Help?!

February 28, 2012

Something’s going on with my setup. I keep getting this low rumble/hum, but not all the time. Here’s what we’ve guessed at/tried to fix so far.

The connection from the tonearm to the preamp: it’s kind of cobbled together. The cord from the tonearm has been soldered to an RCA end which goes into the little cheapo digital preamp I use. My resident audio engineer (my husband) checked that and thought it might have gotten messed up, so he played around with it and thinks he got it straightened back out. He had originally put it together so he knew how it was supposed to go.

Interference from other devices: there had been some powered speakers plugged into the same power strip as the the turntable and amp. I pulled the speakers, so now the TT and amp are the only things plugged into it.

Vibration: if the platter is spun by hand, there is no rumble.

Bad cords: tested each one.

Bad input: plugged a different device in, no rumble.

Interference from other peripherals in the computer: unplugged external hard drives.

On a record I just played, there was rumble when I first dropped the needle. I picked it up and dropped it again–no rumble.  On the next record,there was no rumble at first, but it started in the middle of the record. When the rumble started, the signal strength as indicated by the waveform dropped way off.  Here’s a screenshot to show you what I mean.

The hum starts at about the 2:00 mark, then quickly grows–and signal fades–until you can barely hear the signal. Where it looks flatlined, you can actually still hear the music over the rumble but just barely.

Does anyone have any ideas as to what might be going on and how I can fix it? My next thought is the cartridge. I do have a spare, so I could try that. I recently changed the stylus, but it’s identical to the one I took out (purchased at the same time, both NOS). Maybe something got messed up in the cartridge connections then? The problem started since that change, but not immediately after it.

If I can’t get this fixed, I can’t get my records done before I move. So please, if you have any suggestions for me let me know ASAP!