I made this one with an on-board pot in mind (an Alpha 90 degree PCB pot will fit nicely on the trace side of the board, just remember to isolate the back of the pot). I’m also fairly sure it’ll fit in a Hammond 1590A enclosure, at least if you omit the switches.

Update (18.12.2012): Now verified as working, thanks to Freppo and Steve.

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17 thoughts on “Request: Xotic EP-Booster

  1. Never mind about swapping the Freq switch wires. I spoke…..er…typed…uh…wrote before testing out what I thought. It didn’t make a difference. Not sure why that switch doesn’t do anything. Still working on that one. Anybody else have any thoughts, or mods that make that switch do something…..anything??lol

  2. I think I’ve figured out the frequency switch problem. The lugs are switched. Freq SW 1 should be where Freq SW 2 is, and vice versa. According to my schematic, anyways.

  3. Hello, I’ve built it but I don’t have any boost. When I switch it on I have the signal of my guitar at the same level as before and the pot doesn’t do anything. I’ve measured the pot and the values are ok. Would you have a clue on which part of the circuit I should focus on to debug that ? Thank you very much

  4. Steve, I’m guessing here, but I think the frequency switch is for when you want to use this with a bass as the guitar frequencies are pretty much covered with the 10uF.

  5. Thanks Harald, I think i’ll just leave it at 9V. I boxed it up today and there was no pop. However, I don’t know if I was hearing things or not, but I can’t get the freq switch to do anything different either. Maybe something subtle, but to go from 10uf to 100uf I think there’d be something noticeable. Eq switch was subtle but more noticeable. Everything else worked fine though.

  6. I think +18v could work as long as you’ve got capacitors/electrolytics that are rated 25v+ (both transistors can handle 30v or more), but you may have to tweak R5 as you want the drain voltage on Q1 to be around +4.5-5v and this probably requires a larger value resistor.

  7. Could this be powered with +18V? Would this give it a little more output? I was going to try, but thought I’d see what you guys thought.

  8. Update: Before you call it 100% verified: I just tested it though my Vox AC15 and the frequency switch actually doesn’t seem to do anything. I’ve checked the connections and resoldered it, but still nothing. The EQ switch works fine and adds alittle highend sparkle. Other then that it sounds amazing. Dunno why the freq switch doesn’t work 🙁

  9. Hi Harald
    I just built this and it sounds great!! No bypass pops or other problems! =)
    The EQ and Freq switches doesn’t do very much. They work but the changes are subtle.
    It’s the best boost i’ve ever tried, really made my amp come alive. Cheers!

  10. Still haven’t boxed it so I don’t know about the “Pop”, but everything else sounds awesome. I wasn’t getting much output with the last J201 I had left, so I tried a 2N5457 and it seems much better to me. Thanks Harald

  11. No, I wouldn’t think that matters, but it really depends on how you’ve wired everything together etc. Both effects are wired as stand-alone effects with true-bypass and they just happen to share the same enclosure? From what I understand the noise is caused by your input cap (or maybe output cap too) slowly building up voltage when the effect is disengaged, which is then released as a pop when you engage the effect, and that’s why you have a drain resistor to ground making sure the cap stays at ground potential. Is there anything at the end of the first effect that could be responsible for this maybe? Also worth checking the resistor to ground at the output of the EP Booster just to make sure.

  12. Ok, tried replacing the Switch, including the capacitor and resistor to mitigate de “Led Pop” and still pops badly.. Anyone have a clue of what could be causing it? Sounds great but the pop is driving me nuts! 🙂

  13. Checked them both and still popping. I have it in a box with another effect. The EP is last in the chain, could that be causing it? The other doesn`t pop…

  14. Tag it Harald!! Only comment is that I`mgetting a POP when engaging it… Have the 1M pull down and everyting… Any ideas why???


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