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Passive tone stack

Discussion in 'Amps and Cabs [BG]' started by PBFACTOR, Feb 12, 2014.



    Dec 21, 2001
    Boise, ID
    A passive tone stack on an amp would mean cut only, correct?
  2. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Google Fender tone stack, you will find lots of useful info.
  3. VerryBerry

    VerryBerry Supporting Member

    Mar 4, 2012
    Alberta, Canada
    That is correct.

    From the Traynor YBA-200 Manual:

    "Tech Note: The YBA200 has been fitted with a traditional passive tone stack. This allows the
    tubes to generate natural sounding harmonics when driven into saturation. Active tone controls
    can generate unwanted harmonics when clipping interrupts the feedback loop in the amplifier.
    Passive tone controls are always subtractive, which means they can only reduce the gain in
    their specific frequency ranges. Active tone controls, on the other-hand, are wrapped around
    an amplifier and will provide gain boost when the controls are turned past the middle position."

    As it was explained in a post I cannot now find, you start by turning up all the EQ controls to max. At this point you are not attenuating the signal. Then, you subtract what frequencies you don't want by turning down the appropriate control.
  4. Sid Fang

    Sid Fang Reformed Fusion Player Supporting Member

    Jun 12, 2008
    In general practice, yes. It's possible to build a passive cut/boost tone control circuit, but it's complicated and AFIK rarely done.
  5. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Actually the "flat" setting of a typical Fender passive tone stack is approximately 2-10-2 if the knobs are marked 1 through 10, or around 8:00/5:00/8:00.


    Dec 21, 2001
    Boise, ID
  7. wcriley


    Apr 5, 2010
    Western PA
    The Fender stack can boost highs and lows, so is it truly passive?
  8. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    The boost is relative to the insertion loss of the tone stack. I think.
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If you didn't have loss when the tone circuit is put in the signal pathway, a boost would run out of headroom.
    BurningSkies likes this.
  10. wcriley


    Apr 5, 2010
    Western PA
    I think I'm starting to understand.

    The bass and treble controls cause less insertion loss as they're turned up. Which then appears as a "boost" after the make up gain stage that follows.
  11. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Correct, it is all related to make up gain.

    Here is the big cheese in the passive EQ world. :bassist:
    Sartori likes this.
  12. With a few exceptions, passive circuits don't boost. Boosting requires active.
    Sartori likes this.
  13. kbakerde

    kbakerde Supporting Member

    Jan 24, 2012
    I don't care if it's active or passive, but IMO the Fender Tone Stack is the foshizzle!! It is exactly what I want out of a bass sound.
  14. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Not necessarily -- it's kind of a semantics thing. When you look at the whole picture of how an amp works, not just the tone stack by itself, you'll see that boost/cut EQ is readily done using a passive stack. IMHO this thread is the go-to starting point for understanding bass amp EQ: http://www.talkbass.com/forum/f15/some-discussion-amp-eqs-950782/
  15. the low one

    the low one

    Feb 21, 2002
    You could almost say that the passive tone stack has a bass and treble boost only. The mid control is just a volume control for the eq.

    I read recently that the tone stack was developed for guitars because the pickups were so mid focused they lacked bass and treble. So, if you put all the tone stack controls at 50% you get a mid scoop which then gives a "flat" response for guitars.

    Do bass pickups suffer the same mid focus as on guitar? Not sure, maybe for passive pickups? Maybe someone can explain.
    Sartori likes this.
  16. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Don't confuse passive tone stack with FMV tone stack. The FMV (fender, marshall vox) bass/mid/treble is a passive stack, but it is only one example. There are others, the other common one is the James stack (often called the Baxendall, although the bax stack is an active version), once insertion loss is accounted for that one can be used to eq a mid bump so is more versatile, although its less knobs (just bass and treble). Since the James stack is fiddlier and appears to offer less in terms of visual knobs, the FMV stack is more popular. This is a useful tool for figuring passive stacks: http://www.duncanamps.com/tsc/index.html
    Sartori likes this.
  17. esa372

    esa372 Supporting Member

    Aug 7, 2010
    Los Angeles, CA
    Last edited: Jun 13, 2014
    oo.viper.oo likes this.
  18. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    *The FMV tone stack explained.
  19. esa372

    esa372 Supporting Member

    Aug 7, 2010
    Los Angeles, CA
    Indeed... edited. :)
  20. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    No it's not. The Fender tone stack pretty much is how you describe but there are other types which are boost and cut. The tone circuit from the B15 and SVT are passive but flat would be at about centre rotation. The mid on the SVT is active and again flat is centre rotation.