Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 38
Sound Retrieval System ( SRS )
In the current range of models fitted with the CA10 chassis there is the option of three different types of
sound output. These are mono, stereo ( NICAM or AV ) ans SRS ( Sound Retrieval System ). Dolby Pro-
logic models are provided in the previous chassis range in the 59CSD8H and 66CSD8H which will
continue to be produced alongside the CA10 models.
Normal stereo sound requires the listener to sit in the correct position to obtain the best advantage from
the loudspeakers and that there is no apparent surround effect, i.e. no sound comes from behind the
listener. Because of these shortcomings the SRS system was developed.
SRS changes the characteristics of the audio signal coming from the two stereo loudspeakers to give the
effect of sound coming from a number of different directions at the same time. This is achieved by the
use of phase shifting the signal and adding or reducing delays at certain frequencies. The overall effect
is to give the signal a ‘surround’ feel. This is similar to the ‘stereo wide’ effect, but includes a depth that
allows the listener to believe that the sound is coming from the sides as well.
As the SRS encoding process acts upon a conventional stereo signal, it is not necessary to encode the
audio as with Dolby Pro Logic. Therefore this system will work with any stereo input, i.e. off air NICAM
signal, from a stereo ( Hi Fi ) VCR or even a audio input via one of the SCART sockets.
Headphone driver stage
As the headphone volume can be controlled separately to that of the main loudspeaker output, i.e. it is
possible to listen on headphones at a different sound level than that coming out of the loudspeakers, it
is necessary to have a separate amplifier and control stage for the headphone socket. This is shown in
the diagram below.
Figure 36 : Headphone Amplifier Circuit
The headphone amplifier is a conventional linear device that is supplied from the +18V supply off the
chopper stage, it does not drawn enough current to justify a class D amplifier stage as is utilised in the
speaker output circuit. Nominal headphone impedance is recommended to be 32 Ohms.