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I do still use the 2SK30A-Y in the 3031. The Y types are still produced by Toshiba and are
easily available. I also use the 2SK30A-GR too. This is used in the FET buffer for the new
VCA circuit. A Y type may be used in its place, and either may be provided in the ‘odd parts’
kit.
The original Japanese NPN pair is the 2SC1583. It is a superb component and although not
made any more is still readily available in most places. Matched pairs are required in two
places in the 3031, the exponential convertor and the differential amp in the VCF. The PCB is
actually laid out to take the newer 2SC3381. This offers a similar performance to the
2SC1583, and is supposedly geared towards audiophile use. I cannot tell the difference
between the two parts audibly, and since the 2SC3381 is still in production I have chosen to
recommend this part.
All the other ICs are dual in line (DIL or DIP) packages. These are generally, but not always,
suffixed with a CP or a CN in their part numbers. For example; TL072CP. Do not use SMD,
SM or surface mount packages.
The PTC is a positive temperature coefficient resistor. This means it resistance goes up with
temperature. Its 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 are
expensive parts to buy, but they are included in the ‘odd parts’ kit. Other PTCs do exist and
good use can be had from the cheaper Meggitt series. Farnell part number 732-278. Its 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 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 all the CV and gate inputs.
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 Scheaffer front panel database was designed so that ordinary 3mm LEDs are to be used.
The prepackaged preformed types will probably not fit my panel design. Two of the LEDs are
not fitted to the front panel. These are the overdrive LEDs, LED4 and LED6. They must be
3mm types otherwise they won’t fit on the board. I use green LEDs to get a good distortion
sound. Changing the colour of the LEDs will alter the sound of the overdrive.
The switches can be any style if you are not fitting them directly to the PCB. However, the
PCB is designed to use the miniature toggle range from C&K, but ones made by MultiComp
also fit very nicely. The C&K types are ‘type 2 horizontal’ non-sealed units.
Two of the switches are ordinary ON-ON switches, sometimes called SPDT. The ‘filter
control’ switch is an ON-OFF-ON. This is the same as an ordinary ‘up-down’ toggle switch,
but it has an additional position in the middle. This third position neither connects the switch's
wiper to either the bottom or top connection.
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