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Author Topic: Issue I can't figure out  (Read 1603 times)

dbmusic

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Issue I can't figure out
« on: January 16, 2010, 04:01:36 PM »

I recently purchased several straight through XLR patchbays (Hosa PDR-369) for my studio. I have a small home studio and these serve my patching needs very well. There is one issue though that I'm unable to resolve.

I use an RME AES-32 out of my DAW to a Crane Song HEDD. Whenever I route from the HEDD via the patchbay to the NSEQ, I get a 6db difference in channel output.

Now I've been in touch with Joel and Jay over an Millennia and with their help have run a number of routing tests. They were thinking this had something to do the the unbalanced I/O of the NSEQ and perhaps a grounding issue with the patchbay.

To summarize the tests, here's what happens: Whenever I send both L and R signals from the HEDD to the NSEQ via the patchbay, there is the 6db mismatched output from the NSEQ. If I take either left, right, or both L/R outputs from the HEDD directly to the NSEQ (bypassing the patchbay) the output signals now match.

Now if I route from the HEDD via the patchbay to my Pendulum OCL-2 (also unbalanced I/O) it shows matched outputs. If I stick the NSEQ AFTER the OCL-2, the outputs from the NSEQ are again matched. If I stick the NSEQ BEFORE the OCL-2, now the outputs from the OCL-2 are mismatched again by 6db.

So the problem occurs when routing BOTH the left and right channels from the HEDD to the NSEQ via the patchbay. The NSEQ must be the first processor in the analog chain. With Jay's guidance I've removed the top panel from the NSEQ and made a visual inspection of what he thought might contribute to this and everything appeared intact.

Does anyone have any ideas why this would happen? And why does taking either the left or the right out of the HEDD directly to the NSEQ (bypassing the patchbay) resolve the mismatch output?

Regards,

Danny
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Halfway Competent

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Re: Issue I can't figure out
« Reply #1 on: January 19, 2010, 12:18:06 PM »

Hey Danny,

Sounds like maybe a signal ground problem.  Reading thru the NSEQ manual, it says that Pin 1 is tied to chassis ground, Pin 2 is hot, and Pin 3 is tied to audio ground.

If there's any difference of potential in your system between chassis and audio ground on one side, I think this could account for a level mismatch...  I would take a multimeter and check your patchbay.  Set it for continuity test, unplug your audio cables, and make sure you have continuity between all pins (1 to 1, 2 to 2, etc).  If you're missing continuity on any of them, that's a possible problem.  Once you've assessed that, then check from the patch bay to the cables at the back of the NSEQ.

If you get the dip in level only after plugging in the other channel, it could be you have a floating ground on one side, and the other pulls the ground up (reducing hot-ground potential, and thus level).

My understanding of this is cursory, and might be inaccurate, so take it with a grain of salt.  Smile  But do check all your pins and cables with the multimeter.

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Geoff Emerick de Fake

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Re: Issue I can't figure out
« Reply #2 on: January 19, 2010, 02:15:40 PM »

The only explanation that makes sense is that for some reason your patchbay is unbalanced. Can you check between pin 1-3 and between pin 1-2 if they are really isolated?
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