GB429987A - Improvements in or relating to sound recording and reproduction devices - Google Patents

Abstract

429,987. Telegraphones. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. Dec. 17, 1934, No. 36166. Convention date, Dec. 23, 1933. [Class 40 (ii)] Leakage is reduced to a minimum in a magnetic sound recording or reproducing head by employ. ing a laminated sheet iron or compressed iron powder ring-shaped core 4 having an air gap 3 filled with insulating material, the core being surrounded by an audio current winding 5 which may also be supplied with direct current to bring the working point to a favourable position on the hysteresis loop. For cancelling and premagnetizing, a ring shaped permanent magnet 1 having an air gap 3 may also be provided as shown. According to a modification, Fig. 3, (not shown), a ring-shaped magnet may be provided on the other side of the carrier 2 and opposite the core 4 in which case the D.C. in winding 5 serves only for accurately regulating the working point determined by such magnet. Alternatively, the magnet may be provided with an adjustable magnetic shunt in which case no direct current is supplied to winding 5. If desired, a separate core carrying the D.C. winding may be arranged on the other side of the carrier opposite core 4, Fig. 2, (not shown). According to further modifications, the core is surrounded by a screen of magnetic material, preferably a highly permeable substance, Fig. 4, (not shown), or the winding 5 may be arranged on the side of the core at which the carrier runs on, Fig. 5, (not shown).