Monday, 1 October 2012

Xotic AC Booster

Info from the manufacturer:

The AC Booster is a natural sounding "overdrive" pedal. Not "heavy" distortion, but a sweet thick overdrive with an "open" non-compressed feel. It's capable of a 20dB+ boost with an adjustable ±15dB two band active EQ which adds a wide range of harmonic content to your ideal sound









35 comments:

  1. Tag. Just a tad too dirty for my lust for clean preamps/boosters, but the bass boost is amazing. Used JRC4558D chip and 5088s.

    Worthwile build.
    +m

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    1. You are truly on fire mate. And yes the active bass and treble control on this look really useful. If you want it to get cleaner, reduce that 47K resistor at the top left. You could go quite low in that 4K7 or something like that should be pretty clean in the CCW position.

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    2. Nothing special. That was just third for today... :)

      It is clean enough with drive down, but to get good boost out of it, it'll get dirty. So that may not be a bad thing to know. I'm happy with this as is.
      +m

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    3. Besides, i think i should build RC for cleaner boost.. I've heard that these are AC for Almost Clean and RC for Really Clean, but i have no idea what the BB stands for.. Bread and Butter? :)
      +m

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    4. The BB stands for Blues Breaker. The claim is it has more of a Marshall sound. The AC is suppose to have Vox like qualities.

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  2. Very boomy with my amps. Great tone with treble dimed...

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  3. Hey guys...fantastic smooth and lead tone, but I end up having not more than unity volume :( I used 4558P and I have 1M pot for gain. Is it possible that this is causing the problem?I could really use some help here because I double checked every value...and what makes me crazy is that it sounds amazingly good like there is no problem

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    1. No the IC is fine and a 1M pot would give you more gain not less volume so there's no problem there either. 99% of the time when a build is quieter than it should be there is a bad solder joint somewhere. Check over everything and if something doesn't look 100% perfect reflow the solder. Check for continuity as well at all points of ground to make sure everything that needs to be grounded, is.

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    2. That is strange..almost magic like all electronics (joking here), but I removed the most of the solder and applied new and of course nothing..
      anything else to to suggest before I will start building a new one?

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    3. I feel like fool..I build a second one and I have the same problem. Only the pots are the same, could that be the problem?
      Any advice appreciated..

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  4. Hellsyeah. After a horrid day at the office, i took this board out and boxed it. I remembered that it worked well when i first tested it back in october.. But.. There wasn't much boost. Actually it was just barely over unity. Oh well. I thought that there may be something wrong with my build and so i built another board..

    That manifested the same symptoms. Dragged the schematic out of the web and started looking for a fault. There is one. Really small. And why that didn't come up with verification of RC? Because. The error in this layout is with the one resistor that is replaced by a jumper in RC. So the 10K at the IC pin 1 needs to be 1K. Not 10K. Mark will prolly fix that soonish :)

    Anyway. Here's a photo: http://mirosol.kapsi.fi/varasto/boxes/ac100.JPG

    You guys wanna guess why it has numerals 1, 0 and 0 on it?

    That's right. I've built 100 finished boxes to date. Let's just say that most of my friends are saturated with boxes for a while :P

    Here's another photo of me celebrating: http://mirosol.kapsi.fi/varasto/boxes_other/100.JPG

    Thank you guys. I couldn't have done this without you all.

    Now.. I should start drawing new layouts .... :)
    +m

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    1. Just checked and the scheme I did it from does show a 10K. But I'll stick with yours seeing as that works! :o)

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    2. This one:
      http://forum.musikding.de/cpg/albums/userpics/17486/xotic-ac-rc-booster_schematic_v2~0.png

      Makes sense in volume level - that 10K attenuates signal passing to tone stack..
      +m

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    3. Hmmm, looks familiar

      http://i76.photobucket.com/albums/j6/IvIark_2006/Layouts/Schematics/xotic-ac-rc-booster_schematic.png

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    4. One i posted is dated 7 months later :)
      +m

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    5. 10K and 1K is easy to mix... I'm betting that the original has 1K in that position.
      +m

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    6. Yes I saw the one you posted was marked as a V2 so he'd obviously made the correction

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    7. Thank you for that...I had the same problem and now I have two working boards :)
      Did anyone tried this with 4580?I saw somewhere that the 4580 is actually made for audio use, this is why I'm thinking of trying one but I don't have any at the moment

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    8. I haven't tried this with the 4580 but I've tried a few other pedals and have always been impressed with it.

