Aphex 1788A Instruction Manual
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Aphex 1788A Instruction Manual

Microphone preamplifier
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Manual
IMPORTANT NOTICE
This manual contains valuable information you will
need to install and use the 1788A.
A separate remote control manual has been
created to deal with remotely controlling the 1788A,
use of the PC and Mac software, and use of the
1788A-R dedicated hardware remote control unit.
Please be sure to maintain a copy of that manual
together with this one.
P/N 999-4320 Revision 1 Released 05/12/2005
Manufactured by
Aphex Systems Ltd.
11068 Randall St.
Sun Valley, CA 91352 USA
S Y S T E M S
Copyright 2005 Aphex Systems Ltd. All rights reserved.
Produced by: Donn Werrbach. Creation tool: Adobe InDesign 2.0. Printed by: Stuart F. Cooper Co., Los Angeles.

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  • Page 1 This manual contains valuable information you will need to install and use the 1788A. A separate remote control manual has been created to deal with remotely controlling the 1788A, use of the PC and Mac software, and use of the 1788A-R dedicated hardware remote control unit.
  • Page 2 Additional years of use of the original Model 1788A in some of the most critical audio applications resulted in the significant improvements that are embodied in the 1788A.

  • Page 3: Table Of Contents

    3.6 OUTPUT CONNECTORS — 11 3.7 INPUT TRANSFORMER MODE — 12 3.8 MIDI CONNECTIONS — 12 3.9 COM PORT — 13 3.10 INSTALLING NEW FIRMWARE INTO THE 1788A — 13 3.11 AUX OUTPUT POST/PRE MODE SETTING — 13 4. FUNCTIONS IN DETAIL – 15 4.1 LOCAL BLOCK —...

  • Page 4: Introduction

    LAN ports are provided. Anything producing MIDI such as a light controller board, a show control system, a sequencer, a DAW, a MIDI controller, or a keyboard can act as the 1788A’s controller. The Ethernet connection facilitates high speed remote control networking of a constellation of 1788A’s.

  • Page 5: Simplified Block Diagram

    The whole eight channel array of preamp functions can be stored to presets and recalled. You can reconfigure a single 1788A or a very large array of them just by recalling a preset. This works out great when you need to re-set mics by the scene or act, or to get fast setups at new venues.

  • Page 6: Quick Start

    AUX OUT, and the Channel, Device, and 16. REMOTE ACTIVITY LED indicates the Net numbers in the Status Readout Display. For 1788A is receiving control data from a remote secondary control it sets the display brightness. device. 5. GAIN SELECT button determines the 17.

  • Page 7: Rear Panel

    DA-88 or compatible input. 2. MIDI CONNECTORS: provided for controlling the Model 1788A remotely. 9. BNC Clock I/O: syncs the Model 1788A to an external clock source (word clock or super-clock) 3. LAN CONNECTOR: for standard CAT5 and links multiple 1788A’s to the same clock.

  • Page 8: Getting Up & Running

    MICROPHONE PREAMPLIFIER 2.3 GETTING UP & RUNNING Here’s a step by step instruction on using the 1788A. Please plug a microphone into Channel 1 and connect the CH1 Main Output to a mixer or recorder input. Turn all units on.
  • Page 9 If you don’t know the MIL of your input, then use your mixer or recorder’s meters to indicate full scale input. Simply adjust the 1788A’s Main Output Gain to get just under a full scale reading. When done, tap the TONE button to kill it.

  • Page 10: Rear Panel View

    One of the best ways to know if you have adequate ventilation for a stack of 1788A’s is to feel if the top unit’s chassis is substantially hotter then the bottom unit. If so, you should provide better ventilation.

  • Page 11: Microphone Input

    3. INSTALLATION Ground Loops Ground loops hardly ever cause problems within the 1788A since it was designed with high immunity. However, other equipment connected to the 1788A may experience hum and noise from a ground loop. Ground loops can occur when various interconnected equipment is powered from separate AC circuits that are fed from opposite phases of the power feeder.

