The ZP3 actually has no residual hum, as evident when the turntable is disconnected from it. The hum is coming from the turntable itself.
Below are some tips for chasing hum down to a benign level that I have pulled from other posts.
Quote: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.
Quote: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.
And from turntablehumreduction.pdf a few more good tips;
Quote:1. Plug the amp, preamp, and turntable into the same outlet strip
Voltage differences between system components get amplified. You can minimize undesirable voltage differences by plugging all the components into the same outlet strip. That assures that all of their power is in phase, and that minimizes the voltage differences that result between the components, minimizing hum. This is the single most effective thing you can do to assure low noise.
Quote:
2. Use good, low ground resistance cables with double shields for
phono inputs. (woven shield plus foil shield)
Even though we’ve done step one, there will still be currents induced onto the phono cable shield. Ohms law tells us that voltage equals current times resistance, so if we want to minimize the voltage, then we must minimize the resistance.
Double shields give us cables that block both hum and radio frequency interference.
Quote:3. Make sure the ground connections (the crowns) of the RCA jacks fit snugly at both the preamp and phono ends
Quote:4. Make sure that the ground connections are clean (no oxidation).
As in the previous step, freedom from noise means you need low resistance ground connections and wires between the cartridge and the preamp. The system is only as quiet as its noisiest element, so low resistance cables with high resistance contacts for the grounds owing to either a loose fit or connector oxidation will be noisy!
Quote:5. Use the shortest practical cable length to connect the phono to the
preamp
Long cables have more opportunities to pick up noise. Therefore, you’ll want to use the shortest cables that are practical for your setup.
Quote:6. Make a clean, low resistance connection between the turntable
ground and the preamp ground
Most turntables come with a separate green ground wire that should be run to a ground screw on the preamp. Make sure that the connection is tight and clean so it will have low resistance.
Quote:7. Keep the tonearm/cartridge away from large magnetic fields like
those generated by large transformers
Remember how much gain the system has at low frequencies? Recall also that the cartridge responds to small magnetic field changes generated by a moving stylus on the LP. External magnetic fields impinging on the cartridge from power equipment will generate hum. Sometimes the hum comes when the arm gets close to the turntable motor. Sometimes an adjacent component creates a magnetic field that creates hum. In such cases, your best defense against hum is to place distance between the source of the magnetic field (hum) and your phono cartridge.
Quote:8. Experiment with an additional green wire ground in strategic
places.
An additional wire to a good ground can sometimes help the noise. Where to get a good ground? If the chassis of one component is grounded, then you might run a wire between that grounded chassis and the chassis of some component with a two-wire plug. This is a somewhat advanced skill, and if the idea makes you nervous at all, then don’t do it.
Quote:9. Experiment with reversing two-wire plugs
Some components with two-wire plugs are polarized, with a wide blade and a narrow blade. You can’t reverse them. However, a fair number of components have two-wire non-polarized plugs. This is especially true of vintage components. Reversing the way you plug a two-wire non-polarized plug into the power strip can significantly reduce system hum.
Hope that helps!
Steve