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Some Discussion on Amp EQs

Discussion in 'Amps and Cabs [BG]' started by dunwichamps, Jan 21, 2013.


  1. vgbob

    vgbob

    Jan 15, 2007
    Nick, thanks for taking the time to put all this together.
    It explains, in a way that finally makes sense, why I've always
    liked Ampeg or Baxandall style eq vs. FMV. To me the Ampeg
    eq is just more intuitive in working the way you expect the
    controls to work. That is not to say the other is bad, just that
    it works in a different manner.
     
  2. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    yes the James/Bax is definitely more representative to what you think is happening. Also my favorite
     
  3. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Nice post! Thanks for the info!
     
  4. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    you're welcome!
     
  5. J-O

    J-O

    Jun 27, 2010
    Awesome post, thanks for taking the time to put all this info up. I can see why I love my v4 so much.
     
  6. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    no problem. The V4 i believe has the same james/bax as the ampeg but the component values might be tweaked. The scheme does not show the part values unlike the SVT schemes which do. The mid control is the same circuit but I think they changed the inductors and caps around a little to get slightly different center frequencies on the bandpass.
     
  7. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Very nice job. For completism I would just like to post Mr Baxandall's original article here so interested people can decide for themselves if calling the James stack "Baxandall" is appropriate. Personally, I think the distinction between an active stack and passive one is hugely important, but at the same time common vernacular makes it just amount to whizzing into the wind at this point...;)

    Baxandall Negative Feedback tone control article.
     
  8. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    thanks for the extra info! I am probably super guilty of spreading the improper terminology in my posts. I learned most of the difference from Merlin/Valve Wizards book and articles like the one you posted.
     
  9. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Nearly everyone just calls the passive version Baxandall or James/Baxandall these days, so as you say it's basically down to semantics really.

    I recently got around to building my own active stack in my last DIY tube bass preamp. It took a lot of digging around to find even a handful of interesting variants, and I ended up doing a ton of brainstorming in LTspice before I even touched a soldering iron. It really is a great tool for stuff like this.
     
  10. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    nice and LTSpice is my best friend. I pretty much simulate every amp in there to get an idea of whats going on. Hours spent on phase inverter design.

    The baxandall in the article would be nice to try out someday, although I might try it with a triode instead of a small signal pentode.
     
  11. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    I'd like to see the FMB set at 666 and at 2-10-2. 666 is sort of considered the sweet spot for fans of the fender Telecaster guitar. I've used it myself but pushthe mids higher. (My tele has a Charlei Christian in the neck position and it justifies more detail all on it's own.

    2-10-2 is of course the commonly agreed on 'best approximation' of flat with the RC/Fender tone stack.

    As Passinwind knows all too well I'm a big fan of that stack. For all it's flaws, I find it musical in a way that many others aren't. I'm currently rockin a Music Man Rd100 which as I gather is not far off. Lovely amp in my rock'nroll life! Need not apply when doing my normal acoustic thing though...
     
  12. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    I could do those sims. There is definitely a segment of people who love the Fender 60s clean tone and that gets some of its feel from the strong mid cut on the tone stack so it can be quite musical. As always if you dig then its good.
     
  13. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    That depends on actual pot tapers and some other things that make not all Fender tone stacks the same. You already have the Duncan Tone Stack Calculator widget, don't you Mal?

    Here's an actual measurement I took of my old Alembic F2B at 2-10-2:

    [​IMG]
     
  14. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    I should have mentioned Duncan Tone Stack Calc. It is fairly useful if you wanna play with the common tone stacks. I find LTSpice better as I can do more pots and more controls with more accurate sims
     
  15. oinkbanana

    oinkbanana

    Oct 20, 2011
    what kind of eq is used in OR120 orange amps?

    and from what i'm reading, vintage SVT will use type 1&2?
     
  16. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    Matampas and Oranges uses James/Baxandalls, so #1

    yes SVTs use 1 and 2
     
  17. jungleheat

    jungleheat Inactive

    Jun 19, 2011
    DC
    Interesting stuff. I have a MM 65-112 and eventually I want to get the tone stack modded so it's a bit more useful. Not necessarily wider response, but just shifting the frequencies that are emphasized to be more conducive to the tones I like. The bass on the "FMV's" is usually too tubby, the mid's are too boxy, and the highs are too nasal. So it would be great to push down the bass and mids, and push up the treble (frequencies). My ultimate goal would be something close to a Roland JC-120, but maybe swapping out component values to be more Marshall-esque would be a good start. Disappointed though that the presence control on most Marshalls wasn't included, as that is a big advantage to their design over Fender.
     
  18. dunwichamps

    dunwichamps Commercial User

    Jul 23, 2012
    Owner: Dunwich Amps
    You can mod the TS around to get a better response, You can use Duncan's Tone Stack Calc to see how it mods the EQ around as you change components. Google It!
     
  19. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Don't know which is correct, but I like saying "Baxandall" more than "James" so I stick with it ;)

    Very interesting thread as a longtime SVT/B-15 lover. Were your results directly from the preamp of an SVT or were they coming out of the output transformer? The reason I ask is that most folks say that the SVT won't be flat sounding with knobs at noon. I don't know how to test mine but I have compared it to an amp that has pretty flat response with knobs at noon and ended up with a couple knobs pretty far off noon on the SVT to match tones. But from what I've heard out of the post-EQ DI on SVT's, they do come across to my ears as flatter than through the cab.
     
  20. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    From the OP:

     
  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.

     
    Apr 12, 2021

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