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New XTi 2000 amps


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#1 rickrock

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Posted 19 November 2006 - 05:51 PM

Is the 1% THD that is stated on all the data sheets significantly audible?  I'm pretty disappointed with what I've heard so far.  I'm bridging two xti 2000's into two new jbl srx 722 cabinets (2 x 12" and a horn in each).  I'm also biamping them, so in addition to the xti's into the 12's, I have a separate amp for each horn driver (two little d-75's).  I'm using a driverack pa model dsp, and I've programmed everything according to the jbl website on the PEQ and crossover.

The xti's just seem very noisy compared to what I used previously (a crest pro8200, I didn't want the crest because of its 30 amp plug and my concern that we'd blow breakers in the small venues we play, and I liked the low power draw shown in the specs for these Xti models).  Each of the the dual 12" cabinets is 4 ohms, so each of the bridged xti 2000's  is supposed to be putting out 2000 watts into those 4 ohms, but GEEZ, the noise floor is upsetting.  Is that what 1% THD sounds like?  I'm thinking of putting these amps on the subs and just using my ce4000 (which I was bridging mono into two connected single 18" subs) in  stereo on the mid speakers (giving me 1200w in stereo, just meeting the program power, but not really giving them the overpower I'd like with the 2000w I'd get from the xti's, but the ce4000 has only 0.5% THD).

But that's not why I bought them, I'm happy with the ce4000 as a sub amp, I wanted this to be a good mid amp.  Bottom line, I just want to cut down the noise in the more audible midrange speakers.  

Both new amps are right out of the box, and both have exactly the same noise issue, and both are born in November 2006.  Is there something I can do about t his other than get used to it?

#2 DGlass

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Posted 20 November 2006 - 03:38 PM

The 1% THD is the worst case you would measure/hear at the onset of clipping.

Is the Noise there with no input plugged in?

Are you running the amps wide open all the time?
If you are I would run the system hotter and turn the amp(s) up only as load as I need them.

It could also be that you are hearing the noise made by multiple A-D/D-A conversions. First you go into and out of the dpa one A-D/D-A conversion then into the amp and A-D/D-A in it's internal DSP.
Have you tried putting the speaker settings into the amp and not using the dpa?

#3 rickrock

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Posted 20 November 2006 - 08:52 PM

QUOTE(DGlass @ Nov 20 2006, 03:38 PM)
The 1% THD is the worst case you would measure/hear at the onset of clipping.

Is the Noise there with no input plugged in?

Are you running the amps wide open all the time?
If you are I would run the system hotter and turn the amp(s) up only as load as I need them.

It could also be that you are hearing the noise made by multiple A-D/D-A conversions. First you go into and out of the dpa one A-D/D-A conversion then into the amp and A-D/D-A in it's internal DSP.
Have you tried putting the speaker settings into the amp and not using the dpa?



Okay, maybe we're getting somewhere.  I will check to see if it's there without any input.  I have not field tested the system, this post is all based on first basement wire up and test--but I've run this system many times live but with a different mid amp (the 8200 referred to)

But the d/a to a/d etc. makes sense.  Here's the question.  The DSP in the Xti can be turned off, but then, how do you get the thing bridged?

#4 DGlass

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Posted 21 November 2006 - 10:45 AM

QUOTE(rickrock @ Nov 20 2006, 08:52 PM)
QUOTE(DGlass @ Nov 20 2006, 03:38 PM)
The 1% THD is the worst case you would measure/hear at the onset of clipping.

Is the Noise there with no input plugged in?

Are you running the amps wide open all the time?
If you are I would run the system hotter and turn the amp(s) up only as load as I need them.

It could also be that you are hearing the noise made by multiple A-D/D-A conversions. First you go into and out of the dpa one A-D/D-A conversion then into the amp and A-D/D-A in it's internal DSP.
Have you tried putting the speaker settings into the amp and not using the dpa?



