THE MICHAEL TODD COMPANY, INC.
ENGINEERING BULLETIN #5
70 VOLT LINE
The 70 volt line system is the recommended method of connecting surround sound (effects) speakers where a low level speaker system is desired. It possesses the following advantages:
(1) Freedom from complication in determining impedance matching values for multiple speakers in series, parallel and series - parallel circuits.
(2) It permits all speakers to carry varying amounts of wattage as required by their location and rating without pads or volume controls.
(3) Permits low cost interwiring in concealed auditorium areas using 2-conductor #18-#16 shielded rubber covered microphone cable.
(A) In amplifiers having a 70 volt line output, each speaker shall be supplied with a 70 volt transformer. The transformer is connected as shown in Figure "A". (See drawing #E - 5.)
(B) In amplifiers not having a 70 volt line output, a special 70 volt line transformer must be provided. The primary shall match the constant impedance output of the amplifier and the secondary shall be of the rated wattage of the amplifier. It is connected as shown in Figure "B".
(C) All transformers shall have a frequency response of +/- 1 dB 30-10,000 CPS and shall have a minimum insertion loss of 0 - .5 dB with nominal loads. The Delivered Power shall be within 1 dB of the Rated Power over the entire frequency range.
SOURCE OF SUPPLY FOR 70 VOLT LINE TRANSFORMERS
If these transformers cannot be secured locally, contact The Michael Todd Company, Inc.'s Engineering Department in New York. Transformers to modify power amplifiers for the 70 Volt System are available in: 20, 30, 50, 60, 75, 90, and 120 Watt ratings. 70 Volt speaker matching transformers are available in ratings from 0.25 -15 Watts.
ISSUE 3 – 8-12-57