Tweaking your Record-Player Page 5

Viewing the cartridge from dead-on in front, check to see that it is absolutely parallel to the mirror. If there is any azimuth tilt error, the mirror will show this as being doubled, giving you twice as much adjustment accuracy as you can get otherwise (fig.3). Some arms have a locking collar for the headshell, which can be loosened to adjust the tilt angle. With others, it will be necessary to add thin metal shims or washers between the high side of the cartridge and its headshell. (The arm base itself should not be shimmed, as this will upset the arm's lateral balance and impair its dissipation of tracking-induced disc vibrations.)

Fig.3 A mirror under the cartridge doubles the visibility of any cartridge tilting.

Shimming will separate the cartridge body from the arm, reducing the latter's ability to transmit vibrations from body resonances. The intervening space should be filled with some dense plastic material like automobile undercoating, "Plasticine" modeling clay, or the stuff sold in hardware stores as "rope caulk" weather stripping.

The cartridge screws should now be tightened fully (footnote 9).

If the arm has a separate wire ground, connect this to the Ground terminal on the preamp. Turn the volume all the way down, set the input selector to Phono, load up a loud disc with little dynamic range (any garbage rock will do), and turn on the system. Advance the volume until it is about as loud as you will ever listen, then take the pickup off the disc and note the hum level. If hum is audible at all, shut everything off again and read the next few paragraphs. (If there's no hum problem, go straight to the next section. Do not collect $200.)

Hum is 60Hz AC-supply energy where it doesn't belong: in the signal circuitry. It is induced, magnetically or electrostatically, into any wiring in the vicinity of a potent source of it, but is usually only troublesome in circuits where the signal level is low—like phono equipment.

Electrostatic hum is only a problem with high-impedance moving-magnet cartridges, and usually stems from inadequate shielding. When an MC hums, it's nearly always because of interference from a nearby power transformer, AC cord, or (occasionally) the phono motor. Here's how to source it.

Shut off the turntable motor. If the hum stops, try reversing the TT's AC plug, and try running a wire from the motor frame to the preamp's Ground terminal. If neither works, the turntable may be unusable with that cartridge. (An example of such incompatibility is one of the Grados when used on an AR turntable...)

With the turntable motor off, swing the cartridge through its disc-playing range. If the hum gets louder as the cartridge approaches the electronics, move the turntable farther away or, perhaps, to the other side of the equipment pile.

Unplug both phono inputs. If the hum remains the same, the trouble is with the preamp. Pick it up and move it back and forth and side to side. If the hum level changes, the hum is being induced from another component. Spacing them farther apart should cure it. If the hum remains constant, the preamp is defective (unlikely) or inadequate (likely).

Try connecting the turntable's Ground wire to the power-amp chassis, or even try disconnecting it altogether. Go with whatever works.

Adjust the arm's anti-skate control (if any). Use the manufacturer's setting recommendation for this, but be prepared to change it later. This is only a starting point.

If your cartridge is highly compliant, you may notice when playing discs that the stylus is deflected to the left. As bad as this looks, it's normal. (It is not normal with a linear-tracking arm, and indicates absurdly high lateral friction or a tilted carriage rod.) Because of the cartridge offset, which minimizes tangency errors, the tangent line does not pass through the tonearm base, so the rotating disc pulls the stylus inward, placing more load in the inner groove wall than the outer. Equalizing this inequity with the antiskate force deflects the stylus.

Footnote 9: With some arms using high-precision gimbal bearings, such as the Linns, the manufacturer insists that the arm be removed from the turntable for this step if the bearings are not to be damaged.—JA
Share | |
Site Map / Direct Links