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Stagehand
06-28-2014, 09:43 AM
I have a Sojing silent tenor and the preamp has been disconnected.
I can't seem find a schematic on line.
Can someone please photograph all of the wire connections. Especially the pickup to pre amp and end pin jack.
Please post or pm me the pictures.
Thank You in advance...Sean

I just realized that this belongs in Uke Tech Support.
Mods please move if necessary. Thank you

iamesperambient
06-28-2014, 12:37 PM
I have a Sojing silent tenor and the preamp has been disconnected.
I can't seem find a schematic on line.
Can someone please photograph all of the wire connections. Especially the pickup to pre amp and end pin jack.
Please post or pm me the pictures.
Thank You in advance...Sean

I just realized that this belongs in Uke Tech Support.
Mods please move if necessary. Thank you


i have always been curious about these.
How 'silent' are these unplugged would it but
quieter than my steel string electric unplugged?
sorry i cant answer your question i was just curious.

Stagehand
06-29-2014, 04:24 PM
They are very quiet. I'm guessing about the same volume as your unplugged electric, perhaps slightly less. There is very little body to resonate.
I can play at night and not disturb my kids in the next room.

iamesperambient
06-29-2014, 04:41 PM
They are very quiet. I'm guessing about the same volume as your unplugged electric, perhaps slightly less. There is very little body to resonate.
I can play at night and not disturb my kids in the next room.

thats pretty sweet nice little practice instrument :)

Booli
06-29-2014, 06:54 PM
I have a Sojing silent tenor and the preamp has been disconnected.
I can't seem find a schematic on line.
Can someone please photograph all of the wire connections. Especially the pickup to pre amp and end pin jack.
Please post or pm me the pictures.
Thank You in advance...Sean

I just realized that this belongs in Uke Tech Support.
Mods please move if necessary. Thank you


When I got mine , the preamp kept cutting out. Despite several attempts to make the connections more secure [I am very much a tinkerer], I ended up removing the preamp completely and rewiring it to run passively [i.e. rod piezo direct to an output jack], and then I picked up a Korg Pandora PXMINI to use for some reverb and as a headphone preamp.

You can see/buy the PXMINI here:

http://www.sweetwater.com/store/detail/PXminiWH

It seems that the black version is 'discontinued' and no longer available. I would have preferred the black version.

I've also fitted the PXMINI to fit securely inside the bottom of the lower bout. this way everything is self-contained with no external wires or other equipment [I did not want to have to fire up the iPad, and connect all the wires each time to practice.

Using the PXMINI, the sound is SO MUCH BETTER this way than for what the factory preamp was, but of course the PXMINI was $99. The PXMINI also gives you other effects, but the most significant to me are the EQ settings in the amp emulation, the compressor, and the choice of about 10 different reverbs. There are other effects [chorus, distortion, delay, etc], but I do not use them.

With decent headphones, with the right settings on the PXMINI you can simulate that you are in a 'space' that has beautiful acoustics.

Most of the 'presets' to me are either overkill with distortion or just strange, but you can make and save 200 settings of your own, which you can backup or edit on your computer (Win/Mac).

At some point I was going to do a full write-up, but have to allocate the time, which is sparse for me right now.

I still have the original preamp [still wired together in the original manner] in a box, I will try to take a photo or two for you in the next day or so.


[I][at the risk of going slightly off-topic, but to help anyone else with one of these ukes, when I bought mine there were only 3 threads here on UU talking about it, and very little in terms of detailed info.]


I felt the original black nylon strings to be quite dead sounding, with almost complete lack of sustain, with terrible intonation.

After testing the Martin M620, Worth Brown BT [tenor], Worth Clear CT, D'Addario T2 Titianium Tenor, and Aquila REDS, I am most pleased with the intonation, sound and FEEL of the Aquila REDS [tenor strings].

While most people LOVE them, I am NOT a fan of Aquila Nylguts on anything, they are too scratchy against the fingernails when strumming, as in LOTS of surface noise, which you will NOT hear unless you have grown out your fingernails] and they cause terrible cuts in the calluses of my fingers on my fretting hand, so I refuse to use the Nylguts strings ever again. Therefore I have not tested the Aquila Nylguts.

