The PNP transistors shown as BC559 on the schematic should be high gain BC559C or
BC560C types.
The SCR in the VCO uses different transistors. Here I have used BC212L and BC182L.
Although these are actually pretty ordinary transistors, they have a different pin out to the
other NPN and PNP transistors used in the TM3030. They also have the same pin out as the
Japanese parts used in the original device. You could substitute these three transistors with the
Japanese parts if you can get them. The BC212L is equivalent to the 2SA733P, and the
BC182L is equivalent to the 2SC536F. It is in my opinion that there are no sonic differences
between the European and Japanese parts in this part of the circuit. Note that the BC212 and
BC182 cannot be used as they are as they have a different pin out to the BC212L and
BC182L.
The FET buffer of the VCO can be one of two parts. The PCB is laid out for both, but you
must ensure the one you use goes into the correct place on the board. Q1 should be a
2SK30A-O. Q2 should be a J201. Do not fit both. The original design and my own TB3030
used the 2SK30A-0 but these are quite tricky to find. In the TB3031 I used the J201, and I
still think this is a very good substitute for the Japanese part. In fact, it's possibly more
accurate since the variation between any two J201 devices may well be less than that of any
two 2SK30A-0.
I will leave the choice of device to you. However, I have tested both parts in the TM3030 and
recorded and compared the resultant audio output. I cannot tell the difference in the outputs
from the two types.
Q18 is also a 2SK30A-Y device. You should seek out this part if you want the envelopes to
behave in the same way as the original. Y types are easier to get hold of than O types and
various places sell them on line although the easiest place to buy is probably Ebay.
As we have seen the original design used two variants of the 2SK30A, the O and the Y types.
These two different types differ only by their value of
Idss
. This is the current that runs
through the device when the gate and source are grounded and the drain is taken to 10V. The
O types are defined as having a
Idss
of 0.6mA to 1.4mA. The Y types are defined as having
Idss
of 1.2mA to 3.0mA. Look at the range of Idss for the 2SK30A-O. It is interesting to note
this, because the sound of the square wave is dependant on the Idss of the O type device. So
no wonder that people have commented some TB303s sound slightly different to one another.
The original Japanese NPN pair is the 2SC1583. It is a superb component and although not
made any more it is still available from some places. Matched NPN pairs are required in three
places in the TM3030, the exponential convertor, the filter ladder and the differential amp in
the VCF. Only in the differential amplifier have I made space on the board to take the
2SC1583. In the other two positions I have used modern substitutes.
For the exponential converter I have decided to use the more easily available THAT300P in
place of the 2SC1583. There will be no sonic difference here and the THAT array is more
easily affixed to the temp co resistor used in our design.
For the filter ladder the original design uses two matched pairs, one at the bottom of the
ladder, a 2SC1583, and one at the top, a 2SC2291. Although the 2SC1583 is available,
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