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CapC 21st July 2012 10:49 PM

Amp Overloading
 
Hi, all. I couldn't find a subforum that seems to match my exact question, so I'll try posting here. I'm not a complete newb to audio, but far from competent at the same time...

Here's my scenario:

Outdoor, poolside audio system, approximately 1000sqft open air space:
Klipsch outdoor speakers model AW-525 (8Ω, 75W nominal/300W peak)
Klipsh CA-800-TSW outdoor subwoofer (6Ω, 150W)
Since the sub is passive and connected in parallel with the L/R, the impedance at the amp will be 3.75Ω
ART SLA-2 power amplifier (280W/channel @ 4Ω, stable down to 2Ω)
Source is a hard-wired Apple Airport Express, controlled by various iOS devices

I know the amp is too powerful for the speakers, so I have the attenuation controls set to midpoint (18dB) to limit the power output. Problem is, this amp will go into thermo-protect shutdown from time-to-time especially with thumping bass tracks.

I have wired it with 18AWG cable which I recognize is far too small, so I rewired it with 14AWG, hoping to make a significant difference.

With the old wiring, I home-ran everything from speaker to amp.

(AMP) <===8feet===> (LEFT) <===7feet===> (SUB) <===7feet===> (RIGHT)

Which means my home run for the left is 8', for the right is 22' and both L/R runs to the sub for 15' each. Total wire length is 60'.

With the new wiring, I ran L/R for the sub back to the amp, and daisy chained the L and R from the sub, meaning my total wire length is 44'.

I thought this would help, but it's even worse! I can only run the volume at half the level before, and even then it still shuts down :confused: I want this to be good enough for background audio, but its not even good enough for that. I 'm not really overdriving it, since I use a Yorkville Elite Excursion 1000W system for parties...it's just not weatherproof...



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Enzo 21st July 2012 11:11 PM

First, the volume control on an amp does not limit the power output. It only changes the sensitivity. So if you have it all the way up and some signal put5s 100 watts into your speakers, you could then turn the volume control down, and yes, there would be less power coming out. Howver, all you need to then do is turn up the signal source, and you can easily be right back at 100 watts even though the amp volume is down some.


Your amp is not thermalling out due to the size of your wires.


If I had to guess, I might think your amp is objecting to the way the sub woofer is wired in. Eliminate the sub for now, just run the main L/R speakers. Still thermal out? Or is it OK that way?

CapC 21st July 2012 11:49 PM

Enzo, thanks for the quick reply.

When I took the sub out of the equation, the amplifer did not thermal out. In fact, the 'smart-cooling' system is not even kicking in and the amp is driving the speakers to the volume I would expect.

I'm actually a little surprised at how rich the lows are without the sub, but I would still like to have the sub in the system.

indianajo 22nd July 2012 01:49 AM

I think connecting the sub to both channels is wrong. You could connect the sub in parallel to one channel or the other, perhaps, but not both. Since it works okay without the sub, try first just the sub on one channel. If that works okay, maybe the sub is really 6 ohm. Then try it with the sub in parallel with one (only ) channel.

CapC 22nd July 2012 01:53 AM

I'll try that, but the instructions call for both channels to be connected. In fact, there are four terminal strips on the back... plus and minus for each channel.

HawaiiGuy 22nd July 2012 06:27 AM

The CA-525T, CA-650T, CA-800T and CA-800TSW include a multi-tap transformer for 70 or 100 volt installations. There is also a bypass position that allows normal 8 ohm operation for installations that do not require a transformer. The switch is on the back of the speaker and can be set using a small flat head screwdriver. Make the appropriate tap selection as indicated below:
CA-525T (Transformer Power Rating: 30W)
70V: 30W, 15W, 7.5W, 3.7W, 1.7W
100V: 30W, 15W, 7.5W, 3.7W
Bypass Position: 8 ohm Nominal

CA-650T / CA-800T / CA-800TSW (Transformer Power Rating: 60W)
70V: 60W, 30W, 15W, 7.5W, 3.7W
100V: 60W, 30W, 15W, 7.5W
Bypass Position: 8 ohm Nominal

When making any type of speaker wire connection, be sure to observe proper polarity. Most speaker wire and connectors are color-coded. Typically, red is positive (+) and black is negative (–), or ground. It does not matter which wire conductor is connected to the positive or negative connection of your equipment as long as it is consistent.

http://mediacdn.shopatron.com/media/...pdf?1288055213

CapC 22nd July 2012 02:30 PM

Quote:

Originally Posted by indianajo (Post 3100208)
I think connecting the sub to both channels is wrong. You could connect the sub in parallel to one channel or the other, perhaps, but not both. Since it works okay without the sub, try first just the sub on one channel. If that works okay, maybe the sub is really 6 ohm. Then try it with the sub in parallel with one (only ) channel.

Problem solved, thank-you! The amp is barely even warming up now. I re-read the manual from the link HawaiiGuy Provided...I'm not sure how I originally came to the conclusion to put both channels into the sub, but it was clearly wrong.

Thanks, all! :)

indianajo 22nd July 2012 05:32 PM

Congratulations!


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