Hum Sound From CQ-18T

[neelabh]

Hello,

I bought CQ18T recently and using XLR to connect to Bose S1 pro+ speaker. I keep getting the hum sound which gets louder as the speaker volume is increased. This hum sound is still there when Main line is muted. I took the mixer to the retailer, and they were also getting the same hum sound when they tested at their store. So they took the unit back and gave me another one. Problem is that the hum problem still persist even with new units.
I am using XLR cable to connect to speaker. I have changed the cable, changed the Main out sockets – L and R, and connected to second input line in speaker. I have also updated the firmware to latest so not sure what the problem is. Really love this mixer so don’t want to return for good, I am sure its me and not the mixer, but can’t figure out the problem. Any help will be appreciated!

[Anonymous]

Reading above, it sounds like you’ve changed everything except the S1 speaker itself. What happens if you have the XLR cable attached to the S1 but not the mixer; is the hum still there? What about with the cable disconnected from the speaker altogether; does the speaker still hum when turned up? I have a Bose L1 on a CQ-20 and don’t really have a hum issue unless the speaker is turned up super loud with little to no input volume from a source.

[millerthriller]

This sounds like a GND loop.

Often this can be fixed by switching to “GND lift” at the speaker, but I believe the Bose S1 doesn’t offer this.

Solution ideas:
* add a transformer with GND lift to the line (e.g. https://www.thomann.de/de/radial_engineering_ic_1_icecube.htm)
* Less clean solution would be to implement thd GND Lift in the cable by removing the shield at the XLR cable at the side of the speaker (male XLR). If you don’t want to solder by yourself a cable like (https://www.thomann.de/de/sommer_cable_sghxu.htm) would do this.

No guarantee that this works, but something to try …

[neelabh]

@mfusa Yes I did try connecting mic directly to speaker via the XLR cable and hum was gone.

Also there is no hum when there is no cable attached and speaker is on, even on high volume(3/4).

[Mike C]

Do you get hum when the speaker is running on battery power and connected to the mixer?

Is the input set to line level? Try the 1/4 inch AUX input.

Are your XLR cables wired with pin 1 tied to the shell of the connector?

[millerthriller]

Goog idea to try the battery mode! Make sure to unplug tha power cord in this experiment.

[neelabh]

Here is what I found, with the help of Guitar Center guy –
1. Hum sound was still there while the speaker was running on battery.
2. When TRS output from mixer was connected to speaker – Hum was gone.
3. When another speaker (some RCF ART model) was connected(XLR to XLR) – Hum was gone.

There is something coming out of CQ18 mixer XLR out(even with muted main) that Bose S1 pro+ speaker doesn’t like. Guitar center guy tried the demo S1 pro+ speaker he had and hum was there too(with XLR output). So it’s not a problem with the speaker I had.

I have returned the Bose speaker and will be going for QSC K10.2.

Hope this helps someone getting the same problem.

P.S. I tried updating Bose’s firmware but it kept failing for me. So not sure if firmware upgrade would have fixed it.

[bridget]

Is one-to-one transformer out of the question?

[neelabh]

@bridget I tried this hum eliminator –

Pyle Compact Mini Hum Eliminator, which I bought from Amazon. It did reduce the hum, but it was still noticeably loud. After that I went to Guitar center and got the troubleshooting done.

I have returned the Bose speaker and bought QSC K10.2. No hum now.

BTW on one of the troubleshooting step at Guitar center, the guy plugged an analog mixer(XLR) to the Bose speaker and there was no hum. That’s when he took back my mixer(CQ18) and gave me another new one. That’s the only time, apart from TRS output, that Bose did not had hum.

Hope it helps.

[Tj]

Neelabh, you are right. I have recently bought a CQ18T. I was setting it up today and realised that something is wrong with its architecture. I attached jbl prx612m speaker and it had this hum even when the out put was muted. I tried changing the cables etc but nothing helped. The hum goes away when I disconnect the mixer from the speaker. I tried a small Mackie fx3 and there was no hum. I’m really disappointed with the CQ18T and plan to return it. Also planning to do a YouTube video on the issue.

[Author]

Posts