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View Full Version : Preamp hum problem of my own doing.



kohanmike
09-22-2013, 06:50 AM
Here's a followup on my member introduction story about swapping out the preamp in my Lanikai LQA-TCA tenor uke. (Yes, I do get very verbose.)

The Lanikai came with a Fishman Sonitone preamp power system and Sonicore piezo pickup. The Sonitone volume and tone controls are inside the edge of the sound hole, and according to Fishman, are supposed to be at the 6 o'clock position, but because the control panel is so deep, it could not fit there, so obviously Lanikai put it where it did fit, at the 8 o'clock position. (I assume it was originally made for a guitar.)

59004

Because I liked the look and feel of the Lanikai, and because it was such a good price ($149 down from $329), I decided to go with it. But after a while, I grew to hate that the controls were is such an awkward place under the strings, and that there was no built in tuner.

I went back to the store to trade it for something else, but they had nothing in stock, they could order a Gretsch G9121 (that had a Fishman Kula preamp/tuner in the side), but it would arrive after my return period, so I couldn't do that.

I decided that I would find that same Kula preamp since it would work with the power unit already in the Lanikai and install it myself. But no, Fishman does not sell that preamp, not even as a replacement part to dealers. So I got online and finally found an earlier Fishman preamp/tuner that uses the same power system, an Isys+ from a place in China for $21. I contacted Fishman, who said that it should work fine.

While waiting for it, I carefully removed the Sonitone parts in the Lanikai, leaving the power box and Sonicore pickup wiring intact. When the Isys+ finally arrived, I carefully marked and cut a hole in the side of the Lanikai to fit. I have to say, I did a very good job.

The wires from the power box plugged right in to the preamp, but it turns out the piezo pickup was hard wired to the Isys+, where the pickup wires on the Sonitone were screwed in. Because I couldn't get the saddle out of the Lanikai to swap the pickup, I had to cut the wires of the Isys+ pickup and splice them to the existing pickup wires (I actually used small connectors).

I put it together and tested the tuner, worked fine. I then plugged in my wireless amp connector and found that the volume was rather low. I then plugged in a cable to the amp, and damn, it hummed like crazy and there was barely any volume. I tested with another cable, same thing, tested all the connections with my other uke (which I also swapped the preamp), and they all worked. So obviously I did something wrong, or the Isys+ is faulty (no return to China).

Does anyone have any experience with this? I'm going to email Fishman again and see what they say, and will probably end up taking it to my luthier and see what he can do.

ricdoug
09-22-2013, 07:20 AM
It could be a bad shield, cold solder joint or reverse polarity. Did you tin the wires? Ric

kohanmike
09-22-2013, 07:48 AM
No Ric, I didn't solder it, I just crimped the pickup wires to the pins that fit into the connectors. I also used shrink tubing to isolate the wires from each other. I thought I was very careful about the polarity, but I guess I should reverse it and see what happens. Adding to this, I just found that when I hold the cable connector in the uke, the hum goes away, which could very well point to what you're saying, almost like it's not grounding.

kohanmike
09-22-2013, 07:54 PM
OK, I cut out the connectors I added, then twisted the pickup wires together, and now there's no hum, so it bviously came from a poor connection. I'm going to twist them real tight, then use the shrink tubing to keep them tight. I'd rather not go through the trouble of soldering them, but if this doesn't work, I'll have to. My idea was to be able to remove the preamp by unplugging all the wires, but if I ever do have to remove it in the future, I'll just cut the wires.

kohanmike
09-23-2013, 08:29 AM
Still not working properly. Looks like I have to get the soldering gun out, or maybe just take it to my luthier.

ricdoug
09-23-2013, 06:17 PM
Try a different instrument cable to the amp, kohanmike. Also, check the connections at the end pin jack. If none of this works, go to Radio Shack and buy:

http://www.radioshack.com/product/index.jsp?productId=2062402&retainProdsInSession=1&filterName=Type&filterValue=Buzzers

Hook the wires to your preamp/controls and tape the piezoelectric buzzer securely the bridge. If it does not sound better, it's your Chinese preamp/controls. If it sounds better, it's the piezoelectric element and/or the connections to it. Ric

ricdoug
09-23-2013, 06:22 PM
Duplicate reply

kohanmike
09-23-2013, 08:43 PM
Thanks, ricdoug. I did change all the cables and that was not it. When I pull out the preamp and twist the wires together tightly, it works, but when I secure the twisted wires with shrink tubing and put it all in place, it hums. I'm sure it's that I did not solder the wires together, twisting just doesn't make a good enough connection.

kissing
09-24-2013, 01:41 AM
It sounds like you may need more parts or entirely new pre-amp unit...

