Hum Problems?

Hum problems with Phono cartridges are common. Here are the steps to troubleshoot hum problem with Phono Cartridges.

Please bear in mind that all Soundsmith cartridges as 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 NOT the cartridge that is at fault.

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 in 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 that FIRST to see if that is the culprit. If not, then proceed with the below. 

Remove (unplug) all RCA audio cables going to your preamp or integrated amplifier to minimize the system – ONLY connect the turntable, and 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. 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 cause 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 grounded, and all else should be floating. 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 tone arm itself be shielded. Many are not – often wood or plastic ones.

Even the flexible exit wire from the tone arm itself may not be shielded, and will cause hum with these cartridges. Why do manufacturers not shield tone arm wires?? Because since many people use LOW output cartridges that are less susceptible to “induced hum” manufacturers don’t worry about hum problems with high output cartridges.

How can you test your setup?? Simply.

Lock the arm down into position and turn up the volume till you hear some hum. Slowly bring your hand near the tone arm. If the hum increases, lack of shielded wires 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 TONE arm is not grounded, and needs to be. It needs a wire from its base that runs to the preamp ground, and connects there with the tone arm wiring ground wire.

Try grabbing the tone arm wires – the RCA cables. If the hum increases, you have very poorly shielded cables. Replace them.

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?

"The Soundsmith Carmen's ultra-low-mass MI assembly plays with more agility, is more naturally detailed, and sounds less stressed than any MC I'm aware of. Its treble is not dull or rolled off—it's just the most authentic treble I've experienced from a phonographic transducer." 

- Herb Recihert, Stereophile

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