Active to passive conversion

Discussion in 'Pickups & Electronics [BG]' started by DanikDarko, Dec 13, 2012.


  1. DanikDarko

    DanikDarko

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    I've got an Ibanez GSR205EX (5-er, active, 34" scale) which died out a few days back. On further inspection/experimentation I found out that one of the connectors(battery to input jack) has come loose.

    Having owned two basses earlier with passive electronics(hassle-free), I intend to convert this baby of mine to a passive.
    After a little research, I found out that this can be easily done if the bass has passive p-ups and an active preamp. Luckily, this bass of mine sports two passive p-ups with two volume pots(one for each pickup), one master tone pot and one "PHAT II EQ" pot which more or less just boosts the low-end(no cut).
    Since it already sports separate volume knobs for each pickup and a master tone knob, I'm guessing the surgery will be easier than most.
    [​IMG]
    [​IMG]
    I'll upload pictures of the open back compartment soon.

    I'm new to soldering and bass electronics for the most part. Any help would be appreciated.
    Also, this being my only bass at the time being, I seek "tried-and-tested" instructions, diagrams and, if possible, pictures.
    (Or is it too risky a procedure that should be done only by professionals?)

    I also read up that i might have to use different pots? I've google-d a million things but still haven't been able to find out if my bass has 50K or 250K/500K pots.
    That is not an issue, though. I'm willing to first try the available pots before I swap them out and experiment(I understand that the impedance might be an issue which will affect my output/volume).

    Before the active/passive debate begins, I just want to state that my experience with active electronics has not been great. In fact, this is the first active bass I have ever owned and it was a disappointment. The signal always has excess gain, over-driving my amp at home, college and shows. To compensate for this, I'd have to roll-off on both pickup volumes, quite a bit on the tone and if I intend to boost the low-end with the PHAT II EQ, I'd have to roll-off the setting further down to stop the signal getting too hot.
    I'm open to suggestions, though. As of now, I need to go passive as I cannot afford a new preamp.
     
  2. bongomania

    bongomania Gold Supporting Member

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    Look on the Seymour Duncan website for an array of clear, easy to follow wiring diagrams.

    The pots will be marked with their value, usually on the side or back. It will say something like "250A" or "50B", where the number is the resistance and the letter is the taper (slope of how it fades).
     
  3. DanikDarko

    DanikDarko

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    Thanks bongomania!

    I did check out the SD site and found this -
    [​IMG]
    I'm completely new to this and am confused about the color of the wires and their specific purposes. (I want to learn everything I can to maintain my bass on my own)

    And how do I take off the pots from the back of the bass?

    One thing I'm primarily concerned about is the use of 50K pots(which I can find out only after I take off the pots from the bass) within a passive setup.
    Any input on how it may affect the output of the bass with these pots(weak/non-usable signal) would be great.
     
  4. DanikDarko

    DanikDarko

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    Also, do I need to take off my p-ups for this surgery?

    As I mentioned earlier, I'm absolutely new to this stuff and would appreciate any and every detail/instruction.

    I can easily replace/fix the battery connector but I'm a bit fed up of adjusting my controls continuously whenever I change some other setting on the bass to avoid over-driving the amp. Perhaps one of the main issue that I would like to clarify is that will converting to a complete passive setup solve the mentioned problem or does it depend on how the pickups are wound and, thus, might just change the "voice" of the bass but not solve the problem?
     
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  6. kleinenenten

    kleinenenten

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    My first response says that you may want to try an active/padded input into your rig. I have always played active basses, and while they are hotter than many (but not all) passives, a padded input has always saved me the time of retooling everything when I switch out a bass. I even have one active bass that I don't use padded because it is much quieter. I'm sure you know this stuff, but just in case, if your rig has a -10db or -15db switch for the input, or even a separate active or - input, try that. It's designed for hotter signals.

    I love my active Ibby's, and just hate to think of converting mine to passive...
     
  7. DanikDarko

    DanikDarko

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    Thanks kleinenenten for your input.

