Avantic Beam-Echo DL7-35
Beam-Echo Amplifiers
The following history of Beam-Echo is based upon an article written
by Tony Holmes
formerly of "The Juke Joint".
One of the features that distinguishes a British BAL-AMi jukebox from its American AMi counterpart, is the type of amplifier that's fitted. In the case of BAL-AMi, these are Beam-Echo amps.
Beam-Echo began in 1953 when a chap called Henry Rahmer saw an opportunity to buy a run down cine projector manufacturing company called Danson. Rahmer decided that he could build the cine projectors, so he bought the company from the official receivers. He persuaded a friend, a Mr Philip Hounsfield, to give him some space in his factory so he could make a start. Hounsfield ran a company in Witham, Essex called Parion Products that built caravans from a factory on Witham High St. They had just marketed a very successful product in the form of a fold up camp bed called the Hounsfield Safari and thus had capital available for new ideas. A deal was done on the basis of working space in exchange for shares in the new company and this was how Beam-Echo began. The name, incidentally, is derived from cinema jargon. The beam represents the light source and the echo is a reference to the cinema sound track. Soon after setting up manufacturing the projectors, Rahmer got the contract to make the amplifiers for the newly operating BAL-AMi company. Soon most cafes would have a BAL-AMi jukebox playing rock and roll via a Beam-Echo amplifier
By the mid fifties they were selling thousands of units so they decided to branch out into the blossoming Hi-Fi business, at that time dominated by names such as Leak, Radford, Quad, Pye etc. Beam-Echo took on a new designer, Gordon Lawson, who had a good background in amplifier design. The company developed a new range of products which they sold under the brand name Avantic. They later introduced loudspeaker enclosures, a radio tuner, and several other items of Hi-Fi related equipment. So Beam-Echo became established in the UK Hi-Fi market, with an enviable reputation for quality.
The first amplifier to be sold was the 20W monoblock DL7-35, with a matching mono pre-amp. These two units sold for £55. Beam-Echo at that time must have been doing well internationally as the company had its own showroom and sales office in the USA at 820 Greenwich Street, New York City.
All Beam -Echo products were well made, stylish, and many are now highly collectable among audio enthusiasts. In the early sixties the company came to the attention of the growing electronics giant, Thorn Electrical Industries, and they subsequently acquired Beam-Echo in order to get hold of the trade name Glyndbourne, which was part of the company. Thorn then closed down the Beam-Echo plant in the early sixties, possibly as early as 1961.
Some thirty plus years later, in 1994, a man called Stuart Perry discovered a pair of old Avantic amplifiers that had been thrown out for scrap. He restored them and immediately fell in love with their superb quality sound. More than 50 years on from the original start of Beam-Echo, Stuart designed a new range of products, together with products based on original designs offering long lasting products for musical pleasure - just like those BAL-AMi jukeboxes that just keep on rockin' !
A new version of the DL7-35 was launched at the Hi-Fi Show at the Ramada Hotel Heathrow, London. The price for a pair of these monoblock amps was £2,850. Hi-Fi News magazine called it a 'classic in every sense of the word'. Unfortunately, Stuart's Beam-Echo adventure didn't survive and in 1998 the Beam-Echo name was once again consigned to amplifier history.
Stuart's old website can be found at www.beamecho.cwc.net , but it is only there (as of September 2007) because no-one has gotten around to deleting it. All of the email and phone contact points are no longer valid, so don't try them.
Beam-Echo DL7-35
HIGH FIDELITY POWER AMPLIFIER
INTRODUCTION :
The DL7-35 amplifier is capable of the highest standard of reproduction expected of only the very best high fidelity amplifiers. In addition, it has a number of unusual features which make it extremely versatile. Above all, it us built to last and to give trouble-free service.In the following pages we have set out as clearly and as cogently as possible all the relevant facts concerning the amplifier.
TECHNICAL DESCRIPTION :
The DL7-35 amplifier was designed to provide the most realistic sound reproduction in the home. To this end, every possible refinement of circuit detail has been incorporated. The considerations underlying the design of a high fidelity amplifier and the methods by which the required high standard of performance has been achieved in the DL7-35 amplifier are described in this section.
POWER AMPLIFIER :
From the point of view of power output an audio amplifier must be able to cope with the dynamic range of a full symphony orchestra. In the concert hall, this reaches a maximum of about 70db. However, for the purposes of broadcasting or recording this is generally compressed to 60db or less. In terms of power this represents a ratio of one million to one. If we accept that 0.05mW of electrical power into a high sensitivity loudspeaker represents the threshold of audibility in a quiet living room, the required maximum output becomes 50 watts. Fortunately, maximum output occurs for only fractions of a second and the power required under these conditions is known as the instantaneous peak power and this is generally 1.5 times the continuous power output.
There is another aspect to be examined. To provide an agreed standard of measurement, all amplifiers are tested with a pure sine wave input signal. This never occurs in speech or music except, remotely, in the case of the flute. From the point of view of power handling capacity a pure sine wave is one of the most difficult waveforms for an amplifier to reproduce and invariably gives an inferior result. It can, therefore, be taken that an amplifier rated at 30 watts continuous sine wave output will give an instantaneous peak output of speech and music of at least double this figure.
