1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

Complex Build - Help Needed (Active volume mixing/combining two EQ's)

Discussion in 'Pickups & Electronics [BG]' started by Amalgam, Apr 21, 2019.

  1. Amalgam


    Apr 3, 2016
    First I'll apologize for how unkempt these look, but I'm struggling and I know I'll be doing redundant changes until I get a few things right. First off, this is pretty much my first project using electronics, so bear with me as I'm new, but I've tried my best to get as far as I could before asking for help.

    Here's the jist of it. I have two active EQ's with two signal paths where a push/pull on each volume per pickup will determine which pickup goes where. I'm using an Aguilar OBP-3 pre for EQ 1, and an East BTB01 for the second. I want there to be one before the other interchangeably, as well as a passive path, an active mix of the EQ 1, and EQ 2, as well as perhaps the passive path. I'll be using 3 pickups, and I think they'll mix well, but I'm open to suggestions. I've considered a Villex split Jazz as an alternative to one of the the ones I've chosen.

    As I've already heard of issues with mixing two different types/manufacturer's pickups and what the EQ's will do to the signal, I'm very interested in actively mixing the volumes -- at least for the Active EQ's, not the passive signal (up to all three with one tone).

    I know there's probably a lot missing in these diagrams (and I know of quite a bit), but I really need to know how viable this is, and what to focus on learning next to make this whole thing work together. I think the active volume mixing (similar volumes), and where to place it in the signal chain (before volume knob, with it, after it?) is a very important step in getting this to work, and then figuring out how to place the EQ's in front of each other EQ1 --> EQ2, EQ2 --> EQ1 as well. The passive signal chain will be moved as closely to the volume's as I can, but it's currently in the middle when both EQ's are off because I'm not sure where the active mixing of volumes will occur.

    Here is the current (mostly finished, I think) interface, and a confusing, complicated, partially finished wiring diagram that I'll clean up as I learn more.

    *The squigglier the line the more likely it is power/ground as I did that last.

    latest build 2019 6 stringv3.png
  2. Killed_by_Death

    Killed_by_Death Snaggletooth Inactive

    With 3 hum-buckers, series/parallel switches, & separate volumes, you would not need even 1 pre-amp.
  3. Amalgam


    Apr 3, 2016
    For me it's not about what's necessary, it's about what's possible.

    I'm not trying to sound disrespectful, and it's true that a lot less would work, but my goal is to have something that's fundamentally unique, even though it's completely unnecessary.
    Last edited: Apr 21, 2019
  4. Interesting...

    So you have three (passive) pickups, and two separate eq preamps, and you also want three passive tone pots... right?

    Firstly, (and with respect), don't bother with a switch that changes the order of the preamps. This is wasted effort. (Try doing this with a DAW and you'll see.)

    I'd run 250k passive tone and vol stacks for each pickup, then combine this with an active pickup mixer. There's no 3-input active mixer that I know of on the market, but I can show you a very simple circuit with one opamp that will work for this. (Can you can read a schematic?, make stripboard projects?)

    Then feed both preamps with this signal. Then with the two preamp outputs, you could either use a blend pot to sweep from one eq to the other, or a switch with three positions.

    You'll have to work out where it's all going to fit of course. Oh, and you may need to make a phase inverter. It's not uncommon for onboard preamps to have their inputs and outputs out of phase.
  5. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    the old tobias growler bass had a single MM-style dual-coil pickup with two separate EQs, one for each coil. you could literally turn the treble of one coil up while turning the bass of the other coil down, or vice versa.

    it was mostly pointless, didn't make much difference over a single global preamp EQ, and eventually went away.
  6. Amalgam


    Apr 3, 2016
    Passive was an afterthought. I'm honestly not sure whether I should give it more thought, but I was thinking of having one tone knob as I don't know how these pickups would work together in passive mode. If the tone knob was on the mixing of mixers/mst vol, I guess it could be the on off switch for passive mode.

    I see how the mixing of the two EQ's with the same signal would work, but it feels kind of unintuitive to me, and not what I'd want necessarily. I'd like to be able to fully separate which pickup goes to which EQ, sending the same signal to both would make things much easier, but then all pickups would be connected in one signal. I'd really like two signals that can be either switched between or panned between. That's the diagram I created today below, that uses more parts, but is even more functional than the first one.

