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Sense lines for processor


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What gauge should/can amplifier output to processor sense lines generally (or possibly nearly universally) be? I would expect those conductors could be "fairly thin gauge" compared to suitably gauged amp to speaker cables as I'd suspect the sense lines are carrying very little current.

 

The reason I ask is I've been asked to retro-fit some patchbays I previously assembled to Y sense lines likely out of the Speakon connectors for the amplifiers, and "the thinner the better" from an assembly standpoint. The system owner is changing amps but wants to keep the same processors for the system... the previous amps had both banana and Speakon outputs, so he ran the sense lines off the banana outputs, but the new amps (Powersofts) only have Speakon outputs.

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Sounds like one of Peavey's old processors. They recommend 18 gauge wire if I recall correctly' date=' but I believe that was presuming fairly short runs with the processor in the same rack as the amps.[/quote']

 

I believe they're Yorkville processors (TX8P I believe). I believe the operator's processors are racked up with the amps.

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I use 16 gauge wire for my "sense cables" in my three TX racks (one TX4 and two TX4/8 compo racks). No problems what-so-ever. One rack is 5+ years old with the other two assembled 3 years ago and used many times.

I really like the compression that the TX processors apply especially when providing the rig for DJ's (depending on each tune's amount of data). Some songs are fine once I set the trim....but others are extremely hot...

 

Mike M

 

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Oops' date=' thought I was posting a link to the manual, which is at the Full Compass site.[/quote']

 

Or here, for quicker reference:

 

http://www.fullcompass.com/common/fi...Processors.pdf

 

Why wasn't/isn't the "sense input" method not used more? I had several Peavey 3020/415SUB stacks along with their processor with the sense inputs, powered by Carver PM1200s and I'll admit it saved me from myself many times way back then. What was it actually sensing? Wouldn't changing cabs and/or amps change the results? There were no adjustable parameters to account for this on the processor other than number of crossover points. Sorry for the highjack!

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Extra circuitry, extra connectors, extra pic board real estate equals higher costs and higher retail prices. Obviously most people are happy to buy a more standard crossover and voted not to spend the extra money. Manufacturers look at this when designing new products. We could make things that solve lots of problems, but getting customers to see and pay the money it costs is what drives things. You are correct in that it is either following a preset set of instructions or it needs to be calibrated for each system. Either way it is usually limited to a specific system. It's easier and less costly to include these servo systems inside powered speakers an I suspect it is fairly common in >$500 systems. the servos in ours cover several functions.

 

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The benefit is generally not worth the cost or hassle, there's more items prone to failure, lack of understanding of the basic principles limits this method to high level pro pieces. These days, the quality of drivers and protection algorithems is much better as well.

 

Ironically, the value of servo approach is least beneficial to powered speakers due to the source to load loss impedance ratios and the inherent matching of amplifier to load knowing exactly the applied transfer function.

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So is the predictive nature of current DSP processors, such as Driverack and the like, that are based on factory measured parameters of amps and cabs a better way to go than the reactionary nature of a processor with sense inputs, presuming both processors are calibrated to the system they're being used in?

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The Driverack is predictive only because the output is defined by the input times the transfer function. The problem is that all of the external processing depends exactly on the gain of the amp and the maximum voltage swing into a defined load.

 

The feedback sense method removes the gain and maximum voltage unknown from the calculations, but the result would be (essentially) identical if the gain and maximum voltage swing were correctly entered.

 

On a powered speaker, these parameters are know exactly to the designer, and the driver parameters are also known, therefore the servo method is not nearly as useful because there are fewer unknowns. Also, the source impedance is exactly known, there is no need to apply corrective servo (feedback) to overcome or to null out the source resistance in say 100 feet of speaker cable.

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