Hello all! well I have been on this community before, some may remember, and im just looking for advice and/or help. Mine is a (400) series I, eight fin. It has had the outputs replaced long ago (all mj21196g) and rca410 drivers. I have Don's relay board fitted, as well as a pl14-20 rev.e board installed. I bought the board stuffed. The big PS caps, bridge rectifier and current sharing resistors are all original.
Im trying to figure why I always have so many ground loop issues with this amp. Seems like whatever I connect to it creates a ground loop of some kind. A 60 hz hum that is sometimes very faint but persistent. I use a behringer rackmount line mixer as a preamplifier. This by itself causes no hum. Playing either of my keyboards through the stereo doesn't cause any hum either. Plugging the tv through the mixer does produce a hum. very noticeable. Removing the ground lug from my mixer solves this, yet a ratshack ground loop isolator does not. As a matter of fact the ground loop isolator introduces its own very strange popping and static issues! Sometimes tripping the relay board completely and requiring the amplifier to be shut off and reset.
Anyways I finally relented and disconnected the tv from the stereo permanently and re-attached the ground plug to the mixer and things were great until recently when I tried to listen to some records. No matter how I plug in my record player it produces a faint 60hz hum. Obviously my line mixer doesn't have a phono pre-amp, so I have tried a cheap BBE phono preamp. it hums. then I tried a old hafler preamp and it hums as well. This is a faint hum, not as loud as the one from my tv. Weirdest is that my ground loop isolator has basically no effect! At least I know it worked years ago, maybe is broken? I dunno.
So what gives is the pl400 just prone to grounding issues? or maybe I got something screwy inside the old git, and I need to replace something or move a ground wire
Im trying to figure why I always have so many ground loop issues with this amp. Seems like whatever I connect to it creates a ground loop of some kind. A 60 hz hum that is sometimes very faint but persistent. I use a behringer rackmount line mixer as a preamplifier. This by itself causes no hum. Playing either of my keyboards through the stereo doesn't cause any hum either. Plugging the tv through the mixer does produce a hum. very noticeable. Removing the ground lug from my mixer solves this, yet a ratshack ground loop isolator does not. As a matter of fact the ground loop isolator introduces its own very strange popping and static issues! Sometimes tripping the relay board completely and requiring the amplifier to be shut off and reset.
Anyways I finally relented and disconnected the tv from the stereo permanently and re-attached the ground plug to the mixer and things were great until recently when I tried to listen to some records. No matter how I plug in my record player it produces a faint 60hz hum. Obviously my line mixer doesn't have a phono pre-amp, so I have tried a cheap BBE phono preamp. it hums. then I tried a old hafler preamp and it hums as well. This is a faint hum, not as loud as the one from my tv. Weirdest is that my ground loop isolator has basically no effect! At least I know it worked years ago, maybe is broken? I dunno.
So what gives is the pl400 just prone to grounding issues? or maybe I got something screwy inside the old git, and I need to replace something or move a ground wire
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