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Some Discussion on Amp EQs

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

  1. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Thanks Bobby. The dashed lines are phase, right?
  2. BbbyBld


    Oct 13, 2005
    Meridian, MS
    Not sure if that was directed at me...

    I have an 800RB schematic and maybe a 1001RB schemo. The GK mid topology is a peaking EQ. Many companies including Peavey have used nearly identical circuits for years in various bass amps, active bass preamps, and various live sound products such as mixers. The only appreciable difference between a GK EQ and others is of course that the ranges are limited so that the GK tone shaping stays intact.

    They should have never let me start uploading pictures!

    Yeah. Couldn't remember how to turn off the phase plot. But, kind of a whole other can of worms and is something that I am always trying to learn more about. A waveform can also be called a harmonic series. The phase AND amplitude of various harmonics determine the shape of a signal wave. For example, start with a fundamental frequency and add integer harmonics (2,3.4,5,6,7, etc) halving the amplitude each time. Set all the even harmonics 180 degrees out of phase and all odd harmonics in phase. You'd end up with a sawtooth wave. Harmonics from the bass fall in different areas as you play across the neck, which means that the phase of various harmonics changes depending on what gear you use and how you set the controls, which changes the shape of signal waves. Obviously, hi-fi means controlled phase response across the spectrum but maybe that's not what you want for a musical instrument and maybe it is.
  3. BbbyBld


    Oct 13, 2005
    Meridian, MS
    Since it was brought up, gain and phase response of a GK 800RB EQ set flat...
    GK flat.JPG
    Sweeping the low mid control...

    GK lomid sweep.JPG

    Sweeping the high mid control...

    GK himid sweep.JPG
    blindrabbit likes this.
  4. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Assuming you're in LTspice: left-click on the right vertical axis an untick the phase plot box. I can never remember that either. As you say though, the phase plots are often pretty danged important when working at the design level. My first real electronics gig was building synths and doing unnatural things to harmonic series chains was pretty much the game.
  5. hennessybass


    Oct 11, 2008
    Bayou City
    Just revisiting this thread after a discussion about a Bassman 135 eq. Great thread!
    dunwichamps likes this.
  6. markjazzbassist

    markjazzbassist Supporting Member

    Apr 19, 2005
    Lakewood, OH
    links and images aren't appearing, any chance someone can update them? i have a bassman and would love to learn more.
  7. cfsporn


    Aug 20, 2011
    New York City

    Thank you for the thread! Some of the images you linked earlier are broken. Can you reupload them please?
    markjazzbassist and Sartori like this.
  8. 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 17, 2021

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