    All my above mentioned observations have been made keeping in mind that, in general, active basses have a hotter signal compared to their passive counterparts. That is what triggered the active to passive conversion in the first place. I get an over-driven signal with everything at 80% on the bass going into the active/hi-gain/padded input of the amp(ANY amp).
    I've tried other active basses which have no problem whatsoever when cranked up. The GSR205EX has a bass boost(PHAT II EQ) only(no bass, treble or mid boost/cut). *see second picture on the first post*
    Most passive basses, on the other hand, have a 'balanced' output. In some cases I've found the signal lacking a little gain which can be easily fixed by knocking up the gain on the amp or pedal(if you're using one).

    My previous posts' query stems from the fact that in a few cases even passive bass' signal get too hot if they are not wound correctly, over-wound(?) or some other problem.
     
  8. Stealth

    Stealth Supporting Member

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    Active tone controls (preamps) usually have lower-value pots compared to a fully passive setup. There are two reasons for that: the preamp needs lower-value pots to fully sweep through its working range (bass cut/boost and treble cut/boost), and the volume control is a lower-value one because it's acting on a signal that's gone through the preamp (a so-called buffered signal). Since you have two volumes, a tone and a Phat II EQ, it might just be that the only thing active in it is the Phat II.

    Open up the bass and see where the battery red lead (the hot) goes to. If it goes just to the Phat II, it can be bypassed and you can have a fully passive instruments with literally four soldering steps.

    Can you take a photo of the innards?
     
  9. mcnach

    mcnach

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    I would remove the electronics entirely, just leaving the pickups. Then wire your preferred passive configuration fresh, with the appropriate value pots etc.
    That also gives you the opportunity to restore the bass to stock condition if you ever want to, or to sell the whole preamp wired, easier to sell.
     
  10. Steve Dallman

    Steve Dallman Supporting Member

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  11. DanikDarko

    DanikDarko

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    Thank you Stealth and mcnach!

    Stealth, yes, the red/hot lead goes directly to the PHAT II EQ pot from the battery. I'll post a photograph soon to confirm. Could you please guide me through on the rewiring step? I need to know what to solder where.

    mcnach, I'm guessing this PHAT II EQ pot has some problem with it and, hence, no one would want to buy it(why would I try to deceive a brother bass player for money anyway?). As far as the pots go, I would like to try out the existing ones first and probably experiment with others later. This is the first time I am doing a mod on my bass which includes the electronics and, thus, would leave a complete rewiring procedure for later. And, most importantly, I do not wish to restore my bass' electronics to its stock condition as it gave me tons of problems, as mentioned in earlier posts.
     
  12. bassmeknik

    bassmeknik

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    50k is not appropriate for a passive bass. Change all the pots to 250k.
     
  13. DanikDarko

    DanikDarko

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    The pots are B500K pots. So I'm guessing I wouldn't have to buy new pots right-away.

    Thanks Steve Dallman! This is exactly what I wish to do without the pot changes. Can I get a step-wise instruction list with the same as this is the first time I'm breaking out the soldering gun on my bass. Also, from what I've noticed from the diagram and the wiring on my bass, most of the connections are already there.
    I'm sure there's someone who's experienced enough to guide me through a step-by-step process("First, do this. Now, do this.... And, finally, this."). I do not wish to change the placement of the pots, I just wish to be able to play again soon while learning on the way.
     
  14. DanikDarko

    DanikDarko

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    Thanks bassmeknik! The pots are B500K pots, as I just mentioned.

    Could you please elaborate on why 250K/500K pots are required for passive basses? I've read from numerous sources about this but none of them clearly specified the reason. My understanding of electronics is very limited and as mentioned on an earlier post, I believe the impedance poses a problem(but how?).
    Any input on this would be highly appreciated.
     
  15. DanikDarko

    DanikDarko

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    Here you are -
    [​IMG]
     
  16. bongomania

    bongomania Gold Supporting Member

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    500 K is great for passive setups, don't worry about 250 vs 500.
     
