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Benchmark PRE420

Instruction Manual

4-Channel Microphone Preamplifier/Mixer

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Summary of Contents for PRE420

Page 1: ...Benchmark PRE420 Instruction Manual 4 Channel Microphone Preamplifier Mixer...

Page 2: ...QUALIFIED TECHNICIAN SHOULD PERFORM REPAIRS Fuses CAUTION FOR CONTINUED FIRE HAZARD PROTECTION ALWAYS REPLACE THE FUSES WITH THE CORRECT SIZE AND TYPE 0 5A 250 V SLO BLO 5 X 20 MM LITTELFUSE HXP218 50...

Page 3: ...Headphone Performance 14 Mix Outputs 15 Driving Unbalanced Loads 15 Main Fader 15 LED Meters Mix Outputs 15 Rack Mounting 16 Mounting Near Other Equipment 16 Performance Graphs 17 Frequency Response...

Page 4: ...tputs have a switch that enables mute on headphone insertion The PRE420 includes the HPA2 Benchmark s signature high current 0 Ohm headphone amplifier The HPA2 is capable of delivering the full perfor...

Page 5: ...the PRE420 s performance specifications and sonic performance with any other mic preamp Microphone pre amplifier circuits usually suffer from non linear performance at ultra sonic frequencies This non...

Page 6: ...hone Input 60 dB Maximum First Stage Gain Adjustable to 70 dB 22 to 60 dB Gain pad off 2 to 40 dB pad on 27 dBu Maximum Input Level with pad 7 dBu without pad 29 5 dBu Maximum Output Level on all Bala...

Page 7: ...e The first generation of PRE420 s with five digit serial numbers featured a common mode choke for RF immunity These choke filters were designed for balanced microphone or balanced line level inputs W...

Page 8: ...ay be adjusted to other levels between 20 dBu and 29 dBu The red LED is driven by a peak detection and stretching circuit so that very short transients can be observed The red LED is a warning indicat...

Page 9: ...ISE AT THE MIXER OUTPUTS Blocking RF EMI and Noise The entire signal path of the PRE420 has a generously wide bandwidth 500 kHz This creates a significant demand for exceptional RF filtering and shiel...

Page 10: ...when a microphone is connected or disconnected while phantom power is on The worst possible transients occur when a microphone cable has an intermittent short to ground from either pin 2 or pin 3 The...

Page 11: ...ill be about 17 dB noisier than an input that is properly terminated The 20dB pad applies a 150 Ohm resistor across the inputs of the preamplifier Engaging the pad on an unused input terminates the pr...

Page 12: ...the Solo indicator will illuminate Stereo Mono Solo Switch Microphones may be monitored before the pan control mono or after the pan control stereo Press the Mono Stereo switch for stereo solo Stereo...

Page 13: ...SERTED PRESS THE REAR PANEL BUTTON TO ENABLE THE AUTO MUTE FUNCTION Driving Unbalanced Loads CAUTION ALWAYS LEAVE XLR PIN 3 FLOATING WHEN DRIVING UNBALANCED LOADS XLR to RCA Wiring 1 Connect XLR pin 2...

Page 14: ...These resistors are usually at least 30 Ohms and have a negative impact on performance A headphone amplifier with series resistors may measure very well when driving resistive loads However the same a...

Page 15: ...tion to XLR pin 3 Main Fader The main fader is located at the far right of the front panel This stereo fader has factory adjusted balance trim circuitry to provide accurate L R balance LED Meters Mix...

Page 16: ...below Benchmark DAC1 and ADC1 converters The Pre420 is well shielded but we cannot guarantee that unknown pieces of equipment will not cause interference if mounted too close to the PRE420 Follow the...

Page 17: ...1 0 8 0 6 0 4 0 2 0 0 2 0 4 0 6 0 8 1 1 2 1 4 1 6 1 8 2 2 2 2 4 2 6 2 8 d B r A 10 200k 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k Hz The above graph shows the frequency response of the PRE420 with...

Page 18: ...Thick Data Axis Comment 2 1 Red Solid 4 Anlr Level A Left HP Filter On 3 3 2 8 2 6 2 4 2 2 2 1 8 1 6 1 4 1 2 1 0 8 0 6 0 4 0 2 0 0 2 0 4 0 6 0 8 1 1 2 1 4 1 6 1 8 2 2 2 2 4 2 6 2 8 d B r A 10 200k 20...

Page 19: ...07 11 35 37 PRE420 Inter Channel Phase Response 1 1 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 d e g 10 100k 20 50 100 200 500 1k 2k 5k 10k 20k 50k Hz This graph shows...

