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Crown XLS2502 Stereo Amplifier Review

LumbermanSVO

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Reminds me of the amp/speaker scene in 'Back to the Future'.. Just what speakers can use, and handle, this kind of power?

I have two of these amps, each bridged and powering a 24" subwoofer. They work well and the fans never turn on, even on really demanding movies.
 

DonH56

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Actually, I think you might be right. I've been checking on my cheap SPL meter. What I consider a loudish listening level, the readings will be averaging between 80-84 dB, with it rarely getting into the 90s. The problem is that this is A weighted, (so the unit should be dB(A)).

After looking into it, I've learned A weighting rolls off low frequencies.

I found an app for my iPad which will give measurements for instantaneous/peak measurements in both A and C weighting. C weighting is much closer to a flat frequency response, which I think is what is relevant for thinking about needed power for an amp.

The app A weighting measurement is spot on with my SPL meter...but when I have an average listening level of about 82 in A weighting, the A peaks won't get much above 90dB(A) but the C weighting goes well above 100dB(C) on peaks!

What's weird is that my amp (Kenwood KA-5500) has VU power level meters and at such a level they barely peak above 1 watt. VU meters are an averaging meter, but I find it hard to believe the amp is being driven in to clipping when these meters are down in the low part of their range. The meters have a low level setting, when put on the high level setting, which shows full scale up to 55 watts, the meters are barely moving.

Is it possible the amp is being "asked" to put out 200 watts on the peaks? (It's rated at 55 wpc). I'm not hearing any clipping. Perhaps the amp is doing some kind of "soft clipping?"

I'm listening on ADS L710, which have a given sensitivity of "92 db SPL at 1 watt RMS input at 1 meter." This seems roughly close to what I'm "ballpark" measuring.

It's a complicated subject. There is no exact specification for this concept, as it's dependent on the duration and shape of the measuring "window", the duration of the measurement, and the characteristics of the signal.

A simple approximation of "effective dynamic range" is the "crest factor"of a signal, which is the ratio of the peak level to the RMS average level.

This excellent article has an in depth discussion, and finds that the crest factor of most recordings is between 12-18 dB.

https://www.soundonsound.com/sound-advice/dynamic-range-loudness-war

The more relevant issue to this discussion is how we conceive of the "loudness" of a signal, which includes both average and peak levels, and how much demand our desired average listening puts upon our amplifier.

The AES number I remember is 17 dB, a factor of 50 in power, for peak to average power for music. Better recorders will be better, natch, whilst some pop may be much worse. YMMV.

An SPL meter or VU will not usually give true peak readings -- meter is too slow. The Vu meter does have a defined time response but I don't remember what it is, sorry. :( Try Google, or Wikipedia... As for weighting, use C if the meter has it. See e.g. https://en.wikipedia.org/wiki/A-weighting for a description of various weightings. Be aware C is still not low enough for subs unless you use a compensatory table (C rolls off below 30 Hz or so).

The crest factor of a signal is not for audiophiles the same as the peak to average range of something like music. Crest factor is defined for specific waveforms, eg. https://en.wikipedia.org/wiki/Crest_factor (though that article does not adequately cover the crest factor of typical noise sources used in testing), so does not necessarily correspond to a musical signal. Empirical results indicate 15~20 dB or so for music, and up to 30 dB for movies, IIRC (my memory of various research and posted results on various audio fora). I checked one of my old grad school acoustics texts but it didn't have anything at first glance (it was my theory book, not sure where the "practical" book is in my black hole of a filing system).

A discussion of loudness should include frequency weighting, since we need more power at HF and much, much more power at LF to reach the same perceived loudness as midband signals. See e.g. https://en.wikipedia.org/wiki/Equal-loudness_contour . At 80 dB, a fairly loud level, bass may require 10 to 1000 times the power as the midrange to sound as loud. One of the reasons subs can help (put the power where it is needed, and offload the need for the main amps and speakers to handle it).

