ac128 germanium pnp transistor

Discussion in 'General Electronics Chat' started by stoopkid, Aug 8, 2011.

  1. stoopkid

    Thread Starter Member

    Mar 3, 2011
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    I'm working on a guitar pedal that calls for a ac128 germanium pnp transistor and I was wondering why I might not want to just get a modern equivalent.

    Thanks
     
  2. #12

    Expert

    Nov 30, 2010
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    It depends on the circuit. Germanium has slightly different characteristics from silicon. If you post the circuit, people here will be able to tell if it makes any difference.
     
  3. stoopkid

    Thread Starter Member

    Mar 3, 2011
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  4. Audioguru

    New Member

    Dec 20, 2007
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    It makes FUZZ sound which is extremely distorted sound.
    In my entire career I made circuits with extremely low distortion, not this noise.
     
  5. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
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    Yeah, that's what I'm trying to achieve. Are you saying that without these particular transistors I won't get the fuzz sound?
     
  6. #12

    Expert

    Nov 30, 2010
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    Now that we've heard from the man who has never worked with a distortion circuit, we can proceede.

    Changing to a silicon transistor will change the sound, but it WILL fuzz. You can do this for about $2 retail. Try some 2N3906 transistors from Radio Shack.
     
    kubeek likes this.
  7. stoopkid

    Thread Starter Member

    Mar 3, 2011
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    Cool, thank you... Oh just a small side question, do any of the components in that schematic require especially high voltage or wattage ratings? I wouldn't have thought so but I've seen that be the case with guitar pedal stuff.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    This works with line-level audio; between the instrument and the amp. Low power, very low wattage stuff.
     
  9. stoopkid

    Thread Starter Member

    Mar 3, 2011
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    That's what I thought but I wanted to be sure. Thanks.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    The very old AC128 germanium transistor had a different base-emitter voltage requirement compared to a silicon transistor and had a poor high frequency response so it will sound different to a silicon transistor.
     
  11. Roob

    Member

    Mar 21, 2015
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    Hi Stoopkid, it's a while ago now but just wondering if you made the circuit, how it sounded and what you used in the end...
     
  12. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
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    I'm no good at guitar but that should give an idea of what it sounds like. It will sound somewhat different depending on the transistors you end up with. I sold it a long time ago and never finished the second one so this video is all I have at the moment.

    I just got some AC128 transistors from ebay and the rest was from newark.com, put it together just like the schematic.
     
  13. Roob

    Member

    Mar 21, 2015
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    Brilliant! Sounds pretty good. I've found some ac128 on ebay too so will give this a go.

    Thanks for getting back to me so quick.
     
  14. Roob

    Member

    Mar 21, 2015
    35
    2
    I don't suppose you knew or remember the hfe value of the ac128 that you used?

    There are many examples of these transistors on ebay, npn/pnp matched pairs, untested and tested with hfe values given.

    Does anyone know the likelihood of getting a bad one if it's untested or what value is sensible for the hfe, or the effect of different hfe values with regard to a Fuzz effect pedal?
     
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