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Author Topic: one clip light comes on before other  (Read 5316 times)

David Parker

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Re: one clip light comes on before other
« Reply #10 on: January 11, 2013, 01:44:17 PM »

I have a QSC RMX 4050hd on sub duty. I have it set up in parallel mono mode, both sides get the same signal. One side was blinking the red light and audibly clipping while the other side was not. I later tested it with no speakers connected, and the clip lights came on at the same time with pink noise. What might cause one light to come on early? I tested the subs with a battery and both cones in each cab moved similarly. Normally one might think a bad speaker cable, but the sub in question sounded fine until pushed a little too hard. Also, with the limter enabled, one would think the clip light blinking slightly would not cause audible distortion.

Did some testing today. Subs run off 4050hd with 100hz low pass, just like I run them normally. Both subs started clipping audibly before the clip light came on on the amp. Ran both subs separately and both started clipping at the same level, one on either side of the amp. When I pushed them a little more, the one clip light came on on one side of the amp, just as before. I didn't push them enough to get both clip lights to come on, they were already jumping pretty good. Switched over to a PLX3402 and both subs started clipping at the same apparent loudness as with the 4050. Does the one clip light coming on earlier than the other mean I  have a problem with the amp even though the audible clipping is the same on both sides?
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John Roberts {JR}

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Re: one clip light comes on before other
« Reply #11 on: January 11, 2013, 02:01:00 PM »

As I posted earlier, it may just be a minor tolerance difference.

IMO the better clip indicators actually track the path losing negative feedback so differences between voltage clipping would be minimal, but even this more accurate monitoring the loss of feedback will be triggered before voltage clipping by current limiting that could use 5% tolerance parts (or worse from device varaince).

If they indicate the same for no load, but differ under load, current limiting variance could be the reason.

JR

PS: Note slow clip indication is an old (dirty) trick used to make amplifiers appear more powerful than they are, because customers are not very sensitive to small amounts of clipping.
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Mike Diack

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Re: one clip light comes on before other
« Reply #12 on: January 11, 2013, 03:40:22 PM »

so if that is the problem, could it affect only one side?
Because the power supplies for the two sides are TOTALLY independant. Two power transformers and all the gubbins that follow them. The ONLY way to know what is going on is with test gear (sig-gen, scope and load) - anything else is mere speculation. Common things to look for that give these symptoms are bad reservoir caps and broken (cracked lead) disconnect diodes (quite common in PLXs, which have a similar output topology, though only 2 steps instead of 3).
M
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Re: one clip light comes on before other
« Reply #12 on: January 11, 2013, 03:40:22 PM »


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