  • Page 12: Input Transformer Mode

    Refer to Sections 5 for more information about using the Main and Aux Outputs. 3.7 INPUT TRANSFORMER MODE The 1788A’s Jensen® microphone input transformers can be operated in one of two modes: LOADED and UNLOADED. The loaded mode places a load resistor on the transformer secondary according to the transformer manufacturer’s specifications.

  • Page 13: Com Port

    Determine your current firmware version by going into Local Control, depressing both Test Tone buttons and Channel 8 at the same time. The firmware version will appear in the Global Readout Display. If a new version is available, you may install it on your 1788A as follows.
  • Page 14 1 dB stops EXAMPLE OF USING PRE MODE The FOH position has control over the 1788A’s but the monitor position doesn’t want to be affected by the FOH’s gain changes. In this case, the monitor position gets a fixed gain of 20dB from the microphone that will not change.

  • Page 15: Functions In Detail

    Instruction Manual 4. FUNCTIONS IN DETAIL 4. FUNCTIONS in DETAIL 4.1 LOCAL BLOCK Channel Select and Channel Status Readout Select LOCAL CONTROL and use the CHANNEL SELECT buttons to choose one of eight channels. Only one channel can be selected at a time, unless the MULTIPLE SELECT button is engaged, making it possible to create a group of channels.
  • Page 16 This is especially appreciable when you have to roll through a gain change of 6dB or more very quickly. The 1788A just sounds like a fader was moved with no jumps, pops or zips. The 1788A rolls through the full span of 26 to 65dB in 250 milliseconds.
  • Page 17 Instruction Manual 4. FUNCTIONS IN DETAIL channels is muted. The channel or channels that have been muted will flash double dash marks in the Gain display of the individual channel status readout to indicate their muted status. The flashing dash marks will alternate with the current gain setting. All parameters may be adjusted while a channel is muted.

  • Page 18: Control Block

    This button enables the adjustment and storing of the Channel, Device, and Net numbers that this specific 1788A will respond to for remote control. To provide a level of protection from inadvertent modification of the settings, the procedure for using this button has been made quite specific and you should become thoroughly familiar with it to avoid confusion.
  • Page 19 The Adjust/Store button will go off indicating the values were stored and you’re back in safe mode. 7. Put the 1788A into the correct remote interface port by using the Mode button. 8. Press Local to return the unit to remote control state.

  • Page 20: Digital Block

    Local Control The LOCAL button allows front panel control. Press it once, you’re in local. Press it again, you’re back in remote. The LOCAL button is lighted when the 1788A is in the local state and dark in the remote state.

  • Page 21: Monitor Block

    This puts two extremely useful tools into your hands. First, you have a complete confidence check of all preamp channels of your 1788A, as well as the optional A/D converters. Second, you have a definitive system level reference for matching the 1788A’s output level to any following equipment.

  • Page 22: Secondary Functions

    You can dim or brighten the front panel display by holding down BOTH TONE BUTTONS and pressing the Channel 7 button. This puts the 1788A into “display mode”. Turning the ADJUST dial will vary the display through 5 levels that are indicated in the Global Status Readout window as D-0 (dimmest) through D-4.

  • Page 23: Using The Digital Module

    NOTE: Beware that you will run into problems trying to use TDIF and ADAT Optical outputs with any external clock sampling above 48KHz. External Sync The 1788A can take three types of external sync. All are received at the BNC Word Clock IN jack. 1. Word Clock 2.
  • Page 24 1788A’s may be looped together from a single clock source. When the 1788A is set for internal sync, the BNC input jack is ignored and the BNC output jack is connected to an output driver that supplies a low jitter Word Clock suitable for sync’ing seven other 1788A’s and additional equipment.
  • Page 25 Aphex Systems Sun Valley, CA Remote Clock Mastering Depending on your system design, you may need to sync one or more 1788A’s to an existing clock source. That is made simple by series-looping from the clock sourcebut you you can also use a clock distribution amplifier and configure a parallel clocking scheme.
  • Page 26 1788A’s. You might, for example, need to fan out from a parallel clock D.A. to several racks of 1788A’s which are locally series-looped. With long distance clock runs, you should use impedance matched transmission to minimize jitter problems.
  • Page 27 Termination resistor at each end. 2.5Vp-p With Termination SOLUTION: Aphex has made the 1788A capable of receiving Word Clock down to 1/2 volt p-p Clock Clock so you can safely run very long Word Clock...

