Friday 31 July 2020

Fuzzhead Fx Box of Germanium Mk. II

An updated version of a project I was tinkering with a couple of years ago. The idea was basically to find some use for some low leak USSR germaniums other than in Fuzz faces, Rangemasters and Tonebenders, And to do a germanium version of Zvex Box of Rock. Some biasing tweaks was necessary since BJT Ge's is a completely different animal to MOSFETs but the cap values in the signal path is more or less identical. Couldn't resist to add Boost switch so you can use it as a fuzz as well...and decrease the value of the low pass filter cap in the tonestack to 12nF since I found it a bit muddy with 22nF.

First version was positive ground but I used normal power supply for this version since I have to many unused MP38A transistors but other fairly low gain and low leak NPN germaniums should work as well.


 



26 comments:

  1. I'm ashamed to ask (kind of a challeng): can you think of doing this someday?:
    https://imgbb.com/Nns6nLR

    I promise I'll build it next minute.

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    1. I guess it is doable once we find a suitable socket board for the Spin FV-1....

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    2. Ahem...

      'https://www.pedalpcb.com/product/fv1-adapter/

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    3. i made from there https://the7line.clan.su/publ/diystompbox/fv_1_reverb/2-1-0-46

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    4. should be doable. u still need a loaded EPROM

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  2. Great, man! Hope, old hope, it's the last thing to die. :o)

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  3. And here to, by the way:
    https://www.musikding.de/FV-1-adaptor-pcb

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  4. Any suggestions for gain ranges?

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    Replies
    1. Hfe 60-80 sounds good, you can probably go higher. More important is the leakage which should be really low otherwise you might experience some serious hissing.

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  7. Never mind my previous comments...forgot to add the 100n MLCC in the top row. Sounds awesome - only thing is that I might experiment with a Rev Log for the gain pot, see if the sweep is smoother.

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  8. Question: What would be the easiest way to take the toggle switch to a separate footswitch for the boost? Wire one side of a DPDT, pins one and 2?

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    1. Thats exactly how to do it and if you want a LED indicator you can connect pin 5 to ground and pin 4 to a current limiting resistor that connects to the cathode of the LED. Anode leg goes to 9v.

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  9. Built PCB for this one, Great Fuzz, used mp 38a hfe=60-70, added some mode like TB mk3- ge diod between base Q3 & earth. Use DPDT to flick mode.
    Thanks for the scheme!

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    Replies
    1. Very cool! Glad you like it. Would love to see your PCB layout!
      And how does your diode mod affect the overall sound?

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    2. diode add some smooth & compression.

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  13. https://imgur.com/4lIouSX
    https://imgur.com/MBsOyfW

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  14. This fuzz has a lot of harmonics, sustaine, dirty, so this is my favorite last month!!! Thank you, Fuzzhead!

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