Broadcasting House, Glasgow 

15 March 2024 tbs.pm/80553

 

Cover of World-Radio

From World-Radio for 4-10 December 1938

THE equipment installed in the new Scottish studio centre at Queen Margaret College, Glasgow, incorporates the latest developments which have been made by the BBC in studio and control room apparatus. A description of all the units and circuits in detail is beyond the scope of one article, but an attempt will be made to show how the latest requirements of broadcasting technique have been met.

STUDIOS

The necessity has arisen for the control of programmes to be carried out in studio control cubicles adjacent to the studios, and this facility has been provided in five of the studios, viz., Nos. 1, 2, 3, 5, and 8, in which major productions are made. It will, therefore, only be necessary to describe one circuit. A further innovation is that in two studios — Nos. 1 and 5 — the echo effects can be applied to the programme by the producer.

The layout of Studio No. 1, with its associated control cubicle and narrators’ studio, has already been given. Fig. 1 is a schematic diagram of the circuit used in this studio suite, which is the largest possessed by the BBC at any provincial studio centre and is capable of accommodating a full symphony orchestra of about one hundred players.

 

A schematic

Fig.1 – Schematic diagram of equipment associated with No. 1 Studio.

 

The main studio is equipped with five individual microphone points, each with a “paralleled” point on an opposite wall, served with a ribbon microphone on either a vertical or balanced-arm microphone stand; an announcer’s desk with separate microphone; a studio gramophone desk with two turntables with parallel tracking pick-ups, a compère’s microphone, and a three-channel mixer; a loudspeaker unit with mains-operated amplifier and headphone points.

The Studio Control Cubicle is equipped with two desks, loudspeaker unit, etc. The first desk is fitted with three mixer units, two of which have four channels each, to which are connected the studio microphone points of both the main and narrators’ studios, and a reserve point in the cubicle itself. The output of the gramophone desk is connected to the nearest microphone point in the studio. The third mixer has two channels only, each of which is connected to an output of one of the other mixer units. Thus control can be exercised either individually or collectively over the various microphone circuits. The output of the mixer is taken back to the announcer’s desk in the studio where by means of a switch either this output or the separate microphone can be selected and connected, viâ a repeating coil, to the balanced line supplying the input of the “A” amplifier associated with this studio. This amplifier has two outputs, No. 1 being normally used in the programme circuit and No. 2 for echo purposes. When echo is required, this second output is connected to the loudspeaker unit in the echo room from which a microphone feeds, viâ a repeating coil, the input of a second “A” amplifier.

The No. 1 outputs of both “A” amplifiers are connected to the input channels of a two-channel fade unit on the second desk in the Studio Control Cubicle so that the direct and echo sources can be mixed at the required relative levels and applied to a control potentiometer on this desk. The programme then passes to the “B” amplifier input switching circuits, by means of which it is made available to any of the input channels of the fade units on the control positions in the Control Room.

By simple cross-plugging operations with double-ended cords any individual circuit, or the whole of the circuits, can be cut out. The circuit arrangement then corresponds with that employed at the older studio centres where studio control facilities are not available.

Communication between the studio and its cubicle during rehearsals is carried out by means of a “talk-back” circuit, a microphone and switch unit being installed in the cubicle for this purpose. When the “talk-back” switching is operated, the studio output is disconnected from the line to the Control Room and the “talk-back” microphone substituted in its place. Loudspeakers are provided in both studio and cubicle, but in the normal condition only that in the cubicle is connected to the “B” amplifier output and reproduces the studio programme. The operation of the “talk-back” switching key first silences the cubicle loudspeaker by disconnecting it from the circuit and then, by means of electromagnetic relays, switches the studio line over to the cubicle microphone and the “B” amplifier output to the studio loudspeaker.

The circuit of Studio No. 5 is similar (except for the narrators’ studio associated with Studio No. 1), but as it is much smaller, only one three-channel mixer is provided, with no central mixing facilities. It will be used largely for dramatic productions which do not require the elaborate circuit provided in the Dramatic Control equipment. Studios Nos. 2, 3, and 8 are provided with control cubicles, but no echo circuits. The switching circuits are similar, but simpler.