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  5. Finished this this morning. I had the gain leads off by a hole so they were acting more like a volume control than a gain. Oddly enought it had a lot more gain when at full though. Anyway, fixed it -- this is a very sweet and versatile boost! My buddy has an original so I'll have to borrow to compare with my build.

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  6. Finished it and sounds great - just one problem: When I turn the treble knob, the volume changes - is that normal behavior?

    If it's all the way to the left, I get no boost, the volume knob is at max and the pedal is just as loud as without the effect. If its all the way to the right it gets really loud and more clear.

    So it seems to work since the tone changes, but is the volume change normal?

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    1. You will get a volume change in so much as removing the treble frequencies will make the perceived volume lower because the higher frequencies are more prominent. So it really depends how much of a difference in volume reducing the treble is causing and if you are noticing a reduction in the volume of lower frequencies too.

      Maybe someone who has built this can tell us how theirs reacts.

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    2. I tried the original AC Booster of a friend of mine and it does too have a volume change, but not as much as i am experiencing it.

      Example: (0 is knob all the way to the left - 10 is all the way to the right)

      Treble 0, Volume 10: I gett less Output than without the effect pedal turned on

      Treble 10: If I had Volume on 10 too, I'd get way more than 20dB :D

      Treble 10, Volume 10, Gain 10: It's crazy loud compared to the actual input volume

      Also, I used your tip, to get it cleaner and used a 4,7k instead of a 47k - now when Gain is set to 0, I hardly have any output (volume is set to 10) and when I turn the Gain knob up, it is a very small range where it goes from clean to distorted. So I can't use it as a clean booster, since as long as it is clean, the output level is lower than the actual one..

      I will try a log potentiometer now, to have a better performance concerning the small range, but that won't change the output level being too low as long as gain is low

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    3. I replaced the 4,7k with a 47k again and changed the 500k lin to a 500k log - now it's perfect.

      Guess that top left resistor is affecting more than just the drive..

      Thanks anyway - perfect pedal!

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  7. Is the AC Booster Comp just an AC booster with a clipping switch? Sym, asym and no clipping?

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    1. I second this question! Does anyone know?

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    2. I don;t really know. I think it is odd the RC has 6 diodes and this only has three, yet this has more gain (I understand, though I have not built the other one). Furthermore, there are not many other differences. A good set of circuits to learn on.

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    3. I don;t really know. I think it is odd the RC has 6 diodes and this only has three, yet this has more gain (I understand, though I have not built the other one). Furthermore, there are not many other differences. A good set of circuits to learn on.

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  8. I just built this pedal to asses the active EQ. It sounds good. Personally I prefer heavier gain but this pedal has a very pleasing sound similar to the JCM800 in my opinion (funny, because it is completely different in approach). I think this circuit sounds better with 3904 or 2n5089 transistors than 5088s (all are NPN).

    I haven't had time to experiment yet, but I would like a few suggestions on how I could substantially boost the drive if anyone has a quick idea. I did try adding resistance to the drive pot but did not hear a substantial difference.

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  9. I just built this pedal to asses the active EQ. It sounds good. Personally I prefer heavier gain but this pedal has a very pleasing sound similar to the JCM800 in my opinion (funny, because it is completely different in approach). I think this circuit sounds better with 3904 or 2n5089 transistors than 5088s (all are NPN).

    I haven't had time to experiment yet, but I would like a few suggestions on how I could substantially boost the drive if anyone has a quick idea. I did try adding resistance to the drive pot but did not hear a substantial difference.

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  10. Sounds very cool !
    I made it more as a clean boost but volume knob don't really push the volume up even when fully CW.
    By putting drive up then It get too dirty....


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  11. I just built this but unfortunately it comes out of the amp only an homogeneous sharp feedback that increases by raising the gain knob and disappears when the same knob is on zero.
    Please Ivlark I beg you whether you will be so kind to let me understand where I went wrong.

    Sincerely

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