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 TM3030's
circuitry should be then tied to earth via another wire from the GND pad on the board back to
the bonding point.
There is little more information about using internal mains transformers later in this document.
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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