Output dies after a while

[bsellon]

Hello Bob, You seem to be the expert about the Lexicon MPX G2, so a quick question. Mine mostly works, but after playing a few minutes all audio output will stop. There is still audio going in, you can see the indicator lighting up. Turning to a different patch will get audio coming back out, but after a while the audio output will crap out again. Diagnostics revealed nothing. Could it be the battery? Or the fact that it\'s v1 firmware? The guys at Lexicon were mystified and I obviously stopped using it live. I would like to get it working reliably. Any ideas. Any thoughts would be really appreciated. All the best, Christopher

[bsellon]

Hey Christopher,
That is a strange problem.

A few questions:
Does the audio output from the Send jack die or is it just the main outputs?

Are you using both main outputs or just one?

Are they both dead?

Does the audio come back every time you change the program or just some of the time?

Is there anything else you can do that will make the audio come back besides changing programs?

Does this happen with all programs or just your custom ones? Even Clean Slate?

How is the G2 connected? Is MIDI being fed to it from a computer or sequencer?

Does the audio stop all at once or fade out? Pops, clicks?

The battery wouldn't cause this problem. The battery just lets the unit remember your custom programs and settings.

It's possible that you created a global patch to the main output and the patch's source is changing and messing with you. The Global Patches are under the SYSTEM button (press it a couple of times till you see "System select:" on the top line of the display then turn the knob till you see Global Patches on the bottom line. Press the > button and you'll be on the Global Patches page. There are 3 fields that you move between using the < and > arrows. The fields blink when selected. Select  the # field and turn the knob and you'll see the values of each Global Patch appear as they are selected. These are empty by default but this is a good place to look for problems. A weird patch here could really mess things up.

[Keith]

I was just wondering if it's not a global thing, does it do through the headphones to?

[bsellon]

Hello Bob and Keith,

Well, here’s some more info, though I don’t know if it will illuminate or confuse further.

Deciding that I didn’t have any user patches I couldn’t live without.  I initialized the unit.  I then saved a patch, just to make sure it could and that the battery was working (just to make sure) and it is.  I checked inside to see the firmware chip is seated and everything inside looks ok on the surface.

I’m currently using the unit standalone.  I set it to mono output and tried both front and back gtr inputs.  No difference. 

I played only standalone presets and what happens isn’t that the output craps out all the way, but the output gets cut in about half.  It could be that the input is going down, or the output.  I’m not sure.

On a patch like “Purple Reign,” I can play fine for a couple of minutes, then the sound output just abruptly drops.  No click, pop, or fade down.  Just right down in volume.  When this happened I pulled the output from the Right main out, put in in the left (same thing), output send (same thing), and headphones (same.)  So it’s an across the board issue.

I had checked (as Bob suggested) the global parameters in the system menu.  There were none there, and there are still none after the re-init.

Now here’s where it gets weirder.

So “Acoustifier” cuts down in volume, is there anything besides switching patches that’ll bring it back up?  Yes, two things. (1) press bypass into tuning mode, then come out of tuning mode and I’m back up at the initial volume. Or (2) push EQ (which for this patch is on) turning EQ off, but bringing volume back up.  Hitting it again, turning EQ back on, returns to lower volume.

Then still weirder.  Playing “PdlOctave” which brings in an octave above.  Plays fine for a little bit, then no octaves and the pitch change is reset to a semi-tone up.  Nothing that worked on “Acoustifier” will bring back the proper sound.

That’s as much as I had time to check out today.  Seems like maybe a front panel thing?  Did the firmware upgrade address any of this?  I doubt it.

OK.  Let me know if this rings any bells.

And thanks very much for your help!

Best,

Christopher

[bsellon]

Based on your comments, here are a few more things to check:

Is the Noise Gate turned on? Depending on the settings, it could produce this kind of effect.

Are you using the Speaker Simulator? Would be helpful to confirm that the problem happens when the speaker simulators are NOT being used. These analog circuits which could be intermittent.

Does it happen if you just feed audio into the returns? If the output level DOES still drop, it eliminates 99% of the analog circuitry. The effects and parameters under the Gain button are all analog and there are tons of components which could fail or come loose due to bad solder or corrosion.

Does the level drop on presets that don't use the GAIN effect?

The main thing we want to determine is if it is a hardware problem or a software configuration problem. 

[Keith]

Just to ad to Bobs post, are you using midi or 1/4" jack inputs? It appears to me that both inputs lead to the same circuitry so if the 1/4" and midi inputs are having this problem then you can also eliminate the input circuitry. If you find midi works but 1/4" don't or visa versa. It's all about process of elimination. By finding what works helps narrow it down to what don't work. 

[bsellon]

Other than sending control information to the G2, the MIDI connectors don't have anything to do with the audio so I don't suspect they are involved in this problem.

[Keith]

Yes Bob that would be midi in but what about midi out?