  17. DanikDarko

    DanikDarko

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    I know. I've come to know through numerous sources that passive basses require 250K/500K pots and active ones 25K/50K pots. I want to know how these different pots work, why the difference in impedance.
    As I said earlier, I'm new to electronics and want to gain as much knowledge as I can. Any info will be appreciated.
     
  18. Andyman001

    Andyman001 Supporting Member Supporting Member

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    Read this

    this article explains some with regard to signal chain and loss of frequency response. The values of the pots also contribute to the pick up loading and tone.
     
  19. mcnach

    mcnach

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    Sounds like a bit of experimentation is a good idea then.
    The best way to learn what effect using different value pots etc have on the sound is to try it for yourself. It's easy, and for me at least, fun.
    So enjoy! :)
     
  20. Stealth

    Stealth Supporting Member

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    Here's the catch. A resistance in series or parallel with a signal source (such as a volume pot connected) changes the tonal response of the pickup. Just as a pickup is a length of wire (with resistance) wound as a coil (with inductance) with layers upon layers of wire (with capacitance) with its own sound, the added resistance of a pot and capacitance of a tone cap change that tone. If the pot resistances are kept an order of magnitude above the total impedance of the coil (say, the passive pickup has 10 kΩ, with the pots being 250 kΩ or 500 kΩ), the whole circuit has what's called a resonant peak - usually noticed as brightness in the sound. If you used a 10 kΩ or 25 kΩ pot, which are of equal magnitude as the pickup, that resonant peak would either be flat or would even slope down faster than normal, and would sound extremely dark and dull.

    Demonstrating all of this would either require some electronics and electrotechnics 101 - or look for Helmut Lemme's website where he describes how pots and caps change the tone of the pickups.

    Meanwhile, there are two ways to "passivize" your bass. The first solution would simply be to find the input and output wire on the Phat II EQ, desolder them from EQ and solder them together. That way you'll permanently bypass it, and you can remove the battery and ignore that top knob altogether.

    The second solution is to give each of your pickups a tone control. This can be done on a passive instruments, but it requires a few extra parts, notably, an extra tone pot, an extra cap and two extra resistors which help isolate the tone pots and make them affect only the pickup they're supposed to. The downside of the resistors is that the volume will be a bit lower overall, but I don't think that's a downside in this situation. I made this earlier for another TalkBass user.

    [​IMG]

    Take note that the volume pots should be linear, while tone pots should be logarithmic (audio). You probably have an A500K (logarithmic 500 kΩ) tone pot, if you don't, I highly recommend that you get enough of them for your configuration. The tone rolls off much smoother and you have more precise control if you use an audio pot, while volumes work best if linear.

    Now, the colors up there probably don't correspond with yours - I used them solely to be able to easily distinguish all of them. Just follow them from the source (pickup) across the volume and tone pots to the Phat II to the output. Then you'll be able to see what needs to go and what needs to be changed. Oh, and feel free to rearrange the pots and knobs around as you see fit.
     
  21. DanikDarko

    DanikDarko

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    Andyman001, I cannot thank you enough. This is exactly what I was looking for. Now I just need to find out how all of these elements work/connect/interact together with each other. That, I guess comes from application of knowledge.

    mcnach, I wish to keep experimenting as and when I can to get as much hands-on experience on all of this as possible. Receiving so much info and knowledge has been so much fun, I can't wait to apply it all. I could put on music and go through TB all day if I could and not get bored for even a second(how I wish it were a job I could get paid for!). <--that last bit could easily fit into the Floyd epic.

    Thus, now that I have a diagram with the stock wiring, a diagram with the mod(thanks to Steve Dallman ), I'm going to go ahead and apply all the gained knowledge.

    I thank you all for sharing your knowledge with me. I shall definitely post photographs and audio clips of this tiny project for the collective effort you all have put in which has enabled me to do such a project.

    I have to say, my first interaction/experience with TB and its users has been great and truckloads more than what I had expected.
     

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