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waveform. This will emphasise certain higher harmonics. Use this in conjunction with the
resonance pot and you can get good approximations to hard synchronisation.
VOLUME: Controls the final output level. The 3031’s output level is very high and is similar
to the output of pro-audio equipment.
Components
Most of the parts are easily available form your local parts stockist. I use Rapid Electronics,
RS Components, Maplin and Farnell, here in the UK. The 3031 was designed to be built solely
from parts obtainable from Rapid Electronics and myself only. Rapid’s telephone number is
01206 751166. They offer a traditional ‘paper’ catalogue as well as an on-line ordering
service.
In North America, companies called Mouser, Newark and Digikey are very popular. In
Germany, try Reichelt, and in Scandinavia you can use Elfa. All companies have websites with
their name in the URL. In the Netherlands try using www.telec.com.
The pots are Omeg Eco types with matching brackets. You could use any type you want, but
not all pots have the same pin spacing. Not a problem, of course, if you are not fitting them to
the board. In the UK, CPC, Maplin and Rapid sell the Omeg pots at a very good price.
The resistors can be 5% carbon 0.25W types except where stated. However, I would go for
1% 0.25W metal film resistors throughout, since these are very cheap nowadays. If you do
want to use 5% types, the please note that some of the resistors in the 3031 have to be 1% or
better types. Failure to use good quality parts in these locations will affect the VCO tuning
stability and the stability of your outputs. These critical parts are indicated in the parts list.
All the electrolytics (abbreviated to ‘elect’ in the parts list) should be over 25V, except where
stated, and radially mounted. However, don’t chose too higher voltage either. The higher the
working voltage the larger in size the capacitor. A 220V capacitor will be too big to fit on the
board. 25V or 35V is a good value to go for.
The pitch spacing of all the non-polar capacitors is now 5mm (0.2”). This may differ from
some of the older Oakley boards you have built. For values between 1nF and 1uF, I use
metalised polyester film types. These come in little plastic boxes with legs that stick out of the
bottom. Try to get ones with operating voltages of 63V or 100V.
I would fit a close tolerance polystyrene for the VCO timing cap, C9. This will give better
pitch stability. Use a cheaper part if you can accept a small drift in VCO pitch with time. The
PCB is laid out to accept a 10nF LCR type EXFS/HR series, but these radial types are getting
very rare now. Standard axial types will fit into the board if mounted on one end. The working
voltage can be quite low, 63V is common.
Other alternatives to polystyrene are polypropylene. But make sure you get low voltage types
like 63V or so. Polypropylene capacitors are also used in suppression and can get very very
big.
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