The PIC is a special programmed device that is supplied when you buy the PCB. Spare pre-
programmed PICs, should you break yours, are also available for a small charge. Neither
Sequentix nor Oakley Sound will provide the firmware separately.
The other semiconductors used in the TM3030 are standard parts that you should be able to
get from your local parts supplier.
The PTC is a 1K +3500ppm/K positive temperature coefficient resistor. This means its
resistance goes up with temperature. It's there to keep the VCO’s frequency relatively stable
as the ambient temperature changes. The PTC I now use for this job is made by KRL in the
US. They can be most easily obtained from Oakley Sound with your PCB or via Thonk.
Other PTCs do exist and good use can be had from the cheaper Meggitt series. Farnell's part
number is 1174306 and Mouser's 279-LT300014T261K0J. It's a 1K +3000ppm/K 900mW
device. The old TB3030 used this part and I thought it was great until I tried the KRL parts. I
can simply say that once fitted the KRL parts give much better tuning stability over a wider
range of temperatures.
Input and output sockets are not board mounted. You can choose whichever type of sockets
you wish. However, to reduce the possibility of earth loops you may be wise to use plastic
sockets for the audio output socket.
The LEDs can be any type, although I recommend the use of standard round 3mm types. You
will need to bend their legs if you want them to stick through the panel. More detail about
mounting the LEDs is given on this later on this document. Many manufacturers do ready
made preformed LEDs in little plastic boxes. These may be perfect for the job, but be careful
that your LEDs have the cathode on the right hand side as you look at the front of the device.
The suggested colours for the LEDs are just that, suggestions. You can chose any colour you
want for any of the LEDs. However, bear in mind blue LEDs and other high efficiency LEDs
may appear to be too bright unless you reduce the current with a bigger current limiting
resistor. The current limiting resistors are R64 for the gate, R84 for accent, R31 for slide and
R104 for the power on LEDs. If your chosen LEDs are too bright simply double the value of
the current limiting resistor, say to 2K2, and see what that looks like.
The front panel switch can be any style if you are not fitting it directly to the PCB. However,
the PCB is designed to use the miniature toggle range from C&K. Ones made by Multicomp
also fit very nicely. The switch should be an ordinary ON-ON switch, sometimes called SPDT.
The C&K types are ‘type 2 horizontal’ non-sealed units. C&K’s part number is
7101MD9AV2BE. Farnell part number: 9575502. Multicomp switches are similar but cheaper
and can also be obtained from Farnell. The Multicomp part number is 1MS1T2B4M7RE.
Farnell sell it as part number: 9473297.
The power on switch will probably be fitted to the rear of the unit if you are using a half rack
case or fitting two TM3030 units in one 1U rack. You can chose any type of switch you fancy,
but I normally go for ones that need a circular mounting hole since these are easier to fit.
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