User manual MCINTOSH MAC4275

[. . . ] LOW NOISE ION-IMPLANTED J-FET OP-AMPS 16. The IF filters are permanently sealed and never require adjustment. The IF response curve is extremely selective because of its very steep slope either side of center and yet it has a linear phase characteristic. AUTOMATIC FREQUENCY LOCK New technology low noise operational amplifiers give lower noise and greater bandwidth than conventional devices. 13. ELECTRONIC ACTIVE FILTER ELEMENTS "Active filter" technology is used to generate Perfect FM tuning is assured by holding off the tuning lock signal until manual tuning reaches the center of the FM carrier. WIDE RANGE SIGNAL STRENGTH METER The signal strength meter pointer responds all the way from 1 microvolt of antenna noise pickup to over 50, 000 microvolts of signal strength. [. . . ] FM MULTIPLEX THIRD GENERATION PLL CIRCUIT Tri-level electronic switching in the multiplex decorder gives better separation, lower distortion, and superior SCA rejection. No inductors required, minimizing drift; Integral lamp driving capability to indicate presence of a 19 kc pilot carrier; Excellent channel separation over the entire audio frequency range; Extremely low distortion; Low output impedance; Transient free mono/stereo switching. 20. MULTIPLEX PILOT AND CARRIER SUPPRESSION CIRCUIT 21. 22. 23. 24. The 19 kHz pilot and 38 kHz carrier are removed from the output thereby eliminating the possibility of introducing these undesirable signals to the tape recorder input. "AUTO-ON" AC OUTLETS Power to the entire stereo system can be controlled from either the front panel power switch or the power switch on a system turntable. SWITCHED AC OUTLETS AC outlets are provided for accessory equipment that turn on and off with your receiver. "LED" FUNCTION INDICATORS System status is indicated by long life "LED" indicators. TURN-ON TRANSIENT ELIMINATION CIRCUITS Speaker outputs are connected only after power supplies and circuits have stabilized eliminating turn on thumps or clicks. TECHNICAL HIGHLIGHTS The phono amplifier uses a new high technology integrated circuit operational amplifier. Its differential input stage has been optimized for low noise and low distortion performance. With high open loop gain a large amount of negative feedback can be used around the phono amplifier to further reduce noise and distortion. The feedback network also provides precision RIAA frequency compensation. To achieve low noise performance it is essential that the feedback network be very low impedance. As a consequence, the preamplifier must be capable of operating as a power amplifier to drive this impedance. This eliminates frequency translation and detection of interference from the sidebands of adjacent stations since the third harmonic of the sub-carrier (114 kHz) is excluded and interference from SCA broadcasts since the third harmonic of the pilot tone (57 kHz) is excluded. Unwanted spurious audible components and phase jitter in the PLL with consequent intermodulation distortion are inherently eliminated by this technique. Additional advantages of the phase locked loop stereo demodulation are the elimination of inductors to minimize drift, integral lamp driving capability to indicate the presence of the 19 kHz pilot carrier, excellent channel separation over the entire audio frequency range, extremely low distortion, low output impedance, and transient-free mono/stereo switching. After multiplex detection, 19 kHz pilot and 38 kHz carrier suppression circuits are used to prevent tape recorder interference. It operates both by detecting ultrasonic noise and by sensing correct tuning of the detector circuit. To 'un-mute' it is necessary for the signal to have an adequate signal-to-noise ratio and to be tuned to the center of the FM carrier. The MUTING circuit can be activated or defeated by the front panel muting pushbutton. The switching on and off of the audio signal is done with FET analog switches. FM Stereo Multiplex Section Input Selector Switching Equalizer Amplifier Power Guard Amplifiers are capable of delivering large quantities of power when they are driven to clipping. Clipping is caused when the amplifier is asked to produce more power output than it can deliver with low distortion. The extra energy content of the clipped signal will damage most loudspeakers, particularly the delicate high frequency tweeters. A new Mclntosh advancement helps protect your speakers from this kind of damage. [. . . ] A new Mclntosh advancement helps protect your speakers from this kind of damage. The MAC 4100 has a built-in waveform comparator that compares the wave shape of the input signal with the output signal. If the disparity between the two signals exceeds 0. 5% (equivalent to 0. 5% total harmonic distortion) a front panel signal illuminates in red at the top of the power output indicators. With any further increase in distortion the POWER GUARD circuit will operate. [. . . ]