Theoretical zero of eq stage?

Discussion in 'Amp Central Station' started by A1exand3r, Dec 15, 2019.

  1. A1exand3r

    A1exand3r TDPRI Member

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    For Amps that boast a 3 band eq or more, what setting would be the theoretical unmodified signal?

    Also, does the eq simply cut frequencies, or does it also boost frequencies?

    Thanks to all of you smarter than me!
     
  2. codamedia

    codamedia Friend of Leo's

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    No two amp makes/models are the same. Unless you name an amp, it's impossible to answer.
    The closest you will get to an "unmodified signal" would be to plug into the effect return or the power amp input - if either exist on the amp.

    Most amps are passive... they just CUT frequencies. BUT - some have active circuits, some have partial active circuits.
    In most passive circuits "almost all" controls are very interactive. EG: Adjust the highs and it changes how the mids or low controls respond.
     
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  3. A1exand3r

    A1exand3r TDPRI Member

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    Oh ok, so it doesn't work like the tone control pots on a guitar, where when the pot is maxed, you have the least amount of tone bleed?

    That's a really interesting bit of information. I'll have to play around with my amp and listen for those interactions.

    So does that mean an active eq circuit could potentially shape the tone in ways that you can emulate other amps?
     
  4. peteb

    peteb Friend of Leo's

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    It does work like the tone control pots on a guitar.
     
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  5. codamedia

    codamedia Friend of Leo's

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    As peteb says above... passive tone stacks do work like guitar.... all they do is cut. BUT... that doesn't mean the signal is "unmodified" when they are full. There is more going on under the hood.

    IMO... unmodified equals "flat".. and guitar amps are anything but flat unless you go direct into the power amp inputs.

    If you download the DUNCAN TONE STACK CALCULATOR and play with the settings for each amp you will see how the interaction is working... especially on the VOX.
    http://www.duncanamps.com/tsc/download.html

    Try getting that EQ Curve FLAT with the tone controls and you will see how difficult it is!
     
    Last edited: Dec 16, 2019
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  6. PastorJay

    PastorJay Tele-Afflicted

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    That looks like a great tool.

    In response to the OP, every amp has a different "tone stack," which allows for a range of available EQ curves--what can be achieved by altering the amp's tone settings.

    The tone stack means you're not just getting a flat response, like you might be able to get if you simply plugged your guitar straight into a mixing board.

    Different kinds of amps are known for their distinctive sounds--Fender tweeds are different from bf/sf Fenders, different from Marshalls (although the early Marshalls were essentially louder Fender tweeds), and different from Vox amps. Etc.

    The difference in tone stacks, together with when an amp will begin to overdrive and the quality of the overdriven sound, make each amp unique.

    You could get a taste of the differences by spending some time with an amp that has multiple available tone stacks. Several different Mesa amps have this capability, as does the Egnater Tweaker. The Fender Blues Deluxe supposedly has a bf/sf tone stack on its clean channel and a Fender Tweed tone stack on its drive channel.
     
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  7. Mexitele Blues

    Mexitele Blues Tele-Holic

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    Here is a browser based version - https://www.guitarscience.net/tsc/info.htm

    Edit: Also works on mobile.
     
    Last edited: Dec 16, 2019
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  8. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    While the tone controls on a passive amp tone stack only cut like a guitar, they work with a "recovery stage" in the preamp so they really don't cut in the overall circuit because the recovery stage boosts to make up for tone stack gain loss.
    IOW you don't gain but you also don't lose they way you lose with the tone control in a guitar.

    As far as setting any tone stack for a flat response from the guitar amp, it would be impossible because there are other parts of the amp that change the eq to one suited to guitar.
    Generally a guitar amp cannot do the highs or the lows that a PA or stereo amp needs to amplify for bass, synth, cymbals etc.
    For a guitar amp to survive it has to cut bass in the power section and the eq, and for it to sound good it has to cut treble, but part of that happens in the speaker and maybe also in the output section, which in a tube amp has it's own eq in coupling cap.

    If we run a guitar signal into the fx loop return the power section of most tube guitar amps will still cut bass because other parts including the OT, the speaker and maybe even the power tubes will melt down if sent a strong bass signal.

    There are generally coupling caps in or near the power section (IIRC) that only pass above a certain frequency.
    That particular (high pass?) cap is smaller in vintage BF amps than in vintage Marshalls IIRC, and you can swap it for a cap that passes lower frequencies to get more bottom and low mids from you BF Fender.
    I've done that mod as detailed in one of Weber's tube amp books, and what one generally finds is that such changes to the eq of a whole guitar amp doesn't sound as cool as expected because the rest of the amp is not designed to carry that much bottom.
    So instead of more bass we get more mud.

    Much of the design of guitar amps was based on '50s/ '60s speaker tech where speakers couldn't handle much bass, and over time the music played on electric guitar evolved around the bass cut the guitar amp was designed with during the development of Rock & Roll.

    Now we get long scale drop tuned 7 string guitar and those "new" instruments need whole different amp designs because the old guitar amp eq is not capable of reproducing the eq of those "guitars".
     
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  9. Wally

    Wally Telefied Ad Free Member

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    all of the Fender Blues/Hot Rod amps have a single tone stack because they are in reality single channel amps. The drive options occur by dropping in gain to the single preamp.

    theoretical zero of EQ stage.....I don’t know, but I have heard some amps that yield no tone at all for my ear no matter what one does with the tone controls. (;^)
     
    Last edited: Dec 16, 2019
  10. LuthRavin

    LuthRavin Tele-Meister Ad Free Member

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    ^^^ THIS ^^^
     
  11. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    In amps with passive EQ (the vast majority), all EQ controls on 10 (or all the way 'up') is the closest. But, even then there's still a load on the EQ signal, cutting some of the frequencies.

    What's kinda funny about this is that so many of us test an amp with the tone controls on Noon... Like that's a flat response. Been doing it my whole playing life. Still do, even though I know better.
     
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  12. codamedia

    codamedia Friend of Leo's

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    FWIW.... On a BF/SF Fender, mid on full and treble/bass down around 0 - 2 will produce the flattest response. Again... that produces the "flattest" tone, but it does so by "cutting" highs and lows" that are already present within the amp.

    LOL - I do the same thing when I try an amp... and I also know better ;)
     
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  13. powerwagonjohn

    powerwagonjohn Tele-Meister

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    I do the same thing, just habit I guess.
    Then you get into Baxandall tone controls. Are these controls zeroed at center?
    Thanks John
     
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  14. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    Then, add Wally and my's favorite tapped treble pots from the blond and brown and everything really gets wacky!
     
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  15. printer2

    printer2 Poster Extraordinaire

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    Should be unless the designer had other ideas.
     
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