TDA6812-5

The dematrixing and switching of multichannel TV-sound signals of TDA6812-5 are performed in the matrix and switch section by the dual-carrier method. Crosstalk compensation is on the sound 1 input. The compensation stage has a range of ± 3 dB with a smallest increment of 0.2 dB, and gain can also be switched between 0 and 6 dB. In addition to the two inputs for the demodulated sound carriers, there are three dual-channel SCART-inputs. The two matrix AF-inputs of TDA6812-5 can be bypassed internally so that decoded stereo signals of other systems (NICAM) can also be processed. The switch section terminates in the SCART-output and signal paths for the loudspeaker and headphones outputs. AF-inputs can be randomly switched to AF-outputs (8-6 matrix).

In the loudpeaker signal path of TDA6812-5 there is an inital volume control with a range of 0/ 15 dB and an increment of 1.25 dB. In conjunction with the main volume control tha follows the tone control, very high overdriving immunity is ensured. The switchable quasi-stereo section that follows produces a stereo listening effect for mono signals through a 180 ^oC phase shift at mid-range frequencies (approx. 1 kHz) in one channel. The following bass control of TDA6812-5 has an increment of 3 dB in its setting range of + 15/ 12 dB. The cut-off frequency for each channel is set by an external capacitor. The circuit for enlarging the stereo sound base can be cut in for stereo signals to make the aural impression even more stereo-like by frequency-dependent antiphase crosstalk of 55 %. This works with the same cut-off frequency as the bass control, but the function is largely independent. The treble control, whose cut-off frequency is also set by an external capacitor, likewise has an increment of 3 dB in a setting range of ± 12 dB. The main value control  with maximum gain of 10 dB, which can be adjusted separately for L and R, terminates the loudspeaker signal path. 57 steps with an increment of 1.25 dB mean a setting range of 71.25 dB. Functions like balance or loudness are implemented by software setting of the appropriate tone and volume controls. In the tonecontrol section there is a clipping detector that can be read on the I²C Bus TDA6812-5 and enables automatic volume correction by the controller. After each reading the clipping bit is reset, which enables a renewed check for clipping with each I2C Bus read operation.

The headphones signal path of TDA6812-5 includes a volume control with joint L/R-setting. 32 increments of 2 dB produce a range of 62 dB (31 x 2 dB = 62 dB).