Okay, maybe we're getting somewhere.  I will check to see if it's there without any input.  I have not field tested the system, this post is all based on first basement wire up and test--but I've run this system many times live but with a different mid amp (the 8200 referred to)

But the d/a to a/d etc. makes sense.  Here's the question.  The DSP in the Xti can be turned off, but then, how do you get the thing bridged?

The DSP cannot be shut off as it is an integrated part of the amplifier. You can turn on and off functions but the DSP is always in line. "DSP OFF" just means there are no DSP functions engaged.

#5 rickrock

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Posted 25 November 2006 - 05:43 PM

QUOTE(DGlass @ Nov 21 2006, 10:45 AM)
QUOTE(rickrock @ Nov 20 2006, 08:52 PM)
QUOTE(DGlass @ Nov 20 2006, 03:38 PM)
The 1% THD is the worst case you would measure/hear at the onset of clipping.

Is the Noise there with no input plugged in?

Are you running the amps wide open all the time?
If you are I would run the system hotter and turn the amp(s) up only as load as I need them.

It could also be that you are hearing the noise made by multiple A-D/D-A conversions. First you go into and out of the dpa one A-D/D-A conversion then into the amp and A-D/D-A in it's internal DSP.
Have you tried putting the speaker settings into the amp and not using the dpa?



Okay, maybe we're getting somewhere.  I will check to see if it's there without any input.  I have not field tested the system, this post is all based on first basement wire up and test--but I've run this system many times live but with a different mid amp (the 8200 referred to)

But the d/a to a/d etc. makes sense.  Here's the question.  The DSP in the Xti can be turned off, but then, how do you get the thing bridged?

The DSP cannot be shut off as it is an integrated part of the amplifier. You can turn on and off functions but the DSP is always in line. "DSP OFF" just means there are no DSP functions engaged.



I'm pretty sure my noise problem was a ground issue.  I've been able to get things working well now.

rickrock

#6 difflvl

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Posted 16 December 2006 - 06:53 PM

QUOTE(rickrock @ Nov 19 2006, 05:51 PM)
Is the 1% THD that is stated on all the data sheets significantly audible?  I'm pretty disappointed with what I've heard so far.  I'm bridging two xti 2000's into two new jbl srx 722 cabinets (2 x 12" and a horn in each).  I'm also biamping them, so in addition to the xti's into the 12's, I have a separate amp for each horn driver (two little d-75's).  I'm using a driverack pa model dsp, and I've programmed everything according to the jbl website on the PEQ and crossover.

The xti's just seem very noisy compared to what I used previously (a crest pro8200, I didn't want the crest because of its 30 amp plug and my concern that we'd blow breakers in the small venues we play, and I liked the low power draw shown in the specs for these Xti models).  Each of the the dual 12" cabinets is 4 ohms, so each of the bridged xti 2000's  is supposed to be putting out 2000 watts into those 4 ohms, but GEEZ, the noise floor is upsetting.  Is that what 1% THD sounds like?  I'm thinking of putting these amps on the subs and just using my ce4000 (which I was bridging mono into two connected single 18" subs) in  stereo on the mid speakers (giving me 1200w in stereo, just meeting the program power, but not really giving them the overpower I'd like with the 2000w I'd get from the xti's, but the ce4000 has only 0.5% THD).

But that's not why I bought them, I'm happy with the ce4000 as a sub amp, I wanted this to be a good mid amp.  Bottom line, I just want to cut down the noise in the more audible midrange speakers. 

Both new amps are right out of the box, and both have exactly the same noise issue, and both are born in November 2006.  Is there something I can do about t his other than get used to it?



I would assume when bridging into a 4ohm load, each channel is running 2ohms. Running in 2ohms is pretty tough on the amp, and doesn't sound that great. Its "okay" for a sub, but probably not for the mains. I could be wrong though, but having heard the difference between XTI1000 bridge, and XTI4000 no bridge, the XTI4000 with no bridge sounded a lot better.