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!

There have been a couple of comments mentioning that it sounds like the speed of the recordings might be off. It is entirely possible. Let me describe the process I’m using to get these programs from the records to the web.

I am using the 1948 Presto 64-A turntable (described and pictured in “About -> The iPod”) as I have no other turntable. The output from the tonearm is going directly to a digital preamp, and that is connected to my computer. Unfortunately the 33rpm motor on the Presto started malfunctioning about a year ago, which leaves me only able to play records at 78rpm.

So I play the records at 78rpm into a program called Audacity. It takes about 6-7 minutes to play a 15-minute program this way. Audacity has a preset effect for altering the speed of an audio file, which I run on the completed wave form. I spot check to make sure it sounds human, then save as a .wav file.

When I’m getting ready to upload a new program to Bandcamp, I open the .wav file in a different audio editing program, Cubase. Audacity is great for making the original recording and changing the speed, but it’s not so good for editing.  With Cubase I can manipulate the wave form to repair skips, trim dead space at the beginning and end of the files, and fade out the ending if I had to trim it (sometimes the edges of the record are in such bad shape I can’t play them right to the end).  Then the completed project is outputted to a new .wav file and uploaded to Bandcamp then cross-posted here.

With the help of my audio engineer husband I just did some checking and found that it looks like the turntable might be running just a tiny bit fast. He clocked it at about 78.5rpm, which is a very, very slight difference. However, when the recording speed is changed to 33.3 that difference gets stretched, so to speak. I just did a test with a file that I just recorded yesterday. First I changed it back to 78rpm. Then instead of using the preset of -57.265%, I slowed it down a tiny bit extra: -57.96%. He and I both think it sounds better that way, so from now on I will use that conversion rate instead. I can also fix the records that I’ve already done but not yet posted by running the fix when I’m ready to edit them. This will only add a couple of minutes to my editing time, so that won’t be any big deal. However, with trying to get the remaining records copied to the computer before we move overseas (while trying to get rid of everything we own, homeschool my three kids, and take care of life in general) there is absolutely no way I can go back and change the recordings that are already posted. But remember that you can download lossless files of everything on Bandcamp. If you have audio editing programs and want to play with it on your own, go for it!

The total time I put into a 15-minute recording start to finish can be as little as 30 minutes for a program with no skips to several hours for one in really bad shape. There are about 250 records in my collection (15 minutes per side), although some are only recorded on one side, some are too deteriorated to play, and others I’ve chosen to skip for now because they’re not actually radio programs but just random prerecorded music my grandpa put together.  I have somewhere around 125-150 records left to do. I’ll let you do the math for how much work I have ahead of me. I don’t really want to know.  

As far as inconsistencies in the speed of some of the recordings (where they sound kind of warped), there is absolutely nothing I can do about that. I just don’t have the time, knowledge, or technology to do it. But once again, those of you with more time, experience and better programs than I have are welcome to download and play with the files. The only limitation I’ve put on them is that they are not to be used for profit.