  • Page 28: Sending Digital Audio

    13 12 11 10 9 25 24 23 22 21 20 19 18 17 16 15 14 * PINS NOT CONNECTED IN THE 1788A ADAT® Optical This runs on a plastic optical fiber that can transmit over a limited distance of typically 10 meters maximum.

  • Page 29: Typical Operation

    If your console does not have separate line inputs, but does have “Insert” jacks, you can use these to bring in the audio from the Model 1788A and reap the sonic benefits. Console channel inserts with a “send” and “return” allow you to interrupt the signal path following the input gain stage to introduce signal processing or effects.

  • Page 30: Direct Tracking

    You can refer to this manual’s appendix on proper wiring to get information on how to match the 1788A’s Main and Aux Outputs to balanced and unbalanced inputs (there is a difference between Main and Aux unbalanced wiring).

  • Page 31: Using All Outputs To Feed Five Destination Devices

    A picture is worth a thousand words. The above illustration gives you an idea of the flexibility of the 1788A. Substitute a digital house or monitor mixer, analog recorder, or any other combination as your design may require. The point is, all the audio outputs are available for use at the same time.

  • Page 32: Using The Microphone Output Limiter

    With MicLim now available you will seldom find it possible to overload the Model 1788A mic preamp, even under severe conditions. That’s because there is typically 20dB of limiting headroom. Effectively that means you get 20dB more preamp headroom before distortion.

  • Page 33: Grouping Channels

    Several properties of group operation are important to know as they may affect the way you use grouping. 1. The Model 1788A computes the modified individual channel gains in an invisible workspace that can retain over- and under-range values. This allows the unit to be able to restore the channels’...

  • Page 34: Warranty & Service

    Any and all warranties are limited to the duration of the warranty stated above. EXCLUSION OF CERTAIN DAMAGES Aphex Systems’ liability for any defective unit is limited to the repair or replacement of said unit, at our option, and shall not include damages of any other kind, whether incidental, consequential, or otherwise.

  • Page 35: Specifications

    Instruction Manual 8. SPECIFICATIONS 8. Specifications 8.1 GENERAL SPECIFICATIONS MIC INPUT Connector: XLR-3F Type: Jensen Transformer Coupled Input Z: 1.6KΩ nominal Maximum Input Level (MIL): +27dBu (with input pad) CMRR: 99dB @60Hz, -72dB @ 10KHz Nominal Preamp Gain: 26 to 65dB Phantom Power: +48VDC Pad:...

  • Page 36: Architect's Specifications

    MICROPHONE PREAMPLIFIER 8.2 ARCHITECT’S SPECIFICATIONS Basic Description A multichannel microphone preamplifier comprising eight identical channels that are both locally controllable and remotely controllable by MIDI protocols through MIDI and Ethernet ports. The multichannel preamp shall further comprise an optional digital audio output module.

  • Page 37: Appendix A: Balanced And Unbalanced Lines And Operating Levels

    Instruction Manual APPENDIX A Appendix A: Balanced and Unbalanced lines are the same. They both need two conductors. Lines and Operating Levels What makes a system unbalanced is when one of the wires is formed into a tube that wraps around Interfacing all types of equipment with balanced and the other conductor, without touching it, such that unbalanced lines and can sometimes be trouble-...

  • Page 38: Appendix B: Dealing With Grounds And Hum

    MICROPHONE PREAMPLIFIER 1 illustrates how the hum is induced into both wires just changing one piece of equipment in a studio can equally and therefore is cancelled out. cause hum to appear somewhere else. When you are using unbalanced gear, it is a very good procedure Since the balanced line has wires that are twisted to power all your equipment from one large power together, each wire tends to pick up the same...

  • Page 39: Appendix C: Proper Wiring Techniques

    Level Interface Units need to make sure you don’t overload the one ac cir- Aphex manufactures the Model 124 Level Interface cuit your strip is plugged into. If the load is too great box which is designed to electronically convert two...
  • Page 40 MICROPHONE PREAMPLIFIER CONNECTOR WIRING STANDARDS tion from Aphex Engineering is this: In the majority of cases maximum noise rejection occurs when the The 3 pin XLR, 1/4” (63.5 mm) TS mono phone and shield is connected to the input ground only (espe- the 1/4”...

