Hello all.
As always I appreciate all the help and advice.
I know this is off topic, but I don't know of another place where I can contact as many knowledgeable and helpful people. If anyone knows of a site, I would be happy to remove this from the board, or removve it any ways if it just plain doesn't belong. Thanks.
I have a 4 string electric bass. Its a Kimaxe, I found their website, and some info about them, but ultimately found no help.
It is wired as active. What I am wondering, is if it would be ok to wire it like my guitar, as passive. What is the difference? Anyone know of any real beginner sites or resources where I can do this with step-by-step instructions?
The reason I am asking, is that the pots are shot, and so is the 1/4" socket. lots of crackling and on-again off-again stuff. So, I decided, rather than trouble-shoot, I would just buy new pots and a jack. Maybe even replace the pick-ups.
Major problem is I have no idea how to wire an active p-up circuit, and can't find 30k pots, didn't look real hard, but couldn't find them.
Any ways, sorry if this post wasn't totally clear, have some nasty bronchitis and and under the influence of some codeine cough syrup :wink: , but I would appreciate any tid-bits of info or leads as to where I can learn about how to do this.
Thanks much all, Matt.
Check mouser for the pots. I don't know about the p/u's, they may be set up specifically for an active system. You may be forced to change p/u's to switch over to passive.
The mim forum http://www.mimf.com/ has a helpful bunch of people on it. Most of them are familiar with guitar and bass wiring. Their library should contain all of the info that you need to start.
Is the main reason you want to wire you bass as passive because you aren't sure about active wiring? If so don't worry about it.
You mentioned 30k pots I assume you bass goes something like Pickups -> pots (30k etc) -> preamp -> 6.5mm jack. If not, please correct me.
Because the pots are 30k it is highly likely your pickups are active. You might be able to see the power wires going to the pickups. If that's the case then you can't really wire the bass as passive anyway, the pickups need power. At best you can do is remove the preamp (it has got a preamp?) but there is little point doing this.
You mentioned cracking are you sure it's the pots or is it only the 6.5mm jack? If the pots are crackly you might be better off cleaning them out with some electrical cleaner or perhaps WD-40. You spray the insideof the pot and wiggle it to the extremes about 50 times. Perhaps repeat this a second time. If you can clean them up then that saves a lot of mucking around.
The pots might be hard to get because the are concentric types or something. There are people who sell specialist guitar stuff - you can try a web search. The values are critical I suspect a 20k ot 25k pot would be fine provided it matches the existing ones mechanically. There's also the possibility of contacting distributors for spares.
As far as wiring goes perhaps you should describe the what pickups you have, the controls, the pot sizes and if it has a cap on a tone pot - because it does make a difference. I'm don't know of any recipe sites but there are some resources on the web.
Here's an active bass schematic you can peak at:
http://www.musicyo.com/planet/graphics/tbyactvcrct.gif
Most of this circuit is on the preamp PCB. The part that concerns you is the pots at the input. Your pickups will have power going to them which isn't shown on that schematic because that bass used passive pickups.
If you can fill in some of the gaps then perhaps we can find something.
Right on. Thanks for the help. I am going to attempt it next weekend I think.
Thanks again, Matt.
As Boofhead said, just describe the internals with some more detail and we can give you what options are open to you.
My guess is that the 30K pot could be substituted with a large range of values from probably 10K to 100K and it would wouk fine.
You asked for the difference between active and passive. Active pickups have amplifiers in them to present the coil with very minimal loading and to drive the signal at a good level down the cable. Because they have amps, they are typically wound with fewer turns but I don't know what that does to the sound. Even if you could remove the amps (assuming they're built into the pickups) the resulting coils would be underpowered. If your bass has a preamp circuit board inside, then you might have a passive option.
Take care,
-Peter
Quotevalues are critical I suspect a 20k ot 25k
I actually meant the values are *not* critical. However, it would be wise to keep in the 20k to 30k region because the pot values often determine the output level - too high and you get clipping, too low and you get a weak output.
First, I dig your handle. Now that I'm closer to my home, rather than inside looking out, I'd be happy to help out someone in an American Band, as opposed to being a heartbreaker. :lol:
There is active and there is active. You can smack an active preamp with tone controls on ANY guitar for the purpose of improving S/N ratio or optimizing high end sparkle or even just for the convenience of having on-board EQ. I have a guitar like that, and a great many commercial production guitars are like that too. You could take the same guitar, slap some standard passive electronics on 'em (500k pots, tone cap, etc.) and they'd work just fine with a standard amp. At the same time, some companies depend on active on-board electronics to complement the quirks of the pickups. For instance, the pickups may be very low impedance to optimize bandwidth, futz around with resonances, or just to be single coil without the hassle of picking up hum (more turns makes a pickup a better "antenna" for interference). As a result, the electronics may be specially designed to interface those pickups to an amp that is expecting to see something very different. If the pickups are, say, 1k impedance, then a 30k pot makes sense for any on-board electronics, but 500k pots don't. If the pickups are 8k impedance, then 30k makes little sense but 250k does.
