• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Double Bass Ideas on grounding my EUB???

Nate74

Nate74

Mar 3, 2007
789
78
DFW
#1
I built an EUB about 2 years ago and used a K&K Big Twin with both sensors under the bridge. I also used a homemade hi-z/low-z circuit internally which just didn't work. It cut the signal way down and sounded really thin.

I recently pulled it out and got a K&K Pure XLR preamp which dramatically improved the sound, but now I have a pretty fair amount of what I believe is 60Hz humm. It improves when I touch the chassis of the Pure XLR, making me think somehow grounding it somehow might help the noise.

I'm wondering if adding some grounding plates in the control cavity might help? Any other ideas on trying to tame it down?
 
#2
i'm going to guess that the way you have the transducers mounted is causing the hum....isn't the K&K Big Twin designed to be attached to the bridge face with foam tape? the pressure of the bridge feet on the transducers may be the problem.
 
#3
Hmmmm.... interesting thought and easy enough to check. I'll pull 'em out from under there and see. Doesn't explain why grounding the preamp helps though.

You may be right on the Big Twin. I had them mounted that way originally but there wasn't enough vibration in the bridge. Bob Gollihur, who I bought it from originally, suggested putting it under the bridge IIRC.

Thanks for the idea. I'll check it out.
 
#4
Now that you have the KK preamp, you should have plenty of gain when you mount the pu's on the bridge. Hopefully, the pressure of the bridge hasn't damaged one or both of the transducers.
 
#5
Thanks MR PC. You may be right. I now have them on the side of the bridge close to the strings with some double sided tape. I can get a decent sound but the buzz/hum is even louder than it was when the tranducers were under the bridge.

Have I killed them?

Interestingly though, when I touch the ground path, the hum gets way softer... still too much but softer none the less.
 
#7
MR PC said:
are you sure the leads from the pu aren't soldered/connected backwards at the out put jack? in any case, sheilding the cavity is a good idea
Click to expand...

Anything is possible. I have the solder joints in shrink tube so can't easily check but I'd guess i have the braided part to ground and the center leads to the "tip" connection. I'll take a look in the morning. I'll also pick up some grounding foil from the electronics store this weekend.

Is there a way to check the transducers to see if they're damaged. Like check the impedence or something?

Thanks again for your insight and help on this!
 
#9
Yeah, but $60 for a new set of transducers ain't in the budget right now. But time in the garage is free. :)

Yeah, I'll scrape together some funds and get another Big Twin soon.

Thanks again for your input.
 
#10
UPDATE 12/2: I removed both pickups and soldered each one at a time to the output jack. One is quiet and even more quiet when I ground it to my body. The other is humming like a vacuum cleaner so I found the culprit.

I'll order another big twin and go with the side bridge mount. I also realize I could use the one remaining good pickup from the original set and put a pickup between each string. Might improve balance, clarity, etc.

Any suggestions on what to use to stick the old pickup to the bridge?
 
#11
FWIW, lot's of folks feel that using one transducer is best. i do. why not try just using the one transducer in an optimum placement....experimenting won't cost anything.
 
#13
generally speaking you aren't going to get more db gain with more transducers.....just more sonic information.......it's common to have weird phase problems with more than one sound source......i'd suggest check out the treads on this subject in the amps and pickup forum
 
#14
MR PC said:
generally speaking you aren't going to get more db gain with more transducers.....just more sonic information.......it's common to have weird phase problems with more than one sound source......i'd suggest check out the treads on this subject in the amps and pickup forum
Click to expand...

Outstanding man! You are a wealth of knowledge and I really do appreciate it. To bad you can't email a beer in thanks :)
 
#15
UPDATE: This is somewhat embarrasing but maybe I can help somebody else avoide the same issue in the future...

I ordered a second Big Twin and before soldering it into my EUB, I decided to try a test to see if the same hum existed. I plugged the pickups in with the jack they came with and they were dead quiet. "hmmmm" I say. I then put them onto the bridge with the included glue. Still dead quiet and really weak signal, even with the preamp in line.
I then put some cork on them and put them between the body and bridge and it sounds fantastic. No hum, full range response.

So at this point I'm scratching my head thinking, where does the hum come from the minute I solder these into the bass? Then it hits me. I've been soldering the two shielded cables from each piezo to a non coax pair that runs about 8" to the 1/4" jack that is mounted on the bass.

I had a tough time imagining that just 8" of plain 22ga wire could cause that sort of hum, but I replaced it with some coax and presto, the hum is gone.

So the moral I guess is always used shield coax when dealing with Piezo's. :rolleyes:
 

Latest posts

Top Bottom
Back