More than 60,000 Quad 405 current dumping amplifiers are in use around the world providing the "closest approach to the original sound" in the homes of serious music listeners, in recording and broadcasting studios and for sound reinforcement where quality is of prime importance.
The Quad 405-2 exploits improvements in component technology to provide more VA into a wider variety of loads than the original Quad 405 without compromising performance and reliability.
The Quad 405-2 will produce perceptibly higher sound pressure levels from the majority of loudspeakers than the original Quad 405, which will be of significant benefit with the increased dynamic range of modern programme sources.
The 405-2 uses "current dumping", a Quad invention based on feedforward error correction which eliminates many of the problems traditionally associated with transistor amplifiers.
"feedforward error correction" was 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 "feedforward" has found no successful application in audio amplifiers.
What Quad has done - not quite as easy as it sounds - is to produce a current controlled amplifier, apply a special type of feedforward current error correction and then apply overall voltage feedback to convert the whole to a voltage amplifier. There is in effect, both a low powered very high quality amplifier and a high powered heavy duty amplifier, the current dumpers. The low power amplifier controls the loudspeakers at all times, calling upon the high power section to provide most of the muscle. The small amplifier which carries the error signal is so arranged that provided the large power transistors get within the target area of the required output current, it will fill in the remainder accurately and completely.
The quality is solely dependent upon the performance of the low powered high quality amplifier together with four passive components. When correctly designed, all distortion in the output stage is reduced to zero.
With this technique it is possible to produce an amplifier of very high performance without using carefully matched relatively fragile output devices. There are no crossover biasing problems, no alignment or adjustment is required to obtain optimum performance and nothing can go out of alignment during life. In the event of component failure, replacement can be effected and performance restored without realignment.
Specifications
Power Output: the amplifier is intended for use with loudspeakers of 4 - 16 Ω nominal impedance.
Power and distortion for various frequencies
Continuous sine wave into 8 Ω , resistive load
100 Hz any level up to 100 watts : less than0,01% Dtot
1,100 Hz any level up to 100 watts : less than0,01% Dtot
10,100 Hz any level up to 100 watts : less than0,05% Dtot
Output Internal Impedance and Offset: 3,3 µH is series with 0,03 Ω . Offset 7 mV max
Frequency Response:
Ref. 1 kHz
Low frequency -1 dB at 20 Hz. Filter attenuation as curve.
High frequency -0,5 dB 20 kHz -3 dB 50 kHz
Signal Input Level: 0,5 V rms ±0,5 dB for 100 watts into 8 Ω . Amplifier loads th input by 20 k Ω in parallel with 220 pF
Signal Input Slew rate Limit: 0,1V/µS.
Provided the rate of change of input voltages does not exceed this figure which is about ten times the maximum slew rate on a gramophone record and the amplifier is not driven into clipping, then the total of all distortions appearing in the audio range (20 - 20,000 Hz) due to transient or repetitive waveforms with frequency components inside or outside the audio range will be at least 80 dB below full rated power. If the major portion of the input energy is wanted signal then -80 dB (0,01%) represents the maximum possible distortion on programme.
Signal Input Overload: Instantaneous recovery up to =20 dB overload
Crosstalk (Input loaded by 1 k Ω ):
80 dB at 100 Hz
70 dB at 1 kHz
60 dB at 10 kHz
Hum and Noise:
"A" Weighted: -96 dB ref full power
Unweighted: -93 dB ref full power
(15,7 kHz measurement bandwidth)
Protection
The Quad 405-2 is suitable for use under the most arduous music conditions and is electrically protected by current limiters; 8,5 ampers peak current into any load reducing to 3,1 amperes steady state into a short circuit. Shorting both outputs simultaneously for an extended period will result in overheating and eventual breakdown
Stability: Unconditionally stable with any load and any signal
Power Input: 100-120-130 V, 220-230-240 V 50/60 Hz, 30 - 350 watts depending on signal level
Dimensions (W x H x D): 340 x 115 x 195 mm (13,4" x 4,5" x 7,7"). Allow an extra 38 mm (1,5") for plug and socked
Weight: 9 kg (20 lbs)
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