviously, I didn't snip the grounding on any mic inputs.

Bummer though - My Roland JV-1080 seems to have a notable hum in it, regardless of the star-grounding. Not that it was crucial to my setup, but I enjoyed having some of those old sounds in the chain. Maybe I'll grab an ebtech hum-elim for that unit.

Sweet! Glad to hear this resolved your humming.

The Roland is likely unbalanced? Most synths/modules I'm familiar with are (not a keyboard player in the slightest!). If you have a mic pre with a transformer balanced DI Input - that would also likely do the trick in lieu of an Ebtech Hum Isolator...

[alexdingley]

question about insert snd/rtn from the console. I can certainly try it - but I'm curious if this is going to fly with an outboard compressor... going in/out of the snd/rtn TRS connector on the Toft channel. I suppose I can snip the ground lines on the snd & rtn that go in/out of the compressor... just not sure if that will be a problem because it's not a fully balanced signal anymore.