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DIY Phase Shift
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orenradio
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#1
27th August 2013
Old 27th August 2013
  #1
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DIY Phase Shift

Hello all,

I'm looking into creating several DPDT 180 degree phase shift switches, and thought of something that could be better.

Rather than mess with cabling, inserting a DPDT switch in between the XLR cables and wiring them for the phase shift, i was wondering if there was a way to wire an Insert Cable to shift the phase of a signal upon insert.

That way without the "Phase Insert" the signal would be at 0 degrees, but with the "phase insert" the signal would be at 180 degrees.

Similarly, if such an item could be created, a rotary switch could theoretically be created, allowing infinate phase relationships to be created with a simple Insert jack.

Thinking about it has left me in a quandary, how can I phase shift the Tip signal without a "-" lead to shift it with? I know it is possible with different resistors, and more complicated circuitry, but my inexperience must be the bottleneck here...

How would I create a Phase Shift "Insert"?

Alternatively, I could take the mixer apart and rewire a DPDT switch in where the Insert Jack once was... that would work right? And since the Phantom power occurs earlier in the signal chain, I wouldn't ruin anything switching back and forth while Phantom Power is on right?
#2
27th August 2013
Old 27th August 2013
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"...if there was a way to wire an Insert Cable to shift the phase of a signal upon insert"
"how can I phase shift the Tip signal without a "-" lead to shift it with?"

that'd be the problem.

"Alternatively, I could take the mixer apart and rewire a DPDT switch in where the Insert Jack once was... that would work right?"

same problem still.

if you want to keep the mixer channel phase unchanged (i.e. not hit the phase reverse switch), then your easiest way may be to add a transformer - that would allow easy phase inverting without having to add an active invert circuit. a selector switch would pick the phase. this could be internal if there's room, or external to the mixer.

should be no problem with phantom power. the signal should be AC coupled after phantom power to block DC.
#3
27th August 2013
Old 27th August 2013
  #3
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Assuming you're not building active electronics to do the job, you can only phase invert a balanced signal (ok, in certain circumstances it could be done with an unbalanced cable but in most cases the grounding scheme would make it impossible.)

An XLR phase inverter would be wired with pin 1 straight through, and pins 2 and 3 switched.

There isn't any way to do anything other than 180° shift (inversion) without more complex circuitry.
#4
28th August 2013
Old 28th August 2013
  #4
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If you want multiple phase positions, you need to make an Allpass filter or a series of them.

ReaEQ, the vst, has one built in. It works well because comb filtering tends to only occur at smaller points within a bandwidth, and so a few allpass' tend to be able to cure the cure the "Dull one way, no bass the other way" dilemma.
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Why don't you just knock it off with them negative waves?
#5
28th August 2013
Old 28th August 2013
  #5
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Instead of getting too fancy, why not simply wire some phase switched (polarity inverted) cables? As Rabies said, switch pins 2 and 3 on one end.

Clearly mark the cable (possibly use red cable) as to not cause unnecessary issue and use them as needed. Handy to have around and less likely to fail than a switch on a XLR cable.

Out of curiosity, why would you want a phase shift on an insert cable? I am not saying you are wrong for wanting to do that, I just have never encountered a reason to do so.

Good luck and post your solutions!
-e
#6
2nd September 2013
Old 2nd September 2013
  #6
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To be able to continuously vary the phase for time alignment purposes check out the Radial Phazer: Radial Phazer™ - Class-A Phase Adjuster

For simple 180° polarity inversion in a balanced cable a toggle switch or a dedicated pin-reversed version would work, as was mentioned above.
orenradio
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#7
5th November 2013
Old 5th November 2013
  #7
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Sorry for the delay. E3po I was thinking of using the insert jack to send the signal to an external phase reverse and return the inverted signal. Almost like a physical "plug in" that would bypass having to rewire the cable often, and was hoping for something physical as opposed to a vst for analog recordings.

Perhaps I can build a balanced trs cable inverted and use it with a patch bay as needed.

I'll check the other options as well,

Thanks for the input all!

Sent from my DROID RAZR
#8
5th November 2013
Old 5th November 2013
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That is what I was thinking. I like less in the path. It is less to go wrong. In the event it is needed, a hard wired cable seem a more elegant solution. If you have a patch bay your idea is cool too.

Besides, can't you usually flip phase (polarity) in the DAW? (or on a pre or console)

Variable phase would possibly be useful, but would require more circuitry.
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