M909 — Custom Meter

M909 METER/MIX MINUS MODULE

Please refer to module layout drawing A 909-04-002.

1) Legend Strips

Two plastic covered designation strips for identification of the selector functions for the mono and stereo meter selectors.

2) Mono Meter Selector

Momentary switches SW7 through SW12 control the active solid-state switches for source selection to the mono meter. 3) Auxiliary Stereo Selector

Momentary switches SW1 through SW6 control the active solid-state switches for source selection to the left and right auxiliary meters. Meter Amplifiers

Main Meter Amplifier

Two identical meter amplifiers are employed for the main metering in the console. They consist of U28 and U29 and associated components for the left and right meters.

Dual operational amplifier U28 forms the nucleus of a balanced input/balanced output variable sensitivity buffer. Capacitors C74 and C75 prevent external bias from disturbing the meter circuit, while C82 and C83 protect the meter from any offset error present in U28. Trim control R129 is normally factory set to provide a 0 VU indication on the console meters at the specified system levels. Resistor R135 ensures the output impedance of the meter amplifier matches the VU standard (ANSI C16.5-1954).

Mono and Auxiliary Meter Selectors

The mono and auxiliary meters have six input sources, of which only one may be selected at a time. Referring to the schematic on sheet B909-02-002/2, each input is AC coupled to a separate 74HC4053 solid state switch. The outputs of the switches for the mono meter are all connected to the balanced summing amplifier U13. R46, R48 and R52 make up the `T' feedback for U13A with potentiometer R52 providing the gain adjustment for the mono meter output.

The left and right haves of the auxiliary stereo meter selector are identical to the mono meter selector.

Meter Select Logic

Refer to the schematic on sheet B909-02-002/1. The 74HC4053 switches are controlled by logic chips U1 through U6. Since both the mono and auxiliary stereo logic circuits are identical, only the mono meter selector will be described.

Microcontroller U1 reads the switches SW7 through SW12, which are software debounced, and outputs a 3 bit binary code for the depressed switch with the highest precedence.

The clock rate for U1 is set by the RC time constant of R11 and C7. U1 also requires a power on reset signal and this is provided by R17 and C5.

The tally LEDs for switches SW7 through SW12 are controlled by U4, a CD4051 8 channel analog multiplexer. The three bit binary code from U1 determines which channel of U4 is turned "ON". Current flows through current limiting resistor R19 and through the "ON" channel of U4 to the appropriate LED.

Grounding the control line on pins 9, 10 & 11 of the 74HC4053 will connect the associated input to the summing amplifier. The 8 channel analog multiplexer U3 operates in manner similar to U4 except that the "ON" channel of U3 grounds one of the control lines to the 74HC4053 switches. The remaining control lines are pulled up by R18, which turns off the remaining 74HC4053 switches for the mono selector. Mix Minus

Refer to the schematic on sheet B909-02-002/3.

The mix minus portion of the M909 consists of U30 through U34 and associated components. The telephone input is configured as a simple differential input amplifier whose signal is summed with all four mix minus outputs. The mix minus inputs are configured so that the like numbered output does not receive the associated input.

Each mix minus output is electronically balanced for direct coupling to a bridging output load. Power Supply Decoupling

The active decoupling network consisting of Q1 through Q5 and associated components regulates the incoming power for use in the module. Diodes CR1 and CR2 prevent module damage in the event of power supply voltage reversal. The decoupling network drops the ±23 volts down to a nominal ±18 volts. Transistor Q3 further decouples the ±18 volts down to +5 volts for use by the CMOS logic circuitry.

C1 Capacitor 22 uF/25 V Siemens 85200 C2 " 22 uF/25 V " " C3 " 22 uF/25 V " " C4 " 22 uF/25 V " " C5 " 22 uF/25 V " "

C6 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C7 " 330 pF Philips 638-03331 C8 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C9 " 330 pF Philips 638-03331 C10 To C21 " 6.8 uF/16 V ITT 6.8M16

C22 " 220 uF/10 V " 220M010 C23 " 220 uF/10V " " C24 " 47 pF Philips 638-34479 C25 " 47 pF " " C26 " 22 uF/35 V ITT 22M35

C27 To C38 " 6.8 uF/16 V ITT 6.8M16 C39 " 220 uF/10 V " 220M010 C40 " 220 uF/10V " " C41 " 47 pF Philips 638-34479 C42 " 47 pF " "

