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

LEAK Delta 70 (1972)

Circuit description
Power Amplifier - The output transistors and temperature compensation diodes are mounted on the heat sink, the remainder of the circuitry being located on the power amplifier P.C. boards. Power transistors are insulated electrically from the chassis by mica washers.
Quiescent current is measured by removing the appropriate HT fuse, and inserting a current meter. The current is adjusted by P% and should be approximately 40mA.
The amplifier D.C. output voltage (pin D on power amp board) should be +37 V with an HT supply of +75 V. This voltage is set by fixed circuit components, and significant deviation of this "midpoint" voltage indicates component failure,not necessarily an output transistor.
Full output for each channel is realised with 16 - 7 V RMS across an 8 ohm load.

The P.C. contains tone control circuitry (excluding potentiometers) R1AA equalisation for disc input, filter components, and appropriate amplification for all inputs.
With all inputs short circuit, volume control maximum, other controls level, noise output voltages should be less than the following: 7-5 mV on Tuner and Replay, 22 mV on other inputs
The sensitivities for each input to provide full output are indicated in the specifications (1 kHz sine wave). The corresponding output from the preamplifier,measured at the tape sockets is: phono socket output 400 mV approx. DIN output 40 mV approx.

Rated Power Output:
40 + 40 watts into 4 ohms,
35 + 35 watts into 8 ohms,
28 + 28 watts into 15 ohms.
Music Power Output (IHF):
100 watts into 4 ohm loudspeakers,
90 watts into 8 ohm loudspeakres,
60 watts into 15 ohm loudspeakers.
Total Harmonic Distortion: 0-1% at ALL power levels up to 25 watts at 1 kHz each channel into 8 ohm loudspeakers.
Total Intermodulation Distortion: Input - 70 Hz anf 7 kHz in ratio of 4:1, Less than 0-5% for ALL power levels up to 35 watts into 8 ohms
Hum and Noise: 66 dB below 30 watts into 8 ohm load on Tuner and Replay and 56 dB below 30 watts on other inputs.
Cross Talk: between L and R channels, -50 dB up to 1kHz and -30 dB at 10 kHz.
Input Sensitivities:
Disc 1 (RIAA Characteristic) 2 mV at 1 kHz Input Impedance 47 kohm.
Disc 2 (RIAA Characteristic) 10 mV or 30 mV at 1 kHz Input Impedance 33 kohm, 100 kohm.
(Selected by switched input attenuator marked HI and LO on rear panel).
Damping Factor:
40 measured at 1 kHz for 15 ohm loudspeakers.
20 measured at 1 kHz for 8 ohm loudspeakers.
Tuner 1 Mic
25 mV or 2 mV
47 kohm, 47 kohm
Tuner 2:
60 mV or 250 mV
50 kohm, 50 kohm
(Selected by switched input attenuator marked HI and LO on rear panel).
400 mV
47 kohm
Frequency Response: 30 Hz to 20,000 Hz (±1 dB)
Tone Control Range: 50 Hz to 14,000 Hz (±16 dB)
Filter: 12 dB per octave rolloff above 6 kHz
Dimensions: 344 x 118 x 238 mm

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