  • Page 41: Appendix D: Standard Cable Wiring

    Instruction Manual APPENDIX D TABLE 1 - BALANCED & UNBALANCED CONNECTOR WIRING STAN- 3-Pin XLR 1/4” TRS Phone Standard Wiring Convention (Balanced) Pin-1 Sleeve Ground/Shield (Earth, Screen) Pin-2 Positive (Signal, High, Hot) Pin-3 Ring Negative (Signal Reference, Return, Low, Common) 1/4”...
  • Page 42 MICROPHONE PREAMPLIFIER XLR to XLR OK for Microphones Standard store-bought cable. Shield grounded at both ends. Positives: Good for microphones. Negatives: May cause ground loops through the shield grounds if used to connect equipment together. Preferred for Line Levels Shield grounded at receiving end only. Positives: Stops ground loops and reduces noise.
  • Page 43 Instruction Manual APPENDIX D PART 2: BALANCED OUT to UNBALANCED IN Voltage Balanced Outputs It was mentioned that there are several types of balanced output stages in use today. The follow- SIMPLIFIED SCHEMATIC ing diagrams show you how to properly unbal- ance each type of output.
  • Page 44 MICROPHONE PREAMPLIFIER PART 3: UNBALANCED to UNBALANCED Standard Cable (Guitar Cord) Mono (TS) Phone Plug Mono (TS) Phone Plug PART 4: UNBALANCED OUT to BALANCED IN Standard Method Enhanced Method (Pseudo Balanced) Advantage: Reduced Hum and Noise Pickup Mono (TS) Phone Plug Stereo (TRS) Phone Plug Mono (TS) Phone Plug Stereo (TRS) Phone Plug...

  • Page 45: Appendix E: Helpful Wiring Table

    Wire: two conductor with a shield (twisted pair) Cross- Coupled POSITIVE (HIGH) Unity NEGATIVE (LOW) Balanced Unbalanced Unbalanced Gain SHIELD (GND) (Aphex Servo NC Optional (see Note 6) Balanced) Wire: two conductor with a shield (twisted pair) Cross- Coupled POSITIVE (HIGH) Unity NEGATIVE (LOW) Balanced Balanced...
  • Page 46 Diagram 3 Balanced to Unbalanced: This configuration should be used with equipment incorporating a conventional active balanced output stage. Most non-Aphex equipment uses this kind of output stage because of its simplicity and low cost. Therefore, you will find yourself using diagram 3 fairly often when interfacing typical equipment together. In this case, the interface gain will be 50% down, giving a 6dB loss of level.

  • Page 47: Appendix F: Word Clock Cabling

    Instruction Manual APPENDIX F APPENDIX F: WORD CLOCK CABLING useful bandwidth of the line is maximized under these con- ditions, and the pulse waveform is best preserved. Transmission Systems There are basically two systems in use for distributing word That is not to say the pulse waveform won’t undergo some clock by coaxial lines: 75Ω...
  • Page 48 This permits direct feed-through of obvious is sound degrading jitter. clock with almost no loading from the 1788A. If using a 75Ω clock system, then you can daisy-chain the W.C. input to additional 1788A’s or other equipment. If the 1788A is...
  • Page 49 End-of-Line Termination as shown in figure 5. Last Unit In Line Clocking The 1788A With Brute Force Not knowing what the 1788A’s word clock input may be UTIL AES/EBU OUTPUT driven by, we made it automatically accept the brute force 1 2 3 4 voltage levels.
  • Page 50 MICROPHONE PREAMPLIFIER This product is protected under one or more of the following Aphex patents. 4,578,648 4,633,501 4,843,626 4,939,471 5,115,471 5,155,769 5,334,947 5,359,665 5,422,602 5,424,488 5,450,034 5,463,695 5,483,600 5,485,077 5,612,612 5,737,432 5,848,167 5,896,458 5,898,395 5,930,374 6,266,423 Page 50...

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