COLIN’S TECHNICAL CLINIC: Hum and woofer oscillation

Colin Wonfor

Q: Colin – help required please! Hum and woofer oscillation... I have just rearranged my system and entire room. This has lead me to run my Pioneer PL-707 with Denon DL-301II through an AU-320 SUT to my (freshly recapped) Accuphase C-200 and on to my little Cayin TA30. It's the smallest amp I have and it's the only thing that will fit in the given space. Now on to the issue...

I've never run this pre, before or after recap. I've never run this table with this amp. I've never run this amp or pre with these speakers (JBL 4430).

For starters, I'm getting a hum when touching the head shell. If I hold the head shell and touch the amp or pre the hum goes away. If I remove the ground connection from the SUT or the pre, the hum is louder and constant. I have used this SUT, table, and cartridge combo a lot without hum issues. With all that said, the pre and amp are the new players in the game.

That leads me to problem #2. I'm getting woofer oscillation at what appears to be an intermittent 2-3Hz. The more bass heavy the music, the more oscillation occurs. This is with any source; cd, turntable, tape. The subsonic filter on the pre removes some of this but to completely do away with it I have to hit the low filter button. The 4430s don't like low cut filters.

Any ideas on this stuff? Through the years, this is the first time I've run in to either issue. I've read through a few threads as well and what's worked for them hasn't for me yet. Looking forward to getting this up and running tip top! Sincere thanks for even considering thinking about this. Robert Busch

A: Robert, the shell hum does sound like the earth lead is not connected to the arm or motor board. This can also cause – but only rarely – low frequency feedback. That said, I suspect your TT is not mounted on a good isolation table.

The low frequency from the heavy bass is feeding back to the TT, like microphone feedback but not a shriek but rather a deep rumble. There’s lots of online info re preventing or mitigating the effects of TT feedback. The solutions are generally uncomplicated and of course vary very greatly in both expense and effectiveness. Only a home trial can provide any guidance and never try any of these claimed cures without 28-day sale or return.

Thank you for the question.


See what Colin is up to HERE and ... HERE