[bsellon]

The MIDI out would even have less possibility of affecting the audio. MIDI is basically a serial port like RS232; it's used to move control data in and out of a device. MIDI is electrically different from an RS232 and of course uses different connectors. RS232 combines send and receive in a single cable with the digital 1s and 0s implemented as 0 volts and 12 volts, and only really takes 3 wires: ground, send and receive. A MIDI cable only sends data in one direction, which is why there is a seperate MIDI IN and MIDI OUT connector, and uses only a small voltage.

At the end of the day, a MIDI output just provides a signal and return (i.e. power and ground) that connect to an LED in the device with the MIDI IN that you are connected to. The LED in the receiving unit is actually encased in a chip that also contains a light sensitive transistor. When the LED turns on, the light sensitive transistor turns on. When the LED turns off, the transistor turns off. These are the ones and zeros that represent the data.

The use of the LED and light sensitve transistor allow the data to be moved between devices without connecting the grounds. This is why you don't get ground loops when you connect devices via MIDI. The ground/shield in a MIDI cable is only connected on one end for this reason. Because both leads of the LED in the receiver are only connected to the pins from the MIDI cable, the LED can be lit without being connected to the ground or power. If you connected an LED to end of a MIDI cable (with approx. 300 ohm load resistor in line), you'd see it actually light up as data comes  from the MIDI OUT.  The G2 can output a whole range of MIDI messages but normally only sends update information to the R1 if it is detected.

As it turns out, the standard MIDI connector actually has two unused pins that could, and sometimes are, used to send the data in the opposite direction. I'm not sure why this isn't just the standard but you'll notice that the MIDI IN jack on the MPX G2 is labeled REMOTE/IN. That connector implements both MIDI IN and MIDI OUT on one connector saving you a cable (some MIDI cables only provide 3 wires so check them with an ohm meter if you're not sure).

The G2 even ups that one notch by adding an additional set of pins: 7 pins instead of the standard 5 for MIDI. The extra pins provide power to the footpedal so it can be used with just one cable. Very cool. You still need the wall wart which plugs into the back of the G2, and you need a special cable but it makes setup for the pedal a breeze at gigs. One cable. Done.

Getting back to the audio level issue, the MIDI OUT is mostly used to send info to the pedal. The audio on the G2 would work perfectly if the MIDI connectors were completely removed. They are completely different systems. The worst MIDI can do is tell the G2 to turn down its volume which would take a very specific message. The odds of generating it accidentally by a loose connection or something are extremely small.

The MPX R1 footpedal and the G2 were actually designed to play nice together. There are buttons on the R1 for each effect block on the G2 that you can press to turn the effect block on and off (note that the V1.10 firmware fixes a problem with the level changing when to turn the effects on and off. This alone is worth getting the upgrade for).  There are tri-colored LEDs on the footpedal that show green if the effect is available and on, red if the effect is available and off, and off if the effect block is not available. VERY handy on stage.  Even the tuner appears on the R1's LEDs. This is implemented with a series of MIDI OUT messages.

I know this was a bit off topic but you seemed to be confused about what MIDI is so I figured it would be a good opportunity to explain some of the basics.

[bsellon]

Hi Bob,

OK.  Here’s the latest based on you questions.

The drop still happens regardless of the noise-gate being on or off as well as the speaker simulator.  I also thought the soft sat might be something to look at, but no difference there either.

I created a patch without gain (all the presets except for unity gain and clean slate have gain) and I played that for a while and no drop.  Probably ten plus minutes without a drop, which is more than I get on a patch with gain.

The audio also drops when feeding the returns and most of the programs for amp only and amp+fx loop have the gain turned OFF, so this is even more confusing.  Just in case I hooked it up wrong (I’ve not really used fx loops much) I hooked my gtr amps pre-amp out to the right mono effects return on the mpx and then the mpx send back to the pre-amp in.  I connected the guitar to the input on the mpx, not the amp.  I tried it that way and there was no audio.

Let me know you thoughts and once again, thanks for sticking with me.

Best,

Christopher

[bsellon]

If you are hearing the level drop from the Send output, that eliminates a lot of down-stream circuitry.

You can test the send output circuitry as follows:
1. Select program 1.
2. Press Edit
3. Press the Effect 1 button
4. Turn the knob till you see "Test Tone" displayed on the bottom line.
5. The Effect 1 button will blink fast. Click it again to load the new effect.
6. Check the send output for level changes.

This generates a tone internally. If you still hear the level drop, we've just eliminated the input circuitry. If not, it points to the input.

Does it start dropping when you turn on the Gain effect?

If  it only happens with the Gain turned on, try turning the EQ pots on the front panel fully clockwise or counter clockwise. The position of these is checked by the computer but sometimes there noise or other problems with them that falsely trigger and adjustment to the computer.