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
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:-
- 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.
- On Key (Colour Green).
- 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
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
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
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
INTRODUCTION OF THE AMPLIFIER AND LOUDSPEAKER 11A "DORIC"
This circular describes the Sales and Engineering arrangements for the introduction of the
Amplifier and Loudspeaker 11A.
DESCRIPTION AND FIELD OF USE
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
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
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 M184.108.40.206.
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