QSC PLX Tech Question

[BassDemon]

I have a QSC PLX 2402 that I use in my bass rig.

It was built in 99 so is getting on a few years.

A few months back you guys helped me diagnose a tech problem when the amp started to crackle and distort as if somone was pulling the cable in and out.

I took it in for service and the problem was the internal ribbon connectors.

All was well until earlier this week when the same problem occurs.

This time however it only affects channel 1

using the channel 2 input gives no problems.

Now getting this thing serviced in NZ is a bit of drama, last time it took almost 3 weeks.

Not such a problem then as I didn't have gigs booked, but now I need this thing almost every weekend.

 

The amp is rackmounted but the rack doesn't have rear rack rails. I have supported the rear of the amp with some hard foam between the rack and the amp chassis but could the problems be a result of constant movement i.e into the car, up the stairs, onto the stage, back off the stage, back in the car backing the garage.

I've had it this way for 5 years but I'm wondinering if all the movement could be causing the connection problems ?

 

And a quick question for Andy

How would you compare the power section of the GBE1200 to the PLX ?

at the moment I use one channel into 4ohm (700w) so a mono amp would suit me just fine and GB gear has recently reached our shores.

I find that sometimes the amp lacks a bit of low end authority, the bass sounds a bit "soft"

The volume is set so the the clip lights will only come on when I give the strings a wallop.

[Craig Vecchione]

Vibration and humidity are the enemy of mechanical connectors. Your rack mounting sounds okay, but if you drive the amp all over on a regular basis, and the unit sees a lot of dampness, eventually the connections can have problems.

[BassDemon]

Vibration and Humidity........

 

Well it sits on a Mesa 4x12 bass cab so there it plenty of vibration, and the roads here are pretty potholed so it gets jarred about when in transit.

 

As for humidity it's currently 80% and this is the driest time of year.

In summer it's seldom below 90%

 

I am wondering if I should get this latest problem sorted and then sell the amp.

 

I purcahsed it used from a friend very cheap and I could probably get back close to what I paid for it.

[agedhorse]

Rear support of the PLX amps is generally not necessary.

 

Could be a connection, or possible a ribbon cable.

 

The PLX is class H and the GBE-1200 is a class AB. The GBE was overdesigned and has enormous current capability before reaching the protective limiting circuit's threshold, knowing that it will be (ab)used as an instrument amplifier. I wouldn't expect any protective limiting into 4 ohms with the PLX though. Both are pro quality amps, and the SMPS power supplies on the PLX are very well executed. I have not experienced any problems with LF output (quality or quantity) on the PLX amps and Bob Lee from QSC is a bass player so I would expect that he would be sensitive to that issue if there were a problem.

 

Try a GBE-1200 and see if it "rocks your clock". It may be that the preamp in combination with the power amp on the GBE-1200 is a better combination than what you are using now, but your ears must decide. Musiclink is the distributor down there.

[pdiddy]

For what its worth, most of my ribbon cable issues have ended up being the male connectors that the cables plug into. Re-flowing the solder where connectors mount to the circuit board might do the trick if you're up to it.

[BassDemon]

Thanks guys

 

Hopefully it keeps running Ok on channel 2.

I have a quite an important gig next weekend.

I'll see how quick they can turnaround the service and then once it's fixed I might go looking for a GBE1200 to try.

I keep hearing such rave reviews.

[BassDemon]

A quick update

 

Haven't sent the amp away yet but for the last few nights I've used it I've been plugging into the ch2 input and using ch2.

 

I can only guess that the ch1 input has been faulty for a while as the sound on ch2 seems to be much better.

The bass sounds deeper and hitting the strings hard gives a real punch in the chest.

On Ch1 even before the crackle sound started I'd always thought the bass notes sounded a bit soft.

 

It's a noticable difference, even the drummer commented on it

 

I've triple checked the switches and they are the same on both channels.