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Summary of Contents for API 3124mb+
- Page 1 3124mb+ All‐Discrete 4‐Channel Mic/Instrument Preamplifier with Stereo Mixer Operator’s Manual Written by Carl J Houde 2015...
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Page 2: Table Of Contents
Table of Contents Introduction .............................. 3 Overview ................................ 4 3124mb+ Features and Introduction ...................... 4 Signal Flow and Block Diagrams ........................ 5 3124mb+ Signal Flow ............................ 5 Additional Routing ............................ 5 3.2.1 Insert .............................. 5 3.2.2 Auxiliary Send/Return ........................ 5 Preamplifier Block Diagram .......................... 6 Stereo Mixer Block Diagram ......................... 7 Input Section: Mic/Instrument/Line Preamplifier .................... 8 Preamplifier Overview and Features ...................... 8 Preamplifier Controls ............................ 8 Input Selection .............................. 9 4.3.1 MIC Switch ............................ 9 4.3.2 Microphone Input .......................... 9 4.3.3 Instrument Input ... -
Page 3: Introduction
Introduction Thank you for purchasing API’s 3124mb+! This is the 3124mb+ operator’s manual. The purpose of the operator’s manual is to guide you, the audio engineer, through the 3124mb+ features and functions. What follows is a comprehensive guide that will explain how and why each feature can be used in a professional, project, or home studio. Each of the 3124mb+ preamplifier and stereo mixer parameters is covered. Included are signal flow schematics and block diagrams that may help troubleshoot any issues that arise when using the 3124mb+. After reading this operator’s manual, you will be armed with all the necessary knowledge to efficiently use the ... -
Page 4: Overview
Overview Both the 3124+ and the 3124mb+ (see Figure 1) are designed with the professional engineer in mind. Both units give the highest possible quality 4 channel mic preamp. However, the 3124mb+ provides an additional audio mixer with a transformer balanced output, keeping the unit size and price at a reasonable level. Both models are equally at home in the control room, studio, and recording truck or on stage. Figure 1: 3124mb+ Front Panel 3124mb+ Features and Introduction Features Uses API 2520 Op‐Amp Classic Console Circuit Four XLR Mic Inputs Four ¼” Unbalanced Inputs Front Panel Polarity Switch Front Panel 20 dB Pad Switch Front Panel Mic Switch ... -
Page 5: Signal Flow And Block Diagrams
Signal Flow and Block Diagram 3124mb+ Signal Flow Figure 2: Signal Flow Additional Routing 3.2.1 Insert Engaging the INSERT, by connecting a TRS cable to the INSERT jack, will add the INSERT routing to a channel’s signal flow. The TRS cable’s “tip” carries the signal out from the 3124mb+ channel and the cable’s “ring” carries the returning signal from the insert device. This can be useful for adding signal processing to an individual channel. 3.2.2 Auxiliary Send/Return AUXILIARY functions are controlled from the 3124mb+ front panel. Each channel has its respective AUX knob which control how much of a channel’s signal is being sent to the AUX bus. The summed AUX signal can then be sent and returned to an external signal processor via independent ... -
Page 6: Preamplifier Block Diagram
Preamplifier Block Diagram Figure 3 shows a block diagram that illustrates signal flow through each preamplifier channel of the 3124mb+. Understanding the signal flow through each preamplifier channel will help develop a better understanding of how and when each channel’s parameters can be used. Figure 3: Preamplifier Signal Flow 6 ... -
Page 7: Stereo Mixer Block Diagram
Stereo Mixer Block Diagram Figure 4 shows a block diagram that illustrates signal flow through the stereo mixer section of the 3124mb+. Understanding the signal flow through each preamplifier channel will help develop a better understanding of how and when each channel’s parameters can be used. Figure 4: Stereo Mixer Signal Flow 7 ... -
Page 8: Preamplifier Overview And Features
Preamplifier Overview and Features Each of the four 3124mb+ preamplifiers (see Figure 5) is an all‐discrete microphone/instrument/line pre‐ amplifier designed to provide an unusually good sounding front‐end for all types of audio recording applications. Sonically, it offers the distinct API sound, high quality performance, and low noise. Each preamplifier remains faithful to the circuit designs of API’s founder, Saul Walker. Fully featured, Figure 5: Channel 1 Preamplifier Section each carefully preserves the original sound character ... -
Page 9: Input Selection
