KSC3503-D has a Hfe classification of 60-120 whereas KSC3503-E has a Hfe classification of 100-200. I have KSC3503-D at the moment as well as BD139,2SD669A (marked as H669A) which i dont know if they are genuine or not. KSC3503-D is original Fairchild. i will test one of them for the time being until i order new parts..
The datasheet for BD829 is not very informative. Since you are going to use 2SC4793 as drivers, why don't you give them a try in a VAS too? OTOH, if the collector current of Q7 is not very high, you can try some low power NPNs such 2SC2240 etc.
the power dissipation of vas transistor is around 250mW which i think is a bit high for a to-92 device.
Yes, you are right. In such a case the mid-power transistor should be used. I recommended you KSC2690 since I have some of them (Y-grade I think) and I know their Hfe are 220-240. The other choice could be 2SC4793 or 2SC5171 which can have relatively high betas too.
Coming back to a previous concern about the single pole roll-off filters that are created by C2, C3, C4 C7 and C9. AndrewT stated that the RC value of input filter C4*R21 should be the lowest of all the other filters. How are the other filter mathematically expressed?? The filter created by C3 is expressed as C3*R27.What about the others?
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Thanks Andrew.I am trying to apply what you said about input RC value C4*R21 that should be quite smaller of all the others in the circuit so as to define the corner frequency of the amplifier.For the values shown:
C2*(R13//R14) = 76ms
C4*R21= 56ms
C3*R27 = 33ms (C3 has to be raised from 220uF to 680uF or 1000uF for 102ms or 150ms to comply with our rule)
What about capacitors C7 and C9? The load seen by C9 is R18 and that of C7 is R11//R speaker?
C2*(R13//R14) = 76ms
C4*R21= 56ms
C3*R27 = 33ms (C3 has to be raised from 220uF to 680uF or 1000uF for 102ms or 150ms to comply with our rule)
What about capacitors C7 and C9? The load seen by C9 is R18 and that of C7 is R11//R speaker?
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