Sunday, 28 April 2013

Escobedo Duende JFET = JHS MiniBomb

The circuit for these two are verbatim. Escobedo just has a trimmer to bias the JFET, where JHS has 5K1 resistor. He probably uses matched j201s...

JHS info:
A good booster is often the most underrated tool a guitarist can own. When placed before your overdrives or distortions, a thicker, stronger and more saturated tone can be achieved. When placed after, you get your exact same tone except louder. This is great for lead passages and for causing a tube amp to naturally overdrive due to its huge amount of headroom. You will notice a slight touch of presence that lets your tone cut through the mix for those passes that you really want to stand out. Chords are heard with clarity and subtle harmonics shine! The Mini-Bomb JFET boost can do all this and only takes up a small 1.5"x3.5” spot on your pedal board!
Oh yea, and did we mention....this pedal works great on both electric guitar and bass guitar!!!





Here's Geiri's demo of his two boards in series in one A-box:

53 comments:

  1. Hey dude, you can tag this. I built it to test with the gain stage-less DS-1 that mark drew up. To tell you the truth it's not that loud, although I did use a 2n5457 as I couldn't find my J201s. Also if anyone wants to build this don't bother with the one without the trimpot. I built that one first and it was quieter than the bypassed signal, I had to add a trimmer with a daughterboard and after finding the sweet spot it was much better.

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    1. Cool. Tagged. Thanks man!

      Well.. I do think that 2N5457 doesn't bias the same way as J201.. Socket and trial/error of a batch of transistors should yield good results. My batch of J201s usually bias nicely with 12k :)
      +m

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    2. Thanks for the info, I've got a few J201s around here somewhere, I really should label my component boxes and better. I'll have another look and try it with one but at the moment it's got the same sound as the demo video, just not as loud.

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  2. this was my first 1590A. worked great 1st time. I breadboarded it fist and used a b25k pot to determine the resistor value- I used an 8.2k (8.12K reading on my MM). sounds great, and has lots of headroom. unity is around 11 o'clock on the volume.

    I'm thinking of maybe putting in a bass cut switch, as it's a full range boost and can get slightly boomy.

    thanks for your great site!



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    1. I agree it's a nice little circuit, and I also agree it can get a little boomy, so I'd like to add a bass cut option too, but I don't know how because I'm such a noob!
      Actually I think it might get interesting to put a bass cut knob, but then again I got no idea on how to do it...
      Maybe someone could give me some advice?

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  3. here's a pic... I ran out of LEDs, so I still have to add that.

    http://imageshack.us/photo/my-images/854/jwhpedalsduendeboost.jpg/

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  4. really like this boost.. for something with so few parts, it really does a great job. Mine was very quiet and adds some overall sparkle, but was very transparent. Much better clean boost at first glance than the SHO clone, at least to my ears. Not nearly as raunchy though as the SHO.

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  5. sorry for the noob question but how is the input wired on this circuit? would it go from the switch to lug 3, then into the two green wires? this one looks a bit different from most of the others..
    thanks

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    1. There's the Boost knob. Input goes from bypass switchto Boost pot's lug 2.
      +m

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    2. Ok, I am having the same issue. I wired the input to the Boost pot's lug 3, and the two green wires to the Boost pot's lugs 1 and 2. The pedal is not 'firing'. If the input wire off of the switch needs to go to lug 2, which lugs do the two green wires off of the board need to go?

      Any help would be awesome. Thanks ...

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    3. My earlier answer was wrong. The input wire definitely goes to lug 3 as stated on the layout.

      Your problem could be with the bias. If the JFET is completely misbiased, you won't get any singal through the circuit.
      +m

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    4. Yep. That was it. Thanks for the reply ... my fav project so far.

      Delete
  6. I noticed there is no input cap to this circuit, because the input is direct to the JFET and the volume is controlled by a pot how does it affect the frequency control of the circuit, ie: more or less bass/treble in, and how does the volume control work differently then if it were at the end of the circuit like a tradition voltage divider. Also, is the is there a way to remove the volume pot and add an input cap? I was thinking it might make a good starting point for something I'm working on, but I want to control the bass frequencies, and use this to drive a second gain stage, so there would be volume control at the end that's a voltage divider.

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    1. This might be a good read:
      http://www.geofex.com/article_folders/foolwfets/foolwfets.htm
      +m

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    2. Thanks miro. I didn't see that on R.G. Keen's site. I'll check it out tonight.

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  7. Alright gents... I'm tearing my hair out on this one. It's so simple, and yet I'm struggling with it! I've got it all wired up, the switch works, and all of that. The only odd thing is the gain knob. At zero, I get no signal. As soon as I turn it to about 9 o'clock or so, I get loud radio interference, and no guitar signal. At noon, a little more guitar, but plenty of radio. At full gain, I finally get only guitar. Obviously something's not working right... any guesses? I've double checked the board, everything seems to be in the right place, no accidental bridges, etc.

    Any help would be extremely appreciated!

    Charlie

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    1. Probably grounding? I tested mine begore putting into the enclosure and got the same thing as you. Once arranged in a 1590B it worked perfectly.

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  8. I can't get either to boost signal. Both seem to cut it really well for me.

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  9. I'm having the same issue as cmengel with radio interference.
    Anyone know what might be the cause of this?
    I've checked and rechecked several times and can not find anything wrong.
    I went for the fixed resistor version, could the lack of matched J201 be the source of the problem?
    I will try to build one with a trimmer and see if I get the same issue...

