Thanks to Guitarnuts, iAxe modification

[n7188u]

I wanted to drop a line to thank Guitarnuts.com for the assistance in turning my otherwise unusable guitar into something I am really enjoying.

I recently purchased the Behringer iAxe393 USB guitar. I am new to electric guitars and I am sure that this is not a good guitar, but I was attracted to the low cost and the fact that I could experiment with effects without buying any additional equipment (your PC is your amp and effects combo through a very sort-off scaled down version of NI’s Guitar Rig). The MP3 player loopback feature is also great for learning and it’s built in tuner is an added plus for learning chords and setup.

I was able to setup the guitar quite well but, the noise level, when trying any of the distortion effects, was so bad that it was impossible to use. Playing clean notes was OK using the AC combo but the Plexi combo, which I heard this is like a Marshall amp simulation, was useless.

Then I found Guitarnuts. I shielded the guitar and the noise is now GONE. What a difference!! Before, the input level had to be attenuated to -10 dB to eliminate most of the noise, now I can keep it at 0db (midlevel) and crank the master volume up and get very nice sound out of my once crappy guitar (well, its still crappy, but at least I can use it).

When no notes are playing, the noise is almost zero. What makes this possible with the Behrringer setup is that the amp simulation has what is called an input noise gate which cuts down noise when notes are not playing. Before the modification, the gate was useless but now it really works very well.

If anyone is interested in doing such mod to the iAxe I can add the following changes to the Strat Guitarnuts modification instructions:

1.- Since the iAxe has active electronics, extra care must be exercised when performing the shielding. The main cavity and the output jack cavity are all passive so they can be shielded per original Guitarnuts instructions. The USB input cavity contains active electronics and you must be careful here. What I did was create a little pocket (box) with cardboard and shield only the outside of this pocket. The pocket then fits inside the cavity where the USB electronics. You then insert the electronics inside the externally shielded pocket. I left a little extra foil overlapping out of the front of the pocket to wrap around the area where the small metal chassis that holds the electronics screws into the guitar. That way I ensure that the pocket’s foil is grounding properly. The signal negative is already grounded to the electronics chassis so just make sure the shielding of the signal wire is grounded to the shielded box by connecting it to the signal ground or the electronics chassis (which is what I did).

2.- The iAxe has both an USB input and a regular jack for connecting it to a guitar amp. I had to disable the connection to the regular output jack. What happens is that you have an unconnected signal plus wire at the jack when using the USB output and it acts as a little noise antenna. Once I completely bypassed the jack and routed the signal directly to the USB electronics all noise was gone. This is a shame because the regular jack makes the guitar a bit more versatile but I’ll look into a way of getting this to work in the future.

Well, there it is. THANKS to Guitarnuts for the help and I hope this instructions help anyone else suckered into buying the iAxe (actually, I still think it is great for learning) get this guitar to work better.

Chris

[michaelcbell]

Well, it sounds like you've been reading! Welcome to guitarnuts in a very real way. +1 for ingenuity. If you can post a pic of the jack/usb issue, I'd be able to give you some help, but I'm a little imparied whtn it comes to visualizing your description.

[JohnH]

Thats a good description and welcome to GN2.

My son has a basic Behringer guitar. We found that the most craptastic part was the guitar cord that they supplied, which behaved as virtually unshielded. Changing to a home made one was a big improvement.

John

[n7188u]

Hi Michael,

BTW, how do I post the file with the drawing? I have a hand drawing trying to clarify what I did.

At the top is the first configuration I had for the guitar output jack and this was quite noisy. Notice that when this jack is not in use (USB mode), the signal (+) cable just sits there. It is in the female jack inside the shielding so maybe it is ok, but then there is the open jack hole right in front of it. Also note that the signal (-) connects to the shielding at this point. From there, another shielded cable runs to another cavity where the USB electronics reside.

Drawing at the bottom shows my current configuration and it is noiseless. BTW, there is the possibility that when I tried the first configuration there were other environmental factors that contributed to noise but my current configuration seems much better.

BTW, I just read the last posting and yes, I did change the USB cable to a real shielded cable. The improvement was marginal in my guitar. I will post pictures if someone requires further clarification although I have already installed strings and there is only so much I can open now.

Regards,
Chris

[michaelcbell]

To post a drawing, first upload it to your server of choice (photobucket seems to be popular), then copy the url in between [ img] and [ /img] and presto!

