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  1. #1
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    Matching transistors 2SA899/2SC1904

    I have a number of 2SA899/2SC1904 transistors that I am going to sell on eBay, I think that they will sell faster and for a better price if I were to sell them as matched pairs. I think that for a complementary pair hfe is more important than vbe matching. How close in gain do the transistors have to be to claim they are a matching pair, what would you expect if you were buying them?

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    Re: Matching transistors 2SA899/2SC1904

    A reasonable variation is ten percent since a similar tolerance was expected in resistors installed in a great number of amplifiers for years.

    An electronics expert told me that commercial amplifier stages were made to deliver acceptable performance from the supply of transistors, whether low quality (low-gain), even if it meant getting mediocre performance from superior quality. In this way production could be done without need to test every unit.

    I think that for a complementary pair hfe is more important than vbe matching.
    If we want symmetrical response, which is easier to influence in the simplest manner, hfe or vbe? Are these transistors for audio amplifiers? Then is mismatched hfe or mismatched vbe easier to hear?



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    Re: Matching transistors 2SA899/2SC1904

    Hi,

    Maybe these transitors are used at gate drivers for class AB Mosfet audio amplifiers...
    If so, then neither hfe mismatch nor Vbe mismatch will cause audible distortion.
    The very most of the error is canceled out by the feedbacked system (open loop gain).

    This is different to the transistors at the difference amplifier stage. There V_be mismatch may cause (amplified) offset at the output.
    Thus "matching" with transistors in this stage makes more sense.

    But for sure you may sell matched pairs. I assume there are some audio enthusiasts that are happy to get pairs.

    Hfe or Vbe: I tend to match hfe, because Vbe just causes inaudible "static" offset and additionally this is cancelled out by huge open loop gain.
    Hfe mismatch may cause unsymmetric dV/dt at rising and falling edge, which is a "dynamic" error. The faster the signal the higher is the influence of the mismatch. Additionally at fast rising/falling signal the open loop gain is low and thus the error can't be compensated optimally.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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