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Piezo Pickups Problem - HUM!

Discussion in 'Pickups & Electronics [BG]' started by Peter Weil, Jun 16, 2001.


  1. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Dear All,

    Hello from a frequent lurker but an infrequent poster!

    I am having a definite problem with the piezo system I bought to install into my bass. (Hum!) After corresponding for a long time with the nice poeple who I purchased it from, we have collectively reached a dead end - there's no apparent reason for it to be there and no-one has any more ideas. I am turning to you all in the hope that you can shed a little light:

    When I hooked up the piezo saddles DIRECTLY to an output jack (not through any other electronics) and plug it into my amp, there is a huge hum produced. This hum goes away when I touch the ground lug of the output jack. This hum also appears when I play through a friend's amp (at HIS house) - so that seems to rule out any trouble with my amp in particular.

    Trouble is, there is no apparent reason for this hum at all! The piezo saddles came wired together in the correct polarity (at least as far as I know), I have hooked them up correctly to the output jack (not hard..), and the hum is not present when I use the magnetic pickups installed on my bass. My house appears to have no power problems, the amplifier does not hum at all.....I thought that piezos were never meant to hum! (????)

    Iterestingly, the SAME hum appears when I use a home-made piezo pickup (taken from one of those greetings cards that play music) and plug it into my amp (via the output jack, obviously). What the heck???

    Other relevant info:

    1. This is the second set of piezo saddles from the manufacturers, who have been very helpful. They tested out the first set I sent back (which had the same apparent problem) and said they were OK. They are located in Canada; I am in the UK - different voltage systems in use. Is this relevant, anybody know?
    2. The cords I am using to plug everything in check out fine.
    3. The hum gets no worse or better if I move closer to / away from my computer, amp, or anything else in the room.

    Whew!! Monster post. I think I got it all down there, though. Please, anybody, let me know if you have had any similar problems or any insights. I have been struggling with this problem for several months (due to time problems) and have reached a dead end.....

    Thanks all.

    Pete
     
  2. =^..^=

    =^..^=

    Jan 25, 2001
    Stuck on a rock !
    I thought piezo's had to go through a preamp due to difference in impedance ?? isn't the resistance a lot higher than a pup ?

    This wouldn't explain the hum though.

    I think Bob Gollihur is your man - I seem to remember reading about piezos on his site.
     
  3. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    You're quite right RaiD 5 - piezos do need to go through a preamp to match impedances properly.

    However, when I was trying to figure out the source of the hum, I had to keep working back through the circuit and excluding potential problems(preamp, pots, piezos) until I could locate the source. As it turned out, this was the piezos!

    I hope Bob Gollihur is reading this......

    Pete
     
  4. Angus

    Angus Supporting Member

    Apr 16, 2000
    Palo Alto, CA
    I like your last name...thanks for copying me! :D
     
  5. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    I checked out your profile, Angus, but couldn't see your last name listed....

    Do we have the same last name? Good heavens.....well, you, me, and that guy who makes watches in Switzerland (plus the guy who discovered leptospirosis..... )

    Pete
     
  6. Angus

    Angus Supporting Member

    Apr 16, 2000
    Palo Alto, CA
    Yeah, we share last names! And those people are Raymond and Andrew Weil!

    Actually, my dad owns a Raymond Weil watch, just so he can wear his own last name! :D

    Too bad I'm FAR more German than Scottish...
     
  7. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    Does sound like we're talking the same piezos as I am familiar with, use, and now sell:
    GraphTech Piezo Systems - http://www.gollihur.com/kkbass/graphtech.html

    From your symptoms, Peter, it sounds like your typical 60 cycle (50 cycles in the UK??) hum caused by an open ground.

    I don't think that I know any great secrets that the bright folks at GraphTech don't know... but

    Have you hooked the piezo's output wire directly to a loose jack independent of the bass?? I think that would be the first thing I'd try, to rule out the piezos' involvement and narrow it to bass wiring.

