Takamine Classical Hum

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See: Severe Hum Problems with Bose L1® and Takamine Classical

Problem Statement

July 11, 2014

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)

Resolution

October 5, 2014

OK, I have a resolution. Thanks to everyone for all the input.

To recap: loud hum (with secondary poor string balance) when coupling Takamine Hirade Classical (E90 now known as TH90) with Bose L1 compact, or 1S.

As I had anticipated, tracking down a hum problem is a methodical task that takes patience and a series of well planned tests. Ultimately, Takamine USA (which I presume is KMC) verified that there was a "manufacturing defect" in this past year's line of Takamine Nylon-string pickups (Palathetic nylon-string pickups), which directly led to the hum. Takamine-Japan corrected the manufacturing prob (missing shield) and reissued a replacement pickup with proper shielding of the solder connection - addressed the hum, but this did not fix the string imbalance.

Furthermore, it appears that there was what I would consider a "design change" of some sort that led, IMO, to unbalanced string response (i.e. the first two strings are considerably louder - 6-10dB estimate - than the other strings). Takamine USA tech support had no solution for this problem and agreed that I try a 3rd party solution.

So, after much consultation with local setup artists and LR Baggs tech support, I gutted the Takamine electronics and replaced it all with LRBaggs Element for Nylon String. The sound was immediately warm, balanced, and completely hum-free - I could play at high sound pressure levels with no feedback.

As for the Bose L1: I tested the Takamine-LRBaggs combo with two Bose L1 units and it was hum free - and most importantly SOUNDED AMAZING! As I said I do fingerstyle jazz and the warmth and dynamics, even at high sound-pressure levels was the absolute best acoustic live sound I have heard to date. Kudos to Bose on the L1 and miniature-line-array technology!

RE why some acoustic amps reproduced no hum? It appears from research on DSP-based amps, many companies create a "characteristic sound" with DSPs and this includes EQ and in some cases "hum filtering". It is a matter of technical and artistic opinion as to whether this is an advantage/disadvantage. It is my "guess" that some DSP-based acoustic amps are actively filtering hum.

In my opinion, I believe that it is not optimum to be performing with an inherent hum in your instrument rig. In this case, the Bose L1 simply faithfully reproduced a hum that was ultimately traced back to a pickup with a manufacturing defect (the Bose absolutely did NOT cause or contribute to the hum). I agree with the Bose philosophy of minimal filtering in the DSP/digital-processing stage.

Personal opinion: I believe the Takamine Hirade is a good mid-level stage guitar, but the electronics are currently pretty buggy. Takamine USA are great people and very responsive, but IMO the nylon pickups are just not ready for performance level. LRBaggs tech support is second to none - incredible help with the replacement electronics. Bose L1 - I can't think of any portable system that even comes close to the L1 for an acoustic musician wanting a musical, dynamic, reliable rig.

Thanks again for all the help.