Measuring Amplifiers - Page 13

The CE4000 seems to have a solid reputation here, but it's now discontinued. Is the XTi 4000 the next closest thing? Does it live up to the performance and reliability standard set by the CE4000? And what's up with the 0.5% and 1% THD ratings?? Is Crown just being "honest" or do people in that market segment just not care so much about lower THD?

If anyone is wondering, I would be using one of these amps to drive two 4 ohm subs.

The XTi series from what I am told is nowhere near a CE4000. If I recall, the only current Crown amp that has all of the sub friendly features is the I-Tech series which are very expensive. But, of course the CE probably was $2500 when new as well.

Apparently we just don't know all that much about the XTi 4000 yet. Thylantyr said something about it being a Class AB+B design with a tracking power supply which COULD be really cool, but nothing has really been tested or verified. Hopefully he or someone else with more knowledge and/or experience on the subject will chime in here before I do something stupid (like ordering another amp).

Read this thread: http://www.crownaudio.com/forums/ind...showtopic=2088

Thanks for the link. Can't say I'm terribly impressed with the final response from the Crown rep. He did a bit of dancing before coming back with the "FTC = 1 db down from EIA" answer and the following table of extrapolated calculations. I don't know about you, but that didn't give me the warm and fuzzies at all. Who knows what the amp would REALLY do at 20 Hz into two channels at 4 ohms. Obviously the only way to find out is to buy one and test it yourself.

So, uh... anybody got a nice used CE-4000 for sale?

Bingo.

For instance, here are the Crown K2 specs: http://www.gigantsound.com.pl/crown_k2.pdf

And what it did on Chucks bench:

http://i21.photobucket.com/albums/b2...ohm-091707.jpg

It pretty much matches the 20% difference the Crown rep stated between EIA and FTC 20Hz-20kHz specs.

Not saying the XTi 4000 is good/bad/ugly or otherwise, but the way they rate the power just does not inspire confidence. They only rate it at 1 kHz and your choice of either 1% or 0.5% THD.

Compare that to almost anything QSC sells. As you know, I've been looking at the PLX1804: 800W FTC 20 Hz - 20 kHz 0.05% THD, 900W EIA 1 kHz 0.1% THD. On top of that, the owners manual states 2 dB of headroom! I also have a RMX 2450 sitting here which is FTC and EIA rated at 0.1% THD (into 4 ohms per channel).

OK, sorry... I'll stop ranting now.

And I am not defending the XTi-4000. I'd much rather have a CE4000 myself.


The Behringer 2500 is spec'd the same way your 2450 is, but that doesn't mean it performs as well: http://www.behringer.com/ep2500/specs.cfm?lang=eng

But the specs to me are simply a guide of sorts. What is under the hood and how it does on a bench matters a lot more I think.

Lets look at the QSC PLX 1602:
4 ohms (20 Hz-20 kHz 0.05% THD) - 500W

But during Bink's amp test, it only put out 357W at 20Hz (Shootout results: Both channels working, channel A highest clean level or level just prior to 1% THD+N, 117vac supply). It couldn't even put out the rated power at 20Hz @ 1% THD!

Or another QSC, the MX3000a: http://www.qscaudio.com/products/amps/mx/mx.htm

1200W - 20 Hz - 20 kHz, 0.1% THD, both channels driven

Yet again, during Bink's amp test, at 20Hz it only put out 1059W @ 20Hz (Shootout results: Both channels working, channel A highest clean level or level just prior to 1% THD+N, 117vac supply).

I just got back from Las Vegas. I saw one of the backstage setups of a major performer, 8 XTi 4000s and 6 ITech 8000s. And those amps FILLED the show room with more volume than I could stand.
I have one XTi 4000 for sub duty. I haven't measured the output but do know it'll blow up a 400 watt rated sub including the voice coil in 2-3 seconds.
The XTi 4000 is more amp than I need for my 2500 watt rated sub for HT use in a 7000 cubic foot listening environment.
I believe the 1200 watts @ 4 ohm figure is close to accurate for sub use 20Hz to 120Hz.

Thats impressive, I love seeing the gear from bands and stadiums. They were tearing out all of the amps from a local stadium a while back, they had an all Crest Pro setup, 4 Crest Pro 10k's and 16 CP 7200's. I heard they were replacing them with an all PL setup, PL380's to replace the 10k's and 360's to replace the 7200's.

