1.) Create a firm, vibration free mounting environment:
From B.A.S. 1977:
The Shock Platform: An Easy Solution to Acoustic Feedback
The problem of acoustic feedback is far more generalized than most audiophiles recognize. If the system does not actually "howl" when the gain is cranked up, many are confident that all is right with the world. If only it were so. When even the subtlest amounts of acoustic feedback are eliminated, the sonic results are startling.
Solutions to this problem have ranged from sheer mass (in the form of brick platforms) to elaborate construction projects using springs or Barry mounts. Here is a project, courtesy of Mel Schilling and Craig Goff of Music and Sound of California, that is incredibly effective sonically, attractive, and easy to build.
A stonemason will provide the 16" x 20" x 3/4" slate slab required for the top. For the few additional dollars, have the edges and face honed. The results are worth it. Ours cost $30 for the stone and polishing.
It may be difficult to resist splurging on a piece of sexy marble, but as my wife (who shopped for the parts for this project) can testify, marble resonates more than slate. In fact, it actually rings. The greater the marbling, the more the ringing. The dull thud of slate is definitely the way to go. Our piece weighed a hefty 28 pounds.
Your local sporting goods dealer will supply you with six black racquetballs. Use only the black balls, as the blue and green types are not as highly pressurized, their walls not as thick(for support).We used Seamco #558. A stop at the hardware store for six plastic caster cups, and you are done. These are the cups that fit under furniture legs to prevent carpet wear. Get the 1-3/4" size. We liked the clear plastic.
Now, with an X-acto knife, make five evenly spaced, bladewidth slashes across and at right angles to the center seam of each racquetball. Drop a vented ball into each caster cup so that the seam is parallel to the tabletop (and the slashes running perpendicular).Place the slate slab on top of your new shock absorbers.With your turntable atop the slate, adjust each racquetball/caster cup so that the weight is evenly distributed. You may find that you have to experiment a bit for very light turntables and remove a ball/caster or two, or add an additional one for very heavy tables.
What will you hear? If your system is like ours, with "no feedback problem", you should hear greater clarity throughout the entire frequency range. Triangles have a purer ring; a subtle raspiness that affected all instruments is now gone. Bass tightens up remarkably and subjectively goes deeper. Break-up that sounded like mistracking or power amp clipping has disappeared.
We must emphasize that we heard all of these effects on a system previously considered immune to feedback, or at most, subject to minimal amounts. Needless to say, we now consider the shock platform to be as necessary for the full realization of a system's capabilities as proper speaker placement or phono cartridge alignment.
-- Robert & Beverly Wolov (Pennsylvania)
2.) Level the turntable -- using the platter as the primary reference.
* A large ball-bearing is the preferable tool to measure levelness -- if it doesn't roll off the platter, it is level enough
3.) Mount and align the tonearm according to the manufacturers specifications (pivot to spindle distance)
4.) Mount and align the phono cartridge:
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Tonearm geometry -- using the appropriate overhang and offset angle (for a pivoted tonearm), adjust the phono cartridge to minimize tracking errors, allowing the cartridge/tonearm to be perpendicular along the radius of the disc at two "null" points .
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VTF -- Vertical Tracking Force. -- Perhaps the single most important criteria -- fractions of gram count.
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VTA and SRA -- Vertical Tracking angle and Stylus rake angle -- debatable, especially as the appropriate VTA/SRA can change from record to record [ if the idea is to trace the grove as it was vertically "cut"] -- create the best seating of the stylus within the cut grove as possible -affected by VTF.
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Anti skating force -- one needs a counter force to the inward pull that friction between the stylus and the vinyl create.
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Azimuth -- getting the diamond shank in the stylus/cantilever assembly to be perpendicular to the record surface. If the tonearm or head shell is "fixed", then use shims of metal to achieve a rotation. Difficult to certify by ear of eye -- typically requires a test-record and oscilloscope.
5.) Re-check the levelness of the turntable.
6.) Adjust the resistive and capacitance loading on phono-preamplifier according to the recommended cartridge loading.
7.) If possible, verify your settings with test records.
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