    Do you get any bass signal along with the hum?

    Have you used an ohmmeter to confirm the ground is properly connected?

    Are you using the complete GraphTech kit with their blend control and wiring recommendations?

    I'll try to help if I can. I've been very pleased with my GraphTech bridge saddles and am installing more on a new bass tomorrow. They seem to have a smoother response than other piezo saddles I've tried -- which is why I now carry them for sale.
     
  8. lo-end

    lo-end

    Jun 15, 2001
    PA
    what about those Silenzers? they're 10 dollars and they attach to your cable to take away hum. I forget exactly how... check out the bassplayer magazine with marcus on the cover for more details and where to buy them. this may or may not solve your problem, but it might help.
     
  9. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    ....Yes, we are talking about those lovely folks at GraphTech. You may recall we chatted in an older (piezo) post about their products.

    I have to admit, I like thier stuff very much - the sound is very smooth and tasty. Their service has been absolutely top-notch as well - they've been trying to help me trouble-shoot. As I said though, we've all hit a bit of a dead end.

    Now, to address your points in order:

    1. Have you hooked the piezo's output wire directly to a loose jack independent of the bass?? I think that would be the first thing I'd try, to rule out the piezos' involvement and narrow it to bass wiring.

    Yes. This was the first thing I did as well; unfortunately the hum still remains even when independent of the bass's other electronics.

    2. Do you get any bass signal along with the hum?

    Yes. The signal is clear and phat, of course ;-). If I touch the ground lug while playing, the hum disappears but the bass signal still remains.

    3. Have you used an ohmmeter to confirm the ground is properly connected?

    Errr......no, I haven't. How do I do that?

    4. Are you using the complete GraphTech kit with their blend control and wiring recommendations?

    Yes, although I have hooked up the piezos directly to an output jack (and excluded the preamp and blend control) in order to pinpoint the source of the hum.


    Thanks for your input, Bob. I think GraphTech's stuff is pretty nice too.....and their service is nothing short of wonderful. Lea (their engineer), Dave (the company owner) and I have had fairly regular contact over the last month or so, and they've been total gents.

    Angus - my girlfriend owns a Raymond Weil watch too - very nice. I know about the chap who discovered leptospirosis because I'm a med student (though I actually start working as a doc in about a 6 weeks....). So, I'm used to jokes about 'Weil's disease'. (Ha ha, never heard THAT one before.) Funnily enough, my mother's side is Scottish but my father's side is Romanian - so I presume the name must have come from some kind of migration from Germany. Haven't looked into it....

    Pete
     
  10. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    ......so I can't find out about those Silenzer things. Any more info on that front?

    Pete
     
  11. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    If you have wired the output directly to the jack then there is no need to do so. I can see why everyone is stumped there- I can't fathom why this would happen either. A real puzzler.
     
  12. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    I did wonder if this was an amp problem, but the hum appears through many different amps (mine, a friend's, the ones at the rehearsal studio) that I don't think this is the case.

    So - given that the only things in the circuit from piezos to loudspeaker are the piezos, solder, output jack, cord, amp, and speaker - and EVERYTHING ELSE apart from the piezos checks out -
    How/where do piezos pick up (ground) hum from?

    I find it interesting that my home-made piezo pickups ALSO seem to pick up this hum - it seems to indicate to me that something nearby might be the problem. Or could it be that every amp I've tried it through has a grounding problem - would that cause this?

    I wonder if I need to take this to a tech, or whether they'll be just as stumped as I am.....

    Pete
     
  13. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    That is odd and does indicate something in common with all may be causing this (the jack??) -- have you tried wiring the piezos directly, simply tacking their output wire to another shielded cable running directly to an amp input??