Also, the plain acoustic, unamplified sound is loud enough to hear yourself, but in the next room it is barely audible, and downstairs, even with the door open, nobody can hear it, so it's perfect for late nite practice when others are sleeping, which is why I bought the Sojing in the first place.

Despite my tendencies for tinkering, I have left the original nut and saddle, which appear to be either rosewood or ebony, since these woods tend to soften the sound a bit and since this uke has no body cavity to resonate the sound, the sound is not as plasitcky as most nylon-string solid-body electric ukes (I have 2 others, a soprano and a concert, both NOT Sojing), and the wooden nut and saddle seem to make the sound better than what would be bone or micarta [which is what I would have replaced them with].

The intonation is not bad [and I am a real stickler for intonation] [with the Aquila REDS, which gave the best intonation of the strings I tested]- the A string goes about 10 cents sharp after the 5th fret on mine, but you can compensate that by tuning the A string a bit flat, and in 1st position, it has little effect on the perception of the chords being 'in tune'.

The saddle slot in the bridge is very tall on mine, and it seems that the saddle itself is only about 2mm taller than the wood in front of it towards the nut, so to file the saddle to try and fix the intonation, i am worried about interference from the wood on the bridge, where it is already so close.

Also, the bridge on mine was lifting (about 0.5mm), so I removed it, and sanded everything down, and then re-glued and re-screwed it on with Elmers carpenters glue [the only glue I had on hand at 2am]. The bridge has been real solid now and not going to come off. It's been rock solid on there for about 2 months now, and no signs of lifting any more.

For the money, I knew it would SOME need work, but for my time [maybe 2 hrs total] and cash outlay of ~$249, it's STILL way cheaper than a Pono TE, Fluke SB or Godin Multiuke, and NOW, with all the fixes I've done, it's very easy to play. Besides, did I mention that I enjoy tinkering?

If yours is playable out of the box, then you got a nice one, but I would not recommend this for someone who is not able to do some set-up work and to make some minor adjustments...

-Booli

Rick Turner
06-29-2014, 07:22 PM
And the reason for not contacting the manufacturer or the dealer is?

Any experienced luthier should be able to wire it up properly, and properly means dealing well with the shielding which is a major issue with piezo pickups unless you love hum-alongs in the key of 60 cycles. The input to the preamp should take a shielded coax cable from the pickup directly into the PC card or maybe to a 1/8" mini plug and jack on the preamp box. The output would likely be two conductor + shield coax to the jack. One wire is the output signal, the other the battery switching wire, and they'd be inside the twisted or braided shield. There aren't all that many ways to wire these things. You have your input, you have your battery connections, you have your output. Of course, getting the wrong wire to the wrong terminal can lead to a lot of noise and very little music! And if you reverse battery polarity, you can blow the thing up if the circuit is not protected by a diode or two.

Booli
06-29-2014, 08:49 PM
And the reason for not contacting the manufacturer or the dealer is?

Any experienced luthier should be able to wire it up properly, and properly means dealing well with the shielding which is a major issue with piezo pickups unless you love hum-alongs in the key of 60 cycles. The input to the preamp should take a shielded coax cable from the pickup directly into the PC card or maybe to a 1/8" mini plug and jack on the preamp box. The output would likely be two conductor + shield coax to the jack. One wire is the output signal, the other the battery switching wire, and they'd be inside the twisted or braided shield. There aren't all that many ways to wire these things. You have your input, you have your battery connections, you have your output. Of course, getting the wrong wire to the wrong terminal can lead to a lot of noise and very little music! And if you reverse battery polarity, you can blow the thing up if the circuit is not protected by a diode or two.

Hi Rick,

Not sure if you are directing this reply to the OP [Stagehand] or to my post above.

However in the case of the latter [and to help others]-

I am an experienced electronics hobbyist and have done MOST of my work with audio circuits.

Rick, everything you've said here is good advice for Stagehand but I'm not sure that it applies to what I've described, unless I'm missing something. Please forgive my oversight. I apologize.

