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

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Passing your Audio Signal through an Input Transformer

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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FAB2010 XLR Input Module Prototype Testing

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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FAB2010 Prototype – populated with parts

Populated the FAB2010 boards tonight. I put too much solder paste on my resistors so I need to be careful doing that. It’s a little hard because I’m just using a plunger to dispense the paste. I need to get one of those solder paste pump dispenser. I’ve seen them on eBay for around $150 or so.

Anyway, here are some pictures.

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FAB1215 Rev.B – Reducing Voltage Ripple

I’ve been testing the DC-1248 (12Volts to 48Volts Phantom Power) the past few days now, and I was able to further improve performance by reducing ripple down to 128mV, for a 47.7Volts output, fully loaded drawing at 57mA.  Efficiency is computed to be at 76% at this loading.

I reduced the ripple by adding another 0.1uf ceramic and 47uf electrolytic capacitor to the DC-1248 output terminals.  Since there is no more space on the DC-1248 board (measuring only 1″x1″), I added these parts to our FAB1215 PSU Module.  So here’s the new Rev.B design.

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DC-1248 – 12V to 48V DC-DC Converter for Phantom Power

I got my prototype boards for my DC-1248 (12Volts to 48Volts DC-DC Converter).  Quickly built a prototype, and nervously turning on the power, there was no smoke, fyring bacon sound, or anything getting hot.  Yey! So far so good… Measured the output voltage and it was 48.2 Volts. Nice.

I began loading the DC-DC converter and looking at it’s ripple waveform on my scope. Happy to say that performance improved significantly just by moving it from a breadboard into a properly designed PCB!  The board is a tiny 1″x1″ square, with (4) Millmax pins so you can easily plug-it in to our FAB1215 Power Supply Board.

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