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Hi there, welcome to my blog - La Revolution Deux. It's an odd name - but I like it! Here you will find all the info on my various DIY Guitar effects builds, amplifiers and guitars. Everything from a humble Ibanez tubescreamer to the holiest KLON Overdrive.

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Friday, 20 January 2012

Xotic - EP Booster


The Xotic EP Booster has been causing a fuss for a while now. Supposedly based around the legendary Echoplex EP-3 preamp it's been recognised as one of the best boosters currently available.

Here's the description from the Xotic website:

"What do the tones of renowned guitarist such as Page, EVH and Johnson have in common? They all used the legendary echo machine EP-3 as a pre-amp.We've captured that magic in a new Xotic Effects pedal, the EP Booster.

We've used the highest quality parts available with a discrete FET design and low impedance output, the EP Booster provides up to +20dB of unadulterated boost with multi-dimensional, shimmering highs and lows, and no ear fatigue. The internal DIP switches let you choose the boost frequencies, and EQ settings.

Housed in a small 3.5"x 1.5" x 1.5" case with blue LED and transparent knob, the EP Booster can be powered by 9-volt up to 18-volts.

A simple pure boost that pays reverence to the magical EP-3 and captures the celebrated tones of the world's most famous players.
The EP-Booster,great tone starts here!"

And, of course, a ProGuitarShop demo video for you:


Well, the freestompboxes crowd whipped one apart and took a look inside (Thanks to Greg for the initial tracing):


The original transistors are supposedly 2N5457 and 2SC1815. As you can see it doesn't greatly resemble the EchoPlex EP-3 preamp:


But hey, nevermind, because this thing sounds pretty good. Here's a PCB layout provided by Masca of Handmades.br: http://www.mediafire.com/?eb0byo1n9s524q2

Here's a vero layout by IVIark of tagboardeffects.blogspot.comhttp://tagboardeffects.blogspot.com/2012/02/xotic-ep-booster.html

I would make a few modifications to this - firstly it's got to run on 18volts! Then I'd replace the drain resistor with a 25k trim so you could dial in a sweet spot of your choosing. For extra control I would swap out that low pass filter for a version of Mark Hammer's "Stupidly Wonderful Tone Control", that would give you a real handle over your top end. Finally - what's with that nasty BJT transistor output buffer? I'd use a Jfet or Mosfet follower - better fidelity and clipping characteristics!

Anyhow, I might draw a schematic up!

[EDIT] - I told you I'd draw a schematic up, here's the business:


As you can see I've added a master volume control, a tone control (treble roll off) - you could call this control "Sparkle" for added mojo. I replaced the nasty BJT transistor voltage follower with a nice JFET type. I ommited the "bass boost" switch, I didn't like it, it muddied up the boost, you could add it back in if you want. I also included a quick schematic for a voltage doubler to allow you to power this circuit at 18v (where it sounds best) with a single 9v battery. Well, what you waiting for? Go build one :-)

Here's a vero layout drawn by IVIark of tagboardeffects.blogspot.com: http://tagboardeffects.blogspot.com/2012/02/xotic-ep-booster-briggs-modded.html, check out his site for an awesome array of vero board layouts of just about everything!

[EDIT2] - If you want to actually reduce the low end present in the circuit I'd reduce the input cap to 33nF and change the bypass cap on the "Boost" control to 220nF ~ 470nF ~ 1uF depending on your preference. I'd also recommend one other small change - replace the drain resistor on the first FET with a 10k trim pot then use it to dial in a 5.5v bias on the Jfet's drain to make sure you've got it in the "sweet spot". Just thought I'd add that ;-)

[EDIT3] - One last thing, for those interested in booster circuits which add colouration to your tone check this out (schematic below), it's a prototype I was working on back in 2009! The values in the treble control need tweaking to find the best response but it sounds pretty good "as is". This thing also sounds best at 18 volts :-) Build it up and tell me what you think:


For reference here is the freestompboxes.org forum topic: http://www.freestompboxes.org/viewtopic.php?f=7&t=7881

14 comments:

  1. pleeeeeeease lay this out on vero for us...I really want to make one.

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  2. by "this", I mean the Fred Briggs EQ Booster, not the Xotic :)

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  3. http://tagboardeffects.blogspot.com/2012/02/xotic-ep-booster-briggs-modded.html

    IVIark has already done one :-)

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    Replies
    1. ok, cool, building it this week...it looks like there are some differences between the xotic with your mods and the FB EQ Booster...they similar enough not to build both?

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    2. Ahh sorry, I thought you wanted the EP Boost vero - I didn't read properly (Hopefully there'll be a vero up for the Fred Briggs EQ Boost soon!) ! They are similar but also have their own characters:

      The changes are as such - the FB EQ booster has a treble boost/cut control the EP Boost only has a cut. The FB EQ has a bass/input impedance control whereas the EP Boost doesn't this allows quite a large range of gains to be had and it's pretty interactive with all the other controls. The second gain stage on the FB EQ Boost can add quite a bit of grit at max gain.

      I'm going to see if I can find myself a vero manufacturer - I'm terrible at doing layouts! I hope you enjoy the mods :-) If you want it tweaking just ask and I'll advise on values....

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    3. Hi Fred. I'll do a layout for your EQ Booster, but what's the value of that last electro at Q2's drain?

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  4. Hey Mark, chheeers but before you do a layout of it let me get it back on breadboard and all tested up and fully finished. I seem to remember there being some thing I wasn't quite happy with this one which is why I never really released it as a full project.

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  5. this post = bookmarked in anticipation :)

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  6. First of all, thanks for sharing all of this/these!

    I was wondering, what does the replacement of the transistor to JFET do to the sound? And could I, if I made a pcb just swap out the transistor for the JFET? Because I don't need/want the tone and volume control.

    Thanks,

    Joenuh

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  7. Hi Fred, the bypass cap on the "Boost" control it's the 10uf or the 100uf capacitor? thank you and cheers from Spain. Juan.

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  8. i'm sorry briggsy,
    i'm sure this is a great booster,
    but the echoplex ep3 is not a booster. not at all.
    i own two at the moment, put 'em in a TB looper box, and it's unity gain.
    to me, this is nothing buy hyped bullshit. like i said, they probably sound great, (i haven't tried one) but it's riding the coat tails.... like the magnavibe, which sounds great. but it's not a "magnatone in a box", it's a goddamn escobedo wobbletron that actually WORKS. ;)
    i'll have to do a stupid pedal trick showing that this is baloney.
    i know that tony krank guy is trying to pass this stuff off as being related to an echoplex too, but it for sure ain't gonna make anyone "sound" like they have a plex on if it's being used as a boost in my never humble opinion.
    call it a booster, call it what ya will, but echoplex?
    gimme a break... just my opinion, bro...
    rock on
    pink jimi

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  9. Is this LED in this schematic, the blue LED ? Can I remove this part of circuit (33K, Led and 4,7uf)?

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  10. I don't understand the difference between the "Boost" and "Volume" control, aren't those the same thing?

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  11. I built it yesterday!
    Is the bright and fat switches a big improvment in sound, or just a very subtle effect?
    I can't ear any noticeable change, at all.
    As I can read, I'm not the only one out there.

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