MIDIPLUS AMP-73 Quick Start Guide

Introduction

Welcome to the MIDIPLUS AMP-73 Professional Microphone Preamplifier. This product incorporates advanced microphone preamplifier technology, ensuring lower noise levels, reduced total harmonic distortion (THD), and a higher dynamic range even at low gain settings. The AMP-73's gain adjustment feature allows users to optimize the signal-to-noise ratio and bandwidth performance across a wide gain range.

The AMP-73 is equipped with a high-performance, ultra-low noise, high-slew-rate, flagship professional operational amplifier (Op-Amp), audio-specific capacitors, and high-precision, low-temperature drift metal film resistors. Through precision circuit design, it achieves ultra-low harmonic distortion, precisely captures the emotional nuances and overtones of vocals/instruments, and ensures the original characteristics of audio signals are preserved. With a more natural tonal quality, it delivers a multi-dimensional immersive experience tailored for professional recording.

Before use, please read the following guidelines carefully to ensure the safe and effective operation of your MIDIPLUS AMP-73.

Important Safety Instructions

Do not use this apparatus near water.
Clean only with a dry cloth.
Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus (including amplifiers) that produce heat. Protect the power cord from being walked on or pinched, especially at plugs and connectors.
Protect the power cord from being walked on or pinched particularly at plugs, convenience receptacles, and the point where they exit from the apparatus.
Only use attachments/accessories specified by the manufacturer.
Unplug this apparatus during lightning storms or when unused for long periods of time.
The apparatus shall not be exposed to dripping or splashing and that objects filled with liquids, such as vases, shall not be placed on apparatus.
Do not place a lighted candles on the apparatus.

Caution: To reduce the risk of electric shock do not remove cover (or back). No user-serviceable parts inside. Refer servicing to qualified personnel.

Features

80dB of gain on tap
48V Phantom Power Support
Front-Panel Line/DI Input
Independent Input Gain and Output Level Controls
8-Segment peak Level Meter
Phase Reverse and -20dB Pad Buttons
Input/Output Transformer Routing Switch
Jason Transformer
Rack-Mountable Design

Hardware Features

The front panel of the AMP-73 features the following controls and indicators:

1. DI Input: Connect Dynamic microphone, instrument (e.g., electric guitar) or line-level device.
2. 48V Phantom Power Switch: Activates 48V phantom power for the XLR input. The indicator light turns ON when enabled and OFF when disabled.
3. Line Toggle Switch: Switches the DI input between line-level and instrument-level signals. The light indicates Line In when ON and DI when OFF.
4. Phase Switch: Inverts the input signal's phase. The light turns ON when activated and OFF when disabled.
5. Pad Switch: Applies -20dB attenuation to the input signal. The light turns ON when enabled and OFF when disabled.
6. Input Transformer Switch: Routes the input signal through the input transformer when ON, or bypasses it when OFF.
7. Output Transformer Switch: Routes the output signal through the output transformer when ON, or bypasses it when OFF.
8. Gain Control Knob: Adjusts the input gain with stepped gain value.
9. Output Control Knob: Controls the output level.
10. Output Level Meter: Displays the output level.
11. Power Switch: Turns the AMP-73 ON or OFF.
12. Power Indicator: Indicates the power status.

The rear panel of the AMP-73 includes:

1. Power Port: Connect the included AC adapter to power the AMP-73.
2. Output: Balanced output for line-level device connectivity.
3. MIC Input: XLR connector for professional microphone connectivity.

Important Notes

Priority Routing: If both the DI Input and XLR Input are connected simultaneously, the DI Input takes priority, and the XLR Input will be disabled.
Transformer Switching Caution: When toggling the Input, Output Transformer Switches, transient electronic pops may occur. Always reduce the output volume to minimum before operating these switches.
Phantom Power Safety: Always turn off the 48V Phantom Power before plugging/unplugging condenser microphones to avoid potential damage.

Troubleshooting

If your AMP-73 encounters issues, perform the following basic checks to resolve common problems.

No Power

Verify that the AC power outlet is active.
Ensure the power cable is securely connected to the AMP-73 and the outlet.

No Audio Output

For Condenser Microphone: Confirm the 48V Phantom Power switch is ON.
Input Priority: Check if another device is connected to the DI input, which may override the XLR input (see Priority Routing in Notes).
Adjust the Gain Control Knob to an appropriate level (avoid minimum/maximum extremes).
Adjust the Output Control Knob to an audible level.
Inspect all input / output cables for physical damage or loose connections.
Ensure all input/output connectors (XLR, TRS, etc.) are fully seated.
Confirm the AMP-73 is powered ON (check the Power Indicator Light).

Technical Specifications

	AMP-73
Model	AMP-73
I/O	1 × 6.35mm DI Input, 1 × XLR Input, 1 × AC 17.5V × 2 Input Port, 1 × 6.35mm Output
Buttons	1 × 48V Phantom Power Button, 1 × Line In Button, 1 × Phase Button, 1 × Input Transformer Button, 1 × Pad Button, 1 × Output Transformer Button
Knob	1 × Stepped Gain Control Knob, 1 × Output Control Knob
Accessories	1 × AMP-73 Unit, 2 × Rack Ears, 1 × AC Power Adapter, 1 × Rack Ear Mounting Screw Set
Weight	1.17 kg
Dimensions	241.2 × 130.1 × 45.6 mm

Microphone Input Specifications:

Trans In off, Trans Out off, Pad off, 20Hz to 20kHz @ +20dBu output, 48kHz Bandwidth.

Gain (into 600Ω)	@+6 dB	@+30 dB	@+58 dB	@+80dB
Frequency Response	±0.11 dB	±0.11 dB	±0.12 dB	±1.9 dB
THD+N	-108.3 dB	-108.9 dB	-89.9 dB	-66.3 dB
Dynamic Range (A-weighted)	120 dB	115 dB	94 dB	76 dB
EIN @150Ω (A-weighted)	-102 dBu	-121 dBu	-126 dBu	-126 dBu

Trans In on, Trans Out on, Pad off, 20Hz to 20kHz @ +20dBu output, 48kHz Bandwidth.

Gain (into 600Ω)	@+6 dB	@+30 dB	@+58 dB	@+80dB
Frequency Response	±5.5 dB	±0.10 dB	±0.29 dB	±1.0dB
THD+N	-77.5 dB	-80.7 dB	-81.5 dB	-64.3 dB
Dynamic Range (A-weighted)	120 dB	115 dB	93 dB	70 dB
EIN @150Ω (A-weighted)	-101dBu	-120 dBu	-125 dBu	-125 dBu

Connection Example

The diagram shows a typical setup for the MIDIPLUS AMP-73:

A guitar is connected to the DI input on the front panel.
An AC adapter is connected to the power port on the rear panel.
An audio interface or external device is connected to the OUTPUT on the rear panel.
A microphone is connected to the MIC INPUT (XLR) on the rear panel.

Two AMP-73 units can be interconnected via the included mounting bracket (sold separately).

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