Oakley 3031 - Manual (Page 19)

For those of you fitting an internal toroidal transformer. Please, please make sure there is no
way the top metal disc of the transformer's mounting can touch the top of the casing. 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.
The PCB will be supported well 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 prototypes have been very happy just supported by the
pots. However, my rack is bolted to the wall, so it doesn’t get moved around much! If you
intend to take it out on the road, extra support may be a good idea.
Power Supplies and things that can kill if you don’t do them
properly...
The recommended option is to use an insulated wallwart or AC adapter. These can be bought
from most places and are used external to the 3031 housing. They are very safe since all the
nasty dangerous stuff is kept inside the wall-wart. You won’t hurt yourself with the output
from one of these unless you stick it in your mouth!! You need a 12V or 15V AC output at
250mA or higher rating. Do not use a DC output type. Although the latter are the most
common type of wallwart for guitar effects pedals, they will not work with the 3031. To
reiterate, because this is really important, it must say 12VAC or 15VAC on it somewhere.
In the UK they can be bought from Maplin Electronics. In North America, US Robotics make
various types.
To connect your wall wart to the 3031, you need a suitable connector. The standard type is
the barrel type as found on most effects pedals. Make sure you get the right socket for the
plug you have on the wall wart. Some wall warts give you a little bundle of different types to
choose from. Either way, make sure the socket you get allows the plug to slip in easily yet not
break connection when wiggled gently. If you are making up your own plug for it, since it is
AC, it does not matter which wire goes to what. There is no + or -.
The socket must be connected to AC1 and AC2 on the PCB. AC3 is left unconnected. If you
have a metal power socket and metal case, make sure the that AC2 is connected to the outer
shroud of the socket, ie. the one that goes to the barrel of the plug. Failure to do so may result
in burnt out wall warts or at the best excessive hum. This is not to do with the polarity of the
AC. This is to do with the fact that the AC2 pad on the PCB is connected to analogue ground.
You do want the case to be connected to AC1, which will have a voltage on it that is
bouncing up and down 50 or 60 times a second.
If you have a metal case I would ground your casing. Simply take a wire from one of the GND
pads, G1, G2 or G3, and take this to any point on the case. Use a terminal or solder tag to
attach the wire to the metal case.
19