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[Steve Crump]

I was bored and pulled some gear out to mess around the other day. Connected a monitor that I had modified and tested a few months back, powered up a rack with a MR18, no input device (music or mic) connected at this point, then I turned on a QSC GXD8 amp, the speaker let out a bellowing sound that dissipated quickly. I thought crap it probably got my HF driver, but it didn’t.

What could it have been? It sounded like a build up of energy, like capacitance. Is the issue with the amp? I have only used these GXD8 amps a couple times. I periodically would get a failure message from one, carried it to a service center and they said they could not get it to recreate the failure.

A few years ago I had a similar event at the venue, QRX 115s and Crown XLi amp, but this was a the end of the night and it happened a couple times, muted mixer, walk up to rack to power down, when I powered off the amp I would get this HF kind of bellow that dissipated quickly from the QRXs. This amp did eventually fail.

[Dave Pluke]

Might humidity/condensation be the culprit?

Dave

[Mike Caldwell]

Was the amp connected to the mixer?

[Steve Crump]

Might humidity/condensation be the culprit?

Dave

At the venue moisture is definitely an issue. Where the GXD is stored it’s for the most part conditioned.

[Steve Crump]

Was the amp connected to the mixer?

Yes. What are your thoughts? I am just trying to figure out if I need to avoid using the GXD.

[Tim McCulloch]

I think you need to call QSC.  Just 1 channel or both?

[Steve Crump]

I think you need to call QSC.  Just 1 channel or both?

Yelp, I agree. I had only one channel connected when this happened.

[Mike Caldwell]

Yes. What are your thoughts? I am just trying to figure out if I need to avoid using the GXD.

Just trying to eliminate any outside sources for the noise.

[Don T. Williams]

You're not trying to Buffalo us are you?  LOL

[Steve Crump]

You're not trying to Buffalo us are you?  LOL

Don,

I wish I were. The thing that stinks is that I think it is out of warranty now. I bought two of the amps on sale, when I received them one had an excessive amount of hours on it for a new amp, so the vendor replaced it. I did test both and then set them to the side and when I went back to play around with the amps months later, one of them had a failure message at start up, cycled a couple times and it went away, cycled again the message came back.
Contacted QSC they told me to carry it to a service center because it was still under warranty. The service center could not find anything wrong with the unit. I brought it back home, I might have used the amp twice in the field and haven’t touched it in close to a year now, plug it up and then this happened. I am going to play around with it a little more when I get back home.

This amp has left me questioning it’s reliability. Of course, I’m not stressing over this, it’s not like I have a use for them at the moment.

Plus I just wanted a chance to talk gear...LOL

[Mike Caldwell]

It maybe worth trying a firmware update / reload.

[Don T. Williams]

I'm wondering if it just sat so long that the relay contacts might have been dirty and allowed a signal to the amp output that would normally short to ground when powered off.  I am assuming this amp has such a relay and circuit, and I don't know that. It's a model I haven't used or sold. I know this isn't an old product, but it seems a lot of the older amps from the 70's and 80's made funny (or scary) sounds when powered down and connected to speakers back in those days. I may be thinking about Phase Linears' or other less than pro product.  Sorry about the earlier attempt at humor.

[Steve Crump]

I'm wondering if it just sat so long that the relay contacts might have been dirty and allowed a signal to the amp output that would normally short to ground when powered off.  I am assuming this amp has such a relay and circuit, and I don't know that. It's a model I haven't used or sold. I know this isn't an old product, but it seems a lot of the older amps from the 70's and 80's made funny (or scary) sounds when powered down and connected to speakers back in those days. I may be thinking about Phase Linears' or other less than pro product.  Sorry about the earlier attempt at humor.

I am going to circle back around and work with the amp in my shop to see if it does it again. It may become a project for one of my friends.

No offense taken with the humor. Humor is much needed. I appreciate the input.

[Jared Bartimus]

I doubt it would have gone away on its own in this case but does the MR18 have an internal talkback mic that could have been open? 

[Steve Crump]

I doubt it would have gone away on its own in this case but does the MR18 have an internal talkback mic that could have been open?

Nope.

I tried again last night...everything worked fine. Gremlins in these QSC GXDs.

[Jeff Bankston]

sounds like bull to me

[Steve Crump]

sounds like bull to me

Well it happened and I was hoping by posting it here someone would come along with the same experience and give me some insight on what the issue may have been. I am guessing by your post you have not had this issue.  But as always thank you for your insightful input.

[Tim McCulloch]

Well it happened and I was hoping by posting it here someone would come along with the same experience and give me some insight on what the issue may have been. I am guessing by your post you have not had this issue.  But as always thank you for your insightful input.

It's the "bellowing".  Jeff thinks visually.

[Steve Crump]

It's the "bellowing".  Jeff thinks visually.

I really didn’t know how else to describe the sound. I guess I could have chosen a better description, but words are definitely not my gift. Should have asked my wife for a descriptive word, she was in the shop when it happened.

Thanks

Edit. Okay. I am “thick”, I completely missed the pun! And I consider myself to have a good sense of humor. My apologies.

[ProSoundWeb Community]