[sdiy] TB303 transistors

[Fiercefish]

I am soon to be building an x0b0x 303 clone, the square wave and resonance don't sound exactly like a 303 and one of the designers attributes this to the gain of the 303's  2sa733ap  transistors as used in the VCF and VCO circuits of the 303, the part substituted is 2sa733p. The difference is the 733ap part has a gain of 300-350 while the 733p has 270-310. 

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?


Details of the x0b0x notes here http://www.ladyada.net/make/x0xb0x/mods.html

If you listen to this soundfile  http://www.ladyada.net/make/x0xb0x/samples/pattern2-stereo.mp3 you will hear what I mean about the squarewave, the real 303 is on the right channel, the x0b0x on the left, if you use winamp you can pan between L & R to compare.

Thanks for any input!

FF
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