Question about QSC K10.2

[bucephylus]

Hello Sound Engineering TB’ers!

Got a Q about the QSC K10.2.

I’ve recently started using this fab cab in place of a backline amp for BOTH stage mix AND Vocals. It is truly amazing! I’m using CH1 for the vocal monitor feed and CH 2 for Line Level preamp DI feed.

The one issue I’m in the dark about is the CH2 signal chain. The cab is amazingly stout, when EQ’d properly, and fed from a pedal board preamp DI. BUT, if I try to connect the Through XLR on CH2 to a board for the FoH feed, the K10.2 CH2 volume drops to about 1/10th of the output before the Through connection. I’ve tried using an XLR Y out of the pedal board preamp, but get the same result.

For the moment, I’m using a second preamp on the pedal board to separately feed the K10.2 CH2 and FoH board from separate DI’s. But, that seems sub-optimal.

Am I doing something wrong with the CH2 setup on the K10.2? Or is this inherent in the way the CH2 behaves? I can’t find any setting in the CH2 setup menu, which solves this issue.

Seems like this would compromise using a pair of K10.2’s as a backline; if one wanted to go that route.

What am I missing? Thanks!

 

[TommyGunz]

Just to be clear, you have your bass signal coming from a preamp pedal XLR DI line out to the Input on channel B on the K10.2 then you connect an XLR cable to the pass through XLR on channel B that goes to the mixer. And only when you connect the pass through, your bass signal drops significantly coming out of the K10.2 speaker? If all that is correct that does seem like abnormal behavior to me. There is basically nothing between the input and output of the channel.

Here is some troubleshooting that I would do, but its grasping at straws:

1. Is Channel B set to HI-Z or Line? It should be set to Line.

2. Have you tried different XLR cables for both the input and output?

3. Is the mixer sending phantom power back through the line on that channel? Phantom power should be off on that channel.

4. Does the drop in sound happen as soon as you plug in to pass through? Meaning, the other end of that output cable is not plugged into anything?

5. Does the preamp pedal have a ground lift switch for the DI that you can toggle?

Also, is there a reason you are going through the monitor first, and then to the mixer? While that should technically still work, it is kind of backwards, and as a sound guy that would drive me nuts. Do you not have a sound guy to mix your monitor send?

We use K12.2s but I've got a gig Saturday night I can see if they act the same way or not and let you know.

 

[TommyGunz]

I’ve tried using an XLR Y out of the pedal board preamp, but get the same result.

Wait a minute. Are you saying you have tried plugging an XLR Y cable into the preamp pedal DI, sending 1 leg to the input of channel B on the K10.2, and the other leg to the mixer, and then the bass signal coming out of the k10.2's speaker still drops down? If that's the case then the pass through of the K10.2 can't be the issue. Still, that would really only remove my #4 troubleshooting option, it could still be one of the others. It also makes me think there could be some kind of loading issue with the DI on the preamp pedal, it just can't handle driving 2 things.

 

[bucephylus]

Wait a minute. Are you saying you have tried plugging an XLR Y cable into the preamp pedal DI, sending 1 leg to the input of channel B on the K10.2, and the other leg to the mixer, and then the bass signal coming out of the k10.2's speaker still drops down? If that's the case then the pass through of the K10.2 can't be the issue. Still, that would really only remove my #4 troubleshooting option, it could still be one of the others. It also makes me think there could be some kind of loading issue with the DI on the preamp pedal, it just can't handle driving 2 things.

Thanks for your thoughts.

Yes, same behavior with the Y XLR. Does seem to be some kind of loading issue with the DI send.

I’m using a SushiBox Venus preamp; but, also have a Sadowsky preamp. I need to see if the Sadowsky does the same thing.

 

[Mike Caldwell]

Double check your XLR's for proper wiring.
Just for the test what happens if you unplug the input connected to CH.1?

Let us know what happens using a different pre amp/DI.
Are the pre amp DI out puts line or mic level, most standard DI box outputs are in the mic level range, CH.2 on the QSC is only line level or HiZ.

 

[bucephylus]

So, the reduction is still there with the Sadowsky preamp; but mainly in the lows and only about a 5% reduction. Still, it is audible.

Seems there is a loading effect on the preamp XLR Line signals.

 

[bucephylus]

Double check your XLR's for proper wiring.
Just for the test what happens if you unplug the input connected to CH.1?

Let us know what happens using a different pre amp/DI.
Are the pre amp DI out puts line or mic level, most standard DI box outputs are in the mic level range, CH.2 on the QSC is only line level or HiZ.

The pres have balanced XLR Line level outputs. All wiring is correct

 

[Mike Caldwell]

Wonder what the output impedance of the pre amp is? If it's in the 200 or less ohm range it should be able to drive multiple inputs
with no problem.
Try the channel 1 input to see if it does the same thing.

 

[Mike Caldwell]

What is the mixer your connecting to ?

 

[Wasnex]

This is simplified, but I wouldn't be surprised if the channel Thru's are just parallel connections (not buffered). So if something loads down and unbuffered output, it will also load down the input.


Do an experiment: Run the signal through channel 1 set to line level, and see if the same problem occurs.

 

[bucephylus]

What is the mixer your connecting to ?

In my practice space, I’ve just been using a Mackie 402-VLZ3; Phantom Power is OFF.

 

[bucephylus]

Apologies for not getting back sooner. Busy with gigs and Fam events.

At this point, I’m pretty sure the problem I’m facing is not within the K10.2. I’m NOT familiar with ganging Line level balanced sends to multiple downstream amps. always had it in my head to send the balanced signal to the board, and the unbalanced preamp to a backline power amp.

The successful performance of the K10.2 as a stage mix monitor has me considering other backline options; and at least one of my regular gigs can be very nicely covered with the K10.2 alone for stage mix, no backline.

But, it does seem that the ability of the preamp to drive multiple targets with the balanced XLR may be a variable. Could be a better topic for the Amplification forum.

Thanks everyone for the input.

 

[TommyGunz]

You could try using a standalone DI after the preamp. That should work.