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Bass 3- & 4-Band EQ Frequency Points

Discussion in 'Amps and Cabs [BG]' started by Midak, Dec 19, 2017.

  1. Midak


    Sep 4, 2011
    Athens, Greece
    Hello to all. :)

    I am designing a custom bass head (tube preamp, solid-state power amp) and I have to decide on the EQ section of it; my options are either a 3- or 4-band EQ, where I am interested to set the frequency points of the circuit, bass/middle/treble or bass/low-mid/high-mid/treble.
    Generally I would prefer the 3-band set, for the sake of simplicity, but would go 4-band should its benefits make sense.

    So, I need opinions and frequency points suggestions. :)
  2. lz4005


    Oct 22, 2013
    Fully parametric mid band is the most useful and flexible. Frequency, boost/cut and Q.
    Gearhead17 likes this.
  3. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, ChopShopAmps
    Single tone knob going from smiley to frownie in the lower mids. Bass boost and treble boost push in/out buttons.
  4. Wfrance3

    Wfrance3 Supporting Member

    May 29, 2014
    Tulsa, OK
    +1 Agreed. I've eq'd myself into circles. After much of that ojt, I have found that the best way (for me) is to start with everything flat. Amp, preamp pedal (if you got 'em), and active bass controls.
    Step 1 requires a sweepable mid, but assuming you got that, find the sweet spot, then add/cut bass (also having an add-cut is good - not just an add), to taste. Done. For me, 3 band with sweepable mids has always been plenty. John East makes a good one, I noticed the other day that Noll also has this, but don't much about their stuff.
  5. bwildt


    Mar 21, 2017
    Wichita, Kansas
    My favorite EQ is on my Ampeg PF-350. It's a simple 3-band eq, but they are in just the right place for me. This amp is simply punchy.
    Bass 40hz
    Mid 500hz
    Treble 8khz

    I like it a lot better than my PF-500 with a its 5-position selectable mid. None of the mid positions (220, 450, 800, 1.6k, 3k) give me the same sound. Also, on the PF-500, the hi frequency center is 4k.
    johnpbass likes this.
  6. Passinwind

    Passinwind I know nothing. Commercial User

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

    Since you're doing a tube preamp, it can be pretty tempting to just go for one of the classic approaches such as the James or FMV tonestacks. Can you tell us a little about your general design brief? Clean or dirty? Pedal friendly? All around or genre specific?

    One thing to be aware of is that different manufacturers use very different metrics for specifying EQ frequencies. And unless you plan on always diming those EQ controls, those frequencies can and often do shift considerably at lower settings. And then there is the interaction factor, which IME and IMO is a pretty huge deal in the overall scheme of things.

    And finally, what sort of power amp design are you going with?
  7. Midak


    Sep 4, 2011
    Athens, Greece
    Thank you all for your inputs. :)

    I actually had a passive circuit in mind, but it is something to keep in my notes.

    Yes, I was thinking about a classic design myself.
    I aim for a mostly clean approach, with a tad of warmth and character added; I don't want something totally neutral or sterile. I don't use pedals often, my main one is my Aguilar Octamizer, followed by T-Rex Sweeper and TC Electronics ND-1. I play mostly rock, but also blues and jazz - I want clarity and definition in any style, always.

    The power amp would be a B-Class high-end design approach - if you want more details, I would be glad to reply. :)

    The cabinet will be a custom design too, featuring a single Oberton 15MB500.
    My main bass is a Fender Custom Shop '64 Jazz with handwound pickups by O.C. Duff.
    Last edited: Dec 19, 2017
  8. superheavyfunk

    superheavyfunk 音楽は人生だ

    Mar 11, 2013
    I don't know what the frequencies are for for GK amps... They're 4 band (treble, high mid, low mid, bass) but I've always found that with their amps, all I've ever had to do was turn down the bass or treble a bit, depending on the situation.

    I guess that probably didn't help you much but it's all I've got. Lol.
  9. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Cool, sounds like a fun build all the way around. I'm actually gearing up right now for building something more or less the other way around: SS front end, tube power amp. But I've also done a few tube front/Class D SS power ones in the last few years. I did bass and mids in an active format (tube only), roughly 60-40Hz (control position dependent) and 480Hz nominal. But slope and bandwidth matter, and that's going to be hard to interpolate to your design, I think. For the treble section I went pretty far out of the box, very broadband and extremely hi-fi. But I ended up backing that down a bit eventually.

    Anyhow, one thing I haven't gotten around to yet is DIY'ing some inductor based tube midrange circuits. I think that three bands (BMT) with a switchable mid frequency (3-5 choices) is a pretty great way to go. It takes a lot of tube sections to get around the interactivity complications that a second mid band tends to bring, IMO. I'm just assuming you want to stay all-tube for the EQ though?

    And personally, I would be very interested in hearing more about your power amp details. That sort of build is definitely still on my bucket list, even though I've has excellent results using off the shelf power amp modules.
    Last edited: Dec 19, 2017
  10. Midak


    Sep 4, 2011
    Athens, Greece
    Interesting approach, it is the one I though about the least - would be interested to hear more about it as soon as you have make progress.

    Again, very interesting approach to use inductors.
    Yes, I would prefer to stay in the preamp for the EQ.

    Actually it is based on the "Blameless Amplifier" design by Douglas Self, as depicted in his book "Audio Power Amplifier Design". The design itself is fundamental in most of its aspects, with a few tweaks. It is a classic three-stage approach: Differential-Pair Input Stage - V.A.S. - Emitter-Follower Output Stage.
  11. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Think something like the old Music Man amps, with a more modern take on the EQ. If this stays in the DIY realm I'll post a thread eventually. But if it ends up being a commercial thing (i.e. someone buys the design) I probably wont be able to go too deep.

    Well, for inductors, look at Ampeg for starters. I also really like the Sound City EQ topology as seen in the 150 bass head, but that's a whole different thing.

    Nice. I've worked through Self's preamp book, but haven't gotten to the power amp one.

    Best of luck with this build, and please keep us posted as it progresses.

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