I just tested this persons problem and I believe it is directly related to the hum of the amp like yours was.  I inserted a DOUBLE VERB NRM amp. I set the partical verb to 100% dwell, 100% mix and "stable" position and trails on I set the amp HUM to 0 Faded in a chord Turned off the reverb RESULT: The verb hung forever with a nice clean spacious chord. I could play over top without any additional low end I set the amp HUM
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