|
|
Joined:
November 2002
Posts: 3603
Location: Pacific Northwest Inland Empire | Posted this issue on the "ning" site, also. Anything to be gained by shielding around the piezo pickups? |
|
| |
|
Joined:
December 2003
Posts: 1071
Location: Carle Place, NY | I would not think shielding a piezo would do anything.
Magnetic p/u's work by electric flow created by magnetic induction caused by the string vibration. Shielding protects the magnetic pick-ups from any surrounding electromagnetic fields which can cause hum.
Piezos work directly by sensing string vibration, not by magnetic induction. Thus shielding is not necessary. |
|
| |
|
Joined:
January 2006
Posts: 1111
Location: NW Washington State | I wouldn't have thought shielding would help. But I got an Aria with a thin undersaddle pickup- I think it's a Fishman piezo- that hummed. Pushing on the saddle or holding my hand in a particular spot minimized the hum. A little web research I found that this type of pickup is covered with thin aluminum foil for shielding. Sure enough, the foil was torn in a couple of spots. Some manufacturer's installation instructions warn about this. Don't know if this would apply to an Ovation pickup.
-Steve W. |
|
| |
|
Joined:
December 2006
Posts: 6268
Location: Florida Central Gulf Coast | Originally posted by numbfingers:
I found that this type of pickup is covered with thin aluminum foil for shielding. Steve,
I would have thought that the aluminum is an element in the circuitry as opposed to a shielding device. Do you have a link?
Thanx... |
|
| |
|
Joined:
November 2002
Posts: 3603
Location: Pacific Northwest Inland Empire | Thanks...so far. I've got a nasty hum in my no-preamp, volume/tone controls. I think it's a ground loop issue, though.
Hypothetically, what happens if the capacitor on the tone pot is bad? Just no attenuation? |
|
| |
|
Joined:
January 2006
Posts: 1111
Location: NW Washington State | I didn't think that the aluminum was part of the circuit, but maybe it's a ground plane that's also one terminal for the signal. I don't know how these pickups are constructed.
Here's a set of Fishman installation instructions . Look in the section on the left under "IMPORTANT!"
When I was trying to figure out my problem, I found a few other references to damaged foil and hum, but I didn't bookmark them.
-Steve W. |
|
| |
|
Joined:
January 2006
Posts: 1111
Location: NW Washington State | Seesquare, my response was for Iffy, you got in just before me. What kind of pickup is it?
If it's a typical high-cut tone control, with the cap going from a pot to ground, an open cap won't be a problem. You just won't get any tone control.
I'm not a believer in ground loop problems in passive circuits. I know there's a popular guitar wiring site site that promotes this idea, but I think they're nuts. I have no proof, just an opinion. :)
But- carefully making sure that all the ground connections are good, and that the shield on the wires that carry the signal hasn't been stripped too far back- couldn't hurt.
You might learn something by connecting the pickup directly to the output jack. Get the controls out of the circuit and see if it still hums. Then replace the jack. If it still hums, you're down to the pickup and its attached cable.
-Steve W. |
|
| |
|
Joined:
November 2002
Posts: 3603
Location: Pacific Northwest Inland Empire | I did connect the pickup directly to the jack, and got the same hum. I will try a different jack, too. The piezo pickup doesn't look like "standard-issue" to me, but it is a thinline, undersaddle type. Doesn't have the mini-plug, either- just connects to the volume pot lug & ground.
I'm rewiring this critter with all new components & wire, and see if that helps.
Stay tuned. |
|
| |
|
Joined:
December 2003
Posts: 1071
Location: Carle Place, NY | You guys are discussing grounding issues not shielding issues. |
|
| |
|
Joined:
January 2006
Posts: 1111
Location: NW Washington State | The jack is unlikely, but if you have one handy it eliminates one more thing.
I went on a cheap undersaddle pickup buying binge. I might have something you can use if you think yours is bad. I did learn that they come in different lengths and thicknesses, so watch out for that if you're looking for a replacement.
-Steve W. |
|
| |
|
Joined:
November 2002
Posts: 3603
Location: Pacific Northwest Inland Empire | Wow, thanks a bunch, Steve! I have a couple of other thinlines laying around, too. And, I have bunches of saddles, in all kinds of heights & widths. Pretty much, mix-&-match, 'till the combo is right.
Just replaced a couple of drawbolt latches on an old hardcase (sounds like my work at the clinic!). Them rivets are a bit of a pain, eh wot?!
OK, I'll keep you posted on the hum-bug. Thanks for the help!! |
|
| |
|
Joined:
November 2002
Posts: 3603
Location: Pacific Northwest Inland Empire | Well, I'm afeared its hopeless. I tried all the permutations, and it still hums. It becomes close-to-tolerable, if the set-up is connected to the "active" input on the amp, and I crank up the volume on the guitar, and the amp, to get a decent signal.
Good piezo, good pots, new wire, new jack, good cable. Just not quiet. Is there some kind of filter to take out that background hum?
Turned off the computer, radio, most of the lights, too.
I don't have this problem with my other equipment, which is baffling. It hums, with just the piezo connected to the jack. There's interference coming from somewhere, alright- my blood pressure!
So, movin' on to other endeavors. If anybody's got some ideas, let me know. |
|
| |
Piezo shielding