Let's be honest, you are looking to load your listening area with high levels of volume, possibly for HT or your own brand of music. Can you tell me that at 115 db, or even at 100 db you're going to be able to discern whether the amp has .08 THD or 1.0 THD? I think THD statistics are a left over marketing tool from the "Hi-Fi" days when high watt amps were first being designed.
I think for our purposes (driving subs) with enough power (1000 watts) for home use we are willing, or should be, to sacrifice a little bit of distortion (1%) to get that power. We need that power to push the driver's cone 38mm to produce the 10Hz -120Hz @ 110db to 115db or even 125db . . . . . right!!??
What CROWN should do or all amp makers should do is give THD figures at max output AND another THD figure while running at real listening levels like maybe a 90db or 95db or whatever level gets you the amps minimum distortion short of being turned off.
I have my own issues with Crown but it has nothing to do with the performance of their products. Some of their staff seem to believe that none of their products might need or could be improved or modified for the end user's benefit.
For one, their amplifier instruction manual is minimal, "sucks". It looks nice and feels good in your hands but doesn't cover the operation of the (onboard) controls very well and doesn't even come close to covering the setup and use of the DSP and PEQ. The manual comes in 4 languages and each page of the manual has those minimal instructions in each of the 4 languages. The layout is aggravating and confusing. The manual is FAR from complete. As you read from the CROWN forum, some of their answers to questions were unsatisfactory or incomplete. In fact now that I've said that, I realize I got more information about using the CROWN amp from their forum than I did from reading the manual and it was from the users not the staff. Maybe the first page of the manual should state, " Please see our website and read the Forum threads."
The variable speed fan has never turned on during "normal" operation. The fan has turned on when I was running low frequency sweeps at high levels during room setup. After the high level operation was completed the fan slowed and stopped in about two minutes or less.
The amp case does produce some discernable warmth at idle, and gets somewhat warmer during heavy use but I wouldn't ever call it "HOT" even when the fan came on.
When the amp is running and you've got the low end of the response curve adjusted and boosted and when subsonics are present in the material you're listening to, there is nothing better than a CROWN whether it be an XTi 4000 or an I Tech 8000.

Class AB + tracking power supply is a sweet design,
but the question to ask is.... how well did the manufacturer
execute the design? Every design will be different. We need tested data on the XTI4000
to get an idea on performance, I haven't seen any. I know one guy on the forum tried one
and sold it as it seemed anemic in power to him and he replaced it with RMX4050 or maybe it was
a 5050, I forgot which one. I haven't seen *anyone ever* say they got rid of their CE4000 because
it felt weak........ // lol //

I know one thing, the class AB + tracking power supply
found in the Lab Gruppen amps {they call this class T}
didn't do well in Binks proamp test in spite that the FP6400
has a street price of >$4000. But keep in mind, the Binks
test is a 'rms test method' that tortures amplifiers, probably
the only application that can mimick the rms test method is
if you drive monsters subs at high power playing test tones,
otherwise playing music won't be as stressful on the amps,
thus don't freak out too much if the amp didn't do as well
on the stress test. For mids/tweeters, worry less.


http://home.pacbell.net/lordpk/bink/bink.jpg
Lab Gruppen FP6400
Rated; 2200w/ch @ 4 ohms 20hz - 20khz

RMS Test Method results;
1327w @ 20hz @ 117VAC
1010w @ 20hz @ 96VAC


Compare;

CE4000 @ $600 - $800 used = 967w @ 20hz @ 96VAC

If you bought a LAB for >$4000, under AC line sag conditions,
the Lab will only do 43 watts more than CE4000. /// hehehe ///

I have been telling people here about CE4000 in 'secret'
last year but over time, the cat gets out of the bag.... because you don't want to start a 'ebay bidding war' that drives the price higher.

Crest 8002 is another intersting amp if you can find it used. Look at the scores on the Binks test. It does about
what a QSC PL6.0 II does, but if you did find one, I don't
know if the price will be discounted.

To name a few, the amps that really stand out for monster sub duty are the PFC
amps {CE4000, 8002, PL6.0 PFC [not PL6.0 II], PL9.0 PFC}, the tested scores are sweet and none of these amps
are class AB+tracking supply, each uses an interesting
topology. CE4000 is BCA {akin to class D}, the QSC PL6/9
IIRC, are H-Bridge output stage {not to be confused with
class H}. If you are thrillseeker, these are the power house
amps to score on the used market.

As always, thanks for your insight Thy!

One of the selling points for Crown XTI is -> Integrated proprietary DSP with LCD front panel display

http://www.crownaudio.com/amp_htm/xti.htm

This feature alone is worth it for some people as they don't
want external signal processors and they may not require
the highest possible power for their design so this amp makes
sense. On other hand, you may have someone that is 'hardcore'
who would rather have external processors and keep the amplifiers
simple.

