Gradual tone stack bypass?

Discussion in 'Amps and Cabs' started by brokesnob, Jan 13, 2020.

  1. brokesnob

    brokesnob Member

    Dec 23, 2019
    Asked about this in the Komet Silver Cloud thread, but nobody answered, so thought I'd start a new thread...

    The aforementioned amp has a tone stack bypass knob/control which is gradual. I was wondering if turning it up all the way truly 100% bypasses the stack/eq, but then it got me to wondering how a tone bypass can be gradual when it seems like a black and white/on or off thing? Kind of like a train that's going straight but then has its path changed- you don't somewhat change the path; you either do or you don't.

    Can someone explain this to me? I like the idea of having both an eq at my disposal, but also being able to fully bypass it in favour of a shorter signal.
  2. dbeeman

    dbeeman Gold Supporting Member

    Nov 19, 2003
    Allen amps has been doing this with their "Raw" control for quite a while.
    You use a pot to vary the amount of signal going thru the tone stack - which is subtractive. The non-tonestack path has more gain
  3. brokesnob

    brokesnob Member

    Dec 23, 2019
    but is there ever a point/setting at which the eq is truly 100% removed and the signal takes a shorter path? hope that makes sense.
  4. fiveightandten

    fiveightandten Member

    Nov 2, 2004
    Electricity always “wants” to flow to ground. All the circuit elements in an amp (including the tone stack) use this behavior to control the flow of voltage / audio signal through the amp.

    The tone stack is a network of parts that controls what frequencies of the signal are passed on to the rest of the amp, and what frequencies are shunted to ground.

    This is all done by varying the ground reference, or resistance to ground. In much the same way that the tone stack can pass on signal or shunt it to ground, you can add a control that either passes the signal on without running it through the tone stack, or shunts it through the tone stack network.

    In reality, there’s always some level of insertion loss when you run a signal through a network of components (you loose some signal gain). But depending on how you wired such a control, you’re likely to experience a hotter signal with less insertion loss and no real band pass filter frequency shaping, compared to running through the tone stack.
    Ed DeGenaro likes this.
  5. murky69nz

    murky69nz Member

    Aug 8, 2011
    Has anyone tried this on an older Marshall Circuit (JTM45 or 1959 etc) or AC30 TB channel?

    I know Hot/Cool switch on the Vox HW series did this, but I always thought it was a little too much in the hot setting.
  6. brokesnob

    brokesnob Member

    Dec 23, 2019
    So in other words, a circuit which implements this gradual stack bypass system will never be 100% free of the detrimental effects (probably barely noticeable to our ear) of a stack, such as in the case of an amp that has no stack at all? Close, but no cigar type deal. This is what I wanted to know.

    Also, in circuits where there's a switch for stack bypass, is it the same case or is the stack entirely removed in those instances? Sorry if that's a dumb question, I don't know anything about this stuff, I just know I really loved the sound of a friends Komet that had no tone stack.
  7. davidespinosa

    davidespinosa Supporting Member

    Jul 10, 2007
    Silicon Valley

    TLDR: The bypass does a very good job of removing the tone stack.

    Go here:

    Turn the treble and bass sliders all the way down.
    Now the frequency response is pretty flat.
    But the tone stack loss is about 22 dB.
    So it's difficult to overdrive the power section.

    Now let's put a 100k tone stack "bypass" pot in series with the middle resistor RM, at the base of the tone stack.
    We can't change the circuit in the Tone Stack Calculator.
    But we can simulate the bypass pot by changing RM from 10k to 100k.
    To change values do "Edit" then "Apply".
    Now the loss is about 7 dB.
    And the frequency response is still flat.
    JDW3, theRagman and Ed DeGenaro like this.
  8. d95err

    d95err Member

    Mar 11, 2009
    Tone stack bypass is usually just disconnecting the mid pot from ground. This results in a big gain boost and a relatively flat frequency response.

    Instead of disconnecting completely, you can have a resistor across the pot to limit the amount of ”bypass”. Make the resistor a pot and bypass is made gradual.

    Once the added resistance reaches about 100-200k it’s effectively the same as disconnecting (adding even more resistance makes no difference).

    The tonestack ”bypass” resistance is effectively just an extension to the mid pot. An alternative tone stack ”bypass” is to make the mid pot 10x the value of the regular mid pot and with logarithmic taper. From zero to noon this works as the normal mid control. From noon up, it will act as a gradual bypass, with increased gain, while the bass and treble controls have less and less effect.
    davidespinosa and ontariomaximus like this.
  9. ontariomaximus

    ontariomaximus Member

    Jan 14, 2008
    Yes - d95err said it very well.
    And JTMs and 1959's can sound great with the 25K linear mid pot changed to the 50k or even 100k audio taper pot.
    Or you can tack on another pot as a variable resistor between the mid pot and ground.
    d95err likes this.
  10. aynirar27

    aynirar27 All You Need Is Rock and Roll Gold Supporting Member

    Jul 15, 2011
    Great Barrington, MA
    With a TMB stack, I’ve used a larger than average mid pot value to sort of simulate lifting the stack
  11. PhuzzphayzZ

    PhuzzphayzZ Member

    Dec 17, 2019
    gulp... I guess this comes from my ignorance, but I thought by raising all your tone knobs to ten, letting it all go through, WAS "bypassing the tone stack"...?

    (knees start shaking)
  12. hogy

    hogy Supporting Member

    Jan 4, 2002

    While that's a tried-and-true approach, it is not how the Komet Silver Cloud TSB control works.

    Hogy, Komet Amplification.
    davidespinosa likes this.
  13. hasserl

    hasserl Member

    Oct 24, 2004
    So Cal
    Most tone stack bypass mods simply lift the ground from the mid pot on a Fender style tone stack. If you use a switch it just breaks open the circuit, and the TS is 100% bypassed. If instead of a switch you use a high value potentiometer wired up as a variable resistor it makes the effect variable, so when turn fully to zero resistance it is effectively out of the circuit and the amp responds as stock, and when turned to the full resistive position the tone stack is effectively bypassed. This however will leave the ground circuit partially intact though in effect there is no audible difference between a fully engaged 1M pot and a switch.

    However, with the Raw control I designed for Carvin amps, which have a different style tone stack with 2 paths to ground, I used a 1M pot to route the signal path AROUND the tone stack, with variable control. It is very effective and works very well. You could do the same with a Fender tone stack as well. Again, technically the circuit is not 100% bypassed, the tone stack is still in the circuit, but in effect I don't believe it makes much if any difference. At this point we're talking about picking fly **** out of the pepper.
    rumbletone and amphog like this.
  14. Mickey Shane

    Mickey Shane apolitical Silver Supporting Member

    Nov 24, 2005
    Denton, Texas
    Calm down, It's almost true. There is only a small difference from doing that and bypassing the pots. Really small.
  15. rumbletone

    rumbletone Silver Supporting Member

    Jun 19, 2013
    Vancouver BC
    It just depends on what you want. I recently built a high voltage tube preamp pedal with a Blackface clean channel with a mid/raw control but where the entire tone stack - and volume control - can also be completely bypassed (not just ‘lifted’) and instead it inserts a separate volume control - which looks a lot like a tweed circuit at that point.
  16. socalscott

    socalscott Member

    May 27, 2007
    Doood, that's too cool and I am wanting much. What, if anything can be done regarding said wanting?

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