Old Bose System advice, please

[natjones]

Hello all.

 

As a sparky by nature, I have a question about an audio set up. I've inherited a Bose system (4x 402 II tops, MB4 bass, Panaray Controller, 1800 Series IV amp and 1200 amp). I installed it as rehearsal room PA after our venue upgraded to a D&B system 4 years ago. We also use Drawmer limiter and small Behringer desk to complete the set up.

 

The system recently developed a completely random crackle. I've changed out all of the cables & have taken components out to problem solve. It's not the limiter, it's not the desk, it's not the crossover. It's either something in the patch/facilities panel, or the amp driving the 402s. I'm trying to hire an amp to swap out to test this theory, but obviously, most hire companies stock more recent equipment. My PM had been told previously that Bose speakers require Bose amps, but I wonder if this is true. As long as the amp meets the power requirements, could I use something else? Was the "Bose needs Bose" a sales pitch?

 

Your thoughts would be most welcome.

[bruce]

There's nothing special about the amps, others of a similar power rating will be fine as long as you have the right controller.

 

There were some amps (both Bose and 3rd party) which had the controller built in, so no need for an external one - perhaps that's what's confusing the issue.

[timsabre]

Random crackle is normally caused by a dry joint resulting from thermal cycling of the PCB. It's often a simple fix, you just need to resolder the joint, the tricky bit is finding it...

If you feel competent, run the amp with the covers off so you can get at the PCB. Poke it all over with something non-conductive like a drum stick, if you are lucky you will find that you can cause the crackle by poking in a certain area and you will then be able to identify the bad joint and resolder it. Areas which get hot are the obvious place to look so power transistors and power supply components, the board might be discoloured to give you a clue.

 

 

Or, you can just get a nice high powered soldering iron and reflow all the solder joints...

[DrV]

Another, almost invisible, source of crackles is leaking electrolytic capacitors. Electrolyte leaks out onto the PCB and starts causing random conductive paths between tracks and component pins. It behaves like a bad joint in that if you poke the component with your drumstick you get the crackle but no amount of resoldering on the underside will correct it. (Does this sound like the voice of experience?!). Look for staining around the base of vertically mounted caps and corrosion of metal parts (wires, PCB pads etc)

Dave

[timsabre]

Yes good point. Check for visible crud...

[natjones]

Many thanks for all of the advice. Managed to use a Crown XLS 2502 amp to test. Given that the Bose amp is at least 15 years old, and in a rehearsal room system, we've decided to replace it with a Behringer, while I poke at the PCB in my spare time