I did not mess with the surface mount components on the existing preamp. Without a proper schematic for this board and/or and technical reference documents on how the integrated circuit is being used, this is just begging for failure. This may not be Electronics 101, but is good practice any way.

Maybe I should have been more clear, the 3-pin 2mm-pitch amphenol-type connectors-

see picture:
http://i.imgur.com/pgeCoQH.jpg

that are on the main preamp board seemed to not mate well with the plugs that were crimped to the wire ends from the various components [volume and tone pots, headphone breakout, and endpin cable], and with the power on and plugged in, when I would apply pressure to hold them more firmly onto the preamp circuit, the sound would go on, when I would let go, the sound would cut out.

My attempt at a solution to fix the plug more firmly was to use a dab of hot-melt glue to hold the plug into the socket. Even doing so, and while this cured the problem, I was not pleased with the sound, neither in the headphones and nor via the output jack.

From what I can tell just looking at the board, the stock preamp uses an LM386 chip for the output jack and completely separate LM386 with a discrete circuit for the headphone output, my guess is that they are each a different impedance output.

I know that the LM386 chip is well documented and I've worked with it many times in the past, and, well, it 'sounds' like an LM386. AFAIK, there are 7 different versions of the LM386 chip, and MANY different ways to implement it in an audio circuit.

I'm not a fan of the sound of the LM386 unless for low-fidelity or telephone-audio applications.

The manufacturer provides no information on the technical specifications of this preamp that comes with the instrument, as it is a low-end made-in-Asia copy of the original Eleuke.

Having said all that, once I removed the stock preamp, I shielded both the now vacant preamp cavity AND it's plastic cover with copper foil tape, in order shield against interference.

The existing rod piezo that comes with this Sojing uke, already has a shielded wire that terminates into a 2.5mm plug (like most no-solder kit these days), and THAT wire was already sheathed within in a braided nylon sleeve, all along the length, save for about 1" at the end where the 2.5mm plug is fixed.

All I did with it was plug THAT directly into an endpin jack that has a pre-soldered female 2.5mm plug,

like [B]THIS (http://www.cbgitty.com/cigar-box-guitar-parts/chrome-guitar-end-pin-strap-button-jack-with-2-5mm-input-jack/) one:

68368

68369


I then used an EXTERNAL preamp, such that is built into the Korg Pandora PXMINI.

I did not contact the manufacturer because before even buying this instrument, it was my intent to modify it and customize it to my purpose. If there are simple repairs I can do myself, i will NOT be sending the uke back. Fixing a lifting bridge is a simple task for me.

I had previously mentioned that I am a tinkerer [and hardware hacker] and seldom leave things as they are.

OTOH, if this were a K-brand or a custom build then yes, I would first contact the maker of the instrument before doing anything to it.

Rick, I am sorry if this frustrates you as a luthier, manufacturer and engineer, but if you look more carefully, you might see us as kindred spirits.

Hopefully this will clarify my previous post.

-Booli

Stagehand
06-30-2014, 06:55 AM
Hi Gentlemen,
Thanks for taking the time to respond.


And the reason for not contacting the manufacturer or the dealer is?
This uke is an E-Bay purchase. As to contacting the manufacturer, I was hoping to find the answer here first.

All wiring from the preamp is point to point, there are no connectors. The only thing shielded is the pickup lead. My issue is I have 5 disconnected wires. Three from the headphone jack, one from the pickup lead (goes to the back of the preamp board) and one that I can see the break. I assume that the three go to the output jack. It looks like they were cold soldered and the solder pulled cleanly from the output jack pins so I can't tell where they were connected. I also think that two of the wires were joined to a single pin. Once I figure out where everything goes it should be a simple fix.

I have been thinking about wiring the pickup directly like Booli has done but I like having a headphone jack and volume pot.
The external preamp will work but I like the idea of plugging headphones directly into the uke with no external wires or ac.

Thanks...Sean

Booli...After rereading your post, I now realize that you mounted the PXMINI on board the uke. If I can't get this current configuration to work the PXMINI might be an option. Thanks!