The x0xb0x is a very close clone. For the synthesizer section almost every capacitor, resisitor, IC, and transistor are exactly the same with the TB303. Some substitutions have needed to be made. The x0xb0x diverges from the TB303 in 2 major sections. The PowerSupply and the DigitalSequencer.
There are a few things that would need to change before the x0xb0x were to become a 'true' 303 clone that any purist would love.
Replace the 2SC733p transistors to 2SC733ap see HighGainTransistors
Load down the power supply A little more to 'de-stiffen' it with the resonance_warble
Replace the BA6110 to a BA622A
Make the interface of the x0xb0x harder to work with, so that you are not exactly sure what note you are entering, and when that note is. Conversely, take this advice from LadyAda: "The Roland TB-303 also used a strange method of programming which required entering notes and timebases seperately, which sometimes would lead to "'interesting patterns' appearing in memory. This technique is not used, although you are free to drink heavily before programming the x0xb0x, which may also elict 'interesting patterns.'"
comment by vooh: LadyAda might be an electronics genious, she's not a 303 user.. If she would be she'd realise why her approach sucks. It's just way more logical and musical to enter time and pitch data seperate. (as a musician)
See Also Tb303X0xb0xDifferences