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, October 20, 2015

JHS MiniBomb

Here's a simple clean boost circuit built by JHS. It's really just the Tim Escobedo Duente JFET boost with a fixed resistor instead of a trimmer. Because of that you probably want to socket that resistor (5.1k) and adjust to the J201 you use. Or you can just squeeze a 25k trimmer on there like Tim designed it. Should fit in a 1590a just fine.



47 comments:

  1. Hi,
    I need to print this pcb in reverse mod?
    best wishes!

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    Replies
    1. No need to reverse it. Just print it as is. Good luck with the build!

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  2. hi pal.
    unintentionally built this one because my mate needed a booster for his recent gig, it seems more like a treble booster for me. it also has no sound when i turn the boost control to minimum position, just like a volume control.
    i have double-checked my build and everything and found nothing was wrong.
    any idea what's going on?

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    Replies
    1. Try increasing the value of that 100n cap to get less treble. Though 100n should be pretty close to having a flat response. Maybe you used a 10n? The pot will act as a volume control, so you've built it correctly.

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    2. then I have built it correctly. thanks again bro

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  3. Hi and I built it but ... having the potentiometer to the maximum just equaled the volume of true bypass, I guess having the trimmer 25K can adjust the gain and assume that change the resistance of 5.1k would be the solution, any suggestion resistance value? thanks

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    Replies
    1. Yes, you need to adjust the value of that 5.1k resistor to bias the JFET correctly. You could wire a normal sized pot in place of that resistor to bias the JFET. Then once it's sounding good, measure the resistance of the pot and replace it with a similar value resistor.

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    2. Certainly, I had not occurred, thanks

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  4. Nice!
    What would be the sweet spot in terms of voltage for the JFET?

    Cheers from Mexico

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    Replies
    1. Typically around 4.5v. I'd socket the 5.1k resistor and see what value resistor gets you close to that.

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  5. hey bro, I have a problem, in my city havent J201, can i use a similar model? what model?
    thanks!!

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  6. it works! great pedal (for the value lol)
    can i say.. i have an JHS... haha

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  7. hello i built this pedal but it works for decrease volume. I dont use reversed pcb. Iuse pcb on the picture. Thancs for answer

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  8. In what position should the pot be at when measuring drain voltage? On my SHO the voltage changes when turning the pot. Thanks for all the layouts:)

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    Replies
    1. Where the pot is shouldn't matter in this design. All the pot does in this is control the signal going to the gate of the transistor.

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  9. Pode postar a lista de materiais ?? E que n entendo muito de eletronica

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  10. Please could you pass me the subject line?, But I do not understand much of electronics

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  11. Nice jfet tru boost!
    I've end up using a 12k resistor to bias at Drain in my J201.

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  12. I've been trying to boost my shin ei companion fuzz with all types of boosts. This uber simple circuit did exactly what I needed. Figures it's the last one and the simplest one. Thanks!

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  13. Hi!
    A question, could a bs170 transistor work with this project? Thanks

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    Replies
    1. no, bs170 and 2n7000 are mosfet, you should use a jfrt transistor, j201, 2n5457 or mpf102 will work fine

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  14. Greetings from Brazil.
    If I change the capacitor value of 100n, what is the result?
    If I increase the value, do I have more BASS?

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  15. Hi!!
    Can you help me with some problems?
    The IN and OUT of the PCB, where do I have to connect it?
    I'm confused with that, I don't know if I have to connect it
    to the 3pdt switch or to the jacks?
    Greetings from Chile!!

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  16. Hi David,

    how to realize when the bias is well adjusted? when the sound looks clear and fluid it is good? is there a value in mv to respect as on the amps?

    Best Regards

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  17. I've been interested in using the simple circuit for a clean boost, but I was just going to emulate it online first, and I seemed to notice two things, 1 this circuit phase inverts, and 2 looking at the output curve it doesn't look as clean as I would have expected from a clean boost:


    http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+2.1831051418620846+50+5+43%0AR+64+96+-48+96+0+1+1000+1+0+0+0.5%0A174+64+192+128+96+0+1000000+0.27230000000000004+POT%0AO+256+96+288+96+0%0Ag+64+192+64+208+0%0Ar+176+96+176+16+0+3100%0Ar+256+96+256+160+0+100000%0Aw+176+128+176+96+0%0Aj+128+144+176+144+32+-1.5+0.00125%0Ag+176+160+176+208+0%0Ac+208+96+256+96+0+1.0000000000000001e-7+4.822625220565602%0Ag+256+160+256+208+0%0Ad+128+48+128+16+1+0.805904783%0A209+64+16+64+48+0+0.000022+9+1%0Ag+128+48+128+64+0%0Ag+64+48+64+64+0%0AR+64+16+64+-16+0+0+40+9+0+0+0.5%0Aw+64+16+128+16+0%0Aw+128+16+176+16+0%0Aw+176+96+208+96+0%0Ao+0+4+0+4099+2.5+0.00009765625+0+2+0+3%0Ao+2+4+0+4098+5+0.1+1+1%0A

    Any diy clean boosts you think would be better for getting incredibly true to the original input signal just amplified?

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  18. Hi, i have a question. On J201 voltage on drain is about 4.05V, on 2N5457 it's about 0.8V

    What should be the correct value of voltage to have perfect biasing on both transistors?

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  19. Built it point to point in a 1590a using this perf as guide. Used a 4.7k to bias cause it is what I had. Sounded great so I left it in. Used j201. This is a nice little boost. Definitely worth building!

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  20. o meu esta dando um estalo ao ligar e desligar no volume minimo como resolver esse pulldown?

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  21. It works, the drawing is good. I built a few pedals from the drawings here. Thanks for them.

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  22. @Effects Layout - uhmmm dumb question, but the pot in the layout? should it be attached in solder side? looking at the pot in your layout, pin1 is the right most and pin3 is left most?

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    Replies
    1. Yes. Attach it from the solder side. Pot lugs left to right: 3-2-1

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  23. Hi) I collected it. It works. A very good sound. Dense, bright. Collected. I advise everyone to assemble the guys. Just a question, I connected a bass guitar, and when turned on, low frequencies are cut off (below 125 approximately. What can be replaced so that the bass remains? Or not?

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    Replies
    1. Try increasing the output cap value to like 1uF.

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  24. I'm getting an overall volume LOSS. I've got it breadboarded, so I'm able to quickly short the input straight to the output and compare. I've got hot pickups that get a little dirt from the amp when I go direct, but it's super clean running through the circuit.

    I used a B500k, as I didn't have a B1M on hand. I'm wagering that's the culprit?

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    Replies
    1. I figured out the problem. For anyone else having the same issue, it was the bias resistor. I tried every value resistor I have and 1K worked best.

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  25. It workes but it gets distorted

    I used resistor 5.6 instead of 5.1

    And 2n5457 instead of j201..



    It is boosting but there is distortion i lowerend

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    Replies
    1. Sounds a wrong voltage Bias. You need to adjust the value of that 5.6k resistor to bias the JFET correctly: about 4.5v to Drain, use a normal pot as variable resistor to get it, once it's sounding good, measure the resistance of the pot and replace it with a similar value resistor.

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  26. Just put this together and there is a huge amount of noise. Whats interesting and hopefully helpful is that as you turn up the boost pot noise goes from no noise, steadily increasing with signal volume until near the end where it starts to decrease and isnt that terrible by fully CW.

    Gate and source are at 0v, drain is at 4.4v. Any ideas?

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