Weird Wiring

[Mierda de Pollo]

I recently bought an old Yamaha RBX300 precision bass off eBay. According to a Yamaha employee, this basses were in production from 87' to 89'. It's pretty old but in an acceptable physical condition. However, there is terrible humming and buzzing whenever I connect it to my amp or to my Tascam US122L USB interface.

I suspect the problem is the wiring because when I touch the bass jack, the hum disappears. There must be some ground issues, am I right?

I opened the bass to check the wiring and I found something... weird. According to various wiring diagrams I've seen on the net, most appear to be the same (or pretty similar). The wiring on my bass is really different:



Now the questions:
1.- Is the wiring right? Do you find problems with it?
2.- Do the potentiometers values depend on the pickups or are they the same for all P-Basses? Is it safe to replace them? Which values should I choose? Moreover, which type should I get?(linear, logarithmic, taper, etc)
3.- I've heard that ceramic caps are really bad for audio. Should I use an electrolytic or a film cap instead?

[line6man]

I see nothing wrong with the wiring, looks like standard P wiring.

Perhaps your bridge is not grounded?

Pot values are a personal preference.
250K would be the standard for most P basses, but you can use 500Ks for more output/treble.

The composition of a capacitor does not matter for this application. They all sound the same provided that their actual ratings are the same. Ceramics are notorious for having poor tolerances, so you may consider something with a tighter tolerance like a polyester film.

[SnakeKappele]

Looks fine to me. The capacitor is between the volume and tone pots instead of the usual volume to tone with the capacitor running from the tone to ground. The result is the same: the tone potentiometer controls the flow to ground through the capacitor.

20 people will follow and start talking about this for 4 or 5 pages all nitpicking it to death. But I don't think there is any audible difference.

Does the noise go away when you touch the strings?
What did the shielding look like?
For shielding:
Shielding!

I can't find info on this bass, what kind of pickups?
The wiring looks like a single humbucker like a P-Bass.

Standard pots are 250K Ohm but 500K Ohms can give you more highs. I would use an audio taper for volume and linear for tone.

[M0ses]

Uuuh, it's not star grounded??

I jest.

[SnakeKappele]

Originally Posted by M0ses

Uuuh, it's not star grounded??

I jest.

Good one!

[MoireBass]

Originally Posted by Mierda de Pollo

I recently bought an old Yamaha RBX300 precision bass off eBay. According to a Yamaha employee, this basses were in production from 87' to 89'. It's pretty old but in an acceptable physical condition. However, there is terrible humming and buzzing whenever I connect it to my amp or to my Tascam US122L USB interface.

I suspect the problem is the wiring because when I touch the bass jack, the hum disappears. There must be some ground issues, am I right?

I opened the bass to check the wiring and I found something... weird. According to various wiring diagrams I've seen on the net, most appear to be the same (or pretty similar). The wiring on my bass is really different:



Now the questions:
1.- Is the wiring right? Do you find problems with it?
2.- Do the potentiometers values depend on the pickups or are they the same for all P-Basses? Is it safe to replace them? Which values should I choose? Moreover, which type should I get?(linear, logarithmic, taper, etc)
3.- I've heard that ceramic caps are really bad for audio. Should I use an electrolytic or a film cap instead?

1 - It's OK. The tone control is wired oddly, leaving a floating terminal so it will work the same in terms of the treble rolloff but might pick up a little more 60 Hz hum than a grounded-terminal configuration. As Line6Man said, your grounding sounds like it could be a problem.

2 - As Line6Man said, 250 Kohm is typical for p-basses, 500 Kohm will also work fine but be slightly noisier just due to the thermal noise of the resistance. Use an A (audio/logarithmic) taper volume control to get the best resolution, and generally people prefer a linear (B) taper for the tone control. I've used an A taper for the tone control though, isn't a big deal either way. The most common value for capacitor for bass is 0.047 uF, but you could use a higher or lower value, no big deal. Use 0.1 uF if you want that deep 'Astin Barret'-type sound.

