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Old 1st January 2011, 12:18 AM   #1
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Default Amp cutting in and out

I have a fairly new pro amp which is classic a/b design and it's cutting in and out. It takes about 15 seconds to cut in and a healthy dose of gain to boot. It then runs for a bit but becomes distorted after a while, cutting in and out like wiggling a loose connection. I looked for cold joints but could not find any. Both channels exhibit this behavior but the left channel much more so than the right. Any ideas?
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Old 1st January 2011, 12:42 AM   #2
Bone is offline Bone  United Kingdom
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If its still in warranty take it back, but it could be a dry joint in the power supply if both channels are affected?
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Old 1st January 2011, 01:22 AM   #3
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It's well out of warranty.. about 3 years old. I looked at all the joints in the supply board but none I could see were poorly done. I'm not sure if its the supply because the meters are registering signal when i crank it even if there is no output ( cuts out completely, like at startup). The amp is currently running in the garage (just about freezing) in bridge mode at a fairly decent volume and has been stable for the past couple hours. I'll have to bring it in from the cold and try again tomorrow. I'm wondering if I have a bad cap or bad caps in the driver/output boards. The way I have to crank it from cold to start the output has me wondering...
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Old 1st January 2011, 01:30 AM   #4
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What's the make and model?
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Old 1st January 2011, 01:47 AM   #5
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Samson Servo 300
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Old 1st January 2011, 02:11 AM   #6
nac134 is offline nac134  Canada
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The problem strongly suggests a power supply problem of some kind. The meters probably run off of the input board, not the main board, but you will have to check to make sure. It sounds to me like the power is getting to the input board fine, but is having a problem getting to the main board. Do you have amultimeter?
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Old 1st January 2011, 02:22 AM   #7
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I thought I had a mm until I went to try it. I haven't used it in a few months, always a bad sign , and it seem to have died on me. It was over 20 years old so its time for a new one. I'll pop into The Store Formerly Known As Radio Shack next week and pick a new one up. The meters, input boards and output boards are all fed by separate lines from the same power supply so I'll check the lines first and look at where they connect to the ps board for poor joints.
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Old 1st January 2011, 03:25 AM   #8
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On the assumption that it is the ps, I tried tapping the supply caps with a chopstick and sure enough it cuts in and out. This appears to apply whether the amp is currently cut in or out. It looks like I'll have to pull the ps board and reflow the joints. It's a pain to get to but it's obviously the problem. Thanks for all your help, folks! Much appreciated.
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Old 1st January 2011, 11:02 PM   #9
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I redid the connections to the output boards and the main ps caps but it stll cuts in and out when I tap the caps. Could one or both my ps caps have an issue? The joints appear solid.
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