PNP/NPN....explain?

Discussion in 'Effects, Pedals, Strings & Things' started by Garygtr, Sep 11, 2005.


  1. Garygtr

    Garygtr Almost as good! Silver Supporting Member

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    Can someone give me an explanation in laymen's terms as to what these 2 terms mean as applied to transistors/pedals? Advantages and disadvantages of either?
    Thanks!
     
  2. VaughnC

    VaughnC Supporting Member

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    A standard bipolar transistor is basically a bonded 3 layer sandwich of three pieces of silicon (or older style germanium) with a wire lead attached to each layer. The 3 layers are called the emitter, base, and collector. Each layer is "doped" with material to make it either an "N" or "P" type silicon....and the center layer (the base) needs to be the opposite type of the outer layers (emitter & collector) for a transistor to work. So a transistor can be either NPN: N(emitter), P(base), N(collector) or PNP: P(emitter), N(base), P(collector).

    Very basically, the reason transistors are made NPN & PNP is so they can work with either a negative or positive voltage supply. The base/collector junction in a transistor needs to be foreward biased to work properly....so an NPN transistor needs to be powered by a negative voltage supply voltage and a PNP transistor needs to be powered by a positive voltage supply.

    Theoretically, there should be no sonic difference in a similarly designed PNP or NPN circuit.....but, as we all know, tone is very subjective!
     
  3. leofenderbender

    leofenderbender Supporting Member

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    It is an issue of polarity and design: Negative Positive Negative vs Positive Negative Positive.
     
  4. VaughnC

    VaughnC Supporting Member

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    Sort of....but when you say "Negative Positive Negative" (instead of NPN) there's an implication that voltage is being generated in a transistor....which there isn't. NPN or PNP only tells you what applied voltage polarity will fire the junctions.

    If you remove either the emitter or collector layer from a transistor, you end up with a PN or NP junction, which is commonly known as a diode. With a diode, connecting a positive voltage to the P type side and the return negative votage to the N type side, current will flow. Reverse the voltage polarity or the diode direction and very little current will flow. Also, in a diode, the P type silicon is referred to as the anode and the N type silicon is referred to as the cathode. So, essentially, a transistor is two diodes connected together in such a way that they share a common element....called the "base" of the transistor.
     
  5. Garygtr

    Garygtr Almost as good! Silver Supporting Member

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    Great info, thanks to you both!
     
  6. zzzezums

    zzzezums Silver Supporting Member

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    Thanks for the explanation. A related question: I have a power supply (Fulltone Blackbox Jr.) that is tip-negative only. Is there some kind of adaptor I can use so I can use the power supply to power a tip-positive effect?
     
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  7. VaughnC

    VaughnC Supporting Member

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    No. If you have tip negative & tip positive effects pedals, you'll need either seperate power supply's for each type or a power supply that has both positive & negative ground outputs.
     
  8. John Phillips

    John Phillips Member

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    It depends totally if you mean "tip-positive, negative ground" (eg RAT, old MXR - usually a 1/8" mini-jack instead of a barrel connector) or "positive ground" (eg Fulltone '69, Soulbender). The two things are entirely different.

    In the first case it's just a connector issue, and you can solve it by replacing the plug on the cable and reversing the connections.

    If it's a positive-ground pedal, what Vaughn says... you must have an isolated power supply.

    If you don't know which it is, open up the pedal and see which wire from the battery snap goes to the ring connection on the input jack - if it's the black wire, it's a negative-ground pedal regardless of the type of DC connector, and if it's the red it's a positive-ground pedal.
     
  9. zzzezums

    zzzezums Silver Supporting Member

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    Thank you both very much. Specifically, the pedal I'd like to power, rather than using batteries, is a Demeter Tremulator. The Fulltone power suppply has 6 tip-negative inputs in which to put Boss-type connectors. The Demeter uses a different size plug.

    Stupid question: how does one "replace the plug and reverse the connections?"

    Again, thanks!
     

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