is your cable tv near the system? if yes, it may be that you have a ground loop. try disconnecting the coax cable from the cable box and then turn on your system to see if the hum is gone.
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houstonreef, while I do not have the JC1, I did own the A21 and also had issues with the humm/buzzz. I found that the amp was very sensitive to how well the interconnect was seated. Only a slight mis-seat would cause a buzzz. Try wiggling the interconnect around and make sure it is pushed all the way in. I hope this helps.
Thanks for all response. First the system is connected to a dedicated circuit and the pream is Supratek Syrah (tubes). I am not sure it may be possible ics. I disconnect the powercord of the pre but still hear the noise. I then unplug the ics between pre and am. As the result the noise disappears. Any ideas?
Houstoneef, what components do you have connected to your preamp? Try disconnecting one component at a time from the preamp and see if the buzz goes away. If it does that's your problem. To fix the problem get a ground eliminator and inset in circuit between the preamp and the IC connected to the problem component.
Do nothing with the cable jack. You may still want to try disconnecting the coax cable at its first entry. If you have a ground loop that causes this humming, you will know it when you take out that cable. Your amp may not be sensitive to this ground loop, but your preamp may be, since you say the noise is gone when you disconnect the preamp from amp. Try it, if it's not a big deal. Other than that, it could be your preamp that's causing this problem. Tubes, other things......who knows. Also try a cheater plug as recommended above.
it could also be that your rca jacks from preamp to amp are not seated all the way in the amplifier input jacks. If you are using locking type rca connectors, then you may want to make sure they're pushed all the way in. Some input jacks make it seem like they're in all the way, but in reality there's still room.
Also, try connecting your cd player to the amp(but don't hit play) and see if that causes the same buzz as the preamp does. If not, your preamp is causing your problems.
The best info I have seen about cheater plugs is not to use them. The shock from an ungrounded chassis can be lethal. If the interconnects are well made and properly seated, the next step would be to use a good quality power strip and plug all the units into it. Generally that should take care of the problem unless it is a real design flaw in one of the system items. Good luck.