Hum Problems?

Hum problems with Phono cartridges are common. Here are the steps to troubleshoot hum problems with Phono Cartridges. (PLEASE NOTE: If you have a B&O cartridge with hum or one channel out, models MMC5 through 1, or Soundsmith SMMC4 - 1, please click this for "one channel out problems")

  Please bear in mind that all Soundsmith cartridges are six-sided shielded. What does that mean? It means that they are FULLY shielded, unlike all other cartridges, so by design, they are the most hum free cartridges in the world. If you have hum with a Soundsmith cartridge, it is highly likely that it is NOT the cartridge that is at fault. But……..let's rule out a cartridge WIRING problem or shield problem at the cartridge FIRST.

  For Soundsmith cartridges, take a paper clip and unbend one leg of the paper clip. Lock the arm down into the arm rest. CAREFULLY touch the extended end of the paper clip to the bottom METAL BELLY of the Soundsmith cartridge. DO NOT touch the cantilever or stylus at all. If the hum does not increase when you touch it with the paper clip, the cartridge shielding is working.

  The first thing is the most obvious; make sure the tonearm ground wire is well connected to the ground terminal near the preamp jacks on your MM or MC inputs.

  Next, make certain you have connected the color coded tone arm wires correctly to the color coded pins on the cartridge. A reversed wire here can easily cause hum.

  Make sure BOTH channels are making music. If one channel is dead, you may have a broken connection in the tone arm wiring or connector. Usually, it is at one of the small connectors that go to the cartridge, and can be hidden by the heat shrink tubing used at the end of the wire. A gentle tug on each will sometimes show a broken wire hidden inside the heat shrink tubing.

  If one channel is dead – no music - you may also have a bad phono cable. If they can be unplugged from the table, (RCA plugs on each end) try a different pair. It is also possible that the cable end is not soldered or connected properly to the RCA plug. Often, molded plugs (not serviceable) become faulty. Pushing on the wire as it enters the back of the plug may temporarily heal and reveal this kind of problem.

  If you DO have sound out of both channels, and you have hum, then……

  There are two basic type of cartridges, high output, and low. Low output cartridges can have fewer hum problems, and hum problems in common with high output designs, so I will describe BASIC causes of hum first, and then describe additional problems associated with high output cartridges.

  The first thing to do when troubleshooting any problem is “divide and conquer.”

  If you are running the audio from your cable TV system, unplug those cables from your system FIRST to see if that is the culprit. If not, then proceed with the below.

  Remove (unplug) all RCA audio cables going to your system preamp, integrated amplifier or receiver to minimize the system – ONLY connect the turntable to the electronics and speakers. If you have an AC filter or stabilizer of any kind, temporarily do not use it. It is important to have nothing else connected at all. If the hum is now gone, connect ONE piece at a time to see who the culprit is. You MAY need to isolate the AC ground from one of more pieces as described below.

  If you still have hum, then UNPLUG the AC cord coming from your table to the source of 120VAC. With the arm on its rest, see if you have hum. If it is gone, you have a ground loop, which is unfortunately common. Here is why, and here is what to do.

  Equipment manufacturers employ a three connector AC plug to GROUND the chassis of the component. This is NOT to eliminate hum, this is to protect YOU from a rare situation where AC is on the chassis of any piece of equipment due to a severe internal wiring failure. It also protects them from liability in that such a piece of equipment will trip a circuit breaker due to the internal SHORT CIRCUIT.

  However, grounding all pieces in an audio system often causes HUM. While the risk is extremely low, I do need to advise you that this is why gear is wired with three terminal plugs – to protect you from a rare situation.

  If the hum goes away when you unplug the AC cord coming from your turntable, you MAY have a ground loop. (If the hum is only present when you POWER ON the table, then you may have a different issue, covered below.)

  The cure is to purchase GROUND INTERRUPTERS from a hardware store. These are the small cubes that turn three wire plugs into two wire plugs, with a ground tab. It is possible that only ONE on the turntable AC plug will cure the issue - if unplugging the AC cord got rid of the hum. If not….

  Only ONE piece of gear in your system should be three wire grounded, and all others should be “floating” – that is, have the grounds interrupted by these ground isolating adapters. Typically, the PREAMP is hard AC grounded with a 3 terminal AC plug, and all else should be “floating” with ground isolators. Bear in mind that this introduces a very small risk of shock, if one unit internally fails in a very unusual way and puts voltage on the chassis. It is VERY rare, but it can happen, so legally I need to warn you about this.

  If the problems is now gone, then ONE at a time, connect the other RCA plugs from other components to your preamp and verify that the hum does not come back. Bear in mind, you may have to float the ground on their AC cords as well.

High output cartridges.

  High output cartridges present their own unique set of problems. They require that the all wires used be shielded. Including the tone arm wires and wires coming from the turntable to the preamp. Many tone arms do not contain shielded wiring inside the arm, some are also wood or plastic which provide NO SHIELDING. Even the flexible exit wire from the tone arm itself may not be shielded, and can cause hum with high output cartridges Why do manufacturers not shield tone arms or tone arm wiring ? Since many people use LOW output cartridges that are less susceptible to “induced hum” - some manufacturers don’t worry about hum problems that often occur with high output cartridges. How to find out where the hum is from using a high output cartridge?  You can you test your setup - Simply.

  Lock the arm down into position and turn up the volume till you hear some hum. Slowly bring you hand near the tone arm. If the hum increases, lack of shielded wires inside the arm, OR a non-metal arm may be the cause. If it is a metal tone arm, and you touch it, WITHOUT touching anything else with either hand, and the hum increases, the metal TONE arm is likely not grounded, and needs to be. It needs a wire from its metal base that runs to the preamp ground, and connects there along with the tone arm wiring ground wire.

  Also – try this. Try touching or grabbing the signal cables exiting from the turntable – the RCA cables running to your phono preamp. If the hum increases, you have very poorly shielded cables. Replace them OR modify them to shield them. Yes, there are actually cable manufacturers that will sell you turntable cables that are UNSHIELDED. That’s like tires for your car without air pressure in them. Hope you didn’t pay too much for THOSE cables.

  If none of the above works, listen to the hum level while you move AC wires AWAY from the table and RCA cables from the table. If that helps, you need to re-route you AC cables away from your turntable. Any type of component NEAR the turntable can induce hum, especially a power amplifier. Move it to see what happens.

  Many setups with high output cartridges can have hum, so you will have to try the above items to see what the cause is and remedy it.

They Said What?

In short, this is one of the handful of high-end products so good and so different, it really is worth serious travel to hear. 

- Anthony Cordesman, The Absolute Sound

 

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