The remaining studios — Nos. 7 and 9 — are fitted with gramophone equipment, which in the former is for use on dramatic productions and in the latter for record recitals with a compère. Studio No. 7 has three desks, each with two turntables so that six separate channels are available. Each turntable is provided with a pick-up on a parallel tracking device which enables any pre-determined groove on a record to be selected. Mains-operated amplifiers in each desk give pre-fade listening circuits on each channel. A separate microphone channel is fitted on the centre desk, and a loudspeaker circuit enables the operator to listen to the programme as it is produced. This is, of course, cut off if the microphone channel is faded up. Studio No. 9 is equipped with a three-channel mixer, two channels from gramophone turntables and the third from a microphone.

THE CONTROL ROOM

Control Room

Control Room: supervisory and simultaneous broadcast position.

The Control Room is situated on the ground floor and its approximate dimensions are 54 ft. 9 in. by 24 ft. 6 in. The amplifiers, jack fields, meter panels, switching relays, line termination and testing equipment, check receivers, etc., are all rack-mounted on apparatus bays, in five racks of ten bays each. Each rack is mounted on a wooden plinth and secured to the next one and to the rear wall by steel tubing. In order to provide for any subsequent expansion to take place in an orderly manner spare space has been provided on the racks, and, in the final contingency of this being completely utilised, a sixth row of ten bays can be installed on a plinth for which space has already been allocated.

Two control desks, each equipped with two “control positions,” are installed in this room, one on each side of a supervisory and S.B. (simultaneous broadcast) rack of five bays. The first two control positions are intended to be used as main transmission positions and each is equipped with a four-channel fade unit — a combination of three two-channel fade units — followed by a control potentiometer, the output of which is connected to the input of the “B” amplifier — i.e., the second amplifier in the main programme chain. Each of the channel inputs can be connected to any of the programme sources available, and by suitable operation of the controls these sources can be selected or mixed as required.

In addition, the position is equipped with a programme meter and a headphone point for visual and aural monitoring of the programme at the “B” amplifier output, across which are the inputs of the programme meter and trap-valve amplifiers feeding these points. Signalling keys and lamps are provided for studio signalling purposes.

A further innovation is the provision of a pre-fade listening circuit, by means of which the controlling engineer is enabled to listen across the incoming circuit of each of his channels before it is faded into the programme chain. This facility is most useful when the engineer has either to fade up on a particular cue in a programme already running, or to receive a verbal cue from the announcer immediately before the start of a programme. Between the two control positions on the desk, an indicating lamp field is fitted, a vertical row of lamps being provided for each channel on the two positions. Each lamp in the vertical row represents a source of programme, so that both controlling engineers on these positions obtain visual indication of the source which has been applied to any one of the channels.

The second desk, comprising the third and fourth control positions, is similarly equipped except that two-channel fade units only are provided, with corresponding reductions in the numbers of pre-fade listening keys and lamps on the indicating lamp fields.

The supervisory and S B. position, situated between the control desks, and illustrated in the accompanying photograph, is the main operating centre of the circuits and represents a departure in design from previous practice in that the equipment is rack-mounted on a row of five bays instead of being a desk similar in type to the other positions. This gave the advantage of a better layout than was previously possible and enabled more apparatus to be provided.

The first three bays in this rack form the supervisory engineer’s position. Following established practice at provincial stations the selection of sources to channels is centralised at this position and Bay No. 1 is equipped with the operating keys, etc., for these circuits. The ” B ” input switching circuit consists of a network of relays arranged in thirteen rows of thirty-four relays per row; the thirteen rows represent the total number of channels on the control and supervisory positions, and the thirty-four relays in each row comprise thirty “A” relays, one for each of the studio outputs, etc., available, and four “P” relays for selection purposes. This represents the ultimate capacity of the station. At the present time only twenty-three “A” relays are fitted, but the switching bays are wired for ultimate capacity so that additions can easily be made.

