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Re: OT: Bass Hum / piezos

In a message dated 7/20/03 11:22:53 AM Pacific Daylight Time, dave@spnz.org writes:

redrum123 wrote:
>(sorry this is so off topic, but you guys are uberhelpful and informative)
>I've had my acoustic bass for not even a month, and there is a rather severe
>noise issue using the pickup (it has a Fishman Classic4 preamp).  I think it
>is a new problem, I don't remember having this level of noise on the line
>before.  I have the guitar running into an Ultra-DI box (by Behringer), and
>then into an AB switch to my EDP.  I've tested the guitar by running it
>straight into my Tube Preamp, and even straight into a mixer, using either
>an instrument cable or an XLR to 8th-inch cable, and the noise is
>consistent.  I can get rid of the noise by touching the guitar and the DI
>(or mixer or preamp), so the instrument should be capable of much less
>noise.  Also, I've found that if I touch the metal of the cable connector on
>the guitar, the noise disappears.

I had a similar problem with a Fishman bridge piezo.  Turned out the
shielding was broken on the pickup itself.  Nothing that can be done
except to change the piezo element. :(

If that's what's really wrong (and I think that's likely from my experience with making my own piezo pickups) and you don't have warranty support on the pickup, you may be able to re-solder the  connection to the piezo element yourself or get someone who's good at soldering to do it.

For those who haven't played with piezo pickups, or would like to, for cheap:

Piezo "buzzers" sold for a couple bucks each at electronics parts suppliers like Radio Shack are easy to turn into low-cost pickups. Just cut the plastic case away from the piezo disk and solder a shielded cable to the disk. The shield goes to the larger brass "carrier" disk, the hot lead goes to the smaller disk of piezo material deposited on the brass carrier. The shield connection is no problem, strength-wise, but the hot connection to the piezo part is fragile. That connection will often physically break off, taking off part of the piezo with it. That doesn't really hurt anything or change any important audio characteristics of the pickup. Just heat up the hot audio lead and re-solder it to any part of the smaller disk layer. Just touching a soldering iron (use lots of flux to get a clean connection) to the hot, tinned wire and the piezo disk simultaneously should be enough to make the connection. If you hold a hot iron on the piezo part too long it will damage it, so keep soldering time to around half a second or so.

There are some variations in electronic specs listed for these "buzzers", but most will make some kind of interesting pickup.

Hope this inspires some experimentation.