228 unidirectional audio interface 8-CH A N N E L C O N S U M E R t o P R O L E V E L I N T ERFACE [ - 1 0 d B V U NBALANCED IN to +4dBu BALANCED OUT] S Y S T E M S THE SOLUTION DELIVERY SERIES
Solution Delivery Series 228 8-channel unidirectional audio Interface Instruction Manual P/N 999-4180 Revision 1 Released 01/28/2004 Manufactured by Aphex Systems Ltd. 11068 Randall St. Sun Valley, CA 91352 USA S Y S T E M S Copyright 2004 Aphex Systems Ltd. All rights reserved. Produced by: Donn Werrbach. Creation tool: Adobe InDesign 2.0. Printed by: Stuart F. Cooper Co., Los Angeles.
228 instruction Manual A MESSAGE FROM THE PRESIDENT Dear Aphex customer, Thank you for selecting the Model 228 as your interface between consumer level outputs and professional level inputs.
8-channel audio interface 228 Table of Contents 1.0 QUICK START - Page 4 2.0 INSTALLATION - Page 6 2.1 Mounting 2.2 Rear Panel View 2.3 AC Line Connection 2.4 Input Connectors 2.5 Output Connections 3.0 CONTROLS AND INDICATORS - Page 7 3.1 Front Panel View 3.2 Meter and Indicator Window 3.3 Meter Select Button 3.4 Interface Gain Trimmers 4.0 SPECIFICATIONS - Page 8 4.1 General Specifications 42 Architectural Specifications 5.0 WARRANTY AND SERVICE - Page 10 51 Limited Warranty 52 Service Information 6.
228 instruction Manual 1.0 Quick Start 1. Be sure all used channels have properly made-up cables and connectors. 2. Play the audio source and check to see signal presence is indicated for all active channels. 3. While the audio source is playing, select each channel to the VU meter and verify the loudest sounds are peaking to zero VU with maybe a few peaks hitting +3. If the reading is too high, you can trim down the gain of the offending channel.
228 8-channel audio interface Quick Start 5 4 3 2 CHECK VOLTAGE Be sure it is configured for your power mains voltage. It is not user adjustable. 1 FUSE Voltage and Fuse Ratings Label CHASSIS GROUND Connect to local ground bus if needed to reduce hum. OUTPUT TRIMS Set the gain of each interface channel: Fully clockwise, the gain is calibrated so a -10dBV unbalanced input produces a +4dBu balanced output. Fully CCW, the gain is unity. NOTE: No extra gain is provided for input levels below -10dBV.
228 instruction Manual 2.0 Installation 3.1 MOUNTING The Model 228 occupies a single rack space (45mm or 1-3/4 inches) of a standard EIA equipment rack. When rack mounting, use appropriate cushioned rack screws. Never restrict air flow through the device’s fan or vents. When installing the units into a rack, distribute the units evenly. Otherwise, hazardous conditions may be created by an uneven weight distribution. Connect the unit only to a properly rated supply circuit.
-channel audio interface 228 3.0 Controls & Indicators 3.1 FRONT PANEL VIEW 3.2 METER AND INDICATOR WINDOW The extended range VU meter follows industry standard ASA VU meter ballistics. It indicates the average volume level without regard to peaks. Unlike peak meters usually found on digital audio gear, the VU meter is a great indicator of the sound’s loudness to the ear. However, beware that this meter will never indicate the same readings as peak meters.
228 instruction Manual 4.0 Specifications 4.1 GENERAL SPECIFICATIONS Conditions: Gain set to max (calibration of 11.79dB); Unused inputs shorted. INPUT Number: Connectors: Type: Impedance: Nominal Input Level: Maximum Input Level (MIL): 8 RCA Jack x 8 Active unbalanced 22KΩ -10dBV (316mV RMS) +11dBV (3.
8-channel audio interface 228 Specifications 4.2 ARCHITECTURAL SPECIFICATIONS Electrical Description An active electronic device for transforming eight low level unbalanced audio lines into eight high level balanced audio lines. All eight input jacks shall be the gold plated RCA type. The input amplifiers shall be designed to reject ground loop hum that may flow into the unit’s chassis from the input cable’s shield conductor. All eight outputs shall use gold plated standard XLR 3-pin male jacks.
228 instruction Manual 5.0 Warranty & Service 4.1 Limited Warranty PERIOD One year from date of purchase SCOPE All defects in workmanship and materials. The following are not covered: a. Voltage conversions b. Units on which the serial number has been defaced, modified, or removed c. Damage or deterioration: 1. Resulting from installation and/or removal of the unit. 2.
