Shadow Pickup Problems - Please Help

[ISU Trout Bum]

Hi All:

To begin with, I want to offer a BIG disclaimer - I'm a complete piker when it comes to the use of pickups, amps, et. al. This is my first attempt. I know even less about electricity. That said, I really tried to do my homework, and thought that I had made a decent decision before purchasing anything. Nevertheless, here goes:

1) I have a Washburn M-ISDL/TR Mandolin (http://www.washburn.com/acoustics/m-1sdl/)
2) I purchased a Shadow SH 926 Bridge Piezo Pickup that I installed on the mandolin (http://www.shadow-electronics.com/viewp ... _id=&id=42)
3) I plug it into a Genz-Benz Shenandoah Jr. Acoustic Amplifier (http://www.genzbenz.com/img/manuals/gb/shenjrmanual.pdf)

After I bought the pickup and amp, I brought them home, installed the pickup and plugged it into the amp. From the outset I had feedback - sort of a hum - but noticed that when I clasped the metal on the male end of the plug coming out of the pickup (see the picture at Shadow Electronics, above) between my thumb and index finger, the humming would stop (almost as if I was grounding it or something). I messed around with the equalizer on the amp thinking that maybe I had the Mid Freq (or one of the others) turned up too high. But I could never get it to go away, no matter what I did. So I took it back to the store thinking it was malfunctioning. I even plugged it into 3 or 4 amps he had in the store to show him that I wasn't smoking crack. Anyway, he ordered me another one. I picked it up today, installed it, and guess what . . . the same problem.

I have searched in vain on the web for fixes to this problem, but have found nothing. I'm about to pull my stinking hair out. I simply don't know how to troubleshoot this. If anyone has any info at all that might be helpful, I am ALL ears.

Thanks in advance!!!!

Best
Trout

[Tim2723]

Hi Trout,

I'm no electronics expert either, but if you don't find one here, go to the mandolincafe.com and you're sure to find the answer.

It sounds very much like a ground fault of some kind, and since it repeats with two units, it probably has something to do with the installation. Don't loose hope, it's probably something so simple it will make you slap your head and go 'duh'.

[ISU Trout Bum]

Thanks Tim! I just posted over there. Fingers crossed . . .

Best,
Trout

[fearfaoin]

...but noticed that when I clasped the metal on the male end of the plug coming out of the pickup (see the picture at Shadow Electronics, above) between my thumb and index finger, the humming would stop (almost as if I was grounding it or something).

This is going to need more explanation.
If you are able to touch the male tip
of the connector, then it's not plugged
in all the way... Maybe that's the
problem?

[ISU Trout Bum]

Hi fearfaoin:

Thanks for the post.

If you take a look at the photo of the Shadow pickup (follow the link above in the original post), you will be able to see that the male end is all metal. It is not covered by another material. So, that is what I meant when I said 'I grasped the metal end'. Hope that clears things up.

Best,
Trout

[fearfaoin]

If you take a look at the photo of the Shadow pickup (follow the link above in the original post), you will be able to see that the male end is all metal. It is not covered by another material. So, that is what I meant when I said 'I grasped the metal end'. Hope that clears things up.

Ah, my apologies. I read that in a weird way.
So, you grasped the sheath of the plug, which
is considered the ground point, and the buzz
went away. Try taking a wire and taping one
end (stripped of insulation, of course) to the
metal shield on the plug (where you touched).
Attach the other end of this wire to the sheath
of the plug on the output side of the preamp.
This takes your body out of the picture and
would tell you if there's some grounding problem
in the preamp itself.

[ISU Trout Bum]

Thanks fearfaoin! This is really helpful. But, I think my problem is that I don't have a preamp . . .

I was told on the other board that piezo pickups probably need a preamp. Does that sound correct to you? Right now I just plugging directly into the amp.

(Told y'all I was clueless!)

Thanks again for the help!

Best,
Trout

[fearfaoin]

Thanks fearfaoin! This is really helpful. But, I think my problem is that I don't have a preamp . . .

I assumed the part on the right of that picture
was a preamp. Does it take batteries?

[MTGuru]

Yes, it sounds like a ground loop problem. Try lifting the ground on your amp by using a 3-to-2 prong adaptor and not connecting the ground wire, and check if the hum goes away. If so, you can get a safe ground lift box for your amp's power cord.