Bottom line, I think you need to find out, and tell us, a little more about the pickups themselves so that an optimal match between circuit parameters and pickups can be achieved.
Well thanks for getting (got) this thing on the move, and just in (on) time too I was getting paranoid because I am in need of some information so I can play some footstompin' music asap.
Hmmm... How can I get more info about the pickups? I have no problem tearing them apart, but I don't know what I am looking for to tell you. The bass is fairly nice in design as far as the body and finish, but it is definitely a cheaper bass.. I would be a little surprised if it sold for over 300 new.
Will the impedance be printed somewhere on there?
I am assuming, since its not the highest quality bass... that the preamp may be there cause the pickups are weaker in some sense...
Well, there is a circuit board inside. There are two 30k Ohm pots, a 25k Ohm pot, and another that looks like a dual.. whatever.. 6 terminals for soldering..250k Ohm? on the circuit board there are about 6 polarized caps ( or +/-) 4 others, a number of resistors, and something that looks like an IC.. it has 8 leads, says 2904D JRC 4031G on it.
The pick-up config is like a fender combo p-jazz.. has a jazz bridge p-up and an offset pbass pickup.. or two or whatever it is. The body cavities where they sit are filled with wax, and it looks like the insides or the undersides of the pickups are filled with, or coated with some wax as well.
Don't really know what else to say. The thing has crackled and stuff for so long, I dont even remember what the pots do.. I mean I am sure tone and volume, but that dual pot thing.. maybe a blend? I don't know.
BTW, there is a 9v battery in the junk cavity with everything else.
Any ways, anything else I can ad, just ask.
Thanks again all, I really appreciate it... a lot.
Matt.
QuoteHow can I get more info about the pickups?
It might be difficult to find out specifics about the pickups. However it's usually possible to infer a significant amount about them from the pot values, wiring and type of wiring. A multimeter measurement can tell you a lot too.
Do you have a multimeter? If so measure the resistance of the pickups.
Another useful piece of information is the number of wires from the pickups. To each pickup you willl either have two wires, three wires, two sets of two wires, coax with the shield and core, or coax with two core wires and the shield. Active pickups usually have coax with core two wires and a shield - more often than not one core wire is red. Passives might have single wires as oppose to coax, although you can also get coax coming out of them.
I wouldn't be pulling the pickups appart yet that's for sure - you are more likely to do damage to them if they are sealed types.
With the 250k pot in there, I'm assuming these are 250k as opposed to 25k. and the fact it's dual I suspect you may have passive pickups with an (active) preamp. I also suspect the controls were 25k = volume, one 30k = treble, other 30k = bass and the dual is a pickup blend. The bass would be wires as, assuming passive
P pickup to 250k dual pot
J pickup to 250k dual put
dual pot -> preamp board input terminal
30k bass to preamp terminals (for bass pot)
30k treble to preamp terminals (for treble pot)
Preamp output to 25k volume pot then to the output jack.
You can get the idea of how to wire the blend/balance pot, the volume control, how the 9V power connects and the jack wiring from this drawing,
http://happybob.com/rstrand/status100.gif
The bass and treble pots will just go to the PCB.
Don't pull any wires off the PCB without taking good notes.
If you have a means of taking a photo that might be helpful too.
I'm sure you will be getting some idea of the wiring based on the two links I've posted. Feel free to throw back any more info, or anything you can determine.
I'm with Boof on this. The pot values are a dead giveaway, and the primary reason I made a distinction between different sorts of active electronics. In this instance, the manufacturer made a conscious choice in pickup design and deliberately used the electronics to compensate for the things they had to forfeit (output level) in pursuit of things they would gain (bandwidth, noise levels).
The JRC2904 is the same as an NJM2904. It is a dual op-amp in a standard 4558-type pinout. The datasheet indicates it will work down to 3V supplies. I am assuming it was selected so that a 9v battery might be expected to provide sufficient power for a reasonable length of time.
Right on, thanks. I am working on getting some clear pics together. I took some with a webcam, but yeah they sucked. I am going to borrow a digital camera so I'll have them up shortly.
Thanks again, Matt.