Why the difference in how 9 volt pedals are wired?

Discussion in 'Effects, Pedals, Strings & Things' started by soldano16, Sep 16, 2008.

  1. soldano16

    soldano16 Member

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    I just got my used Analogman Beano Boost and reading the info and opening mine up, I see it's one of the earlier ones. So mine is wired one way and the later ones are wired reverse when it comes to using an external power supply.

    So my questions are?

    1) Can a builder use the exact same transistor for the different wirings?

    2) If it's the same transistor, is it just reverse wired?

    3) if 2) is yes, does it sound the same?

    4) if 3) is no, do they change because they ran out of the best transistors, or to accomodate user wants?

    I was confused before but now seeing the same pedal wired 2 ways, my confusion is deepened.
     
  2. jstone

    jstone Member

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    Your question is not very clear.
    Is the wiring of the adapter plug different or the whole pcb?

    If only different polarity on the DC plug it does not matter as long as you feed it the right way.
     
  3. soldano16

    soldano16 Member

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    I'm saying you could own 2 Beano Boosts and they would need different adapters. My basic question is why? Why are some of his wired one way and some the other?

    Why do you occasionally see, when looking at pedal specs. that one pedal says it takes the normal Boss 9 volt adapter and others say you can't use it, even though the pedal is 9volts.
     
  4. amp_surgeon

    amp_surgeon Member

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    A brief history...

    Back in the 60's most pedals only operated on batteries. Many of them had a separate power switch for turning them on and off. It was easy to forget to switch off a pedal after a rehearsal or gig, and a lot of dead batteries were the result. At some point, a bright pedal designer got the idea that you could use the input jack as a switch that would automatically turn off the pedal when it wasn't in use. The idea was based on the fact that when you plug a mono 1/4" plug (like the one on an instrument cable) into a stereo 1/4" jack it will short the sleeve and ring connections together. Since the sleeve is already grounded, it means that the ring connection will also be grounded anytime there's a plug in the jack. All they had to do was connect the ground side of the battery to the input jack ring connection, and they had a power switch! For most pedals, the ground side of the battery was the negative side.

    When pedal makers started adding power adapter jacks to their pedals they needed a way to disconnect the battery when the power adapter was plugged in. The type of jacks they used had a switch built into the sleeve connection specifically for this purpose. Since the negative side of the battery was already being switched by the input jack, they decided to use the switch in the adapter plug to switch the positive side. This meant that the positive side of the adapter had to be connected to the sleeve of the adapter jack, and the negative side of the adapter had to be connected to the center pin or "tip". Hence, the adapter was "tip negative".

    Well, this setup was fine and dandy, as long as the pedal circuit was negative ground, and as long as the power adapter jack wasn't designed so that the sleeve (the positive side) was connected to ground. However, this wasn't the case with circuits that used PNP transistors, which is what most germanium transistors were. It also wasn't the case if the pedal maker used a metal power jack that had the sleeve connected to the chassis.

    The Beano Boost uses PNP germanium transistors. The older circuits used a positive ground, just like the original Dallas Rangemaster. Newer models have been redesigned to work with a negative ground and conventional power adapters.
     
  5. tlpruitt

    tlpruitt Member

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    It sounds like you are referring to some pedals being wired as positive ground or negative ground. You see this a lot with transistor based fuzzes and treble boosters.

    These effects can usually be wired either way (positive ground or negative ground) and some builders and kits give you the option of picking either way. The critical part is when you use an external wall wart type supply you need to use one with the correct polarity on the plug that goes into the pedal.
     
  6. soldano16

    soldano16 Member

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    Does that mean the juice runs through the tranny in a different direction, depending on the choice of P or N ground?
     
  7. amp_surgeon

    amp_surgeon Member

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    No, and I'm not sure his statement about freely choosing positive or negative ground is entirely accurate. Most of the kits that give you this option do so because they give you the option of using either NPN or PNP transistors. The GGG FuzzFace kit is negative ground when you use NPN transistors, and positive ground when you use PNP transistors.
     
  8. soldano16

    soldano16 Member

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    OK - progress I think.

    So it does matter in which direction the juice flows, specific to the polarity of the specific transistor used.

    So if the Beano Boost in different versions comes wired differently that would mean he has used different transistors from one batch to the next, going from a PNP to NPN or vice versa. On his site he mentions different transistors being used.

    Seems to make sense. I won't ask why some trannys were made PNP and some NPN.

    Let me guess.

    Could one be silicon based and the other germanium? Is that the fundamental difference that drives this?

    I don't understand this stuff but it's fun to pretend.:YinYang
     
  9. tlpruitt

    tlpruitt Member

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    Not exactly. NPN and PNP transistors can be used in a circuit with negative ground or a circuit with positive ground. For example, you could make a PNP Beano with negative ground and a PNP Beano with positive ground. You could also make an NPN Beano with negative ground and an NPN Beano with positive ground.
     
  10. amp_surgeon

    amp_surgeon Member

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    Not if you use the same circuit design.

    A common emitter stage (which is the most common) is basically the same, whether it uses a PNP or an NPN. What is different is the polarity of the power you have to feed it. If it's PNP then the collector MUST be more negative than the base, which in turn must be more negative than the emitter. If it's NPN then it's the other way around.

    The term "common emitter" means that the emitter is common to both the input and output of the circuit. This is where the signal's ground is ultimately going to be connected. With a single polarity power supply (like a battery) the emitter of an NPN is going to be connected to the NEGATIVE side of the battery (often through a resistor), while the emitter of a PNP is going to be connected to the POSITIVE side of the battery (again, often through a resistor).

    Now, you could certainly connect either side of the DC power supply to the chassis, making the chassis either positive or negative ground, regardless of whether NPN or PNP transistors are used. However, on the circuit board the signal ground is still going to be connected to the positive side if it's PNP, or the negative side if it's NPN. The only real way to get around this is to use a bi-polar power supply, or split the voltage down the middle and set the signal ground level at 4.5V. You could also isolate the signal return path using transformers.

    The only time any of this really matters is when you daisy chain the power supply of pedals with opposite grounds.
     
  11. IvIark

    IvIark Member

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    I don't know what transistors are in the Beano, but for common transistors the manufacturers have, more often than not, done an NPN and PNP version of the same thing. The AC128 transistor which is very commonly used is PNP, but they also manufactured an AC127 which was the NPN version. A good alternative to the AC128 is an AC188, and they also make an AC187 NPN version.

    So any effect circuits out there that have a positive ground can be adapted and a suitable transistor can be used in place of the PNP transistor selected by the manufacturer. But bear in mind that simply swapping the transistor won't change a PNP fuzz or boost into an NPN one. The circuit has to be modified to make allowances for the change in transistor.
     
  12. tlpruitt

    tlpruitt Member

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    I agree. I don't believe my post said you could use the same circuit.
     
  13. analogmike

    analogmike Gold Supporting Member

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    Our Beano Boost has always used PNP germanium transistors. We just modified the power circuit a bit to make it negative ground so it would be easier to use. There is no difference in sound or performance with the newer ones. That's the simple answer, hope it helps!
     

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