Harman Kardon A310 Owners Manual - Page 3

fSUTPUT Two receptacles, marked "Output" will be found at the rear of the chassis. For your convenience in connecting to the amplifier, a 36" shielded cable will be found in the Theme package. Plug one end of this cable into either one of the two output receptacles, and the other end into the appropriate amplifier input receptacle. Since the output circuit of the Theme includes a cathode-follower, this cable may be extended to any reasonable length without deterioration of tone quality. The second output receptacle may be similarly connected to a tape recorder, to provide program material unaffected by the tone and volume controls of the amplifier. VENTILATION All electrical equipment generates heat which must be allowed to escape. Although the Theme is well ventilated in itself, sufficient space should be allowed around it to permit free air flow. If it is placed in a bookcase, it should be located well toward the front, to provide as much clearance as possible at the rear. Do not put books or other objects on top of the Theme. Covering the perforated tube grill will reduce the ventilation and result in sharply reduced component and tube life. OPERATION CONTROLS The Harman-Kardon Theme has only two operating controls. The Function Switch (at the left) serves to turn the power off in its extreme counterclockwise position. In any other position the power is turned on. This switch also selects among AM reception, FM reception with AFC and FM without AFC. The Tuning Knob (at the right) is used to tune to the desired station. TUNING METER The Theme tuning meter operates both on the AM and FM bands in a similar manner. When the receiver is tuned completely off any station, the meter will point to the left end of the indicator scale. As you tune through a station the meter will swing to the right a maximum and to the left again, returning to the initial position as you tune away from the station. Proper tuning exists when the meter points to a maximum. Note that the pointer will show a small excursion on a weak signal and a correspondingly larger excursion on a stronger signal. The meter thus can be used as a relative field strength indicator helping you to evaluate reception from different stations and to optimize your antenna system for best reception. AUTOMATIC FREQUENCY CONTROL (AFC) FM Broadcasting, by its very nature, eliminates almost all natural and man-made static. However, the characteristics of FM which make this possible also make for problems in tuning. The Harman-Kardon Theme incorporates an effective Automatic Frequency Control (AFC) circuit that overcomes these problems and insures proper tuning even if the manual tuning is not accurately done. The following experiment will lead to an understanding of AFC, and the fuller enjoyment of the Theme. Note that the function selector switch has four positions. The position marked "FM-AFC" should be selected whenever you wish to tune with the assistance of AFC. Should you wish to disable the AFC circuit fully, however, select the position marked "FM. " In this position the AFC circuitry is eliminated. Tune across the FM scale with the function switch in the FM-AFC position. Note how the stations "pop" into place and how the tuning meter pointer simultaneously indicates near-optimum tuning of each station by a rapid deflection to a maximum position. Now tune to any station, preferably one with a musical program. Defeat the AFC by turning the function switch to the FM position, and tune slowly through the station from left to right. Notice that there are three points where the station sounds clean, interspersed with points of distorted sound. The middle clean-sounding point is the proper tuning position for the best tone quality with minimum noise and interference. This should correspond with the maximum deflection of the tuning meter. Detune the station so that the tuning meter returns to near its minimum position and the sound is distorted. Turn the function switch to FMAFC, and notice how the sound clears up and the meter shows near optimum tuning again. Actually, the tuning has been readjusted by the operation of the AFC circuit, which automatically retunes the electronic circuits to the center of the station channel. The AFC circuit of the Harman-Kardon Theme performs the further function of overcoming any tendency of the tuner to drift. In order to take maximum advantage of the benefits of AFC, it is suggested that fine tuning be done with the function switch in the FM position. When the switch is then turned to the FM-AFC position the AFC will improve this careful tuning by a factor of 10 to 1. This procedure is especially recommended in those cases where a weak station is found close to a strong station. Under these conditions, the AFC may tend to reach for the strong station, and completely skip over the weak station. If the weak station is tuned with the AFC defeated, the AFC will lock it in, after it has been reinserted. MAINTENANCE AND REPAIR In some installations, hum may be encountered due to a voltage difference between the amplifier, tuner and record changer chassis. This may be eliminated