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metroiss

UX8 Clipping on Both Instrument Inputs

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I've had my UX8 for a long time now and have never seemed to have any major problems.  Lately though while running my bass through both the Instrument inputs on my UX8 i noticed that there is a constant clip on the attack every time I hit the lower strings.  Odd part is if I hit a low string and let it sustain and turn the volume up and down on my bass the clipping also occurs on every volume swell.  The clip light does not light up on the input and the pad does not seem to make any difference.  I can then move my bass onto input 3 for instance as a line in and have no problem what so ever. My bass is a Ibanez SR405 running active Seymour Duncan soapbars.

 

Is there a protection circuit that may be prematurely going off?  Any way to find out if an input transistor may be going bad?  I've attached a picture of the clip i recorded and normalized.  I appreciate any help or suggestions.

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post-32656-0-20235400-1437938904_thumb.jpg

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Strange that this is just happening now.  Did you change the battery in your bass recently?  I've heard of some people having input problems with active pickups with the Spider amps - overdriving the input voltage.  Do you have a stompbox (not full bypass) you can use to buffer your bass signal into the UX8?

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I can't say that this is just happening now, normally i only run my guitar through the UX8 but my situation changed where i'm starting to run my bass through it as well.

 

Strange that an active pickup would cause an over voltage scenario, input of the UX8 (as far as i can tell) is about 18V p-p which i don't believe an active pickup running 9V battery can achieve.  All of the batteries are fresh and this also happens with my second bass, also with active pickups.  I'll try running through a stompbox today (I have a Morley wah I can try) and see if there is any change.

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Tried through the Morley Wah with no change.  Also decided to try plugging in my gibson and run it through dry and found it does the same thing so its not an active vs. passive pickup problem.

 

I did switch the input 1 to line in and the problem goes away  so its only an issue when channel 1 is set to instrument.

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If you're getting a usable signal using the 'line' setting, then something is definitely amiss in the input circuit - a passive instrument plugged into a line input should result in a barely-audible (and noisy) signal.

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Did you find a solution?

I have the exact same problem with my UX8.

 

I have tried everything from changing power outlets to passive/active instruments and "preamping" the signal between the guitar and the UX8.

 - The problem is solely with the instrument sockets.

 - It doesn't matter if I have POD-farm turned on or not (or any other software for that matter). The clip remains.

 - the clip does seem to go away if I turn the guitar (electric - humbucker) down enough. So it seems to have something with the UX8 instrument socket being more "sensitive" now than before.

 

What to do?? Is it possible to fix by remplacing hardware inside the UX8?

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I have the same problem. Here's what I found:

 

When the source is set to "Instrument" on input 1 & 2, the signal is routed internally to two ADC channels at different gains. If the signal is close to full scale on the high gain channel, it switches to the lower gain one & compensates somewhat (there is some hysteresis to prevent the unit from constantly switching back and forth between channels). I have no idea what this design is trying to accomplish - increase the "perceived" dynamic range?

 

With time, the coupling capacitors will degrade eventually (doesn't help that there's a hot running voltage reg right next to these caps)

As these caps degrade, the gains will no longer match, so the switching becomes very noticeable

 

I had to replace all the coupling caps after ~6 years of continuous operation. Having it done by a tech may not be worth the expense, though

 

I pretty much gave up on the instrument inputs however (The impedance onfthe line inputs is close to that of most effect pedal anyways)

 

Mp

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Thank you!

That might become helpful. I already talked to a tech and am going to let him have a look (€40) and give me price for fixing it.

I'll be sure to let him know what you found!

 

(I've had my ux8 for some five plus years so it sounds about right)

 

//AC

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I've has some time to play with this some more and mpaquette comment makes perfect sense as a fix.  I'll try to determine which caps are the problem and try the fix over the weekend, hopefully with some pictures.  If someone could give me direction on which caps to focus on that would be very helpful.

 

Looking at the unit i'm seeing 6 470uF electrolytic caps around what looks like 5 voltage regulators.  I was expecting to see the nice mushroomed tops but no luck. Are these the caps that need replacing? some of the numbers are C136, C219, C145, C133, C132, and C120.

 

I actually took the time today to pull out the main board and find out what voltage measurements i should be getting.  Luckily Line 6 put a nice set of test pads on the bottom of the main board and indicated what voltage you should see at those locations.  What i found is that my +20 and -20 volt signals are showing somewhere around +-13V and what should be an 8V source is showing 3.13V, these are feeding +15V, -15V, and 3.3V regulators.  I'm actually surprised i'm not finding more issues with the unit other than the instrument inputs.  Surprisingly the regulators are all outputting what they should and my theory is that they are able to do this at the sacrifice of current and the instrument inputs require more current then the other inputs to operate correctly.  This then starves the high/low gain switching unit of power causing the instant drop just after initial attack.

 

My next approach will be to replace the coupling caps for the corresponding voltage sources.  For those interested it is the set of 3 caps that are glued to a set of 3 inductors right next to the transformer.  If this works i'll post my results.

Edited by metroiss

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After replacing the capacitors that i thought could be suspect there is no change to the instrument inputs.  I also found that all the voltage values in the power supply area are correct, turns out my old DMM from college is no longer reliable.

 

At this point I'm thinking the main DSP chip could be the issue, I believe the high/low gain channel switching logic is controlled by the main DSP.  Without a schematic its really hard to trace any of the signals back to the DSP to test everything along the path.  Has anyone been able to get a schematic from Line 6?  I would think since this unit is out of production they shouldn't have any issues selling the schematic to users.

 

Brad

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After replacing the capacitors that i thought could be suspect there is no change to the instrument inputs.  I also found that all the voltage values in the power supply area are correct, turns out my old DMM from college is no longer reliable.

 

At this point I'm thinking the main DSP chip could be the issue, I believe the high/low gain channel switching logic is controlled by the main DSP.  Without a schematic its really hard to trace any of the signals back to the DSP to test everything along the path.  Has anyone been able to get a schematic from Line 6?  I would think since this unit is out of production they shouldn't have any issues selling the schematic to users.

 

Brad

Hey I just came across this topic while experiencing the same issue! I posted questions about it earlier today. 

 

http://line6.com/support/topic/24894-ux8-issues/

 

Did you ever have any luck? 

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Im impressed if theres a fix, mine are probably getting to that age too but no problems yet. I bought two because I liked the UX8 so much.

$125....I saw a third for $119 and almost bought it but thought this is nuts...lol

 

I had a clipping noise on the pad button, dirty or whatever. I wonder if a person takes this out of the "loop" (jumper it) if it would quit switching hi/lo? or solder a resistor in the circuit to lock it in to HI or LOW and not this auto-switching thing.

 

maybe a Line6 Expert will chime in.....

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