Wiring the Bridge Pickup in a Yamaha RBX270

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Wiring the Bridge Pickup in a Yamaha RBX270

Post by ITHertz »

Hi All,

I have a Yamaha RBX270 which I use for recording in my home studio. The RBX270 has a P-J pickups and uses a Blend configuration (Volume, Tone, Blend). The J pickup is really noisy so I'd like to replace it. I've bought a Dimarzio Area J Bridge pickup however I'm unclear as to how to wire it up.

The original bridge pickup has one wire that connects to the back of the pot furthest from the bridge. The Area J has five wires (Red, Black, White, Green, Grey).

How does the Area J connect to a Blend configuration?

Cheers,

Chris
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by Wonks »

Start by looking at the DiMarzio wiring diagrams.

https://d2emr0qhzqfj88.cloudfront.net/s ... gram_0.pdf

The grey is the shield/screen, which needs to be twisted together with the green wire and wired to where the current screen wire goes (probably to the back of the blend pot).

The white and black wires are twisted together and soldered, and the joint insulated; ideally with a bit of heat shrink, but electrical tape will do.

The red wire is the signal wire, so that goes to the tab on the blend pot that the current pickup signal wire runs to.

If in doubt, post a picture of the current wiring.
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by ITHertz »

Wonks wrote:Start by looking at the DiMarzio wiring diagrams.

https://d2emr0qhzqfj88.cloudfront.net/s ... gram_0.pdf

The grey is the shield/screen, which needs to be twisted together with the green wire and wired to where the current screen wire goes (probably to the back of the blend pot).

The white and black wires are twisted together and soldered, and the joint insulated; ideally with a bit of heat shrink, but electrical tape will do.

The red wire is the signal wire, so that goes to the tab on the blend pot that the current pickup signal wire runs to.

If in doubt, post a picture of the current wiring.


Thanks, that should be enough to get me going!

Cheers,

Chris
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by ITHertz »

Hi,

I finally got a chance to wire up the new pickup however I've run into a problem.

When the Blend control is in the centre position (giving me an equal signal from the two pickups) I losing something like 6-8dB in level. When set to the two end positions (each pickup on its own) it's fine.

Could this be a phase problem? Or is it something else? And is there a way to fix it?

Cheers,

Chris
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by Wonks »

I recently found out that blend pots come in two flavours.

The sort I'd pick for blending guitar/bass pickups has a 'MN' taper. The other sort has an 'AC' taper (log + anti-log). This type is more used as a pan control in mixers and the like (so one input and two outputs as opposed to two inputs and one output for standard guitar/bass use).

MN Taper:
Image

AC taper (ignore the B plot)
Image

The AC type should ideally have a 3dB reduction on both pots at the 50% point, which would give a constant level output if both input signals were the same. But the reality is that it's more likely to be a drop of much more, resulting in a loss in output level at this point. Don't forget that with two pickups pickups, you also need to add in phase cancellation; thinning the sound and reducing the volume a bit.

So for a blend without a noticeable drop in volume, make sure you have an MN taper pot (Bourns do one). If you think you may have an AC type, then you should be able to check it with a multimeter, as the resistance on an MN pot will only change over half it's travel (you may have to unsolder some wires to stop the other half of the pot interfering with the readings).

I'd also recommend using a 500k pot rather than a 250k pot. The pot track/resistance will be in parallel with the volume pot track resistance, so will reduce the effective volume pot resistance considerably. Regardless of whether you've got single coils or humbuckers, 500k is the minimum resistance blend pot I'd be looking for if you have passive pickups.

Blending active signals is different, and you'd probably use 25k or 50k pots at most.
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by Wonks »

The pickups could also be out of phase, as there is no fixed standard used by all manufacturers, so there's a 50/50 chance that two pickups from different manufacturers will have opposite polarity outputs when wired up the manufacturers recommended way.

But these will sound very thin and nasally if they do have opposite polarity, as well as having a drop in volume (mainly due to so many cancelled frequencies), it's not a subtle effect.

Simply swap the live and ground connections round on one pickup and all will be well. Note that if its a 4-wire pickup, then you'll probably have to desolder and unwrap the braid ground wire from the currently grounded pickup wire, then connect the current hot signal wire to the braid ground and connect that to the back of a pot (or another ground connection) and the previous ground wire to the blend pot input tab.
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by Wonks »

Oh, and if one pickup is a single conductor + braid screen type, then always swap the wire around on the 4-conductor pickup. If they are both the single conductor + braid screen type and reversed polarity, then you can't just swap the brain and conductor round on one of them as you'll get a very noisy signal from it. You'll have to re-wire the output connections at the pickup itself, which can get very messy.
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by ITHertz »

Thanks wonks for all the info.

I tried reversing the connections to the P-style pickup (not the new one that I added) and that's fixed the problem. The bass sounds great now with virtually no hum from the new J-style pick-up. Also, it balances very nicely (tonally and volume-wise) with the P-style pickup.

Now I just need to work on my bass playing :thumbup:

Cheers,

Chris
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Re: Wiring the Bridge Pickup in a Yamaha RBX270

Post by Wonks »

Hurrah!
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