Power output of course means nothing unless distortion is taken into account. Modern standards for high fidelity reproducers demand a harmonic distortion content of not greater than 0.1 per cent and an intermodulation distortion level of not greater than 1 per cent.
The next consideration is frequency response. The fundamental frequency range of a symphony orchestra is from about 35 c/s (the lowest note of a harp) to about 5,000 c/s (the highest note of a piccolo). The piano ranges from 25.5 to 4,186 c/s, but the instrument of widest range is the concert organ, 16 to 8,000 c/s. However, this is not the whole picture. All instruments produce harmonics and it is the number and strength of these that produces the characteristic sound of each instrument.Without these it would be impossible to distinguish, say, an oboe from a violin. In order to reproduce the harmonics, the response of an amplifier must extend to about 16,000 c/s. Furthermore, the response must be linear. In other words, the relative intensity of sounds of different frequencies must be the same at the output of the amplifier as at the input. Any deviation introduces colouration of the original. A frequency response of this magnitude brings difficulties in its wake. Great care has to be taken with hum and noise. For high fidelity reproduction, these must be at least 60db below maximum output.
Finally, there is transient response. Transients are sound waves produced by percussion instruments including plucked strings. The waveform is of a special character very rich in harmonics and the waves are of short duration giving a shock effect to the loudspeaker. The effect of this is to cause the loudspeaker cone to continue oscillating after the transient wave has passed. To eliminate this effect the loudspeaker must be heavily damped. This can be done by causing the internal resistance of the amplifier to be very much lower than the loudspeaker impedance. This is known as damping and the damping factor is a measure of the transient response of an amplifier.
CIRCUIT DESCRIPTION :
To achieve these objectives, the Mullard EL34 valve is used in the DL7-35 amplifier. This is a pentode output valve capable of a dissipation of 25 watts. A pair of these are used in the output stage under distributed load conditions. Sometimes known as "ultra linear" working, this type of circuit produces the highest output at the lowest possible distortion under conditions of the highest efficiency. Driving these valves is a Mullard ECC83 double triode used as a cathode coupled phase splitter. The first stage of the amplifier is a Mullard EF86 low-noise pentode, d.c. coupled to the phase splitter stage to reduce the overall phase shift to a minimum. High stability resistors are used in the input stage in the interests of low noise. Overall feedback of 30 db is used.
External services provided by the octal socket on the amplifier chassis are as follows:
Pins 1 and 8 For switching mains externally
Pins 2 and 3 6.3V. A supply (heaters)
Pin 4 410V. DC Decoupled B Supply (H.T.)
Pin 5 440V. DC B supply (H.T.)
Pins 6 and 7 6.3V., 2.5A, A supply (heaters)
The two, two-pin sockets are mains outlets.
The performance is graphically illustrated. Figure 1 shows the frequency response; Figure 2, the sensitivity and Figure 3, distortion plotted against power output.
SUMMARY OF PERFORMANCE :
Power output:
20 watts at less than 0.05% total distortion
27 watts at 0.1% total distortion
Instantaneous peak power output: 45/60 watts.
Intermodulation distortion measured with a carrier frequency of 10K c/s and a modulating
frequency of 40 c/s in the ratio of 1:4:-
0.7% at 20 watts output
1% at 29 watts output.
Frequency response:
+/- 0db from 5 c/s to 30 K c/s
+/- 1db from 2 c/s to 100 k c/s
(Reference level 1 k c/s)
Hum and noise: -89db relative to 20 watts output with 10k ohms source resistance
Input/output voltage characteristic linear to 35 watts output.
Damping factor:
50 - equivalent to an internal resistance of 0.3 ohms with a loudspeaker impedance of 15 ohms
Sensitivity:
220mV for 20 watts output
240mV for 25 watts output
270mV for 30 watts output
Output impedance of 4 ohms, 8 ohms and 16 ohms may be selected by a switch which automatically adjusts the negative feedback to the output impedance.
INSTALLATION :
A unique method of ventilation (patent pending) is used on the DL7-35 amplifier. However, this can only operate satisfactorily if adequate room is allowed for the air to circulate around it. When mounting the amplifier in a cabinet, make sure that cold air can enter the cabinet and hot air escape from it.
OPERATING INSTRUCTIONS :
1. Adjust Mains Voltage Selector to correct line voltage. Make sure that the amplifier is set for the correct voltage range. This can be ascertained by examining the underside of the power amplifier. Through one of the apertures will be seen a coloured plug. According to the colour of this plug, the selection of voltages are as follows:
2. Connect loudspeaker unit to appropriate terminals and adjust impedance matching to suit by switch provided.
3. Connect ancillary equipment to the appropriate sockets at the rear of the pre-amplifier taking care to select those that give the appropriate sensitivity.
4. Connect DL7-35 unit to mains (or Line Socket) and switch on with Volume Control Knob.
WEIGHTS AND MEASURES :
Dimensions.................................. (L) 36 x (W) 23 x (H) 22 cm
Weight......................................... 16.2 kg
Power consumption...................... 140 watts