    This is all find and dandy in my head, but I understand practicality may prove fatal to this idea. I didn't add power to the diagram as I'm not sure if the mixers require power, or how that's handled, but I know that the EQ's do, and I think there are pluses and minuses to pan knobs, and passive/active master volume, but I do not know them. I'm not sure if this will work, but I'd like your opinion. Also, I haven't heard of people panning a signal to two mixers. Would that work? And I think I'm just going to have the EQ1/EQ2/Both ON switch just kill power on the EQ if this all works out, because the pans could just send the signal to the other one.

    I don't know how to use stripboards or know how to read schematics. I did buy a couple books on electronics, one being on how to read schematics, but the other two advance so quickly, I'd given up on it for a while. I see that as a mistake now, but I'm kind of playing in the dark. I expect to have someone make this for me when I finish the plan, but it's kind of a chicken and egg problem much of the time lately.

    boxdiagram3.png latest build 2019 6 stringv4.png
    Last edited: Apr 22, 2019
  7. Amalgam


    Apr 3, 2016
    Huh, that's pretty interesting that they'd do that for each coil, although I guess they didn't have more to work with, haha. Do you know if both EQ's were the same or if they varied from each other?
  8. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    John East used to make a version of the BTB01 that also included a small two-channel unity gain mixer. It was called the BTBM01. Not sure if he still makes them. I have one, and one day I’ll do something brilliant with it.... :cool:
    Amalgam likes this.
  9. With active mixing or individual buffers, it won't matter.

    So you're saying you want it to be like a stereo 3 channel mixing desk with two different EQs instead of left and right? This is likely too much for bass installation. Also it will realistically need a custom active pickup mixer to be designed, built, installed. Unless you can do this yourself, this will be a lot of money, providing you can find someone who can and will do it. Honestly, just finding the stacked pots to do this will be close to impossible. In fact you'd need to mod pots I'd think.

    I'd recommend having the three pickups buffered and sent to a multi-way jack of some sort. Then build a breakout box, and try your ideas out with a small mixing desk. You can get little 3 and 4 channel consoles for very cheap these days. Then when you have a clear idea of what you want and need, you'll be able to get the project rolling.
    Passinwind likes this.
  10. Amalgam


    Apr 3, 2016
    Thinking about this some more, the single signal chain mix once split makes a lot of sense. With a blend knob an EQ can be favored, and the entire distribution of volumes would hold for all. I do like the idea of doing more, and having greater control, but practicality is winning this time, though it could be argued for the best as there are enough controls as is. I'll draw up an image for my own reference, and add it later.

    What does the three input mixer schematic you mentioned look like? I can learn to read schematics, and build stripboards. I can always get a mixing board as well.
  11. Amalgam


    Apr 3, 2016
    They used to sell a four channel mixer+ piezo, but now he sells it with only two channels+piezo. His website has the PDF for the earlier version though. Seems you've caught a keeper.
  12. Amalgam


    Apr 3, 2016
    To be honest, I'm kind of stuck, but I think I know where I want to go with this for the time being. I don't think I'll be completely happy with this until I try my hand at making that custom audio mixer. However, for the time being, I'm going to compromise, and probably get about 95% of the functionality that I'd want as far as the EQ's and pickups are concerned.

    The availability of, or ability to obtain, potentiometer's that would send a portion of the signal to each of two mixer's is a huge part of this of course. I'm not sure what sort of potentiometer's I should look for, and what resistances are needed. I have found potentiometer's with many different values, and a center detente that could send out two signals, but I don't have a grasp on what sort of values would be best, and why they would be best. Would sending the pickup signal through the volume pot (250ka, 500ka), and then through this second stack happen before or after the signal's been buffered? Do I even need resistors if I want all the signal to go to one if not the other... or is that a terrible idea? Also, would these it be best if these pot's were linear or log?

    Lastly: Any recommendations on physical tools, chips, etc. that I should pick up, and how should I tackle learning about electronics, specifically and otherwise, that will help me with this project?

    Current plan:

  13. 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.

    May 17, 2021

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.