What Typically Causes Phono Hum?

I've had hum coming from my old Systemdek II/Grace 707B/Grace F9E Ruby for years. Doesn't matter what amp I feed it into.

Don't listen to vinyl much but that is going to change. Was planning on upgrading the interconnect from the arm in an effort to upgrade the sound and eliminate the hum. The original is pretty cheap looking and I had to lengthen the ground wire a long time ago; it was too short.

I'm hoping this cheap cable is the source of the hum but don't want to spend the money and find out there is still an issue.

Any ideas?

 

It could be a number of things. It might be a lack of shielding and RF interference, but, I suspect, more likely a ground loop. Try attaching the ground wire to various components to see if the hum is eliminated or reduced.

 

Be very careful with the ground wire and your phono interconnects. On my TT the ground lug is between the two RCA connectors (L & R). When I tighten the ground lug if the ground wire spade shifts a little and touchs the outer metal shell of the RCA plug I get a very noticable hum.

 

Found this on the net, from the KAB site:

Item three is where I'm focusing. Do their suggestions for testing make sense and is it safe?

The Stereo
Switch the stereo to CD or AUX, and with nothing playing, turn the volume up to your normal listening position. If there is no hum now, then we can eliminate the stereo. If there is a hum, powersupply service is probably indicated.

The Phono Preamp
This will require one accessory, a shorting plug. You need to get a couple of standard RCA plugs from Radio Shack for instance, and you need to short the center pin to the outside ground. Now, in place of the turntable, plug the shorting plugs into the phono input. Now, set the stereo to phono and turn the volume up to your normal listening position. If there is no hum now, then we can eliminate the phono preamp or phono stage. If there is a hum, phono stage service is indicated.

The Turntable Wiring
This will require one accessory. a pair of alligator clips. You can also get these at RS. You need to clip together, I.E. short out the left and right cartridge pins. Do this on the back of the cartridge. You needn't remove the cartridge connections. Just connect one pair of clips between the red and green pins and another between the white and blue pins. Now, set the stereo to phono and turn the volume up to your normal listening position. If the hum is gone now, then we can eliminate the turntable wiring. If there is a hum, something is amiss with the turntable wiring. either a bad connection. or perhaps someone has changed the factory wires for some "fancy" wires that do not give sufficient shielding.


The Phono Cartridge
If you've come this far, then the problem must be the phono cartridge.
Most cartridges use hi permeability steel shells to protect the coils from electrical fields that can cause hum. However, not all companies use this system. As such , there are some cartridge brands that are sensitive to external electric fields and will hum. The only solution you have is to replace the offending cartridge. Or, if you love the sound and want to keep it, you will have to play with the location of the turntable and try to minimize hum. Sources of hum fields are power transformers in equipment, wiring in the walls, certain turntable drive motors. Experiment by listening to the hum while you move the tonearm through its arc(cued up!!) and see if you can find a null location that will give you the best results.

 

Luckily my ground lug is about 1.5 inches away. They cannot touch.

 

You might also have a look at the connecting wires between the cartridge and tonearm... simply touching them, or carefully repositioning them (to keep them isolated from one another) can possibly change or cure the hum factor.

Happened to me, anyway.

 

I have seen this a fair number of times from some low and midgrade moving coils. Is that what you are using, by chance?

 

No, the Grace F9 Ruby is an MM.

I do have an identical spare Grace cartridge, maybe I should try it.

But that means aligning it properly which I'm not good at.

 

If you have an identical one alignment should be easy. With a very fine pencil point mark on the headshell or the cartridge where the cartridge aligns right now. The come as close to those lines with the other one as you can.

 

Sounds like the cartridge is not shielded, and it is picking up electromagnetic interference from the turntable's motor.

 

Just had an issue develop with my Gyrodec SE and new ortofon cartridge (MC black)
Seems the Technoarm is not grounded , but the base is , go figure !. The cartridge mounting screws were connecting the guts of the cartridge to the Tonearm (Antenna) I took the cowards way out and used insulting washers under the screws ! I guess I should have used plastic mounting screws or tried to fix a ground wire to the arm ! (Yech)

 

haha! Just love the "fancy" wires description, and I think there is such a thing as being too "fancy". Line hum on the phono input is a very common problem, especially for the moving magnet cartridge. Moving coils are less susceptible due to their low impedance.

I am assuming your phono interconnect cable is good, and the plugs and jacks are free of oxidation.

The first thing to look for is the cartridge pin connection. Check for any oxidation or loose connectors. Try to carefully pull each one off the pin, then reconnect, which will at least temporarily break any oxidation. A common error is to incorrectly connect the hot leads to cartridge ground pins. Some cartridges have color coded pins to avoid this problem.

Wht L hot
Red R hot
blue L gnd
Grn R gnd

The cartridge L gnd pin is internally wired to the cartridge body. Make sure the ground wires (blue and green) are connected to the ground pins on the cartridge. Many MM cartridges will produce normal stereo sound when the ground and hots are flipped, but will hum. The next culprit could be "fancy" wiring inside the turntable. The turntable chassis and tone arm should be connected to a dedicated ground wire, and terminate to your pre-amp chassis. If the cartridge ground pins are bridged to the turntable chassis ground (connected together somewhere) then you may have a ground loop problem.

Also here a few other useful tips when everything is working properly, BTW there will always be at least a faint hum at max gain. It is unusual that you would have zero audible hum at full gain, much higher than normal listening level. At normal listening levels, there should be barely audible hum in an extremely quiet room, or none at all. That aside, the TT should be away from all wall warts, and the unsuspecting 12 volt halogen desk lamp, which will emit a 6o hz magnetic field into your cartridge. Also no fluorescent lights, no light dimmers, (notorious for inducing hum) no refrigerators or other heavy electric appliances with electric motors on the same branch circuit. Your turntable should be located away from every other stereo device.. if on a rack, leave an empty shelf space below the turntable.

Best of luck, rock on,
Steve VK