I was in a similar situation as you with my Luna Baritone and it's pickup system giving out hardly any tone (with some hissing noises).
My procedure was simpler than your's - I just ordered a new ukulele undersaddle pickup that plugged into the existing pre-amp.. and voila, problem gone.

If you need more parts, check this website out (not advertising, just anecdotal recommendation):
http://www.eyguitarmusic.com/

I think I recall seeing various Fishman ukulele pre-amp systems for sale there. From my one experience of ordering from them, I was very happy.
Good prices, well packaged and genuine parts.

kohanmike
09-24-2013, 08:22 PM
Thanks Kissing. The Fishman Isys+ preamp has the piezo pickup soldered to the motherboard, no plugin, so changing the pickup will not work. I also could not get the saddle out of the Lanikai, seems to be glued in. I actually do have plugin type piezo pickups, and I ordered a couple of off brand preamps from a similar web site, but I wanted to keep it simple by using the existing Fishman power/connector unit that plugs right in to the Isys+ preamp. (I did swap out the preamp on my Eddy Finn with one of those off brand, and it works perfectly.)

As I mentioned, the Isys+ works when I have the preamp out and tighten the splices, but as soon as I move it, the hum is back. I really think I'm going to have to solder the splices.

kissing
09-25-2013, 03:31 AM
I also could not get the saddle out of the Lanikai, seems to be glued in.

I would find that to be highly improbable. Did you fully loosen the strings?
Perhaps it's wedged in tight with friction, but I highly doubt it's glued stiff.

kohanmike
09-25-2013, 03:37 PM
Yep, strings were almost off, even tried forceps to pull out the saddle, nada. But now that the wires are snipped, I'm stuck doing a splice. I'm taking it to my luthier and see what he can do.

Rick Turner
09-26-2013, 12:43 PM
The hum is probably because somewhere between the pickup element itself and the preamp, you have an unshielded bit of cable.

Twisting wires is simply not a solution to connecting electronics. You have to solder, you have to shield, you have to use heat shrink where appropriate, you have to strain relieve where needed. There's a great deal of craftsmanship in properly done electronics wiring, and there are multiple reasons for all the tricks.

With better pickup systems (note the word "systems"), the preamp input impedance is "fine tuned" to the characteristics of a particular pickup. For instance, with a couple of guitar pickups I've been involved with as a designer, the D-TAR Timberline preamp has a 10 meg Ohm input impedance, but the D-TAR Wavelength has a 100 meg Ohm input. Not all pickups are compatible with all buffer preamps, so switch and swap is at your own risk.

And a glued in saddle? Whew!

kohanmike
09-26-2013, 03:17 PM
I'm coming to the conclusion it's what you're saying. I brought it to my luthier today and he did a quick solder, but it didn't help, so he's going to do more testing. My dilemma is after I cut the pickup off the Isys+ peramp, I threw it away. I may have to start all over again finding another Isys+ and see if my luthier can remove the saddle.

kohanmike
10-05-2013, 09:03 PM
After all was said and done, I decided to forget trying to fix my blunder, so I ordered another Fishman Isys+ preamp system. My luthier was able to pull the saddle, so I'll be able to insert the new one myself properly.

kohanmike
10-24-2013, 07:36 PM
I received the new Isys+ preamp yesterday and installed it. Works great. Good lesson to learn because the Lanikai monkey pod uke I got a couple of weeks ago has the same in the sound hole Fishman controls, so I ordered another Isys+, but now I know the proper way to install it.