Price: £192.50. Manufactured in Japan for the Marantz Company Inc., PO Box 99, Sun Valley, California 91352, USA. UK distributor: Pyser Ltd., Fircroft Way, Edenbridge, Kent, TN8 6HA.

THE Marantz Model 1070 stereo console amplifier was designed by American engineers, but is manufactured under their control in Japan. With a total power output approaching 100 watts RMS, it is compact in comparison with many competitive amplifiers, yet has a wide range of facilities. It comes with an excellent 22-page instruction manual which clearly defines the function of the various controls and has a useful chapter on the correct placement of stereo or quadraphonic loudspeakers in differently shaped listening rooms.

The amplifier is fully screened, with a metal housing finished in imitation wood veneer, and the brushed aluminium front panel is protected by a removable clear plastic cover. The main controls are mounted on a recessed black anodized panel with a clear perspex protective cover over the lettering and control calibrations. This panel is not back illuminated and therefore it is essential that the panel is placed in a good light. The controls on the front panel are a large selector knob for phono, tuner, auxiliary, tape 1 and tape 2. Next comes the tape monitor switch which can select either of two tape machines. In the centre are three slider-type tone controls for bass, mid-range and treble. To the right of these controls is the mode selector switch for left, right, Stereo, stereo reverse, and mono L R, and finally the rotary volume control. Below the main controls are the following: sockets for stereo microphone and headphones, push-buttons for low filter, high filter, loudness, main speakers, remote or ambience speakers, and power on-off. In the centre is the balance control.

On the rear panel are eight spring-loaded terminals for the main and remote pairs of loudspeakers, and below these are a 200W unswitched AC mains flat-contact American socket and a similar switched 100W one. Normally the pre-amplifier is directly connected to the power amplifier but, with the gradual use of graphic equalizers, for example, it is desirable to separate the pre-amplifier from the power amplifier. In the case of the Marantz 1070 this is achieved by having left and right 'pre-out' and 'main-in' phono sockets on the rear panel. These automatically bridge together but, when a phono plug is inserted, the internal connection is interrupted and any external unit can be connected between the two parts of the amplifier. There are input and output phono sockets for two separate tape recorders, duplicated with DIN sockets. Finally there are three pairs of phono sockets for phono, tuner and auxiliary. A 168cm (66-inch) three-core mains cable is permanently fixed to the amplifier.

There are four fuses to protect the amplifier and loudspeakers but to gain access to these it is neces.snry to remove the outer top cover. The well-designed rigid chassis carries a heavy Marantz Model 1070 stereo amplifier power transformer, fully screened. Separate printed circuit boards are used for the stabilized power supply, the input pre-amplifiers and tone control circuits. The fully complementary output stages are mounted on heavy heat sinks together with the penultimate driver stages. Whilst conventional soldering is used on switches, plugs etc, inter-panel wiring makes use of wrapped joints, a technique claimed to have a lower contact resistance than soldered joints.

How it performed

For many years there have been various ways of measuring power output in the USA and, with some, the published figures grossly flattered the true capability of the amplifier. Recently the Federal Trade Commission tightened up the method of measuring and quoting power output so that, from November all American designed amplifiers must employ identical measuring conditions. Briefly, the FTC requires that the audio amplifier power rating shall be measured after one hour of operation with a 1 kHz tone at one third of the published full power rating. This is a very severe test, and a number of manufacturers are opposing the new method of rating as it can be shown that, even under the most stringent programme material, the temperature rise of the output transistors is considerably lower than with a continuous tone.

However, it was thought appropriate that the Marantz 1070 should be tested under the new FTC requirements and, as the rated output is quoted as 35 watts per channel, a measured 12 watts was applied for one hour across a resistive load of 8 ohms. Although this treatment raised the output transistors heat sinks to a considerably higher than normal temperature, it had no ill effect and the maximum undistorted power output measured considerably more, at 48 watts, than the maker's specification.

Figure 1 shows the frequency response with the bass, mid-range and treble controls set to give the best square-wave response. It would be an advantage if the three slider controls had a line scribed across the knob to indicate their exact position against the fixed calibrated scale. This graph also shows the attenuation of low and high frequencies by operating the filter press-buttons. Figure 2 shows the effect of the loudness control, which adequately compensates for low level listening. The usual curves for the bass and treble tone controls (Fig. 3) are joined by the mid-range control, and all meet the maker's specification. Figure 4 shows the (a) Square-wave responses at 100, 1,000 and 10,000Hz were photographed from the oscillograph screen using non-inductive 8 ohm loads for each channel (Fig. 5a, b and c). Adding a 2/LF capacitor across the 8 ohm resistor with an applied 10,000Hz signal shows excellent stability and small phase shift (Fig. 5d). Finally, Fig. 6 indicates that 50 watts sinewave output into 8 ohms produces symmetrical clipping. Total harmonic distortion was measured as follows:

A problem often met in amplifiers is overloading of the magnetic pickup input. Although a pickup might nominally give only 5mV at 5cm/sec., high amplitude peaks can often reach 50mV or more. Unless the pickup input circuit is carefully designed, the first transistor stage can be overloaded and distortion created which no operation of the volume control can eliminate. The Marantz input circuit can accept a signal of 125mV before it is overloaded, and this is far higher than we can expect from normal records and pickups.

For several weeks, the Marantz 104111amplifier was used in conjunction with the lafest B & W DM6 loudspeakers and, for surround sound, a pair of Goodmans Achromat 250. It should be made clear that the amplifier is not a full four-channel type but the rear speakers are connected in series and obtain a signal from the live terminals of the front speakers. This system was developed by David Hafler in the USA and gives a degree of ambience to the overall performance. Push-buttons on the front panel will select either the front or remote (rear) loudspeakers or, by depressing both buttons, simulated four-channel performance is obtained.

There is little to criticize in this excellent amplifier, but one doubts the value of the bass and treble filter switches. From the curves (Figs. 1 and 3) it will be seen that they virtually duplicate the rotary tone controls. Normally bass filters are designed to produce a flat response down to about 40Hz and then have a rapid cut-off, to eliminate turntable rumble. Similarly a treble filter normally gives a flat response up to 7-10kHz and then there is a sharp cut-off to reduce noise on older records or heterodyne whistles on medium wave broadcasting.

Hum and hiss were virtually inaudible and every control worked smoothly. The loudspeakers are protected by means of a fast operating relay which disconnects the loudspeakers if the output transistor circuit fails. This also elminates the low frequency thump often heard when an amplifier is turned on and off. Whether used with disc, tuner or tape, the Marantz 1070 amplifier gave exemplary performance and is a fine example of cooperation between American designers and the Japanese manufacturers.

John Gilbert