How to Instal and Use the Neumann V472 Microphone Preamplifier Modules

Neumann V472 Microphone Preamplifier Modules – Racking Project


Neumann is a well-known name in the world of professional studio recording equipment. V72 is probably the most famous preamplifier made by this manufacturer. V472 is transistor-based microphone preamplifier. Each module contains two independent channels. The gain of each channel can be set up to 40dB. Inputs and outputs are transformers coupled. Neumann V472 modules can be found on eBay or purchased from other online retailers. Usually, modules come without power supply and without input or output connectors. This means that preamps are useless. This article presents a racking solution which converts V472 modules into the very valuable studio equipment. This is the project which I have finished a few years ago.


The beginning

 

This picture shows the condition of the modules when they arrived.

Neumann V472 Modules are available on eBay but usually in a condition which makes them difficult to use preamps in Recording Studio.

Modules were housed in the rack which was used as a part of analogue Summing Mixer.

In this condition preamps, the gain is 0dB, therefore, modules are useless for recording sound with microphones.


V472 Module Design

Each module contains two microphone preamplifier.
Inputs are coupled with high-quality microphone transformers. Transistor preamps circuitry’s are potted in small plastic boxes.
Potted discrete opamps are visible on the picture. After the time new versions of V472 modules appeared.
Updated modules use hybrid transistor circuitry instead of a potted discrete opamp. The gain of each channel can be set up to +40dB with external resistors. This is more than enough for most condenser microphones.
 
 

Power Supply problem

Modules came in the rack but without the power supply. The picture shows the back of the rack. Most probably power supply was made as to the external unit. The power supply connector is visible on the back panel of the rack. This is a good idea especially that Neumann modules are packed with an audio transformer which may pick-up 50Hz hum very easily. In my project, I decided to use the same solution. The picture shows also connectors and wiring assembly which was used later in the new enclosure.
 

The Gain Switches

First, the frame with modules connectors was removed from the old enclosure. Next, it was necessary to make 18 assemblies of gain switches. Each V472 Module contains two microphone preamps so two switches assemblies are required for one module. Neumann V472 datasheet was very helpful to calculate correct resistors values. The gain can be selected from 0dB up to 40dB with 4dB step. The switch has 12 steps therefore after 11th position switch rotation was blocked. Without the gain switches, V472 module is useless as the microphone preamplifier. Some of the original wirings were left and used later for connecting input and output XLRs and Jack sockets.
 

Input Connectors

Adding the input XLR’s connectors was an absolutely necessary step. XLR’s are standard connectors used for connecting Microphones. Because V472 modules do not provide Phantom power simple resistor/capacitor circuitry was added to each XLR socket. Phantom power is required to supply condenser microphones.
 
 
 

 

The Front Panel

The front panel is a major part of the project. Because the unit has 18 microphone preamplifiers it was necessary to use 4U rack enclosure to fit all V472 modules and all gain switches knobs on the front panel. The picture shows the main unit and the PSU front panel. Both panels are engraved on CNC, hand drilled and spray painted with clear lacquer.
 
 

Module Installation

Finally, the modules had to be installed inside the enclosure. I have used some of the mechanical fixtures from the original enclosure. Mainly because modules connectors were aligned in the correct order. Making a new frame would be too time-consuming. The picture shows also cables going to Phantom power toggles and gain rotary switches which were installed later on the front panel. Phantom power toggle switches and the control light are also installed on the front panel.
 

External Power Supply

Because the main unit enclosure was really crowded I decided to build a separate external Power Supply Unit. Another benefit is lower hum which may be induced in the input and output transformers. Increasing distance between mains transformer (separate enclosure) and audio transformers improved hum immunity significantly.
 

The Final Results

Pictures below show how the ready finish Neumann V472 Microphone Preamplifier looks like.
 
 
 
 

The Video:



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