What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Thorens TD 115

 The Thorens TD 115 is a medium-price semiautomatic record player featuring the Thorens TP30 low-mass "Isotrack" tonearm originally introduced on the top-of-the-line Model TD 126. instead of having  a plugin cartridge mount or shell at its free end, the TP30 is designed to have the cartridge fastened permanently in place, and the entire arm plugs into a socket located close to the pivots. This concentrates the arm mass closer to the pivots, where is contributes less to the total effective mass seen by the cartridge. The arm itself is a light, slim, straight tube with a minimum of cartridge-mounting surface at its free end. It is pivoted on low-friction jewel bearings, and its rated effective mass of only 7,5 grams (without cartridge) is less than half that of most record-player arms.
 Like the other Thorens turntables, the TD 115 employs a belt-drive system. Its 2,5 pound cast zinc-alloy platter is driven at either 33-1/3 or 45 rpm by a D.C. servo-motor whose speed is regulated by a seventy-two-pole tachometer generator. The TD 115 incorporates an "automatic pitch control" system intended to correct the motor speed for the effects of drag from a record-cleaning brush or similar accessory.
From the block diagram of the motor drive circuit , it appears that this system monitors the motor current senses the increased current  when the motor is loaded more heavily, and increases the drive to maintain proper speed.  The speed of the electronically controlled motor can be varied over a nominal ±6% range by a vernier control. The tonearm, completely free in normal operation, has an optical velocity-trip mechanism that lifts it at the end of a record. The arm must be returned to its rest manually, and the motor must be shut off by the user. The entire turntable and arm system is floated from the main chassis (to which the motor is fastened) on four damped springs.
The TD 115 's controls are in the form of three flat rectangular plates along the top front surface. At the left is the combined power switch and speed selector (power is off at the center setting; the plate is moved to the right to left for 33-1/3 or 45 rpm operation). Nest to it is a recessed speed-vernier control. The slotted edge of the platter is internally illuminated by a neon lamp to serve as a stroboscope fro 33-1/3 rpm operation. The removable 45 rpm center-spindle adapter has a ring of stroboscope marks for that speed.
At right of the platter is a second plate that starts the motor when it is moved to either right to left. The two positions are similar except that the left [M] is for completely manual operation, with the end-of-play arm lift disabled. The other [Start Up] activates the arm-lift feature. The arm must be moved to the desired diameter manually and lowered to the record by hand or with the third control, the cueing device. This raises the arm when moved to the right and lowers it when moved to the left, both with a slow, damped action.
The tracking force of the arm is adjusted by rotating the counterweight on its threaded shaft after the arm and cartridge have been balanced. The force scale on the counterweight is calibrated in millinewtons (mN) instead of the more familiar grams, but 10 mN equals 1 gram so this poses no problem to the user. The skating compenstaion is applied through magnetic repulsion, adjusted by means of a ring around the base of the arm. It is calibrated in arbitrary units, the instruction manual recommends setting for different stylus shapes and tracking forces.
 The Thorens TD 115 brings many of the featuress and basic performance characteristics of the much more expensive TD 126 to a price range affordable by most audiophiles. Although the importance of low arm mass is well recognized. Thorens is one of the few manufacturers of integrated record players suppling arms whose masses are compatible with the high compliance of modern cardridges. The shifting of the arm resonance  ( with M95 ED cartridge) from the usual 8 or 9 to 11 Hz is dramatic evidence of the benefits of a low-mass arm (which will track warped records far better than the usual record-player arm using the same cartridge).
The unweighted rumble of the Td 115 was lower than that of any direct-drive turntable presently on the market, so far as we know. This does not necessarily mean that its rumble will be audibly lower  (it is already below the hearing threshold), but it does mean that any woofer-cone flutter (and resulting intermodulation  effects) will be reduced compared with that of som other turntable with a worse unweighted rumble level. 
 Thorens continues to show by the performance of their products that, with respect to rumble and flutter, a good belt-driven turntable can equal or out perform some of the best of the direct-drive turntables. 
The TD 115 has a black base with a contrasting silver-color control panel along its upper front edge. The hinged plastic dust cover remains open at intermediate settings. With the cover lowered, the TD 115 is 17-1/2" wide, 14-1/4" deep, and 5-1/16 " high. It weighs 15,5 pounds.
Drive System:  1-step Belt-drive
Motor:  DC motor with 72-pole tachogenerator
Speeds:  33-1/3 and 45 rpm, electronic speed selection
Motor Speed Control:  Electronic regulation with load correcting automatic pitch control
Pitch Control:  ±6% illuminated stroboscope
Turntable Platter:
Weight:  1,3 kg zinc-alloy dynamically balanced
Diameter:  300 mm (12")
Wow and Flutter:  less than 0,05% according to DIN 45507
Unweighted:  -48 dB according to DIN 45539
Weighted:  -68 dB according to DIN 45539
Tonearm TP30
Cartridge wand TP70
Tonearm Length:  222 mm (8-3/4")
Effective Mass:  7,5 g
Stylus Overhang:  15,5 mm (39/64")
Offset Angle:  23°
Lateral Tracking Error:  less than or equal to 0,18°/cm of radius
Skating Compensation:  magnetic force without friction
Stylus Pressure Appliance:  setting scale on the counterweight
Bearing Friction:  less than or equal to 0,15 mN (15 mp) in both planes
Capacitance of Cable:  230 pF ±10%
Mains Voltage:  117 / 220 V 50/60 Hz
Power Consumption:  5 watt
Dimensions (W x D):  445 x 355 mm (17-1/2" x 14")
Dust cover closed/ opened:  130 mm (5-1/8") / 400 mm (15-3/4")
Net Weight:  7 kg (15-1/2 lbs)

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