This is topic Questions About QSC MXa Series Amps in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009837

---

Posted by Jeremy Weigel (Member # 4208) on 04-09-2009, 07:42 PM:
 
Question #1:

I have 2 MX 2000a amps running on a single 20amp breaker. Upon powering up cold at the beginning of the day these amps trip the breaker. I have replaced the breaker, but it still gets tripped occasionally. I recently bought a clamp on amp meter and found that the amperage spikes up to 22~23 amps at first power up.

Does anybody know approximately how much amperage these amplifiers should draw when first powered up?

Question #2

I have several MXa series amps (mostly 1500s) and have noticed that the red clip LEDs on a few fade out in a matter of seconds and others fade out slowly. I assume this is due to the capacitors draining.

Could/Does this indicate that there might be an amp failure about to happen on those that fade out quickly? And could this be a potential reason as to why the amps mentioned in question #1 are tripping the breaker?
 

---

Posted by Louis Bornwasser (Member # 3063) on 04-09-2009, 08:16 PM:
 
Very large amps have very large capacitors, which can draw even more than the current you indicated. Tripping breakers could be normal. If this is a change, it is more likely that the breaker is about to fail than the amp.

If your amps will drive hard and long, then there is no more chance of failure than when the amp was new. Louis
 

---

Posted by Kenneth Wuepper (Member # 1174) on 04-09-2009, 10:26 PM:
 
Jeremy,

The solution to your problem is simple. DO not use the breaker as a main power switch for the amp rack. Rather turn the amps on and off separately by their own power switches.

The surge current at turn on is very high as Louis has stated. By turning them all on at once, the instantaneous current exceeds the rating of the breaker.

Rapidly cycling the power to the amps by turning on, tripping and turning on again can damage the rectifier bank in the power supplies of the amplifiers.

KEN
 

---

Posted by Mark Gulbrandsen (Member # 72) on 04-09-2009, 10:51 PM:
 
The MX is not my favorite QSC amp by far... they are difficult to service and cost more to UPS round trip to QSC than they are actually worth. I recently rebuilt a bunch of MX amps on site for a customer that were 12 years old... they got all new main electrolytics and some smaller electrolytics. There were a number of the old caps that had some leakage around them where they are sealed. Caps have a finite life and need replacement every so often. This life time period varies depending on what type of caps they are but 7 to 10 years is average.

As per the breaker thing and damaging the amps I'll second what Ken suggests... a very logical route to go indeed and it'll work. I have very definately replaced shorted brige rectifiers in those amps several times!!

Mark
 

---

Posted by Tony Bandiera Jr (Member # 2365) on 04-10-2009, 01:22 AM:
 
Or you can do what we do at UC Irvine and leave the amps on 24/7...over 12 years and not one failure of the MX series amps. They do get an annual cleaning of the dust though.

I agree that shipping QSC MX amps is costly..but on the plus side, as Mark pointed out, they are easy to field service and QSC is pretty good about making the service manuals available.

We did have one of the economy series amps (USA Series) for our surrounds that died abruptly..no drama, just went dead. This was after it was about 4-5 years old...QSC not only fixed it at no charge (I dropped it off at their service desk, with instructions that I would pick it up when done, no need to ship it to me), but I was surprised one day to come home to a package from QSC, they shipped the amp back at no charge!!

Great customer support..our friends at Sony should learn from QSC...

And to elaborate on the Question #2 of the original post:

Some of the amps do have different fade times on the clip LEDs on shutdown...my guess it has to do as much with the load on the amp as well as slight differences in the internal caps..as long as the clip lights aren't on all the time or pulsing with the signal, don't worry about them.

Finally, depending on the brand of your circuit breakers, you can get "Magnetic ballast duty" or "high inrush" breakers that will handle the inrush better. I know Square D has them, other brands might. Contact your electrician.

A final caveat: most commercial buildings have a LOT of "available fault current" and you should never be into your subpanels!! One small slip with a screwdriver and you can invite a serious explosion..please have an electrician handle changing out your breakers.

I have seen too many aftereffects of short circuits and I no longer get into subpanels for any client.

Edited to fix QSC Model series..

[ 04-14-2009, 05:38 PM: Message edited by: Tony Bandiera Jr ]
 

---

Posted by Louis Bornwasser (Member # 3063) on 04-10-2009, 08:19 AM:
 
On my home system, I have 5 large Ashly amps fed by (1) 20 amp circuit. It was necessary to use a "step" power system to allow only one amp to power up at a time. Mine are set 4 seconds apart, with the preamps on immediately. Shut down occurs in reverse. Louis
 

---

Posted by Steve Guttag (Member # 268) on 04-10-2009, 08:40 AM:
 
The MXa amps, for us have been pretty darn reliable...probably the most reliable, come to think of it. We are starting to get some noisy attenuators now but by and large, the installed base just keeps running.

QSC does offer rebuild/renew kits for their legacy amps.

QSC customer support has always been top notch.

Steve
 

---

Posted by Eric Robinson (Member # 2966) on 04-10-2009, 12:50 PM:
 

quote: Louis Bornwasser

---

"step" power system

---

quote: Jeremy Weigel

---

I do remember we had a MX2000a amp that went rather violently in the middle of a show almost 12 years ago. It shot flames out the front vent and filled the booth with that ever so pleasant burnt transformer smell for days. Luckily it was on the surrounds and didn't take them out.

---