 

Relay circuit diagram

Fig. 2 – Relay circuit for selecting source of programme.

 

Fig. 2 shows the circuit used for source selection. The channel operating key (shown at the bottom of the diagram) of a particular control-position circuit is first made; this supplies current to the “private wire circuits” of the amplifiers used with that position and so switches them on. These circuits are common to all the channel keys of that position. The “P” relays in the switching row associated with the channel also operate and prepare the “punching” circuit of the source. The source is then selected by momentarily depressing the punching key (a non-locking plunger key) associated with it. This immediately closes the appropriate “A” relay which locks up over its own contacts and at the same time the “P” relays release because their holding circuits have been broken. The holding circuit is a series circuit through contacts of all the “A” relays in that row. No other source can now be punched to that channel. Proof that the circuit is correctly operated is given by light signals on the indicating lamp fields of the control and supervisory positions, showing that the source is on the desired channel, and by the dimming of the light over the channel operating key owing to added resistance being thrown into its circuit by the release of the “P” relays. The arrangement of the keys and lamps is such that immediately the circuit is set up an indicating lamp glows on the same vertical line as the operating key so that the supervisory engineer has an easy visual check on all the control position channels.

Bays 2 and 5 in the rack are similar and are equipped with telephone equipment for communicating with the studios, O.B. points, other stations in the S.B. system, etc. Bay 5 is further equipped with switching facilities for inserting a two-way repeater with balancing networks into any control line network of which Glasgow is an intermediate station. Circuits are also provided to enable the supervisory and S.B. engineers to monitor any programme and give cue signals to any control position. Bay 3 comprises a single-channel control position with signalling circuits to all studios.

When the programme is to be radiated — i.e. is not merely a rehearsal — the output of the “B” amplifier is connected to the lines feeding the transmitting stations, viâ “C” amplifiers, the necessary connexions being made by means of an input switching network similar to that previously described. The operating keys and indicating lamps for these circuits are provided on Bay 4 of the rack so that the S.B. engineer has visual indication of his engaged circuits. Provision is also made to enable this engineer to fade any “C” amplifier into a programme which is passing through the station and, by means of a suitable test amplifier and meter, to measure the level of any incoming or outgoing programme.

CONTROL CUBICLES

Where the programme has not been previously controlled this function is normally carried out in a control cubicle, to which it is transferred by the operation of change-over switching provided on the supervisory position. In this case the inputs to the fade units on the control position are transferred to similar circuits in the cubicle, and the “B” amplifier input is transferred from the output of the control position potentiometer to that of the cubicle potentiometer. Two such cubicles are provided and these are used in conjunction with the main transmission control positions. Each cubicle is, in consequence, equipped with a desk fitted with a four-channel fade unit, control potentiometer, programme meter, pre-fade listening keys, and source indicating lamp field. Monitoring in these cubicles is normally carried out by loudspeaker.

DRAMATIC CONTROL ROOM

The dramatic control unit is used where the production of a programme involves the use of a number of studios or other programme sources. The unit installed at Glasgow is of the latest type developed by the BBC and incorporates twelve channels, arranged in two groups each of five channels, each group being controlled by a main group mixer, and two channels which are independent of the group mixers. The outputs of the main group mixers and of the independent channels are connected to the inputs of a special amplifier (known as DCA) which is provided to make good the mixer loss. The output of the DCA amplifier is controlled on the DC unit and monitored by loudspeaker.

Provision is made for “talk-back” and light cueing in both directions. The circuit provides that each studio shall receive the complete DC programme by loudspeaker except when a particular studious contributing its part to the programme. Talking-back arrangements are incorporated in the circuit for both rehearsal and transmission conditions. In the former case production can be held up for the purpose and the studio loudspeakers can be used, but in the case of transmissions only the headphone circuits are used.

 

A Transdiffusion Presentation

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W J Stentiford, A.C.G.I., D.I.C. Contact More by me

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