I just wanted to clear something up about the 2SA733(AP
) vs. 2SA733(P
The original TB303 used 2SA733(AP
) Transistors, these are harder to get.
The original x0xb0x design used 2SA733(P
) Transistors as they are easy to get.ripe909
tested some 2SA733(AP
)'s pulled from some Roland Gear and got the following results:
I have a bunch of 733AP pulled from Roland synths and they don't have much higher beta than the 733Ps, only one out of 20 tested above 300, the rest were all around 280 (which is mid-high for all of the
733Ps that I tested). The ones I have don't have a manufacturer marking on them, only the part (A733 AP122)
Now according to ripe909 1 out of 20 2SA733(AP) transistors was over 300, therefore a high Beta would be classed as over 300.
I randomly selected and tested 100 x 2SA733(AP)'s, and got the following results for their beta's, sorted from highest to lowest,
Average Beta (Hfe) = 272 <- the mid-High range as ripe909 found.
Highest Beta = 354
Lowest Beta = 222
Conclusion (also according to phono
phono wrote:just pick the highest three from the lot you have and place them Q10, Q9 and Q8, the rest of them arent important.
About 3 out of 10 tested are greater than 300, these are used for Q8, Q9, and Q10
, as it DOES matter
that these 3 have an Hfe > 300
About 7 out of 10 tested are less than 300, these are used for the other 7 transistors as it DOES NOT matter
what the Hfe of these 7 are.
I am emphasizing this as there seems to be an obsession with high beta transistors, if beta was the only consideration then you could use any high beta transistor in a x0xb0x/TB303, but this is not the case.
So why use 2SA733(AP)'s transistors? The short answer is a TB303 used them, and a x0xb0x is the closest thing sonically to a TB303, that has ever been made. Since all transistors have slightly different characteristics, the worst thing that could happen is that it doesn't make any difference, the best is it sounds like a real TB303.