10-14-14: HalcroThe continuous drone you are referring to results from a feedback loop breaking into oscillation, at a low frequency. A feedback loop by definition involves a closed loop, which is to say a continuous path from input to output and back to input.
As anyone with ‘feedback’ problems knows…..with the stylus stationary on the record, as you turn up the volume you will suddenly hear a deep and progressively louder continuous ‘drone’ emanating from your speakers…🔊
This (I suspect) is the Resonant Frequency of your tonearm/cartridge combination being excited by the harmonics of the structure-borne floor....
One thing puzzles me and perhaps Kirkus or Al can help here……😃
The ‘feedback’ on the stationary stylus increases when the volume is turned up….but I thought this is amplified AFTER the cartridge in the preamp stage….❓
In the situation to which you are referring, some fraction of the acoustic output of the speaker is ultimately finding its way back to the cartridge. That acoustical/mechanical path from speaker to cartridge forms part of the loop, which is completed by the electrical pathway through the audio system. The volume control setting affects the gain of that electrical pathway, of course.
The gain that is necessary to set the loop into oscillation at a susceptible frequency can exist anywhere in that loop. Susceptibility depends, in addition to the gains that exist within the loop, on the phase shift and frequency response characteristics of what is in the loop, including any resonances which may exist.
Best regards,
-- Al