The type of hum that you've experienced isn't caused by any electromagnetic interference and is commonly referred to as acoustic feedback. This can easily be identified by an increase and 'swell' in the hum until you lower the volume control setting. It's caused by the sound pressure level in your room being fed back through the wall or floor and the table/arm/cartridge interface exciting its specific resonant frequency which then continues to build upon itself. That resonant frequency is affected by the compliance of the cartridge, so using one cartridge can result in acoustic feedback while another may not in the same room and table/arm setup. It can also be affected by the platform that the table is setup on but it can be a difficult problem to resolve. You might try to relocate your table position in the room or to isolate the table to see if you can avoid the problem, but in many cases the only solution is to find a different combination of table, arm and cartridge that doesn't exhibit the problem in your listening environment. The resonant frequency is also affected by the mass of your tonearm/cartridge combination, so you might try to add some mass to the headshell of the arm (and then of course rebalance it accordingly) to see if that might shift the resonance to a more benign frequency that would work in your room. I wish that I had a quick and easy solution to your problem but exceptional analog replay can be difficult to achieve, however once experienced it's well worth the trouble. I wish you the best of luck in resolving this issue and please let us know if you find a solution.
2 responses Add your response