The Vinyl Circle

Album for images posted to The Vinyl Circle
Thumbnail for Fig 4. Lateral Effective Mass bracket top view. Bracket weighs about 25g. 40 total 1/4 inch cubes of Tungsten provide approx 195g of mass at about 2.6 inches off the rotation axis. The bracket material integrated moment, added, probably brings that up to about 205g effective mass at the 2.6" radius. Top of the bracket was designed to stay just below the top of the yoke - which comes fairly close to the turntable dust cover. (Tungsten cubes are among all kinds of handy weight distribution parts made available for the Pinewood Derby car customizing market. Yay competitive Dads!!)
Thumbnail for Fig 5. Bracket mounting area, prior to installation. Double stick tape sometimes makes an excellent, stable way to mate up parts w/o much stress transmission - and if you don't use too much area, it keeps things decently reversible! The shoulders on the underside of the bracket will contact those tape pads. Weight forces will press down through the relatively strong yoke assembly side frames. Once positioned, weight, balance, cushioning and stickiness will keep the bracket assembly quietly in place. The tie down heavy duty threads will be mostly just as safety - to keep me from accidentally knocking the assembly off.
Thumbnail for Fig 6. Mid-installation with heavy duty threads double strung along intended paths. I recently cruised through a very entertaining book on knots. A great knot for this application is called a double surgeon's knot - basically a square knot with double overhand moves.
Thumbnail for Fig 7. Installation complete - arm at LP lead in groove location - outboard view. The assembly was designed to be positioned high, primarily to free up space for the cueing lever to still be accessible. Also for that same reason AND to keep the far side away from areas where I'll be lifting the outer LP ring clamp on and off, both arms of the bracket were clocked around clockwise, parallel to the armtube. Nominally balanced design is maintained. Riding on the horizontal motion direction bearings ONLY, all that counts is mass amount and horizontal distance from the axis for arm lateral eff mass enhancement. (only downside is that the bracket covers up the cool SME model number graphics on the arm tube - Oh NOOOO!!)
Thumbnail for Fig 8. Installation complete - arm at LP outer diameter location - inboard view.
Thumbnail for Fig. 1 - Test tools/conditions. During readings turntable was running, with stylus in last (locked) groove of record side - placing cart cantilever in a fairly normal frictional drag condition. The applicator stick was used to very lightly strike the indicated surfaces. An oscilloscope was connected as described below to preamp outputs.
Thumbnail for Fig. 2 - Vertical direction impulse response. Scope was connected to one channel output only. My best current recording capability is to take movies of the scope screen with a digital camera and select frames. Scope setting was 50 mS/div - however - rather than fine tuning it there, trusting the modern camera's 15 frames/sec, I found it was actually closer to 58 mS/div. At about 1.9 div/cycle the vert fn = 9.0 Hz.
Thumbnail for Fig. 3 - Horizontal direction impulse response. Scope was connected to both channels output, with same polarity. (for mono signal) At about 3.9 div/cycle the horiz fn = 4.4 Hz. This fig is with the SME horiz damper engaged to about max level with the fluid. Clearly the impulse is being damped out at a generally greater rate than in Fig. 2 but is also clearly less than critically damped, given multiple cycle settling time.
Thumbnail for Fig. 4 - Horizontal direction impulse response WITHOUT damping. Same setup as Fig. 3 but with horiz damper screw removed from fluid. Again at about 3.9 div/cycle the horiz fn = 4.4 Hz. Clearly the relative impulse amplitude is not falling out quite as fast as in Fig. 3 but the natural frequency is not detectably different. (not unusual for damping ratios in the well underdamped region)
Thumbnail for Fig. 1 - Turntable isolation stage - The Overview. (exploded views in upcoming figs) In addition to the basic low natural frequency mechanical goal, desires were to come up with an assembly that was: A) Reasonably compact B) Appeared to be resting on the cabinet below C) Still allowed clear access to the turntable above the dustcover bottom edge. Fixed parts bolt onto the bottom of the TT-1 shelf and extend 4 towers up vertically. The pendulum chains are approx 9 inches long, giving a natural swing frequency of about 1 Hz. The chains suspend the lower swing platform. The upper swing platform is directly coupled to the lower by large tubes reaching up through the shelf bracket internal open spaces. The upper platform carries the turntable and is free to float approx /- 0.4 inch in any horiz direction.
Fig. 1 - Turntable isolation stage - The Overview. (exploded views in upcoming figs) In addition to the basic low natural frequency mechanical goal, desires were to come up with an assembly that was: A) Reasonably compact B) Appeared to be resting on the cabinet below C) Still allowed clear access to the turntable above the dustcover bottom edge. Fixed parts bolt onto the bottom of the TT-1 shelf and extend 4 towers up vertically. The pendulum chains are approx 9 inches long, giving a natural swing frequency of about 1 Hz. The chains suspend the lower swing platform. The upper swing platform is directly coupled to the lower by large tubes reaching up through the shelf bracket internal open spaces. The upper platform carries the turntable and is free to float approx /- 0.4 inch in any horiz direction.
Thumbnail for Fig. 2 - TT-1 shelf frame and first mods - underside view - The TT-1 model has only the one slightly diagonal strut in the center to stiffen the horizontal shelf frame. The mass of all items I was planning to add would push close to the approx 55 lb design load limit. I constructed 2 additional strut assemblies that could be installed to help carry/stiffen the load. These strut assembly's positions can be seen more clearly in fig 4)
Thumbnail for Fig. 3 - Fixed parts and towers - Lower assemblies needed to be constructed to work around the stiffener struts. Screwed and glued interfaces in oak. Top hooks for the pendulum chains are just unbent eye screws. At this point found that a coat or two each of india ink and polyurethane made for a finish approximating the old HW-19.
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