Mullard circuits for audio amplifiers

Capacitances between the various coils 6. The rectifier used in the power-supply stage is the Mullard full-wave rectifier, type GZ Distributed Loading The conditions of distributed loading are achieved by applying negative feedback in the output stage itself.

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The interaction between signals of very different frequencies is quoted as intermodulation distortion and that between signals of nearly equal frequencies is given as beat-note distortion. Tracing distortion consists of odd harmonics. Harmonic Distortion Power which occurs in the output at second, third, fourth, and so on, harmonics of the fundamental signal frequency comprises harmonic distortion.

Mullwrd make realistic reproduction possible, therefore, the amplifier should handle a range of frequencies at least as wide as that which can ccircuits heard.

A poor component can give rise to a high level of distortion and can cause instability. This type of output stage found favour for a number of years in high-quality amplifiers giving about 12W effective output. A busbar earth return is indicated, with only a single chassis connection at the input socket. As shown in Fig.

Mullard Circuits for Audio Amplifiers

The cans should be insulated from the chassis and the negative connection made to the common earth lead. This voltage is expressed in decibels as a fraction of ,ullard rated output voltage measures across the load resistance, so that: With hindsight muolard summer was the end of an era, the following year cicuits Beatles and being 13 made staying in the shed as a short wave listener and building my own one valve receiver Mulllard Luxembourg on Metres and Horace Batchelor's adverts for his Infradraw method of winning the pools together with Keynsham - thats K E Y N S H A M Bristol much more exciting.

Distortion is the presence in the output of frequency components which were not present in the input signal. With valves of the 12W dissipation class, comparison with normal pentode operation is more significant.

This will introduce noise in the recording and impart some 'wasted' remanence to the tape. Hence, an output voltage could be given as, say, lOOmV at 3. These amplifiers were the product of their applications lab and the first design was the Mullard from Moving-iron, stereophonic heads will produce voltages of the order of millivolts for each signal, and crystal heads will give signals of the order of lOOmV.

The EF86 has a rigid electrode structure. But too much bias will cause 'top-bend' distortion and will also cause a lessening in the output, especially for treble signals. Connection to the wrong side of the secondary winding of the output transfonner will give positive feedback and will result in oscillation. The word monaural is at present commonly used to depict conventional 'sound reproduction in which a single-track recording and a single pick-up head or tape playback head are used.

The grid resistors R14 and R15 of the output stage should also be close-tolerance components because they also form part of the anode load of the driver stage.

They should be dictated by strong reasons, and the subsequent variations in performance should be analysed closely. With unsuitable phasing positive feedback the resultant violent oscillation might damage a delicate speaker-coil suspension. The straight lines of the characteristic cannot be achieved in practice, and actual characteristics are more like the continuous curve shown in Fig.

The reserve of output power required for realistic reproduction of orchestral music depends mainly on the size and acoustical nature of the room and, to a lesser extent, on the taste of the listener.

The EF86 is coupled directly to the phase splitter to reduce the phase shift at low frequencies. It does not require a voltage difference between heater and cathode, so that it is suitable for directly-heated valves or for double-valves in which the second sections are needed for other purposes. The low-loading form of operation is, however, suitable only for use in the reproduction of speech or music and cannot be used with sine- wave input without circiits distortion resulting.

Mullard Power Amplifier c | Preservation Sound

The response curve for the recording head alone will depend on various practical considerations. If distortion is to be avoided, the sideways movement of the playback stylus should reproduce exactly the movement of the cutting stylus.

The input for the phase reverser qudio taken from the potential divider R1,R2 connected between the two mullaard. A disadvantage of the cathode-coupled form of phase splitter is that the effective voltage gain is about half that attainable with one section of the valve used as a nonnal voltage amplifier. Over amplitiers restricted range, an increase in the bias current, for example, lessens distortion, but causes treble attenuation and tends to lessen the signal-to-noise ratio.

The function of this chapter is to give brief accounts of the main items of associated equipment needed for disc or tape reproduction and also to discuss some of the causes of distortion, indicating the methods by which imperfections are minimised. For the playback process, the magnetised tape is drawn past the playback head at a constant speed, and the magnetic fields associated with the sections of the tape move and cut the coils of the head, thereby setting up voltages in the coils.

The anode-to-anode loading of the output stage is 7kO and, with a line voltage of V at the centre-tap aplifiers the primary winding of the output transformer, the combined anode and screen-grid dissipation of the output valves is 28W per valve.

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