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Insulated Jacks

6/3/1999 5:39 AM
Insulated Jacks
What is (are) the determining factor in islolating the input jacks from the chassis or grounding them to the chassis? I'm rewiring a Marshall reissue and am planning on grounding the inputs to the chassis and wonder if there's a reason not to do this. thanks, Mark
6/3/1999 6:14 AM

A chassis grounded input jack will have more potential for hum, or problems due to ground loops. Hum or unwanted signal noise at the input jack is the worst place, since this area of the circuit gets the maximum gain from the amp.  
I really don't know how much of a difference it will make. I have an old traynor amp that is essentially a marshall circuit, with the input jacks grounded to the chassis. I also have a hand wired DIY marshall clone with insulated jacls and star grounding. I don't hear much difference in hum between the two amps.  
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6/3/1999 7:21 AM

Thanks Dave, I've also got a couple Traynors and that's why I thought it would be OK to ground the jacks. Mark
6/3/1999 8:27 AM

Ground them to chassis, but plan on insulating them if the hum is too bad. Many amps get away with grounding them, but the potential for hum is there. If you're willing to experiment, you might get away with it. Star grounding is a slam dunk, but other techniques can do well, it's just not guaranteed.
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