Hi-End, Hi-Fi, Home Cinema



Quad 405

The Quad 405 power amplifier is intended for use with loudspeakers of less than normal efficiency. Great care has been taken to ensure that the high power output of the 405 does not increase the risk of damage to the loudspeaker. Although direct coupled, the d.c. offset voltage is confined to negligible values even' under gross overload. A fixed high pass filter is incorporated to prevent spurious subsonic signals from reaching the loudspeaker. The Quad 405 uses a current dumping output circuit, a Quad invention which eliminates many of the problems associated with transistor amplifiers. The basis of current dumping is 'feed forward error correction' first proposed by Harold Black in 1928, in which a derived error signal is added to the output signal of an amplifier in exactly the right amount to cancel the distortion produced by the amplifier. While it is relatively easy to add error current to signal current without Interaction, as in Black's invention, it is very much more difficult to do so in voltage terms. Loudspeakers require a stiff source and so 'feed forward' has found no successful application in audio amplifiers. Weight 9kg.

Quad 405

Quad 405

Power Amplifier


Power Output:

The amplifier is intended for use with loudspeakers of 4-16 ohms nominal impedance

100Hz any level up to 100 watts <0.01% Dtot

1kHz any level up to 100 watts <0.01% Dtot

10kHz any level up to 100 watts <0.05% Dtot


Output Internal Impedance and Offset: 3.3µH in series with 0.03 ohms. Offset <7mV


Frequency Response:

Ref. 1kHz. Low frequency -dB at 20 Hz.

Filter attenuation as curve

High frequency: -0.5dB at 20 kHz, -3dB at 50 kHz


Signal Input Level:

0.5V rms ±0.5 dB for 100 watts into 8 ohms

Amplifier loads and input by 20kohms in parallel with 50pF


Signal Input Slew Rate Limit: 0.1 V/µS

Signal Input Overload: Instantaneous recovery up to +20dB overload


Crosstalk (input loaded by 1k ohms):

80dB at 100Hz

70dB at 1kHz

60dB at 10kHz


Hum and Noise (input loaded 1k ohms):

'A' weighted - 95dB ref full power

Unweighted (15.7kHz measurement bandwidth) - 90dB ref full power



The amplifier is suitable for use under the most arduous music conditions and is electrically protected by current limiters; 7 amps in phase current at peak voltage and 3-1/2 amps at zero voltage. Shorting both outputs simultaneously on signal for an extended period (minutes) is not protected


Stability: Unconditionally stable with any load and any signal

Power Input: 110-130V or 220-240V, 50-60Hz, 30-350 watts depending on signal level


Width: 340.5mm

Height: 115mm

Depth: 195mm (plus 38mm for connectors)

Weight: 9kg

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