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Rakmount 25th July 2005 05:19 PM

Yay! A new ground-issue-scenario!!
I'm having big troubles with my grounding scheme on my Bantam patchbay. Here's what my typical signal flow looks like for a simple mic chain.

Condenser -> XLR Tieline -> (arrives at p.bay)->MicPreIn (with the input Ground lifted, not on the unit, but at the solder points to the input on the bay) -> MicPreOut (ground is connected) -> ProTools In (the ground is connected)

When i use the same input on the patch bay, but with a balanced signal coming from a DI, I can totally great results. No problems whatsoever.

I am thinking that I need to lift the input to all of my Protools inputs, to maintain the consistency of the grounding scheme. But, after reading so much about this stuff, I find myself confused after reading about the many different ways to get this done.

Note: I get varying results. With a dynamic, I can record a vox at very low amplitude. Some mic pres yield some RFI that is audible when you crank CR volume. Some chains yield some absolutely horrendous buzz. Needless to say, I'm this close to just paying someone to do it right for me.

Rick Sutton 25th July 2005 06:11 PM

Are you lifting ground at mic level (right before it goes into a pre) ?
If so, that's your problem. The chain you describe should work without any groundlifts ( but if a chain needs a groundlift never lift at mic level...line level only) In my studio the main mic panel (in the live room) goes both to my board and has additional lines that go directly to the outboard preamps. If I want to patch a mic to a specific preamp it is done there and not in the control room. That way all mic patching is done on xlr's and grounds are solid. I'm not a fan of a mic "patchbay" in the control room as it seems to cause many more problems than any potential benefit. Then again. I don't play around with switching preamps during sessions as I know which mic/pre combo I want as I approach each instrument, and if I do decide to swap it's only a small walk to the main panel....a little excercise is welcome anyway.
cheers, Rick

JonCraig 25th July 2005 07:32 PM

don't lift the ground on the mic input--unless you never want to use phantom-powered condesers, active direct boxes, etc. with no ground, the +48 has no where to go!


Guest 25th July 2005 07:41 PM

Great post!
I was planning on having all my wiring re-done with custom TT panels at the center.

I too was wanting to run my mic lines through this panel.

What are some of the issue that I might run into?
This post clearly being one.

What is the proper way to address phantom?

Sorry for the subtle hyjacking.


JonCraig 25th July 2005 08:13 PM

ground lift, *if necessary* at the input of devices except mic pres. i believe that's the way to go... though i'm not terribly sure.


Rick Sutton 26th July 2005 01:51 AM

Off the top of my head the only two ways that I'd accept for mic patching are xlr's for individual patching and multipin for mass patching. Some of the problems with TT or other schemes are phantom contacting the wrong points on the patch as it is inserted and small contact area resulting in intermittant signal.
As far as ground lifting gear, if you follow good AC installation procedures (like keeping all audio on same breaker or at least on same leg of the 220 service) ground lifts on balanced, line level pro gear shouldn't be necessary in small installations.
When you record low level istruments like a direct on a bass guitar and it also is going to an amplifier....that's when you start learning about ground lifting.

Rakmount 28th July 2005 02:43 AM

Thanks for the responses.

The major point is that you cannot lift the ground on a mic input. That much I now know.

So what have I done in the interim?

Got an XLR Patch Bay (16 points -- ins/outs). So now, it's like this:

Mic Tie Line @ Patch Bay (XLR)
-->Mic Pre Input (XLR)
-->Mic Pre Output (Bantam)
-->Protools Input (Bantam)

Everything is A-Ok with that. Unfortunately, it does mess up my neat configuration and labelling with some other floating XLR cables that I had located on the Bantam patch bay.

Again, thanks for the help.