Page 20: ...1 Red Solid 4 Anlr THD N Ratio Left 60 dB Gain top trace 2 1 Magenta Solid 4 Anlr THD N Ratio Left 50 dB Gain 3 1 Blue Solid 4 Anlr THD N Ratio Left 40 dB Gain 4 1 Green Solid 4 Anlr THD N Ratio Left...

Page 21: ...top trace 2 1 Magenta Solid 4 Anlr THD N Ratio Left 50 dB Gain 3 1 Blue Solid 4 Anlr THD N Ratio Left 40 dB Gain 4 1 Green Solid 4 Anlr THD N Ratio Left 30 dB Gain bottom trace 0 001 0 1 0 002 0 005...

Page 22: ...ion Manual rev E Page 22 Equivalent Input Noise vs Gain The above plot shows the Equivalent Input Noise EIN of the PRE420 as a function of gain Measurement bandwidth is 20 Hz to 20 kHz Input terminati...

Page 23: ...id 4 Fft Ch 1 Ampl Left 145 066 dBr A 149 014 dBr A 200 0 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 145 066 149 014 d B r A 10 30k 20 50 100 200 500 1k 2k 5k 10k 20k 59 6606 1...

Page 24: ...6 104 102 d B r A 150 100 148 146 144 142 140 138 136 134 132 130 128 126 124 122 120 118 116 114 112 110 108 106 104 102 111 404 122 747 d B r A 2k 20k 4k 6k 8k 10k 12k 14k 16k 18k 2 00513k 3 00537k...

Page 25: ...136 134 132 130 128 126 124 122 120 118 116 114 112 110 108 106 104 102 109 271 118 787 d B r A 2k 32k 4k 6k 8k 10k 12k 14k 16k 18k 20k 22k 24k 26k 28k 30k 20 022k 30 0293k Hz dx 10 0073kHz dy 9 515 d...

Page 26: ...off 7 dBu 4 8 dBV 1 7 Vrms Maximum Input Level pad on 27 dBu 24 8 dBV 17 4 Vrms Phantom Power 48V w individual switches High Pass rumble filter 40 Hz second order 12 dB octave Preamp Bandwidth 0 02 dB...

Page 27: ...Type Transformerless Voltage and Impedance Balanced Control Room and Main Outputs Number of Outputs 4 2 control room 2 main Connectors Gold Pin Neutrik male XLR with direct ground feature Output Impe...

Page 28: ...0024 HPA2 Headphone Amplifier Number of Outputs 1 Connector TRS with switch contacts Output Impedance 0 11 Ohms 10 Hz to 200 kHz Maximum Output Level at 0 001 THD N 23 5 dBu into 600 Ohms 0 24 W 19 5...

Page 29: ...modulated signal presence threshold 8 dBu full brightness at 24 dBu Red LED threshold 24 dBu adjustable includes peak responding pulse stretch circuit for viewing fast transients AC Power Requirement...

Page 30: ...nel 11 75 298 5 mm Overall depth including knobs and connectors but without power cord 12 625 321 mm Width excluding 19 rack ears 17 5 445 mm Height excluding removable feet 1 725 43 8 mm Weight PRE42...

Page 31: ...eparation between the equipment and receiver Connect the equipment into an outlet on a circuit different from that to which the receiver is connected Consult the dealer or an experienced radio TV tech...

Page 32: ...PRE420 Instruction Manual rev E Page 32 CE Certificate of Conformity...

Page 33: ...render this warranty void Any PRE420 returned from the European Union for warranty repair must have the required RoHS logo on the product label otherwise repairs will be billed at the normal shop rat...

Page 34: ...ange without notice For products purchased outside the US and Canada please refer to the Extended Two 2 Year International Warranty The Benchmark s Extended 2 Year International Warranty Benchmark Med...

Page 35: ...46 dBu if you wish to set maximum gain to 70 dB or 26 dBu if you wish to set maximum gain to 50 dB 6 Connect tone generator to microphone 1 input 7 Connect audio level meter to channel 1 direct outpu...

Page 36: ...t maximum gain fully clockwise 29 Set audio tone generator to 1 kHz with an output level of 36 dBu or level used in step 3 30 Connect tone generator to microphone 1 input 31 Connect audio level meters...

Page 37: ...n Manual rev E Page 37 Copyright 2007 Benchmark Media Systems Inc All rights reserved Benchmark Media Systems Inc 203 Hampton Place Ste 2 Syracuse NY 13206 USA 1 315 437 6300 FAX 1 315 437 8119 www be...

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