HI‐Z IN: ¼” high‐impedance instrument input LEVEL: Stereo mixer send level PAN: Stereo mixer send pan AUX: Auxiliary bus send level VU METER: 7 LED VU meter Input Selection Each preamplifier can receive three (3) input sources: MIC (Microphone): Rear panel female XLR microphone input with switchable 48V phantom power INST (Instrument): Front panel ¼” unbalanced ‐10dBu instrument level input 4.3.1 MIC Switch The MIC switch is used to select the input source. When the green LED above the switch is illuminated, the rear panel XLR input is the active source. When the green LED above the switch is not illuminated, the front panel ¼” input is the active source. 4.3.2 Microphone Input Select the microphone input by pressing the MIC switch and a green LED should turn on above the MIC switch. The MIC input connection on the rear panel will be the active input. Female XLR microphone input 48V phantom power ‐20 dB pad Green LED illuminates when MIC switch engaged VU meter indicates level of preamplifier output ... -
Page 10: Instrument Input
4.3.3 Instrument Input The ¼” jack on the front panel is the active input when the MIC switch is not engaged. ‐10 dB instrument level input Unbalanced, high‐impedance input (¼” tip‐sleeve) GAIN: Instrument preamp level control 14 dB minimum gain 50 dB maximum gain Polarity Inverter A polarity inverter (sometimes referred to as a “phase reverse”) is available at the input of the preamplifier. POL (Polarity): Inverts the polarity of the signal at the input of the preamplifier. Yellow LED above switch illuminates when engaged VU Meter The preamplifier outputs can be monitored via the VU meter in each input section. Direct Output Each preamplifier’s output is available at its respective OUTPUT connection on the rear panel. XLR connection Plugging into the OUTPUT jack does not break the connection to the INSERT jack ... -
Page 11: Preamplifier Block Diagram
Preamplifier Block Diagram Figure 7 shows a block diagram that illustrates signal flow through each preamplifier channel of the 3124mb+. Understanding the signal flow through each preamplifier channel will help develop a better understanding of how and when each channel’s parameters can be used. Figure 7: Preamplifier Signal Flow 11 ... -
Page 12: Output Section: Stereo Mixer
The stereo mixer also includes an auxiliary bus whose level and return pan can be controlled from the front panel. Figure 8: Stereo Mixer Section Features Full attenuation to +10 dB of gain High headroom +28 dB clip level Traditional API fully discrete circuit design API 2520 discrete op‐amp with transformer output Stereo Mixer Controls Figure 9: Stereo Mixer Controls The Stereo Mixer provides a comprehensive suite of controls: LEFT: Master level for left channel RIGHT: Master level for right channel ... -
Page 13: Auxiliary Return Pan
Controls amount of auxiliary return signal mixed with main output 5.2.3 Auxiliary Return Pan RET PAN: Auxiliary return pan Controls pan of auxiliary return signal mixed with main output Stereo Mixer Block Diagram Figure 10 shows a block diagram that illustrates signal flow through the stereo mixer section of the 3124mb+. Understanding the signal flow through each preamplifier channel will help develop a better understanding of how and when each channel’s parameters can be used. Figure 10: Stereo Mixer Signal Flow 13 ... -
Page 14: Panel Interfaces
Panel Interfaces Audio Path Inputs 6.1.1 Front panel Figure 11: Front Panel Input Connections 6.1.2 Rear Panel Figure 12: Rear Panel Input Connections Audio Path Outputs 6.2.1 Rear Panel Figure 13: Rear Panel Output Connections 14 ... -
Page 15: Ac Power
AC Power The 3124mb+ can operate on either 115 volts or 230 volts 50‐60 Hz AC power. The AC power is supplied via the IEC connector on the rear panel. Operating voltage is determined by the Voltage Selector switch. Voltage Selector Switch: Selects operating voltage 115 volts 230 volts The fuse holder is located on the rear panel. 0.5A/0.25A 250V The AC power switch for the 3124mb+ is located at the lower right of the API logo on the front panel. A blue LED indicator illuminates when the unit is on. Customer Support For further information and inquires, please contact API’s customer support: Call us at 301‐776‐7879 Fax us at 301‐776‐8117 Email us at service@apiaudio.com 15 ... -
Page 16: Appendix
Appendix Specifications Input Impedance: Mic: 1500 Ω Unbalanced: 470 kΩ Hi‐Z Output Impedance: Less than 75 Ω Channel Outputs Nominal Levels: XLR Channel Output +4 dBu Stereo Output Level: Balanced: +4 Unbalanced: Nominal ‐2 Clipping Level: XLR Channel Output better than +28 dBm Frequency Response: +0, ‐5, 10 Hz to 20 kHz (‐0.5 at 10 Hz) Noise EIN: Mic: ‐129 Unbalanced Actual: ‐129 Measured Noise: Better than ‐91 dBm/Below Nominal +4 Distortion: All Outputs at +4 Out, 0.03% All Outputs at +22 Out, 0.09% Gain Range: 150 Ω Input: 10 dB Min, 65 dB Max (Incl. PAD) Unbalanced Input: 14 dB Min, 50 dB Max VU Meter: ...
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