Takamine Classical Hum: Difference between revisions

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<p>I have been trying to solve this problem for some time now and am in contact with both Bose L1 and Takamine support - Bose support suggested I post to this forum.

This solution is most likely related to shielding & grounding, but it also seems to be only occurring when I play through Bose L1 systems (Compact, 1S, & MII).  I suspect the solution is in the purview of an old-school audio person. I would appreciate a technical recommendation.

Here are the symptoms: Takamine Hirade Classical with a palathetic pickup (6 element piezo) played through a Bose L1 produces a very bad hum.  I have played through Yamaha & QSC DSP powered speakers and there is no hum - even at high volume.  I have sort of reproduced the hum with analog powered monitors but with a relatively low hum. Martin D35 with LRBaggs pickup produces no detectable hum.

Doing a lot of research & testing and discovered that at the solder point of the Takamine Palathetic pickup & the pickup cable there is no shielding (this is slightly shorter than 1/2" that is not shielded).  When I hold my finger near the spot the hum increases by about 2X. When I wrap the spot with AL foil the hum seems to mostly be handled.

Seems simple - right? Well, per some electronics guys, I bought some 3M Copper tape (with conductive adhesive) and wrapped the 1/2" spot (this is the recommended solution).  But then the sound from the guitar became "thin" and lost a lot of bass response. (The phenomenon is documented by the electric guitar owners as being indicative of a shield-grounding problem - ex: you must have a shield AND the shield must be grounded.)

Totally weird data => So I contacted Takamine and they verified that the new Takamine classicals no longer include shielding on this 1/2" section of the pickup cable.  They plug into an "acoustic amp" and there is no hum.

Here is my *current* theory (but I am still not sure what to do about it): The L1 has a sub-woofer and so may reproduce the low 60Hz hum more faithfully than most "acoustic amps".  It is possible that the DSP speakers may be actively notch-filtering 60Hz hums (just a guess).  I am fairly certain that the hum is coming from this unshielded solder point, and that when I wrap it with electrical-copper-tape there is some sort of shield-to-ground problem that causes a thin response (again, just a guess).  This appears to be limited to Takamine Classical Palathetic pickups & Bose L1.

So, assuming the Bose L1 is simply faithfully reproducing a hum (that other acoustic amps may be filtering), and that the Palathetic pickup is humming / exhibiting thin response because of a shield-grounding problem (with the recognition that Takamine has intentionally removed the shielding from the pickup design), then what is the explanation and what are the alternatives.  (Well, tabling the idea that I should gut the Takamine electronics and install an LRBaggs system - which would be *very* problematic)</p>

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