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Entering the wonderful world of bass modding...

Discussion in 'Pickups & Electronics [BG]' started by Saxn, Mar 25, 2011.


  1. Saxn

    Saxn

    Oct 23, 2010
    Nashville, GA
    And of course right off the bat I have a question before I start drilling.

    I own a Yamaha RBX374, and I KNEW it would just be a matter of (very little) time before I wanted to start tinkering with the guts. I have not opened it up yet since I am on the road with zilch free time, and I haven't been able to find the service manual for the bass... so everything will be guesswork until I take the back off and do some looking and measuring.

    What I DO KNOW is what I would like my first two mods to be. One is adding a series/parallel switch, and the other is separating the pickup controls. It is the latter that I have a question about...

    Looking at a schematic from another RBX model, I see that the blend control is just a ganged pot that lowers the resistance in one pickup circuit while simultaneously raising it in the other. I was hoping to separate the two pickups for independent control, and I am wondering if there is any reason I SHOULD NOT do that. I only have one real concern, and that is that the Yammy is an active bass, and since i know nothing about the output level of pickups, I don't know if there is any danger of overdriving the preamp input in the event both pickups are maxed at the same time.

    Any takers on this? I can already tell this is going to be an addictive hobby

    Thanks for reading.
    __________________
     
  2. Saxn

    Saxn

    Oct 23, 2010
    Nashville, GA
    Well, I never do this, but I think maybe my accidentally posting this in the wrong forum yesterday might have hurt the cause, so ...

    **BUMP**
     
  3. Tommorichards

    Tommorichards

    Mar 22, 2011
    No problem. The blend pot doesnt increase the output signal. In the centre position, there is full signal going from both pickups to the preamp.

    Itll be fine, although i probably wouldnt put a series/parallel switch in there with a preamp, THAT may overdrive the preamp in series mode, but im not sure on that aspect.
     
  4. Saxn

    Saxn

    Oct 23, 2010
    Nashville, GA
    I seeee... so putting the pups in series may overvolt the op-amp's input? I need a bit more info on that before I commit to that particular project. Is there anyone out there that can give me a little more info on the RBX374 pup output and preamp in limits?

    Thanks for the reply, Tommorichards! You pointed out something I had not thought of.
     
  5. With all active basses, you're going to want to get the right pot values as well, depending on where the volume pots are going. If they're before the preamp, your standard 250k or 500k is fine; 25k is a common value for after the preamp.
     
  6. Saxn

    Saxn

    Oct 23, 2010
    Nashville, GA
    Thanks for the info, Vincent. I am thinking it will be OK to just duplicate the blend pot value (whatever that turns out to be) for the separate control. I think the pup blend is before the preamp if it is like the RBX diagram I have seen, but I won't know until I can get it home and take a look.

    As far as the problem brought up by Tommorichards, I can't find any useful info on the output voltages on the pickups, and I don't really have any sort of meter that will be super-accurate for voltages that low, so any info anyone has on that would be greatly appreciated!

    I also need to figure out what the max input into the preamp can be. That will tell me whether or not to proceed, or maybe if I can put a resistor in the series configuration to ensure I don't overdrive the thing... I don't know. I am really anxious to get home so I can start getting some hard data to work with!
     
  7. Tommorichards

    Tommorichards

    Mar 22, 2011
    try and contact the company who manufacture the preamp, they should be able to give you details if they're good. Otherwise, try googling for a data sheet.
     
  8. Ric5

    Ric5 Supporting Member

    Jan 29, 2008
    Colorado
    I disclose nothing
    I have 15 basses ... all are modified or complete out and out frankensteined parts basses.

    Not a stock bass in the bunch.
     
  9. Saxn

    Saxn

    Oct 23, 2010
    Nashville, GA
    Ric5, do you have any experience in the modding of active basses like the Yammy 375? I have been doing a little reading on the other RXB models, and it says that they are using op amps of some sort as the preamp. If that is the case I am hoping that I can get some info on the supply voltage to the op-amp, and that should tell me whether or not I can go ahead with the series/parallel mod. I am hoping for good news since it is a 9 volt power supply needed, and even if it were reduced some that would still leave plenty of overhead for a 2 volt peak-to-peak pickup output.

    I have just gotten home this evening so I am torn between playing the bass or opening it up and taking readings! Anyhow, I will post results as I get them.
     
  10. 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.

     
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