Random Volume Spikes

[SplinterheadParticipant]

Hi all,
new member here with a quick question.
I’ve been running a Qu-24 for the past year and a half with no issues. Great board!
I’ve since come upon a problem. Channel 3 has these random volume spikes that clip the board and create this annoying “pop” sound. One night I had a condenser mic running through it one night and a wireless mic another night. There are no issues during sound check but half way through the set (1hr or so) it starts spiking and popping like crazy. I’ve switched out the cables and checked connections. From what I can tell all seems well. I was hoping some could shed some light on this issue or I’d like to hear if anyone else has had this issue before.

Thanks!

[Mike CParticipant]

Phantom power on a bad cable will cause what you are hearing.

Are you using a snake cable with the board or are the mics just plugged directly into the board?

Did you have the phantom power turned off when using the wireless mic on channel 3?

Try it with nothing plugged into channel 3 with the phantom power off and watch and listen, if no noise try the same thing with the phantom turned on.

[SplinterheadParticipant]

Thanks for replying!
We have a traditional snake that’s permanently installed from the stage to the mixer about 50′ away or so. The wires are buried in the walls.

So the first night I was running 2 condenser mics (Neumans) both using phantom power. Cables were about 15′ long. One was in channel 2, the other in 3. Channel 3 was spiking like crazy towards the end of the set. At that point I had no idea what was going on. Channel 2 had no issues.

Second night I was running a wireless mic through channel 3 using a short 3′ cable. The wireless unit was right in front of the monitor (not sure if that could affect the signal). After a 1/2 hour or so it started spiking and making audible pop sounds. I had the singer switch to a different mic (SM58). I then switched the cable on the wireless and it seemed to behave while NOT in use (mic was off but unit was on). It was just idling. Phantom power was definitely off.

Third night I had just a regular dynamic (SM58). No problems at all.

During the evening I took the cable out of the board on channel 3 and watched it for a good hour, no issues. I put a cable in with no mic, no issues. I couldn’t seem to replicate the problem. Very weird.

[Mike CParticipant]

Were you always using the snake channel for both the condenser mics and the wireless?

[SplinterheadParticipant]

Yes

[Mike CParticipant]

Check as much as you can of the snake cable, open up the box, check the connector at the mixer, shake and wiggle the fan tail, move the connector that’s plugged into ch. 3 at the snake box. Do all that while someone is watching the ch.3 input level or listening to ch.3 in PFL with headphones at a low level. Do the shake and wiggle test with the phantom power turned on and a mic plugged into ch.3.

[MarkPAmanParticipant]

Intermittent faults are a pain to find.

I think, from here, I’d proceed by checking connectors inside the installed snake at both ends for anything odd. Then re-patching the snake, maybe by swapping 2 & 3 over at the desk, and observe what happens. If the problem then re-occurs on Ch2, you’ve almost certainly eliminated the desk.

One thing you can do for testing intermittent problems these days is use a recorder & computer (and you have a recorder built in of course). Record a test tone, or something, at a low level of several hours, then examine the waveform on a DAW – spikes are very obvious, while dropouts may require some zooming to spot, but it saves having to listen all the time.

[SplinterheadParticipant]

Check as much as you can of the snake cable, open up the box, check the connector at the mixer, shake and wiggle the fan tail, move the connector that’s plugged into ch. 3 at the snake box. Do all that while someone is watching the ch.3 input level or listening to ch.3 in PFL with headphones at a low level. Do the shake and wiggle test with the phantom power turned on and a mic plugged into ch.3.

Thanks again for your reply.
I actually did this at the end of the night. I had a friend of mine plug in a cable while we were troubleshooting and wiggle where the connections met while I watched the levels. i was figuring that maybe the cable was hung up and at a bad angle creating interference in the signal. What I didn’t do was check this with the phantom power on. That’s something I’ll do. I also checked the connection at the board. I tapped/moved channel 3 and there was an effect on the signal level but it turned out that all channels did it when the connection was manipulated. I have this feeling that its not a mechanical issue but more of an electrical interference issue.

[SplinterheadParticipant]

ntermittent faults are a pain to find.

I think, from here, I’d proceed by checking connectors inside the installed snake at both ends for anything odd. Then re-patching the snake, maybe by swapping 2 & 3 over at the desk, and observe what happens. If the problem then re-occurs on Ch2, you’ve almost certainly eliminated the desk.

That’s an excellent idea. I’ll give that a shot.

One thing you can do for testing intermittent problems these days is use a recorder & computer (and you have a recorder built in of course). Record a test tone, or something, at a low level of several hours, then examine the waveform on a DAW – spikes are very obvious, while dropouts may require some zooming to spot, but it saves having to listen all the time.

If all else fails I’ll go for this idea.
Thanks very much for your reply.

[Mike CParticipant]

I also checked the connection at the board. I tapped/moved channel 3 and there was an effect on the signal level but it turned out that all channels did it when the connection was manipulated. I have this feeling that its not a mechanical issue but more of an electrical interference issue.

Some mic cables and snake cables when plugged into a mixers input without a mic plugged in to the cable will make noise when moved around. Cables like that may not be the best cable around but that does not sound like the problem your having or had.

[SplinterheadParticipant]

I agree. Thanks for your reply.

[[XAP]BobParticipant]

If you lose one of the cables you can end up with an antenna instead of a balanced cable as well… just another thought

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