Build your own Preamp – FABModules – FiveFish Audio Building Blocks for DIY Projects Blog Articles

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FAB4312 – Non-Inverting Amplifier Module

The FAB4312 is a standard Non-Inverting Amplifier using OpAmps, accommodating both the PDIP8 IC format, and the API 2520-footprint Discrete OpAmp format.

If you’ll be installing a Discrete OpAmp, MillMax sockets are required to be installed on the board.  An external connection, RGAIN, is required to control the gain of this amplifier. One typically uses a 10K or 22K Reverse Log Potentiometer for RGAIN in this circuit configuration.

Feel free to change the values of RF, RGAIN and R3 to suit your purpose. The formula for Voltage Gain for the amplifier is conveniently printed on the FAB Module.

For CF, we’re using a 100pf C0G NPO ceramic capacitor. You may have to adjust this capacitor value to suit the OpAmp you’ll be using in case you encounter instability or oscillations.

In addition, a trimmer resistor (R2) is provided to let you adjust DC Offset Voltage as close as possible to 0 Volts. By adjusting the DC offset to as little as possible, you reduce clicking noise when changing gain settings. This may not be an issue if you’ll be using a potentiometer for RGAIN, but if you’ll be using a selector switch to vary the value of RGAIN, then you’d want your DC offset as small as possible.

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FAB2110 – Input Transformer Module

Introducing – our FAB2110 Module.  This is basically our Input Transformer Module.

This FAB module will accept CAN type transformers like Jensen, Cinemag, Altran Input Transformers with it’s typical (8) pins.  CAN Transformer dimensions are 1.13″ diameter (28.7mm) with 0.15″ pitch pins.

FAB2110 Input Transformer Modules are designed to mate with our FAB2010 XLR Input Modules.  This allows you to create a complete Transformer-based Input Stage for that Mic Preamp or gear you’re building.

The FAB2010 XLR Input Modules require power (V+, 48V) for proper operation of it’s relays (controlling the -20dB Pad and Phantom Powering) and 48Volts Phantom Power. These power requirements cam be supplied via the POWER INPUT headers of the FAB2110 Input Transformer Module.  You can use a 2×5 (10-pin) Ribbon Cable to connect this POWER INPUT header to our FAB Power Supply*. Continue Reading…

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