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  10. Sorry. I'm confusing this with some other circuit. There is obviously not more than one jfet in this one, so ignor my question about matched j201's...

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  11. Could I turn this into a bass boost just by switching the capacitor value? If anyone already has tried, what kind?

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  12. Hi

    What should the JFET be biased at?

    Thanks

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  14. Anyone know the difference b/t this and the prestige? Any layouts? I tend to lean more toward the pestige from the demos I've heard.

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    1. hi man, have you got some news about the prestige? :)))

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    2. Very little from looking at the photos of the PCB bottom. It even has a tick box for Bomb Boost and Prestige on the same PCB.

      http://proguitarshop.com/media/catalog/product/cache/1/thumbnail/9df78eab33525d08d6e5fb8d27136e95/j/h/jhs-pedals-prestige-guts-c.jpg

      http://static.weloveshopping.com/shop/music-boulevard/extra/11558591.jpg

      The transistor seems to be moved to the other side on each giving the impression maybe the pot works differently. It is on the input of the bomb boost, it may control the JFET gain on the prestige, not sure but very interested to know now. It may also use a different JFET which would explain the character difference. I agree the prestige sounds nicer and a little grittier.

      You know anything more IVIark or mirosol? I haven't seen anything on FSB since the Bomb Boost thread.

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    3. Actually apologies that seems to be the pot that moves sides, so my theory is still possible. I think the transistors may be SMD cos I can't see where they connect in the pics?

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  16. Hi, just finished building this and I'm getting some noise that I don't think should be there when the boost is enabled.

    Anywhere between no signal and just below max I get some interference or noise. Weird thing is after the pot is maxed out, giving me the most boost I can get, the noise vanishes but I still get a nice volume boost.

    Any ideas? Any help would be greatly appreciated.

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    1. I have adjusted the bias giving me less noise with the effect engaged... but less boost too. Any way I could get more boost and less noise? Ha!

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    2. Try a 100uf dc filter cap, and/or a 47r resistor between the 9v supply and the 9v connection on the board. Those might help to quieten any noise.
      Cheers
      Dave

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    3. Thanks, will give it a try and report back!

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  17. I have had the same problem with really bad ground noise... I have not had radio freq but just this super loud annoying noise when the pot is between 0% and 100%. It is super weird... I tried different filter caps but that did nothing but cut the volume out of the pedal.

    What could the problem be?

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  18. this is an effect of a single transistor... this effect does reverse the phase, don't you?

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    1. How did you come to this conclusion?
      +m

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    2. a while ago I read an article about two boosters of a single transistor (one MOSFET and one pnp);
      I read that the boosters of a single transistor tend to reverse the phase of the signal of the guitar 180 degrees and when to use systems amp stereo the phase is canceled and the sound is very dull or opaque, so I wonder if it happens the same with this booster ...

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  19. Just wondering if you could add a master volume pot to this with the same instructions on the SHO compact?

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  20. Any solution to that noise problem between min and max of the pot??

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    1. I tried the 100uf cap... lowered the volume a lot. so no luck. also tried 47uf, noise came back

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    2. Did you box the pedal and it is still super noisy? I noticed mine was noisy but then, I didn't box it (I have to check it out later, I played around with mine very little). Often, boxing a pedal kills quite a bit of noise.

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  21. Any tips on how to set the trimmer please?

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    1. Try measuring voltage between the drain pin on the fet and ground, adjust the trimmer until it's about 4.5v

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  22. Is there any way to make one of these circuits work with a MPF102?

    I've read that they are technically JFETs, but are meant for other applications. I subbed one in, but it was super quiet. Can I change a resistor or something to make up for the gain loss?

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  23. Hello,
    I was going to build this, but I'm planning to put it inside a plastic box because it's part of a project I'm working on, so I'm afraid it would be noisy.
    I read that the noise problem is mostly with the gain control in the middle positions, so I was wandering if it could be any help to remove the gain control (or switch it with a fix resistor) and put a volume control on the output signal.
    Any advice?

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  24. Hi there,
    I would like to do away with the boost pot all together, so it would be on full volume all the time, how would I wire it without the pot?
    Any help would be appreciated!

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    Replies
    1. Try to solder the wire "Boost 2" directly to output.

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    2. Uh, I mean, input to "Boost 2".
      Adam

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  25. Hey guys.
    So after building the pedal exactly like instructions are, i have a problem where if the knob is at 0, there is no sound through the pedal. But the sound does come through as I turn the knob, as well as the amount of boost. Any easy way to fix it where the pedal is on and at 8, there is no boost added until i turn the knob up?

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  26. Built it with BF245A, cool little circuit. It adds a tiny bit of noise to the signal, but makes my darker sounding amp richer and brings some presence to the tone; it's always on for me.

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  27. Built this with a 2N5457 and it sounds amazing! Much fuller and more boost than my LPB1. Used a 10k trim pot in place of the 5.1k resistor to bias is. End measurement was 3.5k so swapped in a 3.3k resistor instead of the trimmer. Also tried adding some back-to-back clipping diodes to ground after the output cap (I extended the layout to be 10x5) and got some really nice overdrive tones. Well worth a play

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  28. Just built and sounds fantastic. I've replaced my LPB-1 boost with this. The MiniBomb makes my Strat (96,US Standard, stock single coils) warmer, louder, and with a nice top sparkle.

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