XTI4000 guessing game

If someone were to do an 'RMS test method', like Binks method,
96 VAC input, 20hz, 1% THD, but test the XTI @ 4 ohms bridged,
what power output do you think the amp will do ?

Rated: 3200w

My guess -> 1920w

I completely understand what you are saying and I don't disagree with you. I would point out that the EP2500, by all accounts, is a blatent rip-off of the RMX 2450 and it's been said the power supply section may not be as good. Would be nice to see a side-by-side test done on them. Maybe I should send my 2450 to Chuck. Actually... might be easier and fun to test it myself.

My point was just that the lack of detailed specs makes you wonder if the manufacturer doesn't have something to hide, or otherwise doesn't inspire confidence. Of course when you put the amp to the (torture) test, it may likely not meet rated specs largely because that type of continuous sine wave stress test isn't how manufacturers test and rate their amps.


I did notice that and found it rather disturbing! Of course many of the amps suffered at 20 Hz but the PLX1602 seemed to do especially bad. So I wonder what the PLX1804 is capable of.

Of course not. That wasn't my point. 1% THD isn't the end of the world but it's not particularly impressive either. I also understand any amp will hit 1% THD or more if you push it hard enough.

October 2007

The difference between XTi and iTech. WOW!
http://srforums.prosoundweb.com/inde...g/27280/0/0/0/

Hey there everybody. This post is more like a "what the hell was I thinking" kinda post.

I just purchased a new VRX/SRX rig this summer. 8 VRX932LAs and 4 SRX728s. So I've done a couple gigs with this system and I could never get type of low end I was looking for.

I have been running 4 bridged XTi4000s for the subs. One on each cabinet. I figured, man, 3200 watts into a 4ohm cab and these thing should shake your teeth loose! Well, this was not the case. Every time I set the rig up, the low end was loose and flubby and I could never get a solid 40-60 Hz out of the cabinet. And 70-80Hz was just ugly sounding!

OK fast forward to yesterday...The crown rep went way out of his way to hook me up with two iTech 8000s. I plugged those babies up to the subs and they came alive!!! I mean, it was violent when I turned it up. In a good way. The low end was focused, clean and the amp recovered way better than the XTi 4000s. I had the whole rig set up in a 15,000 Sq. Ft. performance hall, empty, and it sounded great!

So I guess my question is, WHY!!! I understand the iTech is pushing out 800 more watts and has a better damping factor among other things, but the performance difference was insane. The rep told me initially that I should get the iTech stuff, but of course, I had no idea it would make that much difference.

So, I guess that leads me to a couple questions.

1) Are there still problems with the iTech amps that they had in the past?

2) Is there another alternative out there that doesn't cost an arm, leg and first born child?

Oh yeah, I will be selling the 4 XTi 4000s if anybody is interested.

Thanks for listening.
Marty





... snip ...

Can't answer your question but your post gives me hope. Been using a bridged XTI4000 on a pair of SRX718S's and have experienced the same issues you have. Got an ITech 4000 coming so hopefully I will see the same results as you.

.... snip

I have 10 Itechs. 4x 4000's and 6x 8000's. I have had no issues with them. Mine are all pretty new except for one of the 4000's. I have been pretty happy with them. They do cost quite a bit more than the XTi's, but you obviously saw the difference. Another possibility to look into is the Lab Gruppens. I have a 10000Q, it's pretty awesome on my 728's.

******************************

ITech series is expensive and the only way you can get
ITech for cheap is to buy the CE4000 as the 'power plant'
have something in common.

If it would do an honest 1000 watts (or so) per channel into 4 ohms at 20 Hz, I'd be happy with it. I wonder how efficient the power supply and output stage is. Would be nice to have an amp that draws fewer amps from the A/C outlet and doesn't get very hot under normal/moderate use.

[b]PLX vs. PLX2[b]

Bob @ QSC said in public that the new PLX2 series is really just a
chassis change and a bi-amp circuit added, plus relocation of
switches?, IIRC. In other words, PLX2's power lant will be 99%
identical to the PLX series, therefore, unbeknownst to many, they
will be selling their old PLX to get the new PLX2 just because it's
new.

The folks who don't need a biamp crossover can score better deals
now on used PLX vs. buying new PLX2. PLX/PLX2 is a nice amp,
I have many PLX3402's for non-sub applications as they are
limited in power and as you have to read the published power
specs very closely.

For example; PLX3402
http://www.qscaudio.com/products/amps/plx/plx.htm

It's easy to take a quick peek as say it does 3400w @ 4 ohms bridged, and assume you are driving your sub with 3400w.
But that isn't the case, in spite that it may be working awesome,
you are not realizing these high power numbers.