8-channel audio interface 228 6-.0 Appendices Appendix A: Balanced and Unbalanced Lines and Operating Levels Interfacing all types of equipment with balanced and unbalanced lines and can sometimes be troublesome. First you have to somehow connect balanced to unbalanced and then you have to deal with different levels. This tutorial will teach you about the principles of balanced and unbalanced lines, wiring standards, and how to effectively interface them.
228 instruction Manual Appendices Balanced transmission works something like this. Your balanced input stage looks at the two wires and detects only the potential (voltage) difference between them. Anything that is the same on the two wires (for all practical purposes as seen measuring from ground) is called a common mode signal and is cancelled out by the differential amplifier. Figure 1 illustrates how the hum is induced into both wires equally and therefore is cancelled out.
8-channel audio interface 228 Appendices Appendix B: Dealing With Grounds and Hum Ground Loops Many people equate this term with hum, and that’s just about the bottom line of it. If you have a ground sensitive system, like unbalanced audio equipment for example, then hum will result from ground currents that flow from the ac power system. It is sometimes very difficult to isolate and stop ground currents between unbalanced equipment, but it is quite easy to clean up balanced gear.
228 instruction Manual Appendices Sometimes it just comes down to brute force grounding. That means providing such heavy, low resistance, ground current paths that little current is left to flow through your audio grounds. You can try adding heavy gauge, for example 12 gauge, copper wire from chassis to chassis. You will need to locate a metal screw that solidly binds to the metal chassis of the gear. You may even need to drill a hole through the chassis and install a screw yourself.
8-channel audio interface 228 Appendices that any equipment that still uses Pin 3 as positive on XLR connectors is not adhering to the standard.
228 instruction Manual Appendices ance. Because of these developments, it is now no longer as critical to consider impedance when dealing with interfacing pro line level equipment (impedance “matching” is mostly a requirement of the past). A word on impedance and interfacing adapters: If you are connecting between two line level devices and they have different connectors (example: 1/4” phone to XLR or vice-versa), you do not need to use an impedance matching transformer.
228 8-channel audio interface Appendices TABLE 2 - - TYPES OF ACTIVE BALANCED INPUT/OUTPUT CIRCUITS & INTERFACE WIRING OUTPUT TYPE WIRING DIAGRAM (Interface from OUTPUT to INPUT) INPUT TYPE Wire: single conductor with a shield (coax style) 1 POSITIVE (HIGH) Unbalanced SHIELD (GND) Unbalanced Wire: two conductor with a shield (twisted pair) 2 POSITIVE (HIGH) NEGATIVE (LOW) Unbalanced SHIELD (GND) Unbalanced Pseudo Balanced Balanced No Connection (see Note 4) 3 Resulting Interface METHOD /
228 instruction Manual Appendices NOTES The following notes are referenced in the text and in Table 2 on the preceding pages. Note 1: ADDITIONAL READING SUGGESTIONS: Sound System Engineering by Don Davis and Carolynn Davis (Howard W. Sams and Co.), Handbook for Sound Engineers (The New Audio Cyclopedia) Edited by Glen Ballou (Howard W. Sams and Co.) and Sound Reinforcement Handbook by Gary Davis and Ralph Jones (Hal Leonard Publishing Corp.).
8-channel audio interface 228 Appendices APPENDIX D: Standard Cable Wiring In relation to 1/4” phone jacks, you may see the terms “TS” and “TRS” as abbreviations. Here is a what that means: TS refers to the Tip-Sleeve or “mono” 2conductor type and TRS refers to Tip-Ring-Sleeve or “stereo” 3 conductor type 1/4” phone connectors. This applies to jacks (female connectors) and plugs (male connectors).
228 instruction Manual Appendices PART 1: BALANCED OUT to BALANCED IN 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. Negatives: None 1/4” TRS Phone to 1/4” TRS Phone Balanced Cables OK Standard store-bought cable.
8 8-channel audio interface Appendices PART 2: BALANCED OUT to UNBALANCED IN Voltage Balanced Outputs (Used on the 207) It was mentioned that there are several types of balanced output stages in use today. The following diagrams show you how to properly unbalance each type of output. If you follow these instructions, you should have no problems. SIMPLIFIED SCHEMATIC Unbalancing loses half the output level. You lose 6dB of gain.
228 instruction Manual Appendices 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 Mono (TS) Phone Plug Enhanced Method (Pseudo Balanced) Advantage: Reduced Hum and Noise Pickup Stereo (TRS) Phone Plug (Guitar cord of Part 3 above usualy works just as well) Mono (TS) Phone Plug Stereo (TRS) Phone Plug Not Used Male XLR Male XLR Mono (TS) Phone Plug Mono (TS) Phone Plug Not Used PART 5:
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