Microphonic Nordstrand NJ4
I've recently acquired an Elrick bass that has a set of Nordstrand NJ4 jazz pickups (vintage-style, 60s wind) hooked up to the stock Bartolini NTMBF 3-band volume-blend preamp. The pickups are apparently quite badly microphonic; tapping on the case produces sound, I get a slight hum/buzz when I remove my hands from the strings (even with both pickups on to act as humbuckers), clicks from the input jack can be heard, and string "clank" is so loud --- especially right above the neck pickup -- that merely tapping on any string produces a clank that's often louder than the tone produced by the pickup when the string is plucked.
I've read that Nordstrands are wax potted so I don't figure that's the problem. The pickup leads appear to be soldered correctly to the blend pot, and the installation appears to be a fairly clean one, though I have no idea if it was done professionally.
Any idea what could be the issue? Maybe improper grounding, evidenced by the hum-when-hands-are-removed phenomenon? Any advice would be much appreciated; I'd really like to not have to take the bass to a luthier to have this looked at ...
I plan on checking grounds in the preamp cavity tonight using the NTMBF wiring diagram, but like I said: the install looked fine in the cavity last night ... I mean, one basically solders four wires to install these (positive to the blend pot & negative to ground x 2) and that's it. These NJ4s are pristine; hardly any wear on 'em. Maybe a wire's shorting out/grounding beneath a pickup? I'm really a bit perplexed ... any guidance would be greatly appreciated.
It's possible, although very unlikely, that the pickups are not waxed. Our production setup and QC check system don't currently allow pickups to go out unwaxed, but those pickups may be a bit older and we didn't always have such a bulletproof system.
If that's the case, we will be more than happy to wax them for you, or send you a replacement set if you can't be without a functional bass for very long. Email us and we'll see what we can do to help.
It's also possible that it's not the pickups. Sometimes issues like you're describing can come from odd things. There could be something going on with the preamp, there might be something odd about the pickup mounting (we prefer foam under the pickups), it's hard to tell.
But you definitely have a problem that is not normal. Hopefully we can get it sorted for you.
A response from the man himself. Love it ...
I'll send an email tomorrow, Carey. I've taken a look at the NJ4s; they've got foam underneath, and it's definitely possible that they're not waxed. I've got pics that I'll send with the email.
I've inspected the preamp connections and grounds; all look good, though I've noted that a thin bare wire -- it appears to be a bridge ground wire and runs out of a route from the bridge area to beneath the bridge pickup, then through that pickup's wire route to the preamp cavity-- was grounded in the same place as both pickups in the cavity. Figure that's normal?
Played the bass some at rehearsal tonight; no feedback from the amp, though the sensitivity was there ... and occasionally a very short crackle-like pop would come from the bass, as if there was a short of some sort.
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