A Close Look at Record Hum & Noise
This narrative traces my search for causes of
hum and noise in my record recording system. I was able to resolve my
problems but I think that my search for solution was haphazard. I
hope others can resolve their noise problems easier.
I define hum as a 60 cycle unwanted electronic wave that gets into the audio system. It can come from any device that runs nearby and there can be lots of such devices. It can be picked up by any wire not properly shielded. It can be introduced by any component, cartridge, turntable, pre-amp. sound card, amplifier, or speaker.
I suppose the first thing to do is isolate each component of the system and be able to look at the wave pattern one at a time. Below is my basic setup. It goes from cartridge to tone arm wires to RCA cable to preamp to sound card. My preamp cable was shortened to 2 feet and double shielded. My sound card cable was 5 feet long and also double shielded. Other configurations that go into an amplifier can instead be plugged into a laptop and the signal can be analyzed with software. However even a laptop can introduce noise depending on the quality of the onboard sound card. The best of all is a signal analyzer. Some of my past efforts to fix hum are documented here.
I looked at my sound card. As seen below after all the standard precautions were taken I was still getting a small 60 cycle spike in the background noise. It was only slightly noticeable on soft passages and only between tracks. This test was on a Technics TT carrying an AT green cart using a recon SB sound card. Here is the signal in cartridge up position. All other obvious EMI was reduced as much as possible.
This 60 cycle spike pretty much pointed to the sound card as being the cause. I changed from a Recon SB to an ASUS Xonar DG and did a similar test, first with no cables then with cables and pre-amp volume full up. Here is the signal with cart up and it is quite good.
I noticed a much smaller 60 cycle spike but perhaps acceptable depending on what would happen in actual music recording mode. I recorded my usual selection taking a sample between tracks and was pleased with the results. This was on the same Techniques with an AT green. As expected the frequency drops off at 22k and the low end is more than good. There was no 60 cycle spike. It does however show a very low frequency increase perhaps due to turntable rumble but it's well below 20 CPS. This passage was from Columbia BS8252, side two, between 1st and 2 song.
Pops are caused by imperfections or more often by minute dust particles that get trapped in record groves when handling or during play. Sometimes they can get there during manufacturing as suggested here. If a stylus wares to less than .6 or .7 mil at its rounded tip it then sweeps a larger area and starts to settle down to the bottom of the groove where more little imperfections lurk. The larger area a stylus sweeps the higher the chance of colliding with particles. Ideally the stylus should only touch the middle of the groove.