Quad Cortex output volumes

andyg_prs

I found something really weird about the QC at rehearsal yesterday.

 Used the XLR output for the first time. The XLR outputs are called 1 and 2. The guitar lead (TRS/TS) outputs are called 3 and 4.

 The XLR outputs are supposed to be 6dB quieter, fair enough.  But I found the volume difference massive.

 I had made sure all the outputs on the QC were set to their maximum without clipping  -there's a volume meter, goes red when it clips.

Once back in my home studio, I took the guitar lead output into my DXR at about 9 o'clock was bloody loud......the XLR output into the DXR at maximum volume (which I don't want to run it at) wasn't quite as loud.

I assume the volume must be enough for FoH (I've never offered a soundman a TS jack)....but it's odd.

 I never lacked volume in the XLR output from an AX8 or Kemper.

 And the different on the scale seems to be more like 18dB, even though the - / + on the dB scale confuses meand I can see that there are different values on the inputs.



I did the same experiment with a Mackie SRM350 which has a combo TS/XLR jack and the volume difference as very similar.

Any ideas?

Thanks,
Andy

Octavio

If you swipe down the I/O page are the XLR outs set to 0dB?

Actually scrub that, I think you mention it in your post. I thought that you may have been referring to the OUT block on the grid.

When I use XLRs I experience a lot more noise issues when compared to outputs 3/4.

andyg_prs

Octavio said:

If you swipe down the I/O page are the XLR outs set to 0dB?

Actually scrub that, I think you mention it in your post. I thought that you may have been referring to the OUT block on the grid.

When I use XLRs I experience a lot more noise issues when compared to ouputs 3/4.

I actually increased the output 1 / 2  level to the maximum I could without it clipping.

Danny1969

Generally running anything balanced differential using XLR outputs into a balanced differential input like a mixers mic input is twice the audio voltage, as the different input of the mixer amplifies the difference between pins 2 and 3 

So if  pin 2 is + 2V then pin 3 will be the opposite phase of -2V and the mixer amplifies the difference between -2 and +2 = 4V

If you tie 3 to ground by using a mono jack one end or plugging into a non balanced input then pin 3 is tied to ground and input amplifies the difference between pin 2 and ground which is half the balanced differential signal voltage

But many units will have a low level on an XRL output because they are expecting you to plug it into a microphone channel on a mixing desk ... fed by a stage box on stage. So it makes sense to have a similar output to a microphone. Then it won't need padding down. I would expect a mic / line / guitar input to amp option though

Many active speakers will need a far higher level, others have a switch between mic and line and can operate to full power with either. 

Main thing is try and keep connections true balanced differential because then any noise picked up from the units  power supply, or along the cables journey  will be picked up on both pins 2 and 3 equally and thus  be cancelled out by the input of the next device. 

andyg_prs

Danny1969 said:

Generally running anything balanced differential using XLR outputs into a balanced differential input like a mixers mic input is twice the audio voltage, as the different input of the mixer amplifies the difference between pins 2 and 3 

So if  pin 2 is + 2V then pin 3 will be the opposite phase of -2V and the mixer amplifies the difference between -2 and +2 = 4V

If you tie 3 to ground by using a mono jack one end or plugging into a non balanced input then pin 3 is tied to ground and input amplifies the difference between pin 2 and ground which is half the balanced differential signal voltage

But many units will have a low level on an XRL output because they are expecting you to plug it into a microphone channel on a mixing desk ... fed by a stage box on stage. So it makes sense to have a similar output to a microphone. Then it won't need padding down. I would expect a mic / line / guitar input to amp option though

Many active speakers will need a far higher level, others have a switch between mic and line and can operate to full power with either. 

Main thing is try and keep connections true balanced differential because then any noise picked up from the units  power supply, or along the cables journey  will be picked up on both pins 2 and 3 equally and thus  be cancelled out by the input of the next device. 

I should have known you'd have a thorough explanation I wouldn't quite understand.

It sounds like from what you've said you'd expect the mono jack to result in half the output, but in fact it feels more like double the output.....

Due to my ignorance, a few questions if I may.

1. I only work in mono, I assume using a pair of XLR outputs from the Quad Cortex would make no difference to the volume?

2.  For my amp / Captor X set up which only had an XLR output, I built an XLR to XLR passive volume control to operate with my foot for my personal monitoring.......this helps me for gigs where I can't get a personal mix, or it's not going to plan, so I can use my own speaker controlled this way.  I'm concerned that using it this way with my QC I might not get enough volume if the stage gets noisy.  I'm guessing that changing the XLR input on the DXR10 setting from line to mic wouldn't be appropriate as it's not a mic, so it might damage the DXR10 - or is that wrong and could I do that and just be cautious starting with the DXR volume nice and low?

3.  I'm assuming the XLR level is fine for the PA person even if it's quite a bit quieter?

4.  Just out of interest, would you expact a soundman to accept being offered a TS cable (mono guitar jack) saying, that's my output?

5.  By expecting a mic/line/guitar input to amp option, you mean you'd expect to be able to define on the QC what the XLR output is going to?  That's even more interesting because the QC can handle two separate inputs - they are combi TS/XLR, and they specifically say either of those can be for a microphone used by a vocalist.

By the way, sod's law is I don't think I currently have a passive volume pedal.......the QC doesn't seem to introduce any noise using a mono guitar cable via a volume pedal to my DXR10.  I've experiemented with an active pedal and there is no noise.  When I tried using TS to XLR converters to use a volume pedal on the XLR output of my CaptorX it was horribly noisy, hence the box I built based on advice on this forum.

Thanks,
Andy