atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging sound system problems

The manual says it is closer to 20 amps, but if they told you 13, so be it. It wouldn't be the first time a manual was wrong...

Jim
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Speaking from a secure undisclosed location.

You are chasing the symptom rather than the cause Jeff. With a 70 volt system when something like low frequency high level pop comes along the transformers on the speakers will saturate and pretty much present a dead short on the amp output that is probably being driven to more than it's rated 70.7v output also. One would expect the amp to go into protection but it might not be as fast as the breaker in the panel that is supplying it. I would not be surprised if the instantaneous mains current draw during an episode like that is several times the rated peak spec. Hence the breaker trips.

If you have DSP, absolutely insert a hard limiter that clamps just about where the clip indicator on the Crowns illuminate as a start,(if you have no other means to determine levels within the system) then back it down from there until you have eliminated your problem. The limiter(s) should be last in line and right before the inputs to the Crowns.

-Hal

If you haven't already, make sure the High Pass filter is dialed in on those channels. It's probably good to have it as a default, unless you specifically need to go lower then that.. 80hz would be a good place to start, and move up from there..

There might also be a HP filter on the amps.. If you're using ceiling speakers, they probably don't go down that low anyways, and you should set your HP filters appropriately to protect them.

That is a good point. Because of the transformers on the speakers saturating at low frequencies as I said above you want to high pass and 80Hz is a good number. The better and heavier the transformers are the better the low frequency response so if they used really good transformers on the speakers and an amp that is direct drive with no output transformer you could get decent low end and not have to (or want to) use any high pass. But usually you find that most ceiling speakers are el cheapo and only go down to around 100Hz.

Those Crown Com-Tech amps are top of the line and direct drive 70.7V so you are in good shape there.

-Hal

I don't have the specs for the speakers off hand but I know they are JBL.
I will mess around with the DSP that is built into the DX8 mixer.

If they are JBL Control series they are very good with excellent transformers built in. I have installed exactly what you have, Crown Com-Tech 800 with JBL Control 24CTs in the ceiling.

Nothing to do with your problem but did you know that those Com-Techs require Class 1 wiring to the speakers?

-Hal

Hal, would that be due 70.7 AND the probable 15 amp capability on the amp output? Close enough to 110VAC and 15 amp branch to scare me!

These are not 24CT, they are square...

Hal, would that be due 70.7 AND the probable 15 amp capability on the amp output?

No, nothing to do with what you are saying at all, in fact most amps today that are even larger only require CL2 wiring. Those Com-Tech amps are a few years old (8-10) and back then installers either didn't know or didn't care about speaker wiring unless you had an inspector who was sharp enough to know LV wiring and knew to look at the back panel of those amps where it says "Class 1 wiring required".

The class of wiring required is determined by UL or other testing lab specs which use a complicated formula of output current, current limiting, voltage and voltage limiting. The engineers that design commercial amps today are smart enough to design something that can deliver full power yet (and I'm guessing here) react quickly enough to a fault so that only Class 2 wiring needs to be used.

When I used those amps the wiring was in conduit and Greenfield whips to each speaker. I had a couple of thousand feet of 18ga TFFN in red and black twisted up which I pulled for the wiring.

If this ever should become an issue Jeff, it would, without a doubt be less expensive to just replace those amps though I would be crying because they are bullet proof.

-Hal

They used West Penn C206 unjacketed speaker wire, says CL2 on it...
According to the manual, class 1 wiring must be used if the amp is configured for 100 volt output...