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XTi / Band Manager strangeness


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#31 ozob

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Posted 14 April 2013 - 02:39 PM

At the time I discovered the problem and during the discussions with Kevin Heber, I had the latest firmware.  I am not aware of any later versions - but I will check anyways and report back.

As far as Band Manager 2, yes I am using it.

Odd now but with BM2, every time I disconnect the usb from any amp- the program self terminates.  BM1 did not do this!

#32 joust

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Posted 17 April 2013 - 11:29 AM

Hello ozob,

I hope you are well! As for your problem, did you update the firmware recently (current SA3.4)? It is possible that your current mishap has been cured and updated.
I will also check out your observations. When you mention BM or SA, which versions are you talking about?

Alain

#33 ozob

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Posted 20 April 2013 - 09:12 PM

View Postjoust, on 17 April 2013 - 11:29 AM, said:

Hello ozob,

I hope you are well! As for your problem, did you update the firmware recently (current SA3.4)? It is possible that your current mishap has been cured and updated.
I will also check out your observations. When you mention BM or SA, which versions are you talking about?

Alain

Verified, all my XTis are and already were firmware v1.1.5.6.  Latest v SA3.4 and BandManager2.  Not aware of anything newer v wise.

Just try this and tell me what happens:

1. Set up a simple 2 way system on one Xti amp.  A sub on ch1 and a top on ch2.  Use Bandmanager or System Arch.
2. Write a preset with y input and basic x-over at 100hz with independent channels. Store it.
3.Plug in a sound source to ch1 and turn up ch1 front panel knob.  Play some generic rock with good bass.

Everything should sound and work as expected - so far so good.

4. Now use Bandmanager or System Arch. to mute the tops.  You will see button change color and hear only the sub.
5. Now slowly turn up sound source and feed more input to amp.  It may need to be loud - but not stupid loud.
6. As soon as the muted top is sufficiently excited by the sub you will see the amp read "SHORT 2".
7. As soon as the bass drops down or you turn down, the amp channel goes out of "SHORT 2" and forgets that it was muted and BINGO - the tops suddenly come back on by themselves.  This change is not reflected in Bandmanager or System Arch.  They still think the tops are muted.  You have to toggle the mute buttons to get back to condition normal.

So two problems really.  One, the amp interprets back EMF from a muted speaker channel as a short and two, the amp responds by unmuteing itself, and Bandmanager doesn't know it.  

This problem will also happen across amps, as in using one amp for mains and one for monitors.  If you mute the monitors and play the mains such that the monitor speaker is excited, monitors will un mute.

It does not matter if the amp is connected or un connected to Bandmanager or if the mute command is a temporary edit or stored in a preset.

#34 joust

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Posted 24 April 2013 - 08:21 AM

Bonjour ozob! So, I've tried your simple setup and did find something interesting, though, not exactly the same behavior as you have.
Did your setup and found that the top channel MUTEs then when sub gets overly drastic, Ch2 pops out of Ready mode! Unfortunately, I was not able to get the SHORT2 message but I get the point. (Note: You may have a problem with the Tracker circuit. Or, you really have a low impedance load on Ch2! I was using 4 ohms loads (not speakers!))

Did another test using same setup but no loads and unMute Ch2; Cranked up the signal until Peak indicators flash (a lot!); Bring down the signal; The amp shuts down! Bizarre...

I will advise Crown on this behavior. Thanks for your patience, ozob!

Alain

#35 ozob

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Posted 24 April 2013 - 10:42 AM

View Postjoust, on 24 April 2013 - 08:21 AM, said:

Bonjour ozob! So, I've tried your simple setup and did find something interesting, though, not exactly the same behavior as you have.
Did your setup and found that the top channel MUTEs then when sub gets overly drastic, Ch2 pops out of Ready mode! Unfortunately, I was not able to get the SHORT2 message but I get the point. (Note: You may have a problem with the Tracker circuit. Or, you really have a low impedance load on Ch2! I was using 4 ohms loads (not speakers!))

Did another test using same setup but no loads and unMute Ch2; Cranked up the signal until Peak indicators flash (a lot!); Bring down the signal; The amp shuts down! Bizarre...

I will advise Crown on this behavior. Thanks for your patience, ozob!

Alain

Basically I just copy/pasted the procedure I first posted on 10-2011, that I knew would demonstarte problem.  The specifics of seeing malfunction are related to drive level and resonances/sensitivity/positions of speakers, etc.  So problem MIGHT be harder to notice sometimes.  In my case I did not have to clip or drive into protect - or do anything special really.  Just lucky, I guess.  :unsure:

However since that time - and playing around - I have found a very easy way to demonstrate issue.
I am convinced problem is related to back emf on a muted channel.  Here is an easy way to see the basic behavior:

Just plug in a monitor wedge to each output channel.  DSP off.  No special settings needed.  Set the wedges on the floor literally faceing into each other a few inches apart.  Play music to both channels and mute one channel.  Adjust drive level and BINGO - amp reads "SHORT" and muted channel turns itself back on.

Certainly not a "real world use" but just to show what can/does happen when conditions are enough to produce sufficient back voltage on a muted channel - that confuses the amp.

2 real world scenarios where this is a problem for me:

a. Trying to write presets for a 3-way system with xover, delay, eq, etc.  Testing and measuring response one passband at a time, thus muting sections and driving others alternatly.  Pretty frustrating when passbands randomly turn themselves back on!  :blink:
b. Set up show with floor wedges on floor next to FOH subs.  Band goes on break - mute monitors - play break music and get, "Hey dude, the monitors are still on"!  :huh:

#36 joust

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Posted 24 April 2013 - 11:17 AM

Now I can visualize what is happenning with the back EMF! It's an odd behavior but I can see this happenning too!
I've contacted Crown with this behavior; Hopefully they'll respond with a comment soon!
Note: I don't think it's the back EMF that is causing 'my' amp to fault: I didn't use wedges, only resistive loads. Still, the behavior (Ready indicator turning on) was noticeable.