I can't see a pic, so I'll hold off on commenting in that department until we figure out the pic issue.

As for the shielding, I believe John was referring to the normal 1/4 cable (the one that fits in the jack you disconnected) not being up to snuff. As a slight bit of a purist, I'd love to see you still be able to play the guitar for "real". Maybe we'll be able to figure something out when we get the pic working.

[sumgai]

n7188u,

I'll add my Welcome message, glad to have you here!

It would seem to me that if you disconnect the regular ¼" jack, and things get quieter on the line going out the USB jack, then there's still a shielding issue. That's providing that you don't have a cable inserted into the standard jack, of course.

If you do have a cable inserted thusly, then it'll have to be plugged into an amp that is also plugged into a power outlet, in order to effect all the grounding requirements. At that point, you also should not perceive any "additional" noise in the USB output. Again, if you do, it's a shielding issue, but now, it could be the cable at fault (low/poor quality), or the amp itself may not be fully compliant. Both are easy to fix, just try differnet units.

It is also possible that your amp and computer are not plugged into the same outlet circuitry, therefore it's possible that a ground issue exists within your home wiring. Small possiblity, to be sure, but nonetheless.........

And you did use the IMG and /IMG tags correctly, so we aren't seeing your picture due to either a bad URL, or a server gone gunny-sack.

HTH



sumgai

[n7188u]

Yay!! I was able to post a picture. Well, learn something new every day.

BTW, it is very possible that the noise issue I had when the regular amp jack was internally connected is not related to the circuit shown. Maybe I had something touching or ground loop. Since I only use this guitar with my laptop then all is fine for now. I don't even own a real guitar amp and thus the purpose of this USB guitar.

Also sumgai, I never had a jack connected to the guitar output jack. Things got quieter when I bypassed the jack internally.

On the subject of grounds, what is really baffling is that I use this guitar connected to a laptop which is not grounded. How can the shield work??? But it does somehow. I did experiment creating a ground by connecting a cable to the ground pin in a wall outlet and connecting this to the laptop shield, which connects to the guitar shield via the USB cable shield, and interestingly I got more noise.

Maybe now that I know how to post pictures I'll take some of my guiatr and post them.

Chris

[JohnH]

Thats a nice drawing. Im not sure why the bypassing improved the noise, but if there are indeed + and - signal input to the USB board, and in the original case the - one was also to the jack ground/casing, then it might explain it.

I'm curious - does anyone know what the nature of the USB signal output would be? presumably some kind of streaming digital signal? I wonder if its possible to get hold of those boards to play with?

John

[sumgai]

John,

........
I wonder if its possible to get hold of those boards to play with?

Sure! Just buy an iAxe unit, rip out the guts, and sell the remaining guitar on eBay for 50-60 bucks! Nearly instant 40 dollar purchase of USB goodies! ;D

And yes, it is a standard digital audio stream, USB is merely a transfer protocol, and adds nothing special to the equation.

HTH


sumgai

[n7188u]

JohnH, the signal (-) was being grounded to the jack faceplate. From that point it went to the signal (-) connection of the USB board. My change was to eliminate the grounding at the jack location and let it go directly to the USB circuitry. Seemed to work.

Talking about the USB circuitry, although relatively unimpressed about the quality of the guitar, the USB electronics are small, simple and impressive. I don't know about the quality of the sound because I am not experienced enough with guitars but it sound good to me (particularly after shielding). The ASIO drivers Behringer provides result in a claimed latency of 4-9ms. All I can confirm is that when you pluck the strings the sounds seems to have no discernible delay.

Whats more, the USB board in the guitar provides the audio output connection so that you can plug headphones or active speakers. Think about it, the board in the guitar is processing the analog guitar signal, sending it digitally to the PC, the PC software applies all modifiers to the sound and sends it back to the guitar were it is converted to analog audio. I am impressed.

The NI's Guitar Combo software is a charm and easy to use. I have an external USB gamepad based box I built (that was another project by itself) to control the knobs of the virtual amps and switch presets and it is a blast to play with the different effects available.

Last, check out www.behringer.com/UCG102/index.cfm?lang=eng. You asked about buying the electronics separately (they sell this for $39). I suspect this external box is essentially the same as what's inside my guitar. It even comes with the NI software. When I saw this I though that it would have been a better deal to buy a better guitar and try this little box to achieve the end result I was lookign with the iAxe, but with better hardware.

