Quad 306

 The Quad 306 is a two channel power amplifier primarily intended for use in high quality sound reproducing systems. The amplifier is usually used wit a Quad control unit though other signal sources can readily be accommodated.

The amplifier uses a current dumping output circuit  a Quad invention which eliminates many of the problems associated with transistor amplifiers, and covered by patents in several countries. In a current dumping amplifier there is in effect both a low powered very high quality amplifier and a high powered heavy duty amplifier. The low power amplifier controls the the loudspeakers at all times, calling upon the high power section to provide most of the muscle. The small amplifier is so arranged - it carries an error signal - that provided the larger power transistors (the dumpers) get within the trget area of the required output current it will fill in the remainder accurately and completely. The reproduced quality is solely dependent on the small amplifier which because of its low power can be made very good indeed.

Problems of crossover, crossover distortion, quiescent current adjustment, thermal tracking, transistor matching, all disappear. There are no internal adjustments or alignments and the choice of power transistor types is less restrictive.

 Amplifier protection

The amplifier is protected by a resettable trip which interrupts the incoming AC supply if the amplifier is grossly overdriven for a period of time. To restore operation simply press the red reset button on the back panel. The amplifier is thus fully protected against gross overload, short-circuited output etc. But not necessarily against seriously inadequate ventilation.

Input Connections

Signal input is via phono sockets, clearly marked L and R. if the amplifier is used with a Quad 33/34/44 control unit with a DIN output socket, you wiull need a 4-pin-DIN-to-2-phono-plugs load.

Loudspeakers Connections

The Quad 306 is fitted with standard 4 mm sockets and two red and black plugs are packed with the unit. The amplifier is unconditionally stable and may be used with any type of speaker cable.

The Quad 306 is entirely compatible with the ESL-63 loudspeaker but should not be used with the earlier model which could easily be damaged.

Specifications

Power Output:  50 watts per channel at 8 ohms

Distortion (continuous sine wave  into 8 Ω resistive load):

20 Hz (any level up to 50 watts) :  less than 0,01%

1 kHz (any level up to 50 watts) :  less than 0,01%

20 kHz (any level up to 50 watts) :  less than 0,03%

Output Internal

Inpedance and offset:  1,5 µH in series with 0,05 Ω . Offset tipically 7 mV

Frequency Response: 

-0,25 dB at 20 Hz to 20 kHz

-1,0 dB at 13 Hz to 40 kHz

Power Response:  -0,25 dB at 20 Hz to 20 kHz

Signal Input Level:  0,375 volts for 50 watts into 8 Ω

Signal Input Overload:  Instantaneous recovery  up to 15 dB overload

Crosstalk (input loaded by 1 k Ω):

100 dB at 100 Hz

85 dB at 1 kHz

65 dB at 10 kHz

Hum and Noise:  -105 dB (unweighted)

Stereo Separation:  85 dB at 1 kHz

AC Input:  110 - 120 V;  220 - 240 V,

Power Consumption:  30  - 250 watts, depending on signal level

Dimensions (W x H x D):  321 x 64 x 207 mm