    Would you consider relocating to Canada or the US? ;-)>
     
  14. lo-end

    lo-end

    Jun 15, 2001
    PA
    well, you dont have to subscribe to BP to read it. Just go to Borders or Barnes and Noble and find it there. The issue i was talking about is the newest issue (the one with marcus miller on the cover) and the silenzer thing is in that issue in the new gear section, whatever they call it.
     
  15. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    The same thought about the jack occurred to me - so I bought a few and tried them all, as well as tacking the piezo leads directly to the cord. Every time, the good ol' hum was there. (Strangling noise)

    Now here's something I found last night and which I had not noticed before - when plugged in to the amp, the hum goes away if I touch another one of the amp's instrument inputs (i.e. if I touch the 'Active' input, the 'Effects send' 'Effects return' inputs, or the 'line out' input). (P.S. This amp is a Trace Elliot 7215 SMC 300 watt combo.)

    I wonder - does this mean this is an amp problem? But why does it appear through other amps? Arrrghhhhhhhhh............

    I used to live in the US....maybe it IS time to relocate :). On the other hand, I can WALK to the pub here instead of having to drive to it....very advantageous... ;-)

    Pete
     
  16. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Err, lo-end, there are no Borders/Barnes & Noble bookshops in Scotland - and no shop I know in Edinburgh carries Bass Player (they used to, but the place which did closed down). So, my access to it is non-existent. Unfortunately.

    Pete
     
  17. NJXT

    NJXT

    Jan 9, 2001
    Lyon, FRANCE
    I'm sorry to interrupt and to not be helpfull at all but ... can you develop that greeting/card piezo thing, please ?
     
  18. Peter Weil

    Peter Weil Seeker of The New Supporting Member

    Mar 29, 2000
    Edinburgh, Scotland
    Okay NJXT.

    Most greeting cards that play music use a piezo as their output - not only do piezos work as transducers, but also as little 'speakers' too.

    So, after reading this particular resource on the net (http://home.earthlink.net/~jasband/piezo.html) I decided, before I was going to buy any piezo system and shell out $$, that I would try one out for myself.

    Buy a greeting card that plays music. Take out the little PCB board and piezo in there. Remove the piezo disc from inside the plastic casing in which it will be encased (carefully - we don't want to bend it AT ALL, that can disrupt the piezo crystal on the disc). Throw away the board.

    Then, quite simply, solder a lead to the piezo crystal (the white stuff in the centre, fiddly - it's very thin and burns easily, so 'tin' the lead you are using and have some solder already on the end of the soldering iron) and another lead to the outside of the disc (but NOT touching the piezo crystal in ther centre). These are your 'hot' and 'ground' leads, respectively.

    This piezo can be taped directly on to your bass and the leads connected to an output jack and plugged into an amp (note: in order not to lose all the lows, your instrument input on your amp needs to have a very high resistance rating e.g. 1 megaohm. Even so, the sound will be okay but mediocre.). You can try out different spots, hit it (kind of a neat drum nound), and generally see how you like the sound.

    It's okay as a test setup - and if I was inclined to build my own preamp, it could be a very cheap way to build your opn piezo system. However, it won't look as good as commercial kits, and will require a lot of time input. However, I know one chap who I corresponded with in Holland who has done this very successfully. There are a lot of electronics issues - impedance matching being a prime one - which can be fiddly. So, better I think to take advantage of Graphtech's expertise and support a great company.

    That's how I figured out that I like the 'piezo' sound.

    Pete

    P.S. I am no electronics expert - perform this at your own risk. Still, it's pretty darn hard to mess up so much that you hurt yourself somehow doing this......
     
  19. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    Radio Shack sells a couple different types of inexpensive piezo buzzers that can also be used. I experimented with them myself, but found their quality to be spotty and the sound quality not nearly as good as commercially available pickups.
     
  20. NJXT

    NJXT

    Jan 9, 2001
    Lyon, FRANCE
    Peter and Bob, thanks for the explanation/tips.
    Is it possible to hook the "home made" piezo pick-up to common onboard preamp instead of a "standard" pick-up ?