Leak Delta 30

 The Delta Amplifiers inherit some of the well accepted characteristics of previous Leak models, e.g. plug-in printed circuit boards. Uprating circuitry, heat sinking and fusing has led to significant performance improvements, particularly under high duty conditions.

There are four plug-in boards:

Two identical preamplifiers (left and right);

Two identical power amplifiers (left and right0

The power transistors, transformer and other power supply components are mounted on the chassis.

Due to the similarity of construction and circuitry between the Delta 30 and Delta 70, both units are incorporated any differences.

 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 P5 and should be approximately 40 mA.

The amplifier D.C. output voltage (pin D on power amp board) should be +23 V with an HT supply of +48 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 11 V RMS across an 8 ohm load.

Pre-Amplifiers

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,  24 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.

Specification

Rated Power Output (both channels sine-wave driven at 1 kHz): 

20 + 20 watts into 4 Ω

15 + 15 watts into 8 Ω

10 + 10 watts into 15 Ω

Music Power Output (IHF):

60 watts into 4 Ω  loudspeakers,

40 watts into 8 Ω  loudspeakres,

24 watts into 15 Ω  loudspeakers.

Total Harmonic Distortion: 

0-1% at ALL power levels up to 10 watts at 1 kHz each channel into 8 Ω  loudspeakers.

Total Intermodulation Distortion: 

Input  - 70 Hz and 7 kHz in ratio of 4:1,

Less than 0-2% for ALL power levels up to 15 watts into 8 Ω loudspeakers

Less than 0-2% for ALL power levels up to 10 watts into 15 Ω loudspeakers

Overload Distortion:

Less than 0-1% for input signals up to 20 dB above stated sensitivity from 30 Hz to 15 kHz

Hum and Noise: 

63 dB below 30 watts into 8 ohm load on "Tuner" and "Replay"

53 dB below 30 watts on other inputs.

Cross Talk (between L  & R channels):   -50 dB up to 1kHz and -30 dB at 10 kHz.

Damping Factor:

20 measured at 1 kHz for 8 Ω loudspeakers

40 measured at 1 kHz for 15 Ω loudspeakers

Input Sensitivities (the sensitivities shown below give 30 watts output at 1 kHz into 8 Ω loudspeakers with tone controls "zeroed" and volume control on maximum): 

Disc 1 (RIAA Characteristic) :  2 mV at 1 kHz Input Impedance 47 k Ω

Disc 2 (RIAA Characteristic) :  10 mV or 30 mV  at 1 kHz Input Impedance 33 k Ω , 100 k Ω

Tuner 1 / Mic :  25  mV or 2 mV at 1 kHz / 47 k Ω 47 k Ω

Tuner 2 :  60 mV 250 mV / 50 k Ω 50 k ohm

(Selected by switched input attenuator marked "HI" and "LO" on rear panel).

Replay :   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 roll off above 6 kHz

Dimensions:  344 x 119 x 254 mm (13,5" x 4,7" x 10")