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Ibanez Phat II EQ

Discussion in 'Pickups & Electronics [BG]' started by bluesguy62, Jan 26, 2012.

  1. According to Ibanez, the Phat II EQ circuit provides an "active bass boost" which "offers additional low-end power." The Phat II EQ came as a standard feature on my black GSR205 when I purchased it in 2006. Onstage, the circuit lived up to its promise, providing a discernible bass boost controlled by a dedicated B20K pot. The Phat II also seemed to boost the highs and reduce the mids.

    The only problem was that along with the boost came an intolerable amount of noise, thanks to the single coil pickups. This problem, plus the lack of a bypass switch, prompted me to remove the Phat II EQ and rewire the GSR205 along the lines of a Fender Jazz Bass. Hope you enjoy the pics :).














    Thanks for dropping by :).
    tbplayer59 likes this.
  2. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Umm... Please don't take this as mean, but what is your point or message? Why all the pics, from all angles, of a cheap and ordinary preamp module, one that is no good because it's too noisy? What's to enjoy? I'm genuinely confused.
    Killed_by_Death likes this.
  3. bongomania, thanks for your comments. Yes, it's "a cheap and ordinary preamp module," I totally agree. However, in this neck of the woods there is little or no information concerning the Phat II EQ. My point/message was just to provide a source of information/reference for local bass players/techs who might one day find it useful. I understand that in the US of A things are totally different, and this post holds no meaning. Thanks again for your comments.
    rexdavid7 and InternetAlias like this.
  4. Those are good pics. If everyone who needed help posted pics like these it would have been very helpful.
  5. Darius, your positive feedback is deeply appreciated. I am happy to report that this Phat II EQ module is undergoing servicing and modification (the stock B20K pot is totally stuck). If all goes well, it will find a new home in the belly of a friend's Washburn XB125. Thanks again, you have made my day :)
  6. ergocentric


    Mar 10, 2012
    please post a photo once the pot is desoldered so I can work out the schematic from the components

    excellent photos.
  7. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    I originally thought that's what was going to happen. I was somewhat disappointed when I saws that he never took the pot off. It's hard to see underneath, but it looks like it might be a fairly simple circuit.
  8. SGD Lutherie

    SGD Lutherie Inactive Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    It's just a one band preamp.
  9. Thanks, EC. The Phat II pictured here is already in the control cavity of the XB125 I'm working on. I have another one with a jammed B20K pot that will be desoldered. Will post a pic of the board asap. Stay tuned :)
  10. FMB, I'll post a pic of the board minus the pot asap. Stay tuned :)
  11. Yes, SGD, it is just a one band preamp :)
  12. Here are the pics after desoldering the B20K pot, as promised earlier. Hope they are clear enough.

    Front view of circuit board: visible markings

    Front view of actual circuit board

    Closer view of 1st segment

    Closer view of 2nd segment

    Closer view of 3rd segment
  13. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    Cool closeup. Today I learned about chip resistors.
  14. FMB, I'm glad you found the pics useful. If ever you require the original [full-sized] pics, do let me know. Have a nice day :)
  15. amimbari


    May 6, 2008
    Pittsburgh, PA
    I also do not understand the point or interest in any way of all the pictures concerning a 5 dollar junk preamp they only put in the lowest level GSR's. You are actually going to try to modify it?
    You could have just posted one picture and said:
    "here is the phat2 that everyone takes out to replace with something better due to it's bad hiss, and it's lack of frequency control"

    Your choice for fun and experimentation, but in my case on the GSR200 I had I threw that thing in the garbage the very first time I plugged it in and replaced it with a 10 dollar 2 band Chinese preamp that sounded ultimately better in the same bass in 5 minutes with no hiss or lack of boost in the range the phat should have been set up with in the first place.

    like they say, whatever floats your boat....
  16. Duffy49


    Jul 24, 2011
    What is with the comment about not "understanding" the reason for the post or the interest? And saying he should have done this or that?

    Is this what they call, "trolling"?

    It seems like at least one person learned something. And other people liked the detailed photos.

    I learned something too. I didn't know what that particular pre-amp did or how it did it.

    I hope I don't trip anybody's hair trigger or antagonize anyone's obsessive cumpulsive disorder, but exercising some personal tolerance for others before attacking an OP's thread, is to be expected.

    We are supposed to discuss things here that we, as individuals, want to discuss. We don't ask permission before we initiate a discussion. With this in mind there is a need to be tolerant of posts that might not immediately be understood. This goes without saying.
    KJMO, PawleeP and rexdavid7 like this.
  17. amimbari


    May 6, 2008
    Pittsburgh, PA
    so now you learned from some people here that it is an item worth replacing, not trying to get to do something that it cannot do...what is so wrong with that and how is that trolling?

    like I said at the end of MY post, if this is something that bluesguy wants to do for his experimentation, good for him, but to most others, you take it out toss it in the trash and put something in that actually works in 5 minutes.

    it always makes me chuckle when someone opens a thread and EXPECTS that everyone praises every single thing and is all giddy about "check out what I did" and when someone negatives their post, it's automatically trolling for a fight thread to be closed?

    so what's next? the post that says "if you have nothing good to say then don't post"?
  18. He's new, just joined, and is excited becuase his preamp has the word "Phat" written on it.
  19. M0ses

    M0ses Supporting Member

    Sep 11, 2009
    Los Angeles
    While the rest of your post was pretty much spot on, I think one fact you've overlooked is that the OP has been FAR AND AWAY the most polite person in this thread.

    When Bongo first posted, bluesguy gave a 100% valid reason for his posting, and even thanked him for his comments. That should have been the end of the hate, but people just kept chiming in, despite the fact that there are several people here claiming to be very interested in the thread. If that's not validation enough, then yes, you're a troll. Not every post is for everyone.
    Wakizashis likes this.
  20. Toastfuzz


    Jul 20, 2007
    Pittsburgh, PA
    Hey bluesguy62, I think its cool too, I'm slowly getting into electronics work so I dig all the photo documentation. Have you seen the Ibanez pre they used to put in their SR400 line? It was called a "tone sweeper" or something, it was separate from the 2-band bass-treble EQ, and it swept from super deep and bassy to scooped and slaphappy/trebly, I get alot of mileage out of it (although theres plenty of haters who upgrade for the sake of upgrading..) and I'd love to know how that thing worked.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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