For testing audio, square waves are typically used because they can reveal a lot about the system’s response with just a quick visual analysis. What’s so special about square waves? Why not use a typical “Sine Wave” or “Triangular Wave” for testing instead?

The reason is (if you remember your calculus class), the “ideal” Square Waves are composed of an infinite summation of sine waves of different frequencies. It has a single sine wave fundamental frequency, and all it’s odd harmonics. The amplitude of each odd harmonic is 1/n.   Represented by this equation: (credits: Wikipedia)

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I did a quick test just to see if all the FAB Modules work and play well together.  I’m very pleased with the results…. The modules were quiet, and even with a long signal chain as you can see in the picture, there was hardly any noise I could hear.  (For testing, I hooked up a condenser microphone and connected the outputs to a KRK RP8 8″ Monitors. No humming, no RF noise, nothing.)

Everything works… the logic control Phantom Power, -20dB Pad, Polarity Reverse, and the +6dB Boost (1:2 Transformer Ratio).  To get the FAB4312 Non-Inverting Amplifier working, I hooked up a small 10K potentiometer so I can adjust gain.  For now, I just used a jumper and connected the Phantom Power Logic control inputs directly to a spare V+ terminal on the FAB1215 PSU module.

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Here are some photos showing the FAB1215 Power Supply Module powering some FAB modules via a ribbon cable.

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Here’s one of the simplest way to use our FABModules….  Hook up the following FABs together:

FAB2010 – XLR Input Module
FAB2110 – Input Transformer Module
FAB3010 – XLR Output Module

All that’s missing is Power, if you want to enable the -20dB Pad, Phantom Power and Polarity Reverse functions. Otherwise, it will still work without power applied. After all, it’s just an input transformer inserted in your signal chain.

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The moment of truth… powered up our FAB2010 XLR Input Module for testing. I’m happy to say it works great.  The Logic Control Inputs for the 20dB Pad and Phantom Power works as expected.

So basically, if you want to enable PAD or PHANTOM POWER, all you need to do is apply a small voltage to it’s respected logic pins on the board. See photo below.  A logic level control voltage can be anywhere from +3.3V to 5V up to your V+ level.  These can be switched from hard-wired switches (latching type push-buttons), or from a microprocessor or logic gate chips (TTL or CMOS type).

How it works

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