GB1425519A - Stereophonic signal reproducing apparatus - Google Patents

Abstract

1425519 Stereophonic sound reproduction SONY CORP 11 Oct 1973 [13 Oct 1972] 47559/73 Heading H4R In a stereophonic sound reproducing system antiphase difference signals L-R, R-L are fed to left and right loud-speakers respectively, a sum signal L+R to a centre loud-speaker, and normal left and right signals L, R are made available by a matrix at auxiliary output terminals (e.g. for headphone connection), the difference signals being bass-boosted and treblecut in relation to the sum signal by a circuit which may be disconnected, e.g. when headphones are connected to the auxiliary terminals. The arrangement enhances stereophonic separation from closely spaced loud-speakers and reverts to normal stereophony for headphone listening. As shown, L-R signal at input 11 is amplified 3b frequency-adjusted 10 and fed 3c, 13 to left and right speakers SPL and SPR connected in parallel and in antiphase by a polarity inverter 16 for in-phase reproduction of monophonic signals. An L+R signal at input 12 is amplified 4b without frequency adjustment and fed to centre loud-speaker SPM. Insertion of a stereo headphone jack in socket J changes-over the switch contacts to disconnect all three loud-speakers from transformers 13, 14, connect attenuated L, R signals dematrixed by resistors R 10 -R 13 to contacts t 2 , t 3 , and insert circuit 20 or 20<SP>1</SP> in the emitter circuit of preamplifier transistor Q 1 to cancel the frequency adjustment of circuit 10. Alternatively the circuit 10 may be switched out in the socket J. The original sum and difference signals may be derived from disc or tape records or radio broadcast. The bass boost has a maximum between 200 and 400 Hz and the levels of the sum and difference signals coincide at 3-6 kHz, typically 4 kHz.