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Help With Hum On Bass


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just got a yamaha RBXJM bass. active electronics. the problem is, when the pup blend knob is centered the bass is good to go and dead quite, start to pan in either direction and what sounds like a ground hum starts to come through. hum is equal when panned to either side. 1/4" input needs to be replaced for starters as it cuts in and out with some movement.

but can't track down this hum...

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sounds like they're single coils which cancel hum when combined....


No. dual (neck/bridge) yamaha 2 coil soapbars. haven't pulled the preamp out yet but I did get in there to check for lose/shorted wires. none found. hope to find something when I pull it apart. it has to be a ground somewhere in there.

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This was the 1st result when i googled "yamaha 2 coil soapbars"


For some reason i can't copy and past from talkbass.com???

anyways, your problem is explained in the 4th paragraph of the review.

same here on the copy and paste.

anyway. I can understand the hum now somewhat. I didn't know that they split the coils like that inside a 2 coil soapbar.

seen it on larger single coils for 5'ers and 6'ers. but not the soapbars.

so is there any way to add extra grounding or something to the pups to fix this? or is it just something I'll have to live with and always play with the blend knob centered?

thanks for that review find

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Copy and paste works for me with no problem. This is the fourth paragraph for future reference.

The sound is excellent. This bass doesn't have the piezo pickup of its Japan-made cousin, the TRB5PII, but the two dual-coil soapbars coupled with the 3-band EQ are very versatile. The EQ is very user-friendly; there aren't a lot of bad combinations as far as setting the bass, mid and treble. The treble's frequency center is very high; even with the treble turned all the way down the bass can sound pretty bright (start turning the mids down and the tone darkens quickly from there). The mid control is probably the friendliest of all; there seems to be a built-in notch at 625Hz that reduces the honkiness of the mid control (or the mid's center frequency is high enough that the 625Hz band is in between controls). You can turn the mid knob up and get lots of punch without the bass ever getting a quacky nasal sound. The bass knob of course gives a lot of booming rumble, but you very quickly run out of headroom, and therefore the bass control should be used judiciously. The panpot control is the other of my only two beefs with the bass; turning the knob to its extremes to remove one or the other pickup tends to introduce a small amount of noise. This is most likely due to the way the pickup coils had to be designed; with a 5-string dual-coil design, one coil has to be larger for 3 strings and the other smaller for 2. That throws off the balance of the hum-canceling effect, and the result is a slight amount of buzz. With the panpot at center, the bass is completely noise-free, and the TRB-1006 6-string likely wouldn't have this problem.
Edited by Mender
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