• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

QSC PLX resonance problem

#21
PLX2402 here. At one time a had a rattle/buzz coming from my rack and when I depressed the actual SKB case everything was in, it would stop. The vibration was not serious or causing any feedback. I finally bought an Auralex Gramma pad used for decoupling and it totally stopped the buzz. The rack rig was sitting on top of the Berg HT322 at the time, and that cab can pump out some serious lows. I would be more apt to think it's one of your preamp tubes in your SWR. Another experience of mine, I was trying different tubes in my Dem201s and while trying out the Sovtek 5751 tubes, I got a high pitched zinging sound and a very slight feed back when I cranked the rig. Turns out one of the Sovteks were microphonic even with the reduce output gain the 5751 tubes provide. I also experimented with the gain coming from the preamp. Also, I've read the SWR may not put out enough output gain to the PLX2402 on up. There is a modification available. I would check the tubes. Did I miss something, because I'm suprised all of you way advanced guys didn't mention that. Hope this helps. I am very happy with my PLX2402. If I were to by a new PLX it would be the 3002 is the only difference.
 
#22
I thought of a possibility that IS a QSC issue....might be the problem whether it is microphonic (what I thought you said) or if it is just buzzing along with the speaker.

QSC is a good company...but they changed the way they hold down boards inside their units to a cheaper way, and the PLX series has the new way...

Instead of having several screws hold down the boards, on some of those units they use just one screw per board and the other supports are a sort of pin that slides into a slot on the board. They are usually OK for tightness, but if they happen to be looser on yours, the board might be rattling.

That is not too good, so I think I would take it off the speaker and put it somewhere else. Otherwise it may rattle a component loose and cause a real problem.

Your importers probably would not view the looseness as a problem. But I would think it would be a problem even for sound reinforcement usage.
Bass is a great application for the amps and I have no idea why they would say it isn't.

Sounds like they are not the greatest on customer service, but you could give them a try........
 
#24
Thanks to all. u4oriabass thanks for the kind offer, but I'm in Aberdeen so nowhere near Manchester. I've tried different basses and cabs, but I don't have another preamp to try. I will check whether the preamp valve is microphonic but it seems unlikely given there is no problem with the pre on top of the cab.
 
#25
I have a PLX 1602 and noticed the "resonance" problem when I got my Aggie GS112s. My Peavey cabs didn't have the problem. But the Aggies, being thinner-walled, vibrated more. Most of my vibration was coming from the cardboard heat tunnel inside the PLX. I used some self-adhesive neoprene pads to damp out that vibration. next, I installed some of the same pads between the bottom of the amp and the inside of my SKB case. While this attenuated the sound a great deal, it didn't totally get rid of it...and I just didn't feel comfortable vibrating the snot out of my amp/preamp. My solution was to take two cloth-covered neoprene wrist pads (for a computer keyboard) and place them front and rear, lengthwise between my cabinets and the SKB case. Now the case just "floats" and there is no more resonance from the PLX. Had I tried the wrist pads first, it, alone, would probably have solved the problem. The ones I used were about 3/4 inch thick and not terribly hard---you can hold them by one end and they "flop".

Kim
 
#28
Dave I ordered 'em direct from Acme. Even once you factor in VAT, duty and shipping they were a pretty good deal, around £450 per cab for two Low Bs. Gigged them for the first time on Friday and could not be happier. I can give more details if you need them.
 
#30
Try placing a few mouse pads or similar damping material between the rack-case (holding the power amp + pre) and the cab. I have a PLX 2402 and also experienced a loud vibration/rattling sound when I place the rack on top on either of my cab.s Isolating it somewhat with a couple of mouse pads made the problem go away.

HTH,
Greg
 
#32
I recently went thru the same problem when I purchased a PLX 2402, THE BUZZING WAS SO BAD, that afer using it on one gig I returned to GC to try
another one new out of the box and we experienced the same problem, then we tried a new 1602 and a 3402 and the same problem with buzzing and rattling of the circuit board and fan
was so bad even at low volumes, then one audio sales guy recommended the gramma, I put one under the amp and one on the floor under my 2-epifani 12's and the problem dis-appeared.

GC was cool enough that they sold me both Auralex
grammas at thier cost. It would be nice for QSC to resolve this problem without having the consumer spend additional money in order to use thier product.
 

Latest posts

Top Bottom
Back