3 - NEVER USE AN ELECTROLYTIC CAP FOR PASSING AUDIO UNLESS IT HAS A VOLTAGE BIAS ACROSS IT. Electrolytic (or any polarized) caps pass the positive and negative halves of AC signals differently and cause nonlinear distortion. If the positive side of the electrolytic is biased positive a couple of volts, the nonlinearities go away because the capacitor is no longer sitting at zero offset voltage. You can also buy non-polarized electrolytic capacitors, these are just two normal electrolytic capacitors wired in series and reversed (so that cap1 + is connected to cap2 +).

The two main factors that cause nonlinearities when passing audio through capacitors are the dielectric absorption and the dissipation factor. Mylar, or film capacitors typically have the best DA and DF ratings within the audio band of all types (ceramics are much better at radio frequencies however). The three types of mylar caps are (in order of quality, size, and expense) polyester, polystyrene, and polypropylene. While I have used very expensive polypropylene caps as phantom-blocking caps on the mic inputs of a high-end recording console, that's really excessive for a passive tone control, any mylar/polyester-type will be good.

[line6man]

I disagree strongly on the tapers.

IME, linear taper volumes work best, as they give you a smooth sweep from 10 to 0 without the big jump that is common with audio tapers at about 8-ish.

Linear tones behave more like switches. You have to turn the tone way down to hear any effect.

[MoireBass]

Originally Posted by line6man

I disagree strongly on the tapers.

IME, linear taper volumes work best, as they give you a smooth sweep from 10 to 0 without the big jump that is common with audio tapers at about 8-ish.

Linear tones behave more like switches. You have to turn the tone way down to hear any effect.

You have a right to your opinion, and of course you can (and should) wire your bass in whatever way works best for you.

But linear taper volume controls have a very low resolution vs rotation near the top of the control range. This is the entire reason that logarithmic audio taper controls were invented (linear is much easier to manufacture), to make the volume change better match the way our ears hear amplitude, which is logarithmic. The vast majority of basses use audio taper volume controls rather than linear for exactly this reason. Here's one example: Bartolini's recommended preamp hookup, note the audio taper volume pot:
http://www.bartolini.net/instruction...t/Ntbt_918.pdf

Linear or audio taper passive tone control makes very little diff to me, but most basses use a linear control there.

[line6man]

Originally Posted by MoireBass

You have a right to your opinion, and of course you can (and should) wire your bass in whatever way works best for you.

But linear taper volume controls have a very low resolution vs rotation near the top of the control range. This is the entire reason that logarithmic audio taper controls were invented (linear is much easier to manufacture), to make the volume change better match the way our ears hear amplitude, which is logarithmic. The vast majority of basses use audio taper volume controls rather than linear for exactly this reason. Here's one example: Bartolini's recommended preamp hookup, note the audio taper volume pot:
http://www.bartolini.net/instruction...t/Ntbt_918.pdf

Linear or audio taper passive tone control makes very little diff to me, but most basses use a linear control there.

Have you actually tried it?
There have been huge debates about this in the past.
I used to share your point of view, but my mind changed when I tried the linear taper instead of just going off of theory.

Most basses use audio tapers for both the volume and tone, btw.

[mongo2]

Originally Posted by line6man

Have you actually tried it?

Yes, I have...MoireBass is correct about the effect of the taper.

[Mierda de Pollo]

Originally Posted by SnakeKappele

Does the noise go away when you touch the strings?

Nope, only when I touch the jack.

Originally Posted by SnakeKappele

What did the shielding look like?

Not sure and I'm at work right now so can't tell. But I think that there is no shielding. Shouldn't be a problem though... I use an unshielded guitar (Yamaha too) without any trouble.

Originally Posted by SnakeKappele

I can't find info on this bass, what kind of pickups?
The wiring looks like a single humbucker like a P-Bass.

That's because it's really old. As I said, only in production from '87 to '89. And pickups are like the Seymour Duncan quarter pounders (are they called P-Bass pickups?)

