M402

MATCHED GAIN: 38db FREQUENCY RESPONSE tO.bdb from 2Ohz to 2OKhz (effects controls at zero position) EQUIVALENT INPUT NOISE -115dbm (1Ohz to 1OOKhz bandwidth) HARMONIC DISTORTION Less than 0.5% from 3Ohz to 2OKhz (Measured at +18dbm output level) SOURCE IMPEDANCE 150/600 ohms balanced or unbalanced INPUT IMPEDANCE 150/600 ohms + 10% INPUT LEVEL -38db nominal, ~2Odb maximum LOAD IMPEDANCE 600 hms OUTPUT IMPEDANCE 600 ohms (150 ohms available) + 10% OUTPUT LEVEL +18dbm maximum PHASING The low terminal number of the input pair and the low terminal number of the output pair are in phase.

EQUALIZING CHARACTERISTICS In accordance with specified curves within # 0.Sdb POWER RE QUIREMENTS 48 volts dc, regulated from M848 or equivalent. 65mA AMBIENT TEMPERATURE 0 to 60%c DIMENSIONS 1.58W X 6.6251X 6D (depth below panel) inches WEIGHT : 12 lbs Net

Refer to schematic diagram 402-02-001 The M402 has three main active circuit sections low noise preamplifier, equalizer networks and output amplifier The equalizer section has Unity gain and is switched in and out between the preamplifier and output amplifier via switch SW6 _ With SW6 selected to the "out" position the preamplifier is connected directly to the output amplifier and the equalizer functions as conventional amplifier with flat response characteristics _ The input signal is applied to the preamplifier via the 14 pin connector and transformer T1 The input may be connected on the mating plug to operate from 150 or 600 ohm source impedances.

The Signal is applied to common emitter amplifier_ Q1 base Via T1 secondary. Q1 is direct coupled to emitter follower Q2. R4 and R5 set the gain of the preamplifier and introduce negative feedback through T1 secondary C5 is the preamplifier output coupling capacitor and connects to terminal B of the equalizer 14 pin connector SW6 is interconnected between the preamplifier and output amplifier Via terminals E and J This arrangement allows the use of a remote or external insert switch which may be connected using shielded cable of Up to 24 inches in length _ Thus, the equalizer insert function may be grouped with other illuminated assignment pushbuttons incorporated within custom mixing consoles_ Terminal M is the input to the integrated circuit balanced output amplifier R9O through R93 and C34 through C36 form compensation network to limit the response outside the audio spectrum C37 is the coupling capacitor to the non-inverting and inverting input to 23 and Z4 respectively.

C48 and C49 couple the actively balanced audio output from Z3 and 24 and present a +24dbm capability output Via terminals P and R balanced to ground The equalizer section is interposed Via SW6. Capacitor C6 couples the signal from SW6 to the input of the equalizer section. C6 in conjunction with resistors R1?2 through R17 form 6db/octave high pass filter Attenuation i5 achieved in 8db steps producing 3,6,9,12 and 1Sdb positions at 1OOhz_

The M402 is designed to mount directly on mixing console front panel_ The dimensia s are such that the unit may be mounted in line with a standard straight line mixing attenuator associated with each mixing channel_ cutout 1.56W X 6L and two tapped holes will be required as shown in drawing 402-08-001 The escutcheon of the M402 will overlap the cutout and holes.

External connections are made to the 14 pin female mating connector in accordance with drawing 402-09-001 and Table 1, For optimum results_ use insulated, shielded twisted pairs for both input and output wiring. The optional external insert switch should be wired with shielded twisted pairs and located not more than 24 inches from the module. Dress all audio cables apart from ac and power supply wiring.

Ground shields at one end only and use separate ground return wire to the system common ground for the power supply and shields as shown in the System Wiring Diagram 404-09-002 The metal frame of the M402 equalizer should be bonded to the system ground. In this case it is permissible to loop through each unit with a common ground wire connected via pin "N" When used in system, such as an audio mixing console, the M402 equalizer should be operated from a separate power supply than the ones used to provide dc power to program amplifiers, cue amplifiers or other similar units operating at high output levels _ The latter units produce large current swings and the possibility of instability, noise or crosstalk should be avoided in systems which combine high gain and wide-band amplifiers

The M402 has three groups of concentric controls to be used throughout the operation of the unit. These transient-free controls may be pre-set or adjusted during the operation of the unit. With the exception of the Mid- Low-Frequency boost and Presence Boost (these functions share five positions each side of a common selector switch) all functions are cumulative and may be used in combination to achieve multiple or combined effects Upper Concentric Group Inner (small) knob: 6OIN/6OOUT.

This knob i5 a two position selector and is used to insert the GOhz notch filter. Turning the knob CW places the filter in the circuit and the white dot on the knob aligns with the 60 IN position_ Outer (large) knob: HF The high frequency knob provides 15Khz boost in the CW positions and 1OKhz cut in the CCW positions_ Centre Concentric Group Inner (small) knob: .7 , 1.4 , 2.5 , 3.4 , 5 .

This knob determines the presence frequency and operates in conjunction with the CCW five positions of tne PRES switch. Outer (large) knob: MLF = PRES. This knob produces two effects (separately). In the CW positions and to the right of 0 a Mid-Low- Frequency platform is produced below 1OOhz and in a shelf of 2db increments. In the CCW positions and to the left of 0 the degree of Presence is established.

This works in conjunction with the frequency selector (inner small knob) The frequency is determined by the inner knob and the amount of boost, at the selected frequency , is determined by the outer knob (1Odb max. )

The M402 is designed for dependable, trouble- free service; however as with all high quality electronic equipment, regular schedule of inspection should be established. Any accumulation of dust should be periodically removed with a soft brush and a vacuum hose To gain access to the component boards and switch decks it is necessary to remove the metal side cover which is to the left side of the etched escutcheon_ This is accomplished by removing the two 2-56 flat-head screws on the left side of the M402 escutcheon and the two 4-40 round-head screws located on the bottom of tke unit.

Do not loosen the 4-40 screw immediately adjacent to the M402 connector; this secures the frame ground lug internal to the equalizer The PC boards may be examined by placing the equalizer on a flat work area with the cover removed, the connector positioned to the left and with the control knobs positioned away from the inspector_ The amplifier and equalizer boards are located in position by retaining grooves fabricated from aluminum tabs spot welded to the equalizer case _ Both PC boards may be extended by the length of the cable assembly by gently lifting the boards alternately out of the retaining grooves The boards may be supported by moving each assembly over to the right and temporarily resting the edge of the PC board on the metal enclosure_ Care should be exercised to prevent damage to the interconnecting cable assemblies and upon reassembly, the flexible wires should be channeled Under the PC board notch-outs to prevent crimping