If you look closely, those high power numbers are based on a 1khz
test. For subwoofer applications, look at the 20hz - 20khz spec, in
this case it only shows 2200W @ 8 ohms bridged.

Right now, stop and think......... This power spec is based on
a solid 120VAC input which may be hard to hold if you stress
the amp. If the voltage drops, you will start to get alot less power,
this is how all 'non power regulated' amps work. That 2200w
rating can be easily 1300w if your home electrical system is weak.
If you connect a 4 ohm woofer, expect 2000w as I have tested this
myself as being it's limit under stress. Is 2kw bad? not really, not
if you can score one of these amps for under $700. CE4000 is still
a better amp for sub than PLX.

My guess is 1920w @ 4 ohms bridged.

That would be;

960w/ch @ 2 ohms per channel stereo
480w/ch @ 4 ohms per channel stereo

But that is if you did a 96 VAC stress test. It will do more
if the AC line is solid @ 120VAC, and it will do more if
you did a 'burst' test, all amps do alot more with simple
burst tests, it's a piece of cake vs. sine wave testing. hehe

Burst test = drinking margaritas on the beach watching
females in bikinis

RMS test method = slave labor working the mines 24/7

The efficiency really doesn't matter as you are interested in what the tested power is right?
In other words, if you bought a bunch of Pass Labs X1000 class A amps and placed them in
parallel and tested 20kw, then you know you have 20kw. Then, you can ask about efficiency
as you may be drawing 100kw from the AC line to get 20kw to your sub array - hehehehe

Would be nice to have an amp that draws fewer amps from the A/C outlet and doesn't get very hot under normal/moderate use.

If you play music, normal to moderate use, non-subwoofer use,
even the old Crown XLS series can do the job you desire. The
Crown XLS version A-C are pretty anemic in heatsinking, yet
there are too many happy customers who use them in ordinary
HT use.

XLS 402A [where is the heatsinks? hehehe]
http://home.pacbell.net/lordpk/proam...n_XLS-402A.jpg

I wouldn't use them for monster sub use. XLS version D improved,
bigger transformer, better heatsinking, now this series should
compete better with QSC RMX or Behringer EP series.
http://home.pacbell.net/lordpk/proam...n_XLS-402D.jpg

If you want to draw less AC power for the same output watts,
then upgrading from a conventional power supply design to
SMPS design can help as it's more efficient. You'd uprade from
Crown XLS to Crown XTI [or greater], or upgrade from QSC RMX to QSC PLX/PLX2 [or greater].

If you want more efficiency, then you can look at the output stage
design. Class A is not very efficient, class AB is normal for home
audio amps, but for high powered proamps, class H is the normal,
some are two tier, some are three tier. Then you have the class D
type of designs, Crown's BCA and QSC has a new monster amp
that is class D. QSC has those unique H-bridged designs, IMO,
H-bridge is the best output stage for bass if you want gobs of
power . The class AB+tracking supply ranks high on efficiency
and you didn't see many designs using this method. IIRC, Bob
Carver took the concept, added a twist, got a patent, then made
his Sunfire home amps using this methodology. This methodology
is actually great from a business point of view as you can get
good power numbers with less real estate and lame heatsinking,
I saw some Sunfire pics of Bob's first generation Sunfire amps
and the power transistors were mounted on the chassis as the
chassis was the only heatsink. hehehe

Exactly which QSC models are those?

QSC PL6.0 II
QSC PL6.0 PFC [discontinued]
QSC PL9.0 PFC [discontinued]

There may be more models, but the PFC ones are the famous
amps, in a good and bad way. lol ... I don't recall if they did H-bridge on lesser power models.
Look at Binks tests on the 6.0/9.0 PFC ... sweet..

Cool. Thanks for all the info, thy. Reading this entire thread has helped a LOT.

Nice. What design/class is the output stage? Consuming "only" 3000 watts of power while putting some 2400 watts total into the load is about 80% efficiency, isn't it? That seems too good to be true, so perhaps I'm missing something.

I know Willd was looking at the XS1200 as an alternative, so I guess that amp could only be even better.

Doesn't sound like a bad deal really. The 1200 can be had new for $599, so used should be a real steal.

Thanks to WillD for the use of his new XS900 and thanks again Chas for your excellent equipment setup and testing. This amp shows some power, quality distortion figures, excellent S/N ratio, and frequency response, but like some others the power figures fall short of manufacturer's specifications and claims when using these stringent tests. We are left to decide for ourselves whether or not the amps perform as advertised.