Members Tom Mc1 Posted October 12, 2014 Members Share Posted October 12, 2014 My church has an Accoustic B200 bass amp that the band uses. It has started to make a noise that one of the guys called "motor boating". Yes, it sounds like a boat motor. We tried the ground lift switch. No change. The amp was bought used from a dealer and the problem didn't show up for the first 6 months of use. We really don't want to spend a lot of money to fix it if it is a major problem. Any thoughts? Link to comment Share on other sites More sharing options...
Members DeepEnd Posted October 12, 2014 Members Share Posted October 12, 2014 Here's a reference to bad capacitors in the preamp section that produces a similar effect: http://www.geofex.com/ampdbug/mtrboat.htm. Could also be a bad solder joint. Link to comment Share on other sites More sharing options...
Members Tom Mc1 Posted October 12, 2014 Author Members Share Posted October 12, 2014 Is this for tube or solid state amps? Caps seem to be a problem in amps. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted October 13, 2014 Members Share Posted October 13, 2014 Could be for either. From what I've read a bum tube will also produce the problem (which doesn't apply to your solid state B200) as will a resistor that's out of spec or a grounding issue but generally it's bad caps. Here's the manual and schematic for your B200 if you want to try troubleshooting: http://www.acousticamplification.com...00H-Manual.pdf. Link to comment Share on other sites More sharing options...
Members thelurker Posted October 13, 2014 Members Share Posted October 13, 2014 Yeah, motorboating is usually a voltage issue, and according to my chief engineer at work, it'a always a cap. XD Link to comment Share on other sites More sharing options...
Members WRGKMC Posted October 13, 2014 Members Share Posted October 13, 2014 A when a cap starts to go bad it starts to pass DC. The cap will charge up to a pint then arc out as the DC jumps across the dielectric. This constant charging and discharging produces a square wave in the amplifier circuit that can be heard. The problem can also be caused by a cracked solder joint to a cap too. Since this is a bass amp that receives allot of vibration its the first thing I check. Any solder joints that look flaky should have the solder reflowed with some 60/40 resin core solder. you can lightly wiggle the caps and see if the solder joint on the other side of the board move. Just be sure you don't create solder cracks in your attempt to find them. If all the solder joints are good then you have to signal trace the circuit to localize the issue. This isn't too difficult but you have to at least know the basics and be able to follow schematics before you open any amp . Link to comment Share on other sites More sharing options...
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