Originally Posted by SnakeKappele

Standard pots are 250K Ohm but 500K Ohms can give you more highs. I would use an audio taper for volume and linear for tone.

Ok, I think I'm gonna go with the audio 250k for volume and linear 250k for tone.

I'm also gonna use a .047uF poly cap.

I would like to thank all of you for replying to my questions. All of your help is greatly appreciated.

[ironrat]

to the OP: I love your nick!!!!


































yes, I know what it means...

[luzceloffan]

Originally Posted by ironrat

to the OP: I love your nick!





























yes, I know what it means...

+1 I know what it means .. that's why I don't like it!!!! menos si la piso xD! (less if I step on it ...)

[Diogenes]

Originally Posted by mongo2

Yes, I have...MoireBass is correct about the effect of the taper.

That's a pointless debate here... believe me. I have been tied to the whipping post for preferring A-taper volume pots.

[Bloodhammer]

Originally Posted by Mierda de Pollo

Nope, only when I touch the jack.


Not sure and I'm at work right now so can't tell. But I think that there is no shielding. Shouldn't be a problem though... I use an unshielded guitar (Yamaha too) without any trouble.

Despite taper wars, this seems vaguely important. Sounds like the bridge isn't grounded...

[SnakeKappele]

Originally Posted by Bloodhammer

Despite taper wars, this seems vaguely important. Sounds like the bridge isn't grounded...

+1

[FunkMetalBass]

Originally Posted by Bloodhammer

Despite taper wars, this seems vaguely important. Sounds like the bridge isn't grounded...

+2.

OP, check to make sure the wire that goes to the bridge actually attaches under the bridge and that it's properly soldered to the back of the pot.

If you've got a few bucks and an hour, check out the shielding tutorials and shield the cavities.

[MoireBass]

Originally Posted by line6man

Have you actually tried it?
There have been huge debates about this in the past.
I used to share your point of view, but my mind changed when I tried the linear taper instead of just going off of theory.

Originally Posted by mongo2

Yes, I have...MoireBass is correct about the effect of the taper.

Yep, I've used both and prefer the A taper for volume. Use whatever the heck works for you though, hey, feel free to use a C taper or an X taper if you like.

Originally Posted by SnakeKappele

Does the noise go away when you touch the strings?

Originally Posted by Mierda de Pollo

Nope, only when I touch the jack.

That points very much to the ground wire between the bridge and the pots being broken or somehow no longer making a good connection. If you've got a voltmeter or DVM, measure the resistance between the jack and the bridge. {The best place to poke the probe on the bridge is into the saddle adjustment screwtops, then you won't scratch anything.} The measured resistance should be very small, e.g. I measured ~3 ohms on my Lakland and ~8 ohms on my Ibanez Gary Willis.

You may have to remove the bridge and reposition the contact or replace the ground wire entirely to redo that contact.

Originally Posted by Diogenes

That's a pointless debate here... believe me. I have been tied to the whipping post for preferring A-taper volume pots.

Oh, sorry, I didn't know. I'm relatively new to TB. Seems like a pretty minor thing for someone to get their knockers in a twist over though.

[Diogenes]

Originally Posted by MoireBass

Oh, sorry, I didn't know. I'm relatively new to TB. Seems like a pretty minor thing for someone to get their knockers in a twist over though.

This is a great place with great people and a lot of information. But there are those who are determined to convince you that your opinion is wrong and will go to great lengths trying to argue why.

[BassLife77]

Originally Posted by Diogenes

This is a great place with great people and a lot of information. But there are those who are determined to convince you that your opinion is wrong and will go to great lengths trying to argue why.

I agree, getting involved in a debate regarding personal taste or a subjective topic seems kinda pointless to me. A lot of knowledgable posters at TB and I just do trial and error to find out what works for me. I still give thanks for the information. I realize the ET's and engineers don't really have to tell us anything. I don't look a gift horse in the mouth