35 replies to this topic

[ozob]

I have 3 XTi's in my rack - 2000, 2000, 4000.  The 4k powers subs and a 2k powers mid / hi box ( for p.a.) and are supervised with Band Manager via usb hub into laptop.  The remaining 2k is just a slave and runs a full range control room monitor speaker and is unsupervised.  All 3 amps are in y mode input and all 3 amps receive input from one balanced line - daisy chained in and out of the channel 1's.  So far so good.

Power up and test system - all p.a. amps muted in Band Manager.  Unmute subs - good.  Unmute mids - good.  Unmute highs - good.  Mute all p.a. channels - good.  Turn up front pannel knob on slave amp - good - wait - mids just came back on p.a. by themselves.  Band Manager still shows p.a. mid channel as muted ???????  Unmute mid button and remute - mids go off - then a few seconds later come back on again???? This continues over and over only when slave amp is pushing sound to monitor.

Any ideas on this?

[Kevin Heber]

I'm as confused as you. Can't think of any mechanism which would allow this unless you are talking to the wrong amp.

[ozob]

I'm as confused as you. Can't think of any mechanism which would allow this unless you are talking to the wrong amp.

Thanks for reply.  Can't be talking to wrong amp .  Slave amp is not even USB connected to laptop.  The slave amp is in dsp mode running with a very simple user preset.  The 4k and 2k running p.a. are USB connected to laptop in BandManager and respond well - they show up in order in the virtual rack - all pages and parameters are visible and functional - etc.  

Somehow the act of turning up the channel 1 front pannel knob on the 2k slave amp and passing music signal to the monitor speaker causes the mute to unlatch on the 2k channel 1 running mids on the p.a. even though BandManager still shows the channel to be muted.  Cycling the mute button will remute it but if music is playing in slave 2k amp, mute will pop back off.

Could there be some kind of wireless comm going on between the unsupervised 2k and the supervised one?  Or can there be some ghost of the control data reaching the slave thru the daisy chained inputs linking all the amps?  All 3 amps are touching and are  bolted in the same rack.  Dsp communicating thru ground???

This is a head scratcher.

[ozob]

FWIW after connecting the slave amp to BandManager to look for issues the system worked w/o error, then setting the system back up like I had it and checking it again today - I can not duplicate the problem !  

I can't figure it.  I repeated the fault 5 or 6 times originally.  SOMETHING was telling that amp channel to unmute and the change was NOT indicated in BandManager.  The only action I was doing at the time was turning up the front panel knob on the amp NOT connected to the network.  Wierd.

Ah well........it's working fine now.

[ozob]

Ok,  problem is back.  Seems that I have to drive the system moderatly hard to see it.  No clipping though.  And.......just before the slave amp unmuted itself it flashed a message in the display screen.  It said "SHORT 1".  And in addition to the slave amp unmuting - the mid amp unmuted as well (I was testing the subs only at the time).  Neither amp showed a change of status in band manager.  All three amps were connected to my laptop running Bandmanager.

Is there some problem with supervising the amps thru USB / Bandmanager whilst driveing them hard?

[Kevin Heber]

I wouldn't say there's a known problem, but it's possible that voltage could be sagging in the USB line -- make sure you have a USB hub with its own power supply (i.e. wall wart).  If you are connecting directly to a PC, try running the PC (laptop) on just the battery.

[ozob]

Ok.  Made sure USB hub is powered.  Ran laptop on internal battery.  Put voltage meter on ac and it reads a solid 120.5 volts and shows no signs (dimming lights, etc. ) of sagging.  It does not seem to matter if the amp that un-mutes is connected to laptop at the time or not.

What is the meaning of the "short 1" message that flashes on the amp just prior to it unmuting?  

I have a guess as to what is causing the channel to unmute itself.  Could it be back EMF voltage coming off the monitor speaker as it is excited by the subwoofer?  So far the problem has only happened when the sub is thumping and the (dual 15") monitor sitting near sub is ready to go with front panel gain control up but in mute at BandManager.  It also happened (only once) with the (dual 12") mids sitting on the subs - again - ready to go but muted.  

Disconnecting the monitor speaker at the speaker back or turning down the front panel knob on amp prevents problem.  

Is it a software bug?  When I load a stored preset into the amp and run it - then mute the amp with BandManager - I've effectivly just made a change and I'm in an edit mode or programing mode? Until I then save the (mute) change into that preset - yes?  So is it this temp edit state that is somehow fragile and being kicked out by the EMF voltage?  

I'm going to try saving the mute state into the preset and see if it still gets over ridden.  I am also going to move the monitor out of range of the subs direct output.

I havn't tried swapping the Xti 2ks around to see if it is just a particular amp or if this is a design feature.  Both Xti 2ks are brand new.

A lot of speculation, Iknow - but this bugs me.

[Kevin Heber]

The SHORT message is exactly what you'd expect -- the amp thinks that channel is shorted (or nearly so).

This is indeed bizarre.  So you're saying that when the unsupervised amp unmutes by itself, you can check it with Band Manager and it thinks it is still muted?

My only guess is that you have uncovered a bug.  The amp is ramping down the output in response to the SHORT condition and "forgets" that it is supposed to be muted.  We don't have this bug documented anywhere, though, after 5 years of field sales.  That would be extraordinary I think.

You can change a preset temporarily without storing it -- this will produce the message CUSTOM in the lower left of the display.  A MUTE would qualify as a change.

[ozob]

[quote name='Kevin Heber' date='Oct 24 2011, 03:39 PM' post='15350']
.........So you're saying that when the unsupervised amp unmutes by itself, you can check it with Band Manager and it thinks it is still muted?............

yes.

Also my apology for being less than accurate.  I read my OP and totally forgot that the mid channel was the first to un mute itself.  Then later also the slave amp driving the monitor.  I should have narrowed it down more before posting instead of sussing on the fly.  

I am going to eliminate some variables, rule out shorts, simplify the set up and re-test.  I will re-post with a, hopefully, more concise description of this oddity.  

[Kevin Heber]

Thanks -- if you can document reproducible steps that would help tremendously.

[ozob]

Ok, here it is.  I sorted out my dead ends and noise.  Can't believe no one else ever had this come up before.  This is easily repeatable.

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.

Any ideas?

[Kevin Heber]

Very nice work. Thanks for being so thorough. We'll get this set up in the lab and get back to you.

[ozob]

ozob, on 26 October 2011 - 09:14 AM, said:

Ok, here it is.  I sorted out my dead ends and noise.  Can't believe no one else ever had this come up before.  This is easily repeatable.

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.

Any ideas?

Any thing on this yet?

[ozob]

I know Kevin is gone, but does anyone else at Crown have any insight on this malfunction?  Is there a way to change the firmware perhaps to solve this?

[ozob]

Tap, tap........ is this thing on?    

Is anyone at CROWN supporting this forum anymore since Kevin left?  Have not seen any answers to my questions re: what seems to be a malfunction / bug in the Xti amps.

Heck .... havn't even seen official replys to any questions in several weeks.