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PostPosted: Sun Oct 15, 2017 12:51 pm 
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Location: UK
Hello everyone.
I would like to pick the collective brain for some help please?
My Jack 2x12 with melded array has developed a distorting sound and an annoying bird or cricket like chirp coming out of the melded array. Right up in that sort of 16k range but the 16k on the EQ is virtually off, but it is in that sort of area. I resolved the distorting type sound when I systematically went through all the connections and re-solderd anything I didn't like the look of and removed the Lpad I had installed when I got it made. hoping this would kill two birds with one stone. This chirp is the first issue I have had with the Jack.
As I don't own any of the schematics or build lists for the BFM cabs. What would be the correct value switch for me to use in the melded array to turn it on and off? I presume it is a DPDT of some kind.

It does the chirp at all volumes (above 1) and can be set off by banging your fingers down on the strings, like you would when muting with you neck hand and slightly muting with you picking hand and not really playing any thing of note. Also palm muting the strings and playing with a plectrum makes it do it.
I have had the array out to check its soldering and also to see if it was any particular one of the piezo's is the culprit. It appears to be coming out of all of them or I can't decide which one it is coming from.

Any help, tips or advice on what I should test, fix or otherwise would be great appreciated.
Thank you.


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PostPosted: Sun Oct 15, 2017 1:30 pm 
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You can't use an LPad with piezos. Its presence indicates the cab probably wasn't built to spec.


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PostPosted: Sun Oct 15, 2017 2:06 pm 
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Thank you for replying Bill. Would this mean that all the piezo's are damaged. Or could the cross over be in need of attention? I rulled it out when I looked everything over because there was no burning smell, nothing looked burnt out or an open circuit type situation.


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PostPosted: Sun Oct 15, 2017 3:28 pm 
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Since an LPad was used I can't assume that the crossover was properly done. If it wasn't all sorts of bad things could happen, including amp damage.


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PostPosted: Sun Oct 15, 2017 3:48 pm 
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How would you recommend I go about checking if things were done correctly per your spec please.


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PostPosted: Sat Oct 21, 2017 11:30 pm 
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I see you made it in! :hyper:

CEF wrote:
How would you recommend I go about checking if things were done correctly per your spec please.


Buy the plans!

Using just the feed wires to the array, generate "white noise" using the headphone out of a computer, or a portable radio not tuned to any station. Using the cardboard core from a full roll of paper toweling, listen to each individual piezo transducer, paying attention to the sound levels. Replace any that make no sound at all or are suspect. Remember, your ears can easily be fooled, and RTA spectrum analyzer cannot. Rent one if you can't afford to purchase. Cheers!

_________________
I know money often seals the deal, but seriously, quality is an investment, not an expense... Grant Bunter
Accept the fact that airtight and well-braced are more important than pretty on the inside. Bill Fitzmaurice


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PostPosted: Sun Oct 22, 2017 8:00 am 
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DJPhatman wrote:
Using just the feed wires to the array, generate "white noise"
Use pink noise, not white noise.


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PostPosted: Sun Oct 22, 2017 2:37 pm 
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Thank you gents. This is very much appreciated help.


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PostPosted: Fri Nov 03, 2017 2:58 am 
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Just in case you interested in the out come of the pink noise test. More than certain it is the piezo's rather than the crossover. The pink noise seemed inconclusive at first but after starting listening to the array in different places I think there are a few that were under powered in comparison to others that most definitely had the pink noise coming through. Going to take the backs off the housings and see which ones torn.


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PostPosted: Wed Nov 15, 2017 4:01 am 
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Just an update.
It did turn out IMHO to be the piezo's. Did one last test before taking the backs off the piezo's without the crossover inline and it confirmed that the piezo's were the culprit. I have found a varying degree of unhappy piezo's. Couple sted fastly stuck in place. A large amount of the 14 piezo's that are in place. I have no idea how they stayed in place due to the massive amount of lateral movement and crunchy noise they make when moving them. They are being held inplace but I have no idea by what. So replacing all them is the route I will go with a few in contingency as we can't predict there quality.


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