[sdiy] TB303 transistors

[Tom Arnold]

On Tue, May 24, 2005 at 07:10:02PM +0100, Fiercefish wrote:
>    I am keen to try to get the classic 303 square wave sound which is
>    very different (as is well documented) from any other synth, any
>    pointers on which transitors would be a better substitute (BC327,
>    BC557?) Also is the gain of the transitor affecting the waveshape or
>    PWM in a strange way in the 303? Why does it sound SO different?

Tony Allgood points out that the TB303 uses two different 2SK30's, the Y and
the O.  The O is hard to get, a Y ships with the x0xb0x.  I believe the
transistor in question is Q28.  If you look at the TB3031 docs he talks
about Why -O's are different from -Y's ( differing Idss ) and that the
Squarewave is dependant on the -O's Idss, so he uses a J201 unstead of a
2SK30 in that position.  

Personally I have a TB3031 because it can sound like a TB303, and I'm building
an x0xb0x because it'll be a neat toy, and maybe after its built it can be
tweaked in to sound a little closer to the original.  x0x should arrive
Friday... I figure I'll have it built by Midnight PST if not sooner...

-- 
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