This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Tuesday, August 6, 2019

Benson Preamp

This one just traced over on FSB. It's essentially a modified Wampler Plexidrive with an added bass control. Unless you're really sure any through-hole J201s you have on hand are in spec/authentic, I'd suggest using MMBFJ201s, which are the SMD version which are still in production and much easier to get in spec than the discontinued through-hole version. SMD to through-hole conversion boards here.





Update August 19, 2019:
Corrected a few values that have now been confirmed by Benson. The traces haven't changed however.

12 comments:

  1. Cool post, David! I'll be watching the play-by-play in the FSB discussion.

    Man... there's always something new to learn from this community! Half the time I feel like it's a "more I learn the less I know" situation, but it sure beats how things were when I first tried to build pedals (back in the pre-internet days).

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  2. EarthQuaker Devices Grand Orbiter plz !!! ty

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  3. The resistor right before the master volume is 47K, according to the guy who traced the circuit on FSB.

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  4. Where can I get a board mounted B2M pot?!I can't find them on mammoth or smallbear

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    1. I think you're going to be stuck with solder lug B2M pots. Even Benson had that pot wired up offboard. Mouser has 24mm pots in B2M. Otherwise eBay's probably your best bet.

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  5. I can verified it. I use russian non matched КП303А transistors and replace 12K resistor with 100k trimpot to get 5v drain volage. Its not fuzzy, but fat dark overdrive. I think will be great with treble booster in front of pedal.

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  6. the diagram shows the different capacitances of one of the capacitors, which is the correct 22N or 33n

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    1. Depends on which schematic I look at online (found one that says 33, and one that says 22). I think 33 is probably the better bet?

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  7. hello, pls teach me how to adjust bias with trimpots for this schematic. thanksss.

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  8. It sounds awesome, thanks for posting this! As Simon suggested, it's amazing with a treble booster in front. I tried it with a Runoffgroove Omega. Both full range and treble boost in front works great with it! For people that wonder how to bias the jfets, bias them to 4V. I went with 4.5v, wasn't super satisfied, found out that it's supposed to be 4v on some forums, now I'm having a blast! Thinking of boxing it with Omega as a double pedal :)

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  9. Re-verified.

    FYI, compared to the PedalPCB Son of Ben, this is missing a 10uF cap to ground on leg 2 of Q3. I squeezed on in after building this and I like the extra oomph.

    Nonetheless, thanks for the layout. Sounds great and saved me some time. :)

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