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Thread: Passive Midrange Control

  1. #1
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    Passive Midrange Control

    I built a little Torres/Rothstein style mid cut-boost control from spare parts but I can't figure out how to wire it into my strat. The center lug gets the hot signal, but from where? I'll put a SPST switch to bypass it.

    Thanks if you can help!

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    It depends what you want it to do, do you want it to only affect one pickup or all of them? A schematic would help everyone greatly.
    If you want it as a master mid control then try it just before the master volume control. So take the wire leading to the input of the volume pot, remove it from the master volume and connect it to the INPUT of the mid control. Take the OUTPUT of the mid control and connect that to the INPUT lug of the master volume pot. So you are effectively slotting it in before the master volume. You could also try slotting it in after the master volume, I imagine this will make it less efficient//conventional but I'm assuming thats what you are going for since you're adding ad passive mid control to a strat. Perhaps a switch to instantly test the difference between the 2 locations of the mid control?

    On a side note, if its passive then it wont "boost" the mids, at most it will cut the treble and bass so it SEEMS like it has more mids. And you might want to think of putting in a DPDT to completely isolate the mid control from the circuit because it could drain the tone a bit if its not very efficient, but again, that depends on what this midrange control is actually made up of.
    Last edited by antiunderscores; 06-12-2010 at 01:39 PM. Reason: Edited to fix poor grammar and generally improved.

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    Please post a little schematic so we all know what are we talking about.
    Thanks.
    EDIT: ┐should I add that Natman's post came out narrow formatted?
    All following look normal. ┐┐┐???
    Last edited by J M Fahey; 06-12-2010 at 12:11 PM. Reason: Self evident

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    Here is what I put together. (the leg on the right is not cut, it goes to ground -sorry I didn't catch that & too lazy to start over) It's a mash-up from 2 units I found online. Rothstein makes one just like this, either with of without a center detente pot. I couldn't read the values so I used Steve Ahola's, which he borrowed and/or tweaked from the Torres version. I didn't have a 0.039 cap, so I used 0.047. I'm putting a SPST in to bypass it too.

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    Yep, a SPST will do fine with that. Hook it up to the 'in' of master volume and just for the fun of it, try the out. Excuse my ignorance but what's the blue/grey thing? I've got an idea of what it is, but cant remember the name of it.

    To me it looks like when on low it cuts mids and on full it cuts the highs. Could this really be good for the "tone" of the instrument? Also what value pot are you using? These questions are just for my curiosity.

  6. #6
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    Hi antiunderscores.
    The blue-grey thing is an inductor, as confirmed by the value printed just by it (1.5 Henries).
    Don't know what he used, but a 1M linear pot would be fine, providing a reasonably flat response on 5 and cut of either mids or highs on "0" and "10".
    Personally I would go for an active circuit which would be much better and cost no more than the inductor alone.
    Personal opinion: up to passive volume and tone (cut), fine with me, it's practical and simple.
    Any sophistication beyond that: go active, it's so much simpler !!
    Low power op amps give you over a year of operation, so the hassle of replacing batteries is really minimized.
    And you can always put a switch that sends the pickups straight into the output jack, for emergencies.

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    Yes, it is an inductor, which is essentially a tiny transformer (or choke). There's nothing wrong with filtering frequencies as far as affecting your 'tone'. Every item in the circuit path is doing something to get the end result which you hear as music. I have a 500k log pot right now, I might try others. I just think it will be more useful than a simple tone pot to roll off highs. While that works fine, I'd like a little more variety onboard this guitar. No way I'm messing around with batteries. I don't feel there's a need. Ever.

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    Thanks for the explanation, but i know what an inducer is, just couldnt remember the name and wasnt 100% sure thats what it was.
    I have nothing against filtering, but the problem with that schematic is that you will either be cutting the highs, or the mids. I guess thats why you have the SPST, but i prefer simplicity on guitar electronics. And as a general rule if you have too many filters and shaping without introducing active components i find it can dull your sound, you can fix that by increasing the value of the pot, but that effects the sweep, there's a balance. Plus a well designed schematic can sound great in bass guitars.

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    Ned
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    hello Natman, could you be so kind as to describe or make a diagram as to how I could make just the "Cut" function of this? I am looking for a midrange cut control but all I have found have the boost too. Thanks, Ned

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    You can just hang the hot terminal off of the hot terminal of your output jack. The ground completes the circuit.

    True, it swings between a notch and HP filter, to cut the mids at one end of the travel, and highs at the other. However, the .001 cap shunted by a 1.1M resistor doesn't really cut a whole lot of highs. I'm having trouble figuring out if this is what it was meant to do, or if the value is a typo and was supposed to be .01uF.

    Concerning the pot: I would NOT be using a log taper pot in there. I'd use a 500K or 1M linear with a center-detent, which would essentially be your neutral zone. In fact, I have more than one guitar set up that way with two different value caps for different corner frequencies.

    A REALLY cool mod would be to have switchable caps on the notch filter side to change notch frequencies. This would resemble the old Craig Anderton Passive Tone Control project from his book "Electronic Projects for Musicians". You can also leave out the 270K resistor for better notch filtering.
    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

  11. #11
    Ned
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    Thanks, I am looking for a passive control to cut mids only, not boost mids or affect lows or highs. I was thinking there would be a way to wire it so at one end of the pot it would not affect any freq's and at the other end it would be maximum mid cut.

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    Thanks for that John. I had read the Torres mod is 6 to 18 nF, and I only had a 1 nF in the parts drawer. Unless I`m confused, that`s 0.001 uF.

    Even though I have built it, I have yet to use this thing yet. I understand inductance acts like a spring where it gives up to a point, then pushes back, so the range of impact (at what freq) is a bit unpredictable?? I`ll go by ear and will definitely try a linear pot at some point!

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    Where can I get that inductor?

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