Oakley 3031 - Manual (Page 4)

the tbDAC. The gate is ON when above 3V. A new schmitt trigger circuit is provided for
glitch free triggering.
10. Accent Decay has been provided. The original TB303 produces a fixed short decay time
when accented. This control allows you to alter it, up to the time set by the ordinary decay
pot.
11. VCA decay. The TB303 has a fixed VCA decay of about 3 seconds. This control allows
you to change it to some time between 0.1s to 3s.
12. Power supply. The 3031 comes with a very low noise stable all analogue 723 based power
supply. You will need a AC wall wart to power it, or you can fit an internal mains transformer
if you know how to do it. The on board power supply is over rated. You can, if the wall wart
will allow, use the 3031’s power supply to drive any other ancillary circuitry. For example,
you can supply the Oakley tbDAC with +/-12V. If you do use the 3031 to power other
external circuitry, watch out for excessive power dissipation in the pass elements. If you can’t
touch the power devices because they are too hot, you need heatsinks.
13. The secret grit weapon. In the TB303 the slide function is always triggered prior to any
new note. This was not really by design, more of a by-product due to cost saving. However, it
may be responsible for some of the grit associated with the attack portion of the TB sound.
Many commercial clones have been criticised for not having the bite that the original had. My
spike circuit may well do the trick. This, like the TB303, slews the pitch CV before every new
note for a small fraction of a second. In the TB303 it was tempo dependent, but in mine it is
fixed, since we don’t know what speed the sequence will be run.
14. A slide control pot has been added. This can lead to slide times of up to 1 second.
15. The filter frequency and envelope amount pots operate over a wider control range than the
original TB303. The TB303’s envelope amount could never go to zero, the 3031 gives you
that control.
16. The TB303 and the issue 1 TB3030 featured exactly the same VCO design. However, I
found the pitch of the TB3030 VCO to go slightly flat at very high frequencies. This was no
major problem in a machine designed to play bass sequences of course. However, as I began
to use my original dual TB3030 more and more, I realised that the unit was capable of some
amazing sounds at the high end of the keyboard. Almost guitar type distortions could be
possible. Issue 2 of the TB3030 featured the same VCO core and waveshaping as before, but
the exponential current sink has been improved. The VCO tracked very well right up to the
very highest notes.
The 3031 improves this still further. Temperature stability is provided by a -3500ppm/K
temperature coefficient resistor for a really stable VCO pitch. The CV summing circuit has
been improved too this time around. Setting up is easier than before.
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