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Old 5th November 2011, 01:39 AM   #1
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Default balanced XLR patchbay with phase-reverse switches and ground lift

I'm contemplating buiilding a patch bay for balanced XLR jacks with ground lift and phase switches. Unless there are already commercial suppliers?
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Old 5th November 2011, 02:49 AM   #2
Lavcat is offline Lavcat  United States
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I don't know of any commercial suppliers of what you seek. Try looking on Markertek perhaps?

Since I am planning to mount XLR jacks for a project of my own, I'd be interested to discuss how you plan to make the cutouts in the panel. I have what I hope is the right size Greenlee punch but I am still concerned with finding the best way to drill the hole for the bolt.
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Old 7th November 2011, 08:21 AM   #3
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There are plenty of prepunched panels for XLRs, but I don't know of any predrilled for toggle switches. Still, in the Signex Signex Pro Audio range I use here (know the importer, no special advantage over other ranges) there would easily be space for one two pole changeover and a single pole make/break switch, and they're generally round drill holes, the easiest to put in place.

The problem would be labelling; there isn't much left over space for that.
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Old 14th November 2011, 09:51 PM   #4
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Yes, I want to find something like that SIGNEX panel, but cheaper and probalby fewer channels.
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Old 15th November 2011, 03:42 AM   #5
Enzo is offline Enzo  United States
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Instead of wedging a phase switch into each jack, or at least into each jack pair, consider just making a straight patch panel and having a few phase reversal adaptors on hand. If your setup is like most, you won;t be needing tons of phase reversals. Two forms come to mind. One is those metal cylinder shaped male to female XLR adaptors, the sort you might make an attenuator in, wired for phase reversal. Switchcraft S3FM , for example. Whenever you need reverse phase, insert on in series with the relevant patch cord.

The other is to make up some cross wired patch cords. WHenever you need reverse phase, use a reversing patch cord. Those would be made just like a plain XLT patch cord, but wiresw to pins 2 and 3 would cross. To identify them easily, make them with a different color jacket on the cable, or something else immediately obvious to the eye.

When I was touring, my soundman toolkit included a few short 6" XLR patch cords for reversal and a few wired for ground lift.
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Old 15th November 2011, 04:05 AM   #6
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Quote:
Originally Posted by cyclecamper View Post
I'm contemplating buiilding a patch bay for balanced XLR jacks with ground lift and phase switches. Unless there are already commercial suppliers?
I've been working in broadcast TV for 35 years and can name only a few times when I needed a phase turnover. I would suggest that rather than having a turnover in the patch bay you get some Switchcraft 390 male to female XLR adapters. Wire as a ground lift or phase reverse or what I have done several times is build in an H pad attenuator.

I think it gives you more flexibility to use but OTOH you're not likely to misplace a patch bay.

G
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Old 16th November 2011, 11:47 PM   #7
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I come from a stage background with a lot of mics and constant complications of phase. Comb-filter effects when two performers on wireless mics are moving too near each other, drums on vocal mics, etc. I used to have a 'phase gun' which put out a signal with an assymmetrtical duty cycle, then I had another detector which would tell me which way the phase is. Now without that or a dual-trace scope I rely on my ears. And with 4-way active-crossover speaker stacks there's sometimes no 'perfect' phase alignment and I need to do many comparisons from a remote location. I want a switch for instant comparison. Like an optometrist: bette rlike this or better like this...better like this or better like this... I start with one band on one channel and phase it to the other channel, then each side thru the bands.

Anybody got any good leads on where I can still get a handy phase-signal generator and detector pair? The kind that will work thru mics, board, amps, speakers, whatever...

Last edited by cyclecamper; 16th November 2011 at 11:49 PM.
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Old 17th November 2011, 07:33 PM   #8
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Originally Posted by cyclecamper View Post
I come from a stage background with a lot of mics and constant complications of phase. Comb-filter effects when two performers on wireless mics are moving too near each other, drums on vocal mics, etc. I used to have a 'phase gun' which put out a signal with an assymmetrtical duty cycle, then I had another detector which would tell me which way the phase is. Now without that or a dual-trace scope I rely on my ears. And with 4-way active-crossover speaker stacks there's sometimes no 'perfect' phase alignment and I need to do many comparisons from a remote location. I want a switch for instant comparison. Like an optometrist: bette rlike this or better like this...better like this or better like this... I start with one band on one channel and phase it to the other channel, then each side thru the bands.

Anybody got any good leads on where I can still get a handy phase-signal generator and detector pair? The kind that will work thru mics, board, amps, speakers, whatever...
A polarity switch changes phase 180 degrees at all frequencies.
A transducer's phase may change some 720 degrees (more or less) over it's range of operation.
Polarity switches (what you have been calling a "phase reverse") don't fix phase problems, phase needs to be addressed with delay, although polarity switches can make microphone phase differences subjectively less objectionable.

In/out "Phase" signal/detectors are quite problematic in use, as typical bass reflex cabinets are phase inversion cabinets, a reading near a port will read different than in the center of the cone.
A horn driver has a different phase response (not offset by 180 degree) than a front loaded driver, so results in an ambiguous response when compared.

To really see what is happening with phase requires a dual FFT comparator, like Smaart or Tef.

Art Welter
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Old 17th November 2011, 09:51 PM   #9
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http://www.ebay.com/itm/190600183215...84.m1555.l2649

12 xlr panels w/blanks for the switches!
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Old 17th November 2011, 10:30 PM   #10
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Quote:
Originally Posted by weltersys View Post
A polarity switch changes phase 180 degrees at all frequencies.
A transducer's phase may change some 720 degrees (more or less) over it's range of operation.
Polarity switches (what you have been calling a "phase reverse") don't fix phase problems, phase needs to be addressed with delay, although polarity switches can make microphone phase differences subjectively less objectionable.

In/out "Phase" signal/detectors are quite problematic in use, as typical bass reflex cabinets are phase inversion cabinets, a reading near a port will read different than in the center of the cone.
A horn driver has a different phase response (not offset by 180 degree) than a front loaded driver, so results in an ambiguous response when compared.

To really see what is happening with phase requires a dual FFT comparator, like Smaart or Tef.

Art Welter
You're right, but no new information there, except rubbing in the fact that I don't have access to a TEF test system. It's still worthwhile to be able to ascertain some relative "polarity" relationships and sometimes that's about all I have, short of moving boxes around and maybe a delay knob on one band of my crossover. The phase (polarity) guns are far from ideal when an additional amplification stage may make a 90 degree change, filters may shift phase with frequency, and no speaker or even amp is perfect. But I'm not trying to do much real analysis with this simple tool. For some uses it's more reliable than your ears, a level meter, or an RTA, and that's about all I carry. A relative fixed delay will change relative phase with frequency, and can't correct a polarity problem across a considerable bandwidth. Apples and oranges.

But with multiple mics, better thru the board but even if you detect thru the speakers with some frequency-dependent phase shift, the 'phase (oops, I mean polarity) gun and indicator generally use one frequency and will tell you whether two mics are in the same relative "polarity' even when driving the whole system. A tool that's got variable frequency can be useful at the crossover frequency to get two adjacent active crossover bands working together (assuming that's what you want).

You're stretching the truth behind the phrase "phase inversion cabinet"... The port in your reflex cabinet is supposed to reverse phase so that the reverse-phase signal from the back of your speaker comes out the the front "in phase" with the front direct radiation of your driver. Of course, that's frequency-dependent and not usually tuned to co-incide, and the resultant mix is a mess IMHO. But thinking the port output is out of phase with the driver's direct output is focusing on undesirable behavior.

Best regards and happy thanksgiving.
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