This is a common problem in live sound setups, where the stage wiring (grounding) may by hinky. Some amps, DI boxes, etc. have built-in ground lifts. And every amp you tried in the music store may have had the same problem.

[kkrell]

And if the problem is not the amplifier, then

http://www.kksound.com/mandolintwininternal.html

or

http://www.kksound.com/mandolintwinfusion.html


Often does not even need a preamp, unless you're going through a PA.

[ISU Trout Bum]

Thanks a lot for the responses folks. I will definately try the wire trick, and the 3-to-2 plug in the morning. I really appreciate it!

If you don't mind, a couple more questions/comments?

fearfaoin - I'm not sure if the volume/tone control is technically a preamp. It doesn't have a battery or any power source. It just plugs into the pickup, and then there is a cord that runs from the volume/tone control to the amp. It does turn the volume up and down, as well as tone, but I still get the 'hum' with it. That is why I was wondering if I should buy a proper preamp (Fishman, Bragg, etc.).

MTGuru - I looked in the instructions for the amp (in the link listed above), and it mentions that the XLR output can be 'ground lifted'. I'm wondering if this is what you are refering to, or is there also an option for a 'ground lifted' input?

I apologize if all of these questions seem way too basic, but I am very thankful for the help!

Best,
Trout

[Tim2723]

That volume/tone controller is passive; it's not a preamp of the sort you've been looking at in the other thread.

The ground lift function on your amp is placed on the output stage and works like the DI boxes MTGuru mentioned. But it controls the ground state of the line output of the amp itself when you're connecting your amp to another amp. That switch on the back won't do what you want because you need the ground lift to be on the input side. That's where the preamp/DI box comes in. It increases your input signal strength, matches the impedance of the pickup to the input requirements of the amp, and provides ground lift on the input as needed. Basically, the ground lift on your amp is a 'goes-outta' and you need a device that's a 'goes-inta'.

If the hum is being caused by a ground failure in the amplifier itself, then you need a repair. If it's caused by a bad ground in the AC line it's plugged into, then MT's test will show that. (And he's right, it happens all the time.)

After everything that you've said (multiple pickups, several amps, different AC lines), I would bet the problem is a mismatch that will be solved by a preamp/DI. Like I said, I'm no expert, but these piezo bridges are discussed all the time at mandolin cafe and the result is almost always that you need the preamp that goes with it. People are constantly buying half the set up not realizing that it's really a two piece device. And the guys that sell them often don't know that either.

[ISU Trout Bum]

Tim, I can't thank you enough for that very lucid response. It makes loads of sense. I have spent the morning plugging the amp into different outlets in the house (testing the 3-to-2 on all of them), and it is the same problem everywhere. Tried the wire test and that sometimes 'worked' and sometimes didn't. I'm walking out the door right now to buy a preamp. If that doesn't work, the amp is going back to the retailer and I will pick up a different one. Hopefully one of these two solutions will finally fix the problem.

Again, thanks so much to you and to everyone who has helped me out!! Y'all have been life-savers!!!

Best,
Trout

[Tim2723]

Just remember that you can have two problems at once. Even if the preamp doesn't eliminate the hum, you won't have wasted money on it. You will need it after the troubles are over. I once bought a brand new amp at my local store, and by the time I got it home it had a major failure in the power supply. A wire had broken loose in transport and needed to be re-soldered. So it really could be your amplifier.

Also, when you put the preamp into the line, keep your amp volume way down to start. The signal going into the amp will be huge compared to the pickup by itself, and you don't want to damage anything.

Oh yeah, don't forget to buy the cable you need to go from the preamp to the amplifier.

[ISU Trout Bum]

Well, it was apparently the Shadow pickups . . . both of them.

While buying the Bagg Para Acoustic today, I also purchased a Bagg Radius pickup. Came home, hooked up the preamp, pasted the pickup on the bouzouki and absolutely no 'hum'. Tried it on the mando, and no hum. The Shadow (for the second time) is going back to the retailer. I'm just going to use the Bagg for both instruments.

Now on to the preamp . . . HOLY COW BATMAN!!! I simpy can't believe the sound. It is so clean, clear and LOUD. The difference it makes is shocking, in a good way.

Again, thanks for all of your help and suggestions folks! Y'all stopped me from becoming bald over the weekend.

Best,
Trout