Lee -- Towards the end of your original thread about this problem the hum disappeared, returned, and disappeared again as you did various things (reversing plug polarities, separating and shielding components, etc). Obviously it has now returned once more.
Therefore, what I'm thinking is that it may be an intermittency in the phono stage of the preamp, which happened to not be occurring when you shorted the inputs. So ruling out the preamp on the basis of that experiment may not have really been conclusive.
If it is an intermittency in the preamp, my suspicion would be that a capacitor may be on the edge of failure, as you were led to believe way back at the beginning of that other thread.
Does the problem seem to be temperature or warmup sensitive? If you are not sure, try putting the preamp in either a cold basement or a warm attic for a while, and see what happens.
Beyond that, I agree with Newbee's suggestion to try to get a separate phono stage with return privileges.
Regards,
-- Al
Therefore, what I'm thinking is that it may be an intermittency in the phono stage of the preamp, which happened to not be occurring when you shorted the inputs. So ruling out the preamp on the basis of that experiment may not have really been conclusive.
If it is an intermittency in the preamp, my suspicion would be that a capacitor may be on the edge of failure, as you were led to believe way back at the beginning of that other thread.
Does the problem seem to be temperature or warmup sensitive? If you are not sure, try putting the preamp in either a cold basement or a warm attic for a while, and see what happens.
Beyond that, I agree with Newbee's suggestion to try to get a separate phono stage with return privileges.
Regards,
-- Al