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The other thing to beware is the heatsinks. Don't let either one of them touch the top panel,
since this would cause major problems. This shouldn't happen if you make sure the base of the
regulators ICs are fitted within 10mm of the PCB.
For those of you fitting an internal toroidal transformer you must make sure there is no way
the bolt that secures the transformer can touch both the bottom and top of the metal case. If
the metal support of transformer together with the case makes a complete loop around the
core, then you have a shorted one turn secondary. ('Well, there was a large hum, more of a
buzzy rattle really, then a smell of burning rubber and then a lot of smoke... '). You may also
like to consider the use of a nylon bolt to hold the transformer in place.
When an internal transformer, toroid or otherwise, is being used then the metal case must be
connected securely to earth. This is best done with a M4 bolt, nut, toothed washer and
solder tag directly wired (with thick wire) to the IEC inlet socket's earth tag. The Filtrex's
circuitry should be then tied to earth as detailed in the power supply section in this document.
Once again I should stress that building a component level mains transformer into any DIY
project should not be taken lightly as the consequences for getting it wrong can be severe.
The PCB will be supported well enough by the pots and pot brackets. However, this may give
some people nightmares so it for them it will be a good idea to provide additional support.
Small holes, to fit M3 bolts, have been provided on the outer corners of the PCB to do this.
Feel free to enlarge these holes if you wish. My prototype has been very happy just supported
by the pots. However, my unit doesn't get moved around much. If you intend to take it out on
the road, extra support may be a good idea.
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