Chris

[ccoleman]

Yes JohnH and n7188u,
The USB device in the iAxe is simply a standard "USB Soundcard", it is universally recognized without any additional drivers in Mac OSX and Windows 2000 (and newer) operating systems (and Linux too I think). It streams audio in and out simultaneously.. and of course building this into the guitar makes the digitized sound captured from your pickups that much cleaner, plus your whole guitar gets to have 5V phantom power, up to 500mA of current... not bad.
C

[zamzara]

One thing that strikes me is that on the 'noisy configuration' the two shield braids are connected to different points on the shielding, possibly causing a ground loop. On the good configuration they are at a single point.

[JohnH]

ccoleman said:

plus your whole guitar gets to have 5V phantom power, up to 500mA of current... not bad.
C

Yes that is neat - the computer is providing the power back into the guitar, so we could use some for other on-board electronics?

John

[n7188u]

Zamzara,

You are correct, in the pictorial and schematic I made I show the shield grounded at different places for clarity. In reality I had the 2 signal (-) and two cable shields soldered together to a short piece of wire that then connected to the jack (-) which is integraly connected to the cover and cavity shield.

Maybe the problem is that by having the signal (-) and shield connected together at both the jack cavity and the USB cavity locations I am in fact creating a ground loop.

I wonder how I can keep both output options (jack and USB connected in parallel without creating this loop, keeping in mind that you don't necessaryly have a male amp jack connected to the jack output all the time. Maybe an isolated female jack? But then I loose the shield ground connection. Maybe a switch to select output options? ughhh!

Chris

[zamzara]

n7188u said:

Zamzara,

You are correct, in the pictorial and schematic I made I show the shield grounded at different places for clarity. In reality I had the 2 signal (-) and two cable shields soldered together to a short piece of wire that then connected to the jack (-) which is integraly connected to the cover and cavity shield.

Maybe the problem is that by having the signal (-) and shield connected together at both the jack cavity and the USB cavity locations I am in fact creating a ground loop.

I wonder how I can keep both output options (jack and USB connected in parallel without creating this loop, keeping in mind that you don't necessaryly have a male amp jack connected to the jack output all the time. Maybe an isolated female jack? But then I loose the shield ground connection. Maybe a switch to select output options? ughhh!

Chris

I would be inclined to remove the (-) signal wire altogether, as it isn't needed as far as I can see. It's just repeating the role of the braid and creating a loop.

Alternatively, on the cable from the jack cavity to the main cavity, only connect the braid at one end.

[n7188u]

Zamzara, I don't understand your statement regarding removing the signal (-). Remove from where?

In any case, I am going to try the following and then report: I will disconnect the cable shield in the USB cavity and only leave it connected int he output jack side. Since signal (-) connects to the cable shield at both the USB electronics chassis and amp jack cover, a ground loop is created in the cable that goes between these two cavities. I'll re-install the jack using a connector, that way, if this change doesn't work, and if I want to use a regular amp, all I have to do is remove the two screws holding the jack cover and swap the outputs.

Chris

[n7188u]

So as to provide closure to this thread (at least an update), I proceeded to reconnect the amp output jack, ground and cable shield interconnected at this point and eliminated the cable shield connection at the USB cabity (where the signal (-) is connected to the USB chassis and cavity shield.

Result: I bought a Roland Micro-Cube for practice and when connected to the output jack the guitar is essentially noiseless. I'm very happy. On the USB side there is some noise at high gains but it is orders of magnitude better than before and very usable.

I post a couple of pictures. Not much detail because the guitar is all together and I wish to play instead of work on it. Again, thanks guitarnuts.

Chris

[ayeohx]

Hi, I'm having the same problem with my iAxe. I'm having a tough time understanding the steps that you went through to fix the noise issues. Would you mind dumbing it down a bit?
Thanks

[wolf]

Welcome ayeohx

If nothing else, I figured I'd redraw n1788u's "good configuration":



Maybe someone else will be along to explain more.

[ashcatlt]

Just thought I'd drop in and mention that I've got a Behringer strat. No USB, but I'm pretty sure it's the same guitar otherwise. I don't have the vast experience of some of the others around here, but I've played a few fancy guitars in my day. I have to say this is a perfectly playable instrument. The neck's got a great feel, tuning is relatively stable...

It sounds good too. I replaced the pickups in mine, but was really pretty happy with the ones it came with. I've got a Rick 330 and an LP Studio and this little Behringer actually seems to get more play time nowadays.