amb
Member of the Trade: AMB Laboratories
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- Apr 1, 2004
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Quote:
The purpose (and importance) for matching transistors differ depending on which transistors we're talking about. At the output stage of the dyna{lo,hi}, since there are multiple pairs of transistors in parallel, matching the hfe between the NPNs helps to equalize the amount of current flowing through each branch. There are emitter resistors to help this too, so the matching is not too critical. The match between the NPN and the PNP sides are for making the transition between the two halves more linear, but since the output stage is operating in class A for most loads, the transistors never cut off so again the importance of matching here is not that great.
For the input differential stage, though, the matching is important for keeping the basic DC offset low, and to allow the global feedback to do its job properly, minimizing distortion.
| Originally Posted by steinchen but transistor matching is not unconditional neccessary for a working amp, is it ? the pots and the servos will put the offset nearly down to zero (if I understand some infos right). Matching transitors is for minimizing takeover distortion and maximizing performance. |
The purpose (and importance) for matching transistors differ depending on which transistors we're talking about. At the output stage of the dyna{lo,hi}, since there are multiple pairs of transistors in parallel, matching the hfe between the NPNs helps to equalize the amount of current flowing through each branch. There are emitter resistors to help this too, so the matching is not too critical. The match between the NPN and the PNP sides are for making the transition between the two halves more linear, but since the output stage is operating in class A for most loads, the transistors never cut off so again the importance of matching here is not that great.
For the input differential stage, though, the matching is important for keeping the basic DC offset low, and to allow the global feedback to do its job properly, minimizing distortion.
