Building the EVR miniBrute Tesla Coil – Part 1, The Advanced Modulator

On this blog I’ve shown how to build a classic Spark-Gap Tesla Coil (SGTC) and small Solid State Tesla Coils (SSTC’s).  It’s now time to step-up into a Dual-Resonant Solid State Tesla Coil (DRSSTC).   Advantages of the DRSSTC include reduced line-power requirements (more efficient), low-voltage operation (hundreds of volts instead of tens of thousands),  and digital control due to solid state electronic replacement of the spark-gap.    This results in quieter operation and much more precise power control over the SGTC.

Eastern Voltage Research (EVR) supplies a partial kit for their miniBrute DRSSTC.  In addition to the miniBrute kit, a modulator (controller/interrupter) must be constructed, the construction/reference manual “DRSSTC: Building the Modern Day Tesla Coil – miniBrute Reference Manual” must be purchased, and additional material/components acquired to complete the coil.    The additional parts & pieces came to about $500 (toroid, plastic, screws/knobs/inserts, shipping & handling), not including a Variac (variable autotransformer) and spare IGBT‘s.   More detail will be provided in later posts.

This post covers construction of the EVR Advanced Modulator (complete kit with knobs).   Pages 75-81 of the construction manual contains pictures, waveforms, schematics, and parts list for the modulator.   A preview of the manual can be found here; specifications for the advanced modulator can be found here.   Be aware that the construction difficulty of the miniBrute is level 2, advanced.

When ordering the Advanced Modulator kit, custom text for the front panel can be requested.

At this point, it’s assumed that you have the book and modulator kit in-hand, so lets dive-in.   Here’s what came in the complete kit (with knobs) – excluding the clamp & breadboard:

There are no instructions on how-to assemble the modulator, so proceed by installing fixed resistors, diodes, and small capacitors as noted on the schematic into their locations marked on the circuit-board by the white screen printing.  IC sockets are optional, but since the modulator will be used near high-voltage, I recommend them.    My kit came with single-pole, double throw switches, but double-pole, double-throw are required (for at least two of them).   Dan quickly sent me the proper ones.   After assembling the board, your kit should look something like this:

After aligning the faceplate to the top of the plastic box and using a silver “sharpie” to mark the outlines of the switches & potentiometer holes, a Dremmel tool and 1/4-inch drill bit made quick work of the openings (LED holes not shown):

After attaching the front panel, the components were mounted thusly:

The circuit board was secured using four 1/4-inch nylon spacers and #8 screws & nuts.  Shoe Goo was used to secure the 9V battery tray (it’s not just for shoes), and four little rubber feet (LRF’s  not included in the kit) where attached to the bottom of the box.  The Dremmel was used again to make the indents on the inside of the box to accommodate the potentiometer tabs. After installing the proper switches and wiring it up, here’s how it looks (YMMV):

I started by wiring up the power switch, then the Aux (low frequency) potentiometers, and output to J2.   Dan sent me a revised schematic that mentions that the outputs (J1 & J2) should have 750 ohm resistors in series with them when being used with the miniBrute since the logic levels from the modulator are 9-volt, and the miniBrute control board expects 5-volt logic (it has a 1k-ohm pull-down resistor).

Most of the potentiometers will need to be wired so that their resistance increases with clockwise rotation.   The exception to this is R7 (PRF ADJ).   After wiring up each potentiometer, I powered-up the circuit, and checked the output on pin three of the associated 555 timer for proper output.   This way I debugged problems as the circuit was being completed.    This works until you get to U4 and U5; they have a codependent relationship, so R15 and R18  both need to be wired up before that portion of the circuit can be tested.  After initial check-out, the box can be buttoned-up, and final testing performed:

Part 2 will cover the assembly of the miniBrute electronics.   Get your kit ordered, and stay tuned! has a forum covering the miniBrute here.   If you don’t already subscribe to the Tesla Coil mailing list, you might consider subscribing.

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