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XTi 1000 meter light question.


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#1 Rick Rideout

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Posted 24 February 2011 - 10:51 AM

I have a tri amped system using three XTi's (1000, 6000, & 6000)  On the XTi 1000 (serial number 8500400568) the ready meter lights come on both channels, but channel 2 rarely shows a signal input or any other lights about that. Channel 1 will show a signal light as soon as it get a signal but not channel 2.  Even on Band Manager I rarely see any movement on the input side on channel 2.  On Band Manager I do see an output signal near the same as channel 1 output but very little on the channel 2 input meter.  I've switch the XLR cables and reversed the XLR cables at the mixer and channel 2 still rarely shows a signal light.  I have a dbx PA+ and I can balance the room with the RTA mic and it seems I getting an even output on both channels but the channel 2 side shows very little input on the meter and Band Manager.  I did a gain set up (last night) on it using pink noise and with everything right at clipping the channel 2 meter was flickering a few times on the signal light. Yet Band Manager showed very little input but near clipping output.

This amp is powering my highs which are JBL VXR 932 in bi amp.  

Any ideas?  (Like ribbon cable???)

Thanks
Rick

#2 Kevin Heber

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Posted 24 February 2011 - 01:48 PM

This sounds like a known issue with running high frequencies on the XTi's.  The meters are less accurate than we'd like on channel 2, but only at 3kHz and up.  Sorry for the trouble.  The audio should be working fine; it's just a metering glitch.

#3 Rick Rideout

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Posted 24 February 2011 - 02:51 PM

Ouch!  That hurts.  sad.gif  

Interesting issue, I thought the XTi were two completely separate amps in one box.  Why is it that channel 1's meter can see the higher frequencies and channel 2's meter can't.   Cheaper meter on channel 2?

I don't really expect a reason, its just that I really like the Crown brand name and I'm worried these XTi's (with all the issues, recalls, ribbon cable ) is going to change my mind.

So the Band Manager is just relaying what the meters are doing? And that's why I'm seeing the same thing on Band Manager?

I built a new system around the dbx PA+ because I read about how you can Auto EQ a room with the RTA mic and can quickly have a great sounding system.  I bought the JBL VRX speakers, and the amps JBL recommended and then found out the PA+ really can't Auto EQ a room that easy and you still have to do it by ear.  Now I have an amp that I have to overlook a meter not working on one side.  I'm a bit disappointed.  sad.gif

Wonder if the XTi2's will have the same problem.

It is nice that you guys are here helping us with our issue though.

Thanks for replying Kevin.  smile.gif
Rick

#4 Kevin Heber

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Posted 24 February 2011 - 05:00 PM

There were a LOT of constraints we had to deal with when designing the input signal detector circuit.  A very simple RC 1st order low pass filter was implemented to minimize high frequency effects.  With such a slow roll-off, we had to move the corner way back; I donít remember where, but it is well below 20kHz.  

Also this filtered/clamped signal is fed into the micro where the internal ADC takes a 10-bit sample every 50us.  The firmware does quite a bit of filtering and processing on this signal to avoid noise and keep the led from flickering too much.  We had some problems early on with lots of HF noise on the 2k and 4k.  This forced us to overcompensate.  This is the biggest reason you see iffy performance with higher frequency signals.

We spent a lot of time tweaking the circuit and firmware so it would work for audio.  If you are using a sine wave,Ö. yeah it does not work as well.  But that was a tradeoff that was made.

Thanks for the feedback.  We always like to hear what users are saying good and bad.


#5 Rick Rideout

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Posted 25 February 2011 - 09:53 AM

Thanks for taking the time to explain some of the issues you get into designing an amp.  Not that I understand it all, its just nice to know there is a reason why channel 2 meter is not coming on.  This amp does have a lot of ( what I would call ) air noise coming from the tweeters when its just sitting there. (Even with no inputs connected to the amp) The VXR's have three tweeters per box and I think they really amplify this noise.  Its not a problem once you start playing music.

Thanks again.
Rick

#6 Rick Rideout

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Posted 06 March 2011 - 11:54 AM

Kevin,  FYI.  When I stopped using my PA+ for the tunings and crossovers the meters on the XTi's and band manager (input) now move together. Channel two is now working fine.  I guess its from doing the full band pass on the PA+.    smile.gif



#7 Kevin Heber

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Posted 07 March 2011 - 03:30 PM

Yep, thanks, that makes sense, since the XTi crossover comes after the signal presence LED in the signal path.