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Author Topic: Peavey USB-P inverted polarity on one channel  (Read 1629 times)

Jonathan Johnson

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Peavey USB-P inverted polarity on one channel
« on: February 10, 2018, 01:42:33 am »

So I've got me one of those nifty Peaver USB-P audio output devices.

Today I realized that it apparently has inverted polarity on either the right or the left channel, because when I mix a stereo signal to mono, anything that is equal in both channels (such as vocals or speech) cancels out. Same thing happens if I switch the USB-P from stereo to mono output, so I'm confident it's not my cables.

If a play a mono track and switch the USB-P to mono, it is dead silent in both channels.
This is on a Windows 7 laptop.

I'm waiting to hear back from Peavey customer service, but in the meantime, I'm wondering if anybody else has experienced that issue?

(For those not aware, the USB-P is an audio output device — basically an external sound card — that connects to the PC via USB, and has XLR balanced outputs. It does not depend on the onboard sound card at all. It uses an in-box “class” driver, so no driver installation is necessary. There is really no configuration beyond volume control.)
« Last Edit: February 13, 2018, 01:49:00 am by Jonathan Johnson »
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Justice C. Bigler

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Re: Peavey USB-P inverted polarity on one channel
« Reply #1 on: February 10, 2018, 11:39:48 am »

I have several of these in our building and have not seen this apparent defect. I would presume that it would be a manufacturer defect. I guess you could further test this by wiring up a polarity reversed XLR cable and attaching it to one or the other outputs.
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Cliff Fuller

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Re: Peavey USB-P inverted polarity on one channel
« Reply #2 on: February 10, 2018, 04:16:17 pm »

Today I realized that it apparently has inverted polarity on either the right or the left channel, because when I mix a stereo signal to mono, anything that is equal in both channels (such as vocals or speech) cancels out. Same thing happens if I switch the USB-P from stereo to mono output, so I'm confident it's not my cables.



Are there any "spatializer" things going on with your playback app? I discovered the iPod "enhanced" modes would cause similar issues.
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Jonathan Johnson

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Re: Peavey USB-P inverted polarity on one channel
« Reply #3 on: February 13, 2018, 01:49:39 am »

Update...

Still waiting to hear back from Peavey.

Did some tests using a different PC, and still having the same problem. No, it's not some effect of the playback software; it happens with different software and different files. I played around with Audacity, splitting stereo tracks into mono and inverting tracks and I'm pretty confident there's something screwball with the USB-P.

Next step (maybe): open it up and study the wiring.
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Keith Broughton

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Re: Peavey USB-P inverted polarity on one channel
« Reply #4 on: February 13, 2018, 07:29:56 am »

I opened mine up and all the components are directly mounted to the cct board so I don't see where any wiring could be reversed.
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Jonathan Johnson

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Re: Peavey USB-P inverted polarity on one channel
« Reply #5 on: February 13, 2018, 05:05:13 pm »

I opened mine up and all the components are directly mounted to the cct board so I don't see where any wiring could be reversed.

That makes it even more difficult for me to understand how it could be messed up. Here's what I did to prove the issue:
  • Record a mono track in Audacity (or your favorite audio workstation software)
  • Connect the USB-P to you mixer so the Left channel goes to one input strip, and the Right channel goes to a second input strip. For now, pan them left and right, respectively.
  • Play back the mono track with the USB-P in Stereo mode. Observe that the audio plays in both channels.
  • On the mixer, pan the L and R channel strips to center. Observe that the audio cancels.
  • Pan mixer to L and R again. Set Stereo/Mono switch on USB-P to Mono. Observe that the audio completely cancels.
  • Duplicate the recorded track. Set one track to left and one to right.
  • Observe that the audio works in both channels when the USB-P is in Stereo mode. Observe that it cancels when in Mono mode.
  • Invert one of the channels (either L or R) in your audio software.
  • Perform the above tests and observe that no cancellation occurs.

I would be really interested to know if this is a one-off problem with my unit (seems unlikely, given the design), or if it's a systemic design problem that all of these units have and I'm the first to discover.

I had the thought that maybe one of the transformers was miswound, but the stereo/mono switch comes BEFORE the transformers. If it was a bad transformer, flipping the switch to mono wouldn't completely kill the sound.
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Mac Kerr

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Re: Peavey USB-P inverted polarity on one channel
« Reply #6 on: February 13, 2018, 05:57:01 pm »

I have been using 2 of them for several years and I have not noticed this issue. I work with a couple of video companies that use them their Playback Pro video pb machines, and they have not noticed it. While I don’t know where the problem comes from I don’t think it is in all USB-Ps.

Mac
« Last Edit: February 14, 2018, 06:39:39 pm by Mac Kerr »
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Jonathan Johnson

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Re: Peavey USB-P inverted polarity on one channel
« Reply #7 on: February 13, 2018, 06:02:47 pm »

I have been using 2 of them for several years and I have not noticed this issue. I work with a couple of video companies that use them their Playback Pro video pb machines, and they have not noticed it. While I don’t know where the problem comes from I don’t think it is in all USB-Ps.

Mac

To be clear, if you always use it in stereo mode and always have L&R panned full going to a stereo output, you probably never will notice the issue. But as soon as you mix to mono (i.e., a monitor send or feed to an overflow room), you'll notice either missing audio, cancellation, or garbling (when playing back digitally compressed audio files).

Even if you do playback in stereo, you might notice weird effects if your speakers are close together or if you're sitting in the "power alley" between them.
« Last Edit: February 14, 2018, 06:39:57 pm by Mac Kerr »
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Mac Kerr

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Re: Peavey USB-P inverted polarity on one channel
« Reply #8 on: February 13, 2018, 06:08:46 pm »

To be clear, if you always use it in stereo mode and always have L&R panned full going to a stereo output, you probably never will notice the issue. But as soon as you mix to mono (i.e., a monitor send or feed to an overflow room), you'll notice either missing audio, cancellation, or garbling (when playing back digitally compressed audio files).

Even if you do playback in stereo, you might notice weird effects if your speakers are close together or if you're sitting in the "power alley" between them.

I am fully aware of this, and I use my computer playback to set levels of both stereo mains and mono delays, front fill, out fills, and press feeds. Not having your problem. It is not a widespread problem. Send it in for service or replacement.

Mac
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Geoff Doane

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Re: Peavey USB-P inverted polarity on one channel
« Reply #9 on: February 14, 2018, 06:35:10 pm »

I opened mine up and all the components are directly mounted to the cct board so I don't see where any wiring could be reversed.


I can't tell for sure from Keith's photo, but is it possible that one of the transformers was installed backwards (rotated 180°)?  There appears to be a little dot on the PCB that corresponds to a mark on the transformer bobbin.  They line up in Keith's photo, but maybe not on Jonathon's.

GTD
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