AMP & LS No. 11

E5 F1011
Issue 1 - Dec 1979

The BPO Amplifier and Loudspeaker No. 11A, sales name DORIC, is a loudspeaking telephone attachment which can be added to existing handset telephone installations, (except Internal Telephone System) to provide full, voice switched, loudspeaking telephone facilities.

Controls on the unit consist of:-

1. Rotary volume control To adjust the incoming level.

2. A red light emitting diode (LED) indicator, which is illuminated when the DORIC is in the 'Send' mode and extinguishes when the unit switches to Receive mode.

3. Three Piano-type keys. Their function from left to right is as follows:-
  1. Mute key - (Colour Yellow) Depression of this key will mute the microphone such that the distant party cannot hear conversation taking place in the vicinity of the DORIC. The key must be held depressed throughout the required duration.
  2. On Key (Colour Green).
  3. Off Key (Colour Red).

The unit uses voice switching techniques to prevent acoustic feedback or howl when the apparatus is in use. The housing is designed to provide acoustic isolation between microphone, (which is an electret type situated behind the two slots in the front of the unit) and loudspeaker, (situated under the grill to the rear of the unit). The unit possesses omni directional characteristics, and functions without the user having to be situated close to the microphone.

The unit employs circuitry which virtually eliminates speech clipping in normal use and also has a degree of tolerance to constant background noise without switching permanently to the 'Send' mode. However, to achieve good performance the usual requirements for room conditions still apply.

Power for the DORIC is provided by a transformer which transforms mains voltage to 18v a.c.

On-site maintenance of the DORIC is not recommended as components are mounted on a printed wiring board which does not facilitate convenient component renewal. MISCELLANEOUS
During trials of this apparatus a large percentage of faulty units returned were found to be RWT indicating that customers were reporting faults incorrectly. Voice switched LST's do not perform well on noisy lines, these lines tending to bias the apparatus into a receive mode and prevent, or severely clip, outgoing speech. If bad performance is complained of, check with the customer to determine if the line was noisy and, if possible, make a test call to confirm the fault. Poor acoustic room conditions will also degrade the performance of the unit.

There are two methods of operation as shown:-

                             METHOD 1                        METHOD 2

                    Used when connected to:-       Used when connected to:-
                    Plan extensions Nos. 2,1       Plan extensions Nos. 1,
                    2A and 105/107 (main)          1A, 4 and 105/107 (extn).
                    Keymasters 3 and 4.            Exclusive and shared
                    Extensions connected to        service exchange lines:-
                    2/... and 3/... switch-        switchboard extensions.

MAKING A CALL       Pick up the telephone          Pick up the telephone
                    handset and call the           handset and call the
                    desired number.                desired number.
                    Press the "on" key.   The      Press the "on" key. The
                    indicator will light  and      indicator will light and
                    remain illuminated             remain illuminated
                    except while the other         except while the other
                    party is speaking.             party is speaking.
                    The telephone handset          The telephone handset
                    will be disconnected but       will be disconnected and
                    must not be replaced on        may, if desired, be
                    its cradle.                    replaced on its cradle.
                    Adjust the loudspeaker         Adjust the loudspeaker
                    volume to the level you        volume to the level you
                    prefer.                        prefer.

ANSWERING A CALL    The call must be answered      Press the "on" key. The
                    normally be handset and        indicator will light and
                    then transferred to the        remain illuminated except
                    unit (see below).              while the other party is
                                                   Adjust the loudspeaker
                                                   volume to the level you

TRANSFERRING FROM   Press the "on" key. The        Press the "on" key. The
HANDSET TO UNIT     indicator will light and       indicator will light and
                    remain illuminated except      remain illuminated except
                    while the other party is       while the other party is
                    speaking.                      speaking.
                    The telephone handset          The telephone handset may,
                    will be disconnected but       if desired, be replaced
                    must not be replaced on        on its cradle.
                    its cradle.                    Adjust the loudspeaker
                    Adjust the loudspeaker         volume to the level you
                    volume to the level you        prefer.

TRANSFERRING FROM   Press the "off" key.           Lift the telephone handset
UNIT TO HANDSET     Continue your conversation     from its cradle and then
                    using the telephone            press the "off" key.
                    handset. Replacing the         Continue your conversation
                    handset will terminate         using the telephone handset.
                    the call.                      Replacing the handset will
                                                   terminate the call.

Wiring Diagram N4445

S1 B7902
JAN 1979


This circular describes the Sales and Engineering arrangements for the introduction of the Amplifier and Loudspeaker 11A.

The Amplifier and Loudspeaker 11A is an add-on unit which, when used in association with any handset telephone (except HTS/ITS) provides full, voice switched, loudspeaking telephone facilities.

The unit is mains powered and will be issued complete with transformer, the output of which is 18 volts ac.

Approximate physical dimensions are as follows:-

Amplifier and Loudspeaker 11A - 248 mm x 134 mm x 51 mm
Mains transformer - 128 mm x 64 mm x 44 mm

The controls consist of "on", "off" and "microphone mute" keys and a loudspeaker volume control. A red pilot lamp (LED) indicates the mode of operation.

The unit may be wall-mounted by attaching the mounting bracket supplied.
Cord lengths are:-
Amplifier and Loudspeaker 11A - line and power Cord 2 metres approximately
Mains transformer - mains lead 1.725 metres approximately.

The marketing name of the unit is the "DORIC Loudspeaking System". It was introduced on a market trial basis in Leicester Telephone Area during November 1978 to test market demand for the "add-on" concept, and for DORIC as an interim to the planned new generation of loudspeaking telephones (LST 8) which we propose to introduce in 1980/1. Early results of the market trial show good promise of a healthy demand for the product and a follow-on order is proposed. Meanwhile the publicity given DORIC in the market trial area has led to some overspill demand for the product. Sufficient stock is now available for this, and some further small unstimulated demand to be met nationally. It is, however, essential that the product is not publicised pending further supplies.

Requests for provision on service lines will be refused.

Leaflet PH 2436/78 is available for use pending the issue of a Descriptive Leaflet. Supplies will be issued direct to Regions by M2.3.1.3.

Normal advice note and sales application procedures apply. This item of apparatus is not suitable for inclusion in the Appointment Plan. The engineering term Amplifier and Loudspeaker 11A should not be used. On Advice Notes and acknowledgement letters the item must be described as DORIC.

Customers should be advised they will need to provide a 3 pin electrical socket outlet in close proximity to the proposed position of use and for the sole use of DORIC.

Made by Northern Telecom


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