Sony TC-K81 cassette tape deck

The Professional-Grade Performance of Three-Head Design

Independent-Suspension heads

With their superior performance and enhanced operating flexibility three-head machines are obviously attractive. But there are several problems particular to the design of three-head cassette decks. For example, it is no simple matter to fit there heads into the cassette shell's openings. Fitting each head into a different opening raises the problem of tape skewing between the heads which causes azimuth error. Even slight azimuth error can result in audible high frequency losses. Thus, decks that insert each head through its own opening often require the user to re-adjust head azimuth before recording each side of each cassette.

However, placing the record and playback heads through the same opening can cause improper contact with the cassette's pressure pad, as well as interference between the two heads. In this configuration, bias leakage and magnetic cross-feed can degrade the monitored sound during recording when both heads are active. Sony with its long experience in three-head recording,, has solved these problems with a unique, new head configuration;

Independent Suspension.

Unlike the vast majority of three-head cassette decks, the Sony TC-K81 (and TC-K71), with Independent Suspension, use physically distinct, individually-shielded record and playback heads. Separate shielding reduces magnetic cross-feed and bias leakage dramatically. While physically distinct from each other, both the record and playback heads still fit into the cassette's center opening, in fact, the two head gaps are intentionally brought close together - less than 3,1 milimeters apart. As a result, both gaps make proper contact with the cassette's pressure pad. And the gaps are so close together that skewing error is reduced to the vanishing point. There is no need for user-adjustable azimuth.

Sony's Independent-Suspension three-head design ensures that the frequency response of these machines is not only extended, but also extremely stable. You can expect good result on each cassette, from the beginning of the tape to the end, on side A as well as side B. Of course the record and playback heads of these decks boast Sony's Sendust and Ferrite head formulation (as described for the TC-K44 and K61). The S & F design provides high permeability low specific resistance. Un supressed maximum flux density and exceptionally long service life.

 

Bias and Record Calibration

The TC-K81 incorporates even more sophisticated adjustments for each tape formulation. Bias and record calibrations permit the K81 to be handtailored to suit the requirements of each tape. Built-in test-tone oscillators, the monitoring capability of the three-head format and the deck's own Peak Program Meters combine to make calibration quick, simple, and precise.

The bias calibration procedure of the TC-K81 establishes flat frequency response by obtaining equal output for a 400 Hz and an 8000 Hz test tone. These tones are recorded and played back together, and displayed on the deck's meters. To make the adjustment, you simply turn the Bias Cal Knob for equal readings on both meters. Because switching to the calibration mode automatically increases meter sensitivity, the adjustment is accurate to within 0,5 dB.

The result is flat high-frequency response and low-distortion recording with any tape you use. In addition, the K81 provides record level calibration with the 400 Hz tone. You make adjustments with the left and right controls, setting the meters to the Rac Cal reference marks. When set, Dolby noise reduction tracking in encode and decode will be precise, resulting in accurate high-frequency sound during both loud and soft passages.

 

Closed-Loop Dual -Capstan drive

Conventional cassette decks use a single drive capstan, engaging a single pinch rolle; to drive the tape. While single-capstan drive often yields good performance, dual-capstan drive - using two capstans and two pinch rollers - is a superior system. The TC-K81 (and TC-K71) incorporate dual-capstan drive. Both capstans are driven from the BSL motor by the same belt, in a closed-loop configuration. The capstans are located on either side of the head assembly, for better control of tape tension, and minimum modulation noise.

Combining this drive system with a separate spooling motor, and two over-size anti-resonant flywheels, the K81  (and K71) achieve clear, unwavering sound, even during sustained notes.

 

 Specifications

Drive Type:  Belt

Servo Type:  Frequency

Number of Motors:  Two

Motor Type:  Capstan: BSL; Spooling:  High-Torque

Number of Heads:  Three

Record/Play Head Type :  2 x S&F

Erase Head Type :  2-Gap Ferrite

Record Level Calibration:  400 Hz osc.

Fast-Forward/Rewind Time (C-60):  80 sec.

Wow and Flutter:  0,04% (WRMS), 0,12% (DIN 45507)

Frequency Response (±3 dB, Re: -20 dB)

Metallic Tape : 30 - 18,000 Hz

FeCr Tape : 30 - 18,000 Hz

EHF Tape : 30 - 17,000 Hz

SHF Tape : 30 - 15,000 Hz

Re: 0 dB Metalic Tape : 30 -13,000 Hz

Signal-to-Noise Ratio ( Dolby NR Off, Re: 3% THD, Peak, IHF-A Wtd.)

Metallic Tape : 60 dB

FeCr Tape : 60 dB

EHF Tape : 58 dB

SHF Tape : 54 dB

Improvement with Dolby NR On :  Up to 5 Db at 1 kHz, 10  Db at 5 kHz or above

Total Harmonic Distortion (1 kHz, Re: 0 db Record level)

Metallic Tape : 0,8%

FeCr Tape : 0,8%

Crosstalk (1 kHz, tracks):  60 dB

Separation (1 kHz, channels):  35 dB

Erasure (400 Hz, incl. Metallic Tape):  60 dB

Bias Frequency:  105 kHz

Meter Range:  -40 dB, +8 dB

Line Input Sensitivity/Impedance:  77,5 mV/50 k ohms

Mic Input Sensitivity/Impedance:  0,25 mV/Low

Line Output Level: 

Fixed :  435 mV

Variable :  27,5 - 435 mV

Line Output Load Impedance Nominal/Minimum:  50/10 k ohms

Headphone Output Level:  4,9-77,5 mV

Nominal Headphone Impedance:  8 ohms

Power Requirements:  AC 120/240 V 50/60 Hz

Power Consumption:  26 W

Dimensions (W x H x D):  430 x 130 x 290 mm (17" x 5-1/8" x 11-3/8")

Weight:  6,3 kg (13 lbs 14 oz)