C43 " 22 uF/35 V ITT 22M35 C44 To C55 " 6.8 uF/16 V ITT 6.8M16 C56 " 220 uF/10 V " 220M010 C57 " 220 uF/10V " " C58 " 47 pF Philips 638-34479

C59 " 47 pF " " C60 " 22 uF/35 V ITT 22M35 C61 To C73 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C74 " 6.8 uF/16 V ITT 6.8M16 C75 " 6.8 uF/16 V " "

C76 " SOT C77 " SOT C78 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C79 " 0.1 uF/100 V " " C80 " 47 pF Philips 638-34479

C81 " 47 pF " " C82 " 10 uF/25 V ITT 10M25 C83 " 10 uF/25 V " " C84 " 6.8 uF/16 V ITT 6.8M16 C85 " 6.8 uF/16 V " "

C86 Capacitor SOT C87 " SOT C88 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C89 " 0.1 uF/100 V C90 " 47 pF Philips 638-34479

C91 " 47 pF " " C92 " 10 uF/25 V ITT 10M25 C93 " 10 uF/25 V " " C94 " 10 uF/25 V " " C95 " 10 uF/25 V " "

C96 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C97 " 0.1 uF/100 V C98 " 82 pF Philips 638-58829 C99 " 22 pF " 638-10229 C100 " 33 uF/16 V ITT 33M16

C101 " 10 uF/25 V " 10M25 C102 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C103 " 0.1 uF/100 V " " C104 " 82 pF Philips 638-58829 C105 " 10 uF/25 V ITT 10M25

C106 " 82 pF Philips 638-58829 C107 " 10 uF/25 V ITT 10M25 C108 " 0.1 uF/100 V Sprague K104K20X7RFVBWN C109 " 0.1 uF/100 V " " C110 " 82 pF Philips 638-58829

C111 " 10 uF/25 V ITT 10M25 C112 " 82 pF Philips 638-58829 C113

M909 METER/MIX MINUS MODULE

Meter Section

Input Sensitivity: 0 to +4 dBu (for +4 dBu output).

Frequency Response: ±0.1 dB 20 Hz to 15 kHz.

Noise: Greater than 80 dB below unity gain +4 dBu output.

Harmonic Distortion: Less than 0.05% from 20 Hz to 15 kHz.

Input Impedance: Greater than 15K, balanced.

Source Impedance: 600 ohms or less, balanced.

Output Impedance: 3600 ohms.

Channel Separation: 65 dB.

Mix Minus Section:

Frequency Response: ±1 dB 20 Hz to 20 kHz.

Noise: Greater than 80 dB below an operating level of +4 dBu.

Harmonic Distortion: Less than 0.05%.

Source Impedance: 600 ohms or less.

Input Impedance: 15,000 ohms unbalanced.

Output impedance: 60 ohms or less, balanced.

Load Impedance: 600 ohms or greater, balanced.

Crosstalk: 65 dB or greater, 20 Hz to 20 kHz. (Mix minus input to mix minus output)

Overall Specifications

Power Requirements: ±23 volts DC, 100 mA.

Ambient Temperature: 0 to 50 degrees Celsius.

Dimensions: 1.5" wide x 16.2" high x 6.6" deep. (38mm x 410mm x 168mm).

Weight: 525 grams (19 ounces).

GENERAL

M909 METER/MIX MINUS MODULE

The M909 Meter/Mix Minus module provides source selection and buffering for the meters in the console system. In addition, the module can generate up to four mix-minus outputs from the console.

Five meter buffers are included in the module. Two of these are permanently assigned to monitor a stereo program feed; normally console Program 1. One meter has a six button pre-selector associated with it. The remaining two buffers have an additional six button pre-selector for utilization as a auxiliary stereo metering system. All meter inputs are actively balanced. All audio is selected through solid-state logic controlled switches.

Mix minus feeds are generated in the M909 too. To use the mix minus outputs, the mix minus buss in the console is assigned to all input channels except the telephones. The mix minus output from the M907 is connected to the balanced telephone input of the M909. Each telephone input module's post fader direct output (M901) is brought to the M909 individually. The appropriate mix minus feeds are generated internal to the M909 for use by up to four telephone hybrids. OPERATIONAL