Phase/Polarity Inversion (Stereo)

J

Joben Magooch

Well-known member
Hi all! Little question for you… I am currently using a couple of different amp sim pedals for a stereo rig but I’m finding with certain patches I’m experiencing some phase cancellation. I see this is fairly common for folks running a pair of the UAFX amp pedals, or dual Iridium’s or etc.

A common solution I see thrown around is some fancy DI boxes or similar that can invert phase/polarity (tbh I am not sure the difference) which I guess solves the issue - like the Pinstripe DISO, Goodwood Output, etc but these are pushing $200, $300 or so and that seems kind of excessive to me.

So that said anyone have a good DIY solution or similar for flipping the phase/polarity on the balanced outputs of Tonex or other amp sims? I’m a bit in the dark on the topic.
 
TL072s are too noisy for that application - you'll be adding more noise than pretty much any guitar pickup inherently has - I would recommend an OPA1678. As for phase inverting balanced outputs? Haven't seen any schematics/products floating around for an active version of that - only those expensive transformer based solutions you mentioned above. Post this outside of the breakroom sub-forum in general questions and see what ideas people have.

I assume this is an issue you're having in a live situation and are not simply plugging your amp sims into an audio interface?
 
mzy12 said:
I assume this is an issue you're having in a live situation and are not simply plugging your amp sims into an audio interface?
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It’s a little of both… most the time for quick practice I just plug into my interface and direct monitor and my interface doesn’t have the ability in hardware to flip phase (that I know of!). Can be done in DAW easily enough but most of the time I don’t bother running through any DAW for practicing.

Live I’d suppose could always have FoH flip it at the board but I’d rather remove that from the equation (or at least have that on my end to worry about). Maybe I’m overthinking it though - if I’m already going out to a DI to the main board, could I not just make a small XLR patch cable with the outer pins flipped?
 
szukalski said:
TL072s are too noisy for this? They work fine for me for splitting/summing/phase inversion.
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Well, maybe "too noisy" is an overstoverstatement 😂 it will definitely work but it's super sub optimal

I was discussing this with @JTEX and you can see some of their measurements here: https://forum.pedalpcb.com/threads/whats-up-with-the-buffers-in-cornish-designs.19029/post-235436

The TL072 is kind of outdated when it comes to this sort of application. If there's a bunch of them in your signal chain, the noise will ads up, even if you're running with a clean sound.
 
Joben Magooch said:
Maybe I’m overthinking it though - if I’m already going out to a DI to the main board, could I not just make a small XLR patch cable with the outer pins flipped?
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Hahah yeah that would work! Completely overlooked that. Bear in mind, that won't work for unbalanced signals. You'd still need either a transformer or an active solution
 
mzy12 said:
Well, maybe "too noisy" is an overstoverstatement 😂 it will definitely work but it's super sub optimal

I was discussing this with @JTEX and you can see some of their measurements here: https://forum.pedalpcb.com/threads/whats-up-with-the-buffers-in-cornish-designs.19029/post-235436

The TL072 is kind of outdated when it comes to this sort of application. If there's a bunch of them in your signal chain, the noise will ads up, even if you're running with a clean sound.
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I think it depends on what you mean by sub optimal. If we’re doing a master mix, then maybe it’s important. If we’re dealing with a distorted guitar then it may not be anything anyone will ever notice and may save you a specialist order from Mouser.
 
The PPCB inverter board will probably do the trick. If you are in a hurry to try this, you can easily come up with an opamp inverting buffer circuit and put it on vero board or even a breadboard. I think there are good schematics out there for this.
 
Another random thought: I’ve got a cheap little whirlwind Imp DI I use occasionally. Could I not just install a DPDT switch to flip-flop XLR pins 1/2?
 
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