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Double Bass Changes in Full Circle Pickup

jmlee

jmlee

Catgut? Not funny.
Supporting Member
Jun 16, 2005
5,788
14,996
Halifax, Nova Scotia
bme.medicine.dal.ca
#1
In the last couple of months I've been finding that my Fishman Full Circle pickup has been: (i) losing signal strength, and (ii) becoming much more prone to feedback, even in modest volume situations. Now one might think those two issues are backwards, that more signal might lead to more feedback. Sigh...

In any case, it's not amp/speaker dependent (same behaviour with two different rigs), nor to my knowledge has there been any significant change in the instrument. [There was an issue where a kitten chewed through the cable, but the problem was there before and remained after I spliced the cable.]

I had read here on TB that the Realist pickups had an expected lifetime due to some issue around the piezo element. I hadn't heard the same thing re: the Full Circle, but thought I'd ask you folks for ideas.
 
#3
And...it's one of the earlier Full Circle pickups that are glued together, not held together will little set screws. And, yes, the bridge is carefully kept vertical and there appears to be excellent contact between the bridge and the surface of the pickup. (I do read earlier posts...yessir!)
 
#4
Have you turned the First Circle (even a bit)?

I only have the newer screwed one, but I found the sound to be very different depending on the angle. I don't use it in the recommended position because I really dislike the strong mids, so I turn them a bit away from the recommended position until I'm happy with the sound. But you probably know this.
Just an idea that came to my mind if you might have changed height or somebody might have temporarily removed the bridge for some reason.

BTW, the Realist's piezo is much thinner than the First Circles (as I know there a 4 piezo crystals inside). The First Circles piezos might be about as thick as the Underwoods, so I think they won't be damaged as soon as the Realist's. But in the other hand the Underwoods pressure is much less than the Realist's and First Circle's.

I would try to turn it a quarter or half cycle if the sound is the same like before but with less feedback. Maybe one of the four crystals is damaged?
 
#5
Well, I normally keep the lead at 45° relative to the bridge axis (the lower resonance, drier position). When the problem emerged, I tried rotating the lead to the 90° position (more resonant in Fishman's instructions) and the problem is worse. Other than that one rotation, the pickup's been in a fixed position.
 
#6
They do go bad sometimes. I've had to replace mine before. Another time i thought it was going bad, and it turned out to be the bridge was tilting and not getting the same connection tot he top as before. When mine was actually going bad, it would cut out and/or distort periodically until I finally replaced it. Good luck.
 
#7
I would try half a turn (maybe also a quarter turn) from the original position.

If this doesn't help (probably only until you got a new one), I think one of the four crystals in your pickup has gone bad.
That also explains the higher feedback sensitivity, since one of the crystal signals is missing and there now might be some stronger resonance than before (since you tried a position with less resonance). It also explains the lost signal strength.

See it positively, other pickups might not work at all when they died, yours still does but not with optimum sound. Seven years is not that much, but still a bit more than the 5 years Realist life time.
 
#9
Hej, that's good. I thought the pressure was mainly on two of the four crystals, so I thought by a half turn you might get the pressure on the other two who still work both.

But changing the bridge angle (by tuning or manual displacement if needed) might destroy your current luck. In this case try turn it back half a turn.

Earlier or later you need a repair or a new one, but it is nice to have some time to check and decide.
 
#12
OK, here's closing the loop.

My new Full Circle transducer arrived from Fishman two days ago. I disassembled the bass and installed the new transducer. Nothing much to it, really. You need to be sure that the screw thread on the new transducer matches the one on your old one. (There's three screw threads available these days, two from back when mine went in.) Took real pains to mark the bridge location with soft pencil and ensure that the bridge had excellent contact with the top of the transducer (mine's in screw threads down). Then made sure the bridge was nearly perfectly vertical once the bass was up to pitch. Only about 15 minutes soup to nuts.

Had a jazz rehearsal last night and bingo! The bass sounded terrific, clear and articulate (more articulate than my playing, but that's another story...) The feedback issue was gone, too. The piano player actually stopped at one point, looked down at my Contra extension speaker next to him and said, "that bass sounds great tonight. What happened?"

So...if your Full Circle bass loses level, starts to sound muddy, and feeds back like an SOB, you've likely got a failed one-of-four piezo problem like me.

Big thanks to Fishman for being responsive and helping out with advice and a discount on the replacement.
 
#14
I just pulled my FC off the bass to go back to Fishman. Had it about a year and change. Was pretty pleased with the sound until recently. In recent weeks, the quality of sound has been changing while playing, without turning the adjuster. It goes from fine to a little nasal or a little boomy. And, micro adjustments, like a couple of millimeters, changes the sound completely. It was weird. So it's going in so they can evaluate it. Interestingly, I think my bass sounds better without the FC on it, with a regular adjuster. Could be my imagination, but bass sounds louder.
 
#15
wilsonn said:
I just pulled my FC off the bass to go back to Fishman. Had it about a year and change. Was pretty pleased with the sound until recently. In recent weeks, the quality of sound has been changing while playing, without turning the adjuster. It goes from fine to a little nasal or a little boomy. And, micro adjustments, like a couple of millimeters, changes the sound completely. It was weird. So it's going in so they can evaluate it. Interestingly, I think my bass sounds better without the FC on it, with a regular adjuster. Could be my imagination, but bass sounds louder.
Click to expand...

Wilsonn,
I think what happens is that the Piezo crystals wear out faster on basses where the pressure exerted on the bridge by higher string tension and a whole lot of other factors, cause it to detiorate faster. Realists have the same problem. I thought the Full Circle was immune to this because it's housed inside the bridge adjuster. I do know that the Realist only lasted about four years on my basses before it began to loose it's tone quality and volume. I also know that after I removed the Realist, and started using the Ehrlund Pickup and Pre Amp the bass had more volume and presence. All that said, I think a pickup should last more than a year.

Ric
 
#17
Alright, I was reading this thread yesterday morning thinking, "My Full Circle is holding up great after 2+ years." Then, I'm on my first gig of two last night and the PU cuts in and out as well as tone swells on me. Right now, I'm not sure if it's my plug or the PU; Seemed like movement would knock it in and out. It's definitely the PU - not a bad cable, signal chain, etc...

Two questions:
1. What is a reasonable lifespan for these?

2. Could changing from Spiro weichs to reds have changed anything due to increased tension?

Thanks!
 
#18
swmmojo said:
Alright, I was reading this thread yesterday morning thinking, "My Full Circle is holding up great after 2+ years." Then, I'm on my first gig of two last night and the PU cuts in and out as well as tone swells on me. Right now, I'm not sure if it's my plug or the PU; Seemed like movement would knock it in and out. It's definitely the PU - not a bad cable, signal chain, etc...

Two questions:
1. What is a reasonable lifespan for these?

2. Could changing from Spiro weichs to reds have changed anything due to increased tension?

Thanks!
Click to expand...

Swmmojo,
Weichs are lower tension strings than the mitten, (middle gauge), but it seems unlikely to me that the higher tension of the strings alone would cause that to happen, it that were true we'd all be replacing our pickups every time we changed our strings. That said, it is possible that something happened to the pickup when you changed the strings.
If the pickup is still under warranty then I'd send it to Fishman and ask for a replacement.
Piezo crystals degrade over time because they are placed under pressure. So over time they just "wear out", but in the case of the Full Circle that turning mechanism that acts as a tone control can occasionally get out of whack, or the adjuster can get out of alignment with the bridge etc.

Ric
 

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