Calibration Cassettes

A test tape (or service cassette) is a special calibration cassette used by audio engineers to ensure that the tape recorder is operating within standard parameters. The most often used tapes are for calibrating the speed of the motor, and aligning the head azimuth. There are also other tapes for measuring the equalisation, recording bias, and even torque parameters. Many engineers will have come across Sony, Nakamichi, TEAC, and Philips calibration tapes, however many other manufacturers made such tapes as well. The Sony calibration tapes were not for sale to the public and only Sony engineers had access to them. Luckily, it occurred to me to keep my set safe for future use. Back then, they used to come in a special 12-cassette holder album, which contained the complete set, together with instructions to service almost any Sony tape deck.

In the 80s and 90s, home computer users who recorded data on audio cassettes used them, and they were often freebies in computer magazines. Sinclair and Commodore computers also had an azimuth alignment cassette together with a little program. Back then, anyone who was making mix tapes would have had at least one speed reference cassette, because if your decks were not running at the same speed, then there would be a noticeable speed difference in your copy.

WS48, WS48A, WS48B

The WS48A was a speed calibration tape with a pre recorded 3 kHz 0 dB (0.775 V) signal, which was for use by engineers to calibrate the motor speed. The audio output of the tape deck usually feeds a frequency counter with a 16-Ω resistor across the signal and ground wires. You simply adjust the speed of the motor until the frequency counter reads 3000 Hz or a value within ±60 Hz.

Many cheap digital meters have a “F (Hz)” range setting, which allows the measurement of frequency. This is extremely useful to have in a pocket multimeter and is usually precise enough for calibrating tape speed.

You could buy a frequency counter, which would be a large box taking up shelf space, but now days it is not necessary to convert your lab into the bridge of the Star ship Enterprise. With modern laptops and fast processors, it is possible to make such measurements using software.

P-4-A036, P-4-A81S, P-4-A82S

These tapes were for calibrating the head azimuth. They had a 6.3 kHz signal at -10 dB on both left and right tracks. You simply fed these signals to the vertical and horizontal inputs of your oscilloscope, which displayed a Lissajous loop. A circle or a positive slope (/) such as a line, or ellipse was an indicator that the azimuth was correct.

P-4-A100

The P-4-A100 was also for head azimuth adjustment, and had 10 kHz signal at -10 dB.

CQ-009C

CQ-009C was a cassette with small mirrors, which enabled the engineer to see the tape path, and detect tape curl and twist when it happened. This type of distortion usually happens when the height of the head is incorrect; hence, this cassette helps to adjust the height.

You can also make your own cassette by cutting out various parts from a standard cassette to reveal the pinch roller and head. Usually one uses a C120 cassette for this.

P-4-L81

P-4-L81 was a cassette for calibrating the playback level. It had a 333 Hz signal at 0 dB. If your tape deck has a facility to adjust the output level then you could measure the Line Out level with a VTVM, which should be 0.55 V at -3 dB.

P-4-L300

P-4-L300 was for calibrating the playback level. It had 315 Hz signal at 0 dB.

P-4-A-82

P-4-A-82 was a cassette for calibrating the playback equaliser setting. It had a 10 kHz signal at -10 dB. The output feeds a VTVM with a 100-kΩ resistor in parallel to the signal and ground. The adjustments were to ensure the output reading was 206 mV to 103 mV.

CQ-101A

CQ-101A was a special torque meter cassette, which measured the torque produced by the forward spindle. The CQ-102A measured the back tension torque, whilst the CQ-201A measured the fast forward and rewind torque.

CQ-403A

CQ-403A measured the tape tension.

CQ-102C

CQ-102C was for measuring the forward torque and forward back tension.

CQ-102RC

CQ-102RC was for measuring the rewind torque and rewind back tension.

CQ-102B

CQ-102B was for measuring fast-forwarding and rewind torques.

CS-17

CS-17 was a special blank tape for making the record bias adjustment and record level adjustment. These settings are critical to good audio reproduction and involve recording a 315 Hz signal and 10 kHz signal at -30 dB (25 mV). You then play them back to confirm that both signals are 0 dB ±0.5 dB relative to each other.

DP069 BASF Professional Service Tape

The DP069 BASF Professional Service Tape was for calibrating the bias and equalisation.

QZZOW190EX

The QZZOW190EX was a precision audio test tape by the Matsushita Corporation for open reel tape recorders. It was a 19 cm/s full track tape to calibrate the speed and “wow & flutter” parameters.

OA-W411

OA-W411 was a test tape by the Olympus Corporation to calibrate “wow & flutter” parameter of a microcassette recorder. It has a 3 kHz signal at -10 dB.

MTT-111N

MTT-111N was a test tape by the TEAC Corporation to measure the “flutter” parameter of a standard audio cassette. It has a 3 kHz signal.

MTT-111NA

MTT-111NA was a test tape by the TEAC Corporation to measure the “wow & flutter” parameters of a standard audio cassette. It has a 3 kHz signal at -10 dB.

MTT-114NB

MTT-114NB was a test tape by the TEAC Corporation to calibrate the head azimuth setting. It has an audio signal of 14 kHz.

Testcassette 812/MCT

The “Testcassette 812/MCT” was a special service tape by the Philips Corporation. It has 50 Hz and 8 kHz signals.

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Calibration Cassettes
Making a Speed Calibration Cassette