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Can I add an 'in-line' passive tone control to the (active) treble circuit?

Discussion in 'Pickups & Electronics [BG]' started by Fender32, Oct 5, 2013.


  1. Fender32

    Fender32

    Jun 23, 2005
    Kent, England
    :meh: Weird request, huh?

    Here's the story:

    I have just modified a bass by adding a MusicMan StingRay pickup and 2 band (boost only) StingRay EQ. The results are terrific, but I want to find a way to tame the treble, which can be fierce when boosted over half way and is still present when the pot is turned right down (i.e. zero boost).

    Now, I know that some of you will be tempted to suggest using different value pots or modifying the circuit etc., but I am looking for a very specific solution to this problem ;) ....

    I have fitted a concentric pot to use as the master volume on the inner shaft (top knob) and I want the outer shaft (bottom ring/knob) to act as a passive tone control that will affect the treble control only. Onto that 500k stacked pot, I have soldered a tone capacitor, just as you would for a passive (Fender) tone control.

    What I need to know now is how would I wire this into the treble control so that it is permanently connected and will leave the (active) treble functioning normally when the passive tone pot is up full, but will act on the signal from the active treble (regardless of where that active treble is set) and reduce the clarity of the signal :confused:? Which lugs on each pot would I connect with each other?

    My guess is that I would need to interrupt the path of the wire(s) that feeds the active signal back out of the treble pot and route it thru the passive tone pot, but I just don't understand these things well enough to know which wires do what :atoz:!?

    My active preamp has three (yellow) wires coming out of it and going directly to the treble pot. I think that it's the same as this one ...

    BajaMusicmanStingrayBasspreamp.

    Could I interrupt one (or more) of those three wires with my 'in-line' tone circuit and still hear the effects of both the active and passive tone controls on the treble output? What do you think :meh:?


    Finally, I recently asked for help with a different solution to this problem and was very pleased to receive this diagram from lineman6 :).

    SB-CB_circuit.

    Unfortunately, I have a very limited understanding of guitar electrics and when it came to wiring this up, I couldn't figure out where the rest of the wires should go :(. Embarrassing, I know.

    So, once again, I throw myself upon the mercy of the assembled experts. I really hope that someone can help me achieve this, because this is a truly great bass waiting to happen :smug:. Thanks in advance.

    Andy
     
  2. I'm not sure what you're trying to do. Tone controls can't be applied over particular frequency bands. You put a capacitor parallel to the full range signal, and it decreases the impedance at high frequencies.

    If you're trying to do something like Dingwall's OBP-1 treble control, where the control actively boosts and passively cuts, you will need a specialized pot that AFAIK, no one sells. IIRC, MEC will custom manufacture pots, but they are extremely pricey.
     
  3. Fender32

    Fender32

    Jun 23, 2005
    Kent, England
    :p That makes two of us!

    That would probably do what I want it to, but I still don't understand how to wire the pots to achieve that :(.

    You were kind enough to draw me a diagram before, which looked simple enough ... until I came to wire it up today. I wasn't sure if I should be adding extra wires to the switch and soldering them to the contacts that you described in the labels (e.g. run a wire off the switch to the output jack, run another one to the pre-amp output etc. etc.), or if I was supposed to take off the existing wires and solder them to the switch (e.g. remove the output jack 'tip' wire and solder it to the switch etc.). The second option seems unlikely, but I also couldn't figure out which was the pre-amp input and output ... so I gave up :atoz:!

    As it stands, I'd be happy to leave out the switch and just have the tone control acting over all of the frequencies (i.e. the active output), but I don't even know how to wire that! Any ideas :meh:!?

    Not sure what that is, but it's not the solution for me if it involves extra pots etc. I have enough pots already :p - I just need to connect them to something to make them work!

    Thanks for offering to help again though, line6man;)
     
  4. It's really simple. Place the pot/capacitor between the pickup and tone control/preamp thingy. This way you can roll off treble before the active part happens. Easy.
     
  5. Fender32

    Fender32

    Jun 23, 2005
    Kent, England
    :p You mentioned not one, but two of the 'magic' words there, dmusic148; 'simple' and 'easy' :D!

    Now, put yourself in the shoes of a 5 year old holding a soldering iron and please explain (in pictures if possible :p) which wire goes to which lug on which pot.

    For instance, using the diagram above (that line6man drew for me), I can see that the tone cap goes onto the central lug and the other 'leg' is soldered to the casing of the pot. That much I have done already, so I do at least have a 'tone control' (big whoop :rollno:).

    Now, if I want to "place the pot/capacitor between the pickup and tone control/preamp thingy", there are two questions;

    1. Do I only need to cut the 'hot wire' from the pickup and attach this to the passive tone pot (or does it involve connecting the other pickup wires too - mine has six, connected to a series/single coil/parallel switch) :confused:?

    2. Which lug on the passive tone pot do I solder the input from the pickup wire to and which lug do I take the wire carrying the output from the pickup from :meh:?

    Sorry, these are basic questions I know, but I really don't know enough about electronics to be playing around on the inside of my bass - it hasn't stopped me so far though :D!

    Thanks, in advance, for you reply ;).
     
  6. Fender32

    Fender32

    Jun 23, 2005
    Kent, England
    Any further thoughts from anyone? I'd quite like to have a go at this job today, if possible ;).

    Cheers!

    Andy
     
  7. LowB-ing

    LowB-ing

    Aug 3, 2005
    1) Find the terminal on the pre amp where the "hot" wires from from the pickup coils are connected. You do not need to cut any of the existing wires.

    2) Solder an additional cable from this terminal to one of the "side lugs" on the tone pot. Which lug you use will determine if the tone knob goes backwards or forward.

    3) Solder one leg of the tone capacitor to the center lug on the tone pot.

    4) Solder the other leg of the tone capacitor to the pot casing.

    5) Solder a wire from the the pot casing to ground


    Done!
     
  8. Fender32

    Fender32

    Jun 23, 2005
    Kent, England
    LowB-ing, you're a star, thank you :)!

    I did as you said, except for step 5 (as the whole cavity is shielded with copper foil and the pot is grounded by virtue of being screwed down ;)) and ... it works :hyper:!!! I now have a 2 band active circuit, which can be 'tamed' at any stage by dialing back the passive tone control - exactly like the VTC on my previous Sadowsky basses :cool:.

    I didn't pay attention to which way round the pot was operating, but at least if it runs backwards, I know how to fix it now :D.

    This was very helpful - my bass project is almost complete. I just have one more question, which I'll post in a separate thread.

    Thanks to you, to line6man and to everyone else who took time to read this thread and consider whether or not they were able to help me. What a great community we have here on TB :smug:.

    Peace!

    Andy
     
  9. LowB-ing

    LowB-ing

    Aug 3, 2005
    Great! :bassist:

    I actually have almost the same thing on one of my Stingrays (Well, it's just a SUB). I didn't want any extra knobs though, so I just have a switch that selects between tone all the way on or tone all the way off.
     

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