A lot of times musical peaks occur and clip so rapidly we don't notice until they are gone. Different speakers or a different amp that alleviates clipping can lead to less fatiguing sound even if we did not hear overt clipping. At least, that has been my experience, and the experience of many friends over the years.

HTH - Don
 

b1daly

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The AES number I remember is 17 dB, a factor of 50 in power, for peak to average power for music. Better recorders will be better, natch, whilst some pop may be much worse. YMMV.

An SPL meter or VU will not usually give true peak readings -- meter is too slow. The Vu meter does have a defined time response but I don't remember what it is, sorry. :( Try Google, or Wikipedia... As for weighting, use C if the meter has it. See e.g. https://en.wikipedia.org/wiki/A-weighting for a description of various weightings. Be aware C is still not low enough for subs unless you use a compensatory table (C rolls off below 30 Hz or so).

The crest factor of a signal is not for audiophiles the same as the peak to average range of something like music. Crest factor is defined for specific waveforms, eg. https://en.wikipedia.org/wiki/Crest_factor (though that article does not adequately cover the crest factor of typical noise sources used in testing), so does not necessarily correspond to a musical signal. Empirical results indicate 15~20 dB or so for music, and up to 30 dB for movies, IIRC (my memory of various research and posted results on various audio fora). I checked one of my old grad school acoustics texts but it didn't have anything at first glance (it was my theory book, not sure where the "practical" book is in my black hole of a filing system).

A discussion of loudness should include frequency weighting, since we need more power at HF and much, much more power at LF to reach the same perceived loudness as midband signals. See e.g. https://en.wikipedia.org/wiki/Equal-loudness_contour . At 80 dB, a fairly loud level, bass may require 10 to 1000 times the power as the midrange to sound as loud. One of the reasons subs can help (put the power where it is needed, and offload the need for the main amps and speakers to handle it).

A lot of times musical peaks occur and clip so rapidly we don't notice until they are gone. Different speakers or a different amp that alleviates clipping can lead to less fatiguing sound even if we did not hear overt clipping. At least, that has been my experience, and the experience of many friends over the years.

HTH - Don

OK, this furthers my motivation to set up some kind level matched testing. Maybe I’ve been missing out on less distorted sound than I’ve thought.
Thanks for sharing your thoughts and experiences!
 

turbotuff

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Would love to see a test of an older Crown, specifically one of their Macro-tech series. AB design, dual mono, built like tanks.
IMG_20200508_030810.jpg

IMG_20200508_020326.jpg
 

anmpr1

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Would love to see a test of an older Crown, specifically one of their Macro-tech series. AB design, dual mono, built like tanks.
Lux LV-109 above the Crown? I'd like to see that tested.
 

anmpr1

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It is! Good eye.
The McIntosh dealer (now out of business) in the city I lived in also carried Luxman. I recall this unit on display-- likely made during the Alpine ownership years. CD was taking over, but Lux offered an optional stand-alone phono stage for this amp. It was a different look for Lux. They soon went back to their more traditional faceplates.

They also offered a couple of lower cost integrated amps of this same industrial look, but using a tube--I think it was a 6DJ8 preamp circuit. There can't be that many LV-109s out there. It was a pretty expensive item for the day. But that's Luxman for you.
 

turbotuff

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There can't be that many LV-109s out there. It was a pretty expensive item for the day. But that's Luxman for you.

I believe it was $1500 back in the mid-late 80s. And I haven't seen many others.
 

gattaca

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Yeah, that Crown Macro-Tech looks like it is built like a tank. You can practically see the electron flows from huge transformers to the 10,000 uf Philips caps. WOW. TY for sharing.
 

turbotuff

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Yeah, that Crown Macro-Tech looks like it is built like a tank. You can practically see the electron flows from huge transformers to the 10,000 uf Philips caps. WOW. TY for sharing.
And this is the smallest of the series! A measly 310wpc into 8 ohms. The Macro-tech 5000 series are 1300wpc!
 

Pepperjack

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So, I am just starting to seriously read about Amps today. How does one go about co
Park g something like this, or it’s smaller 330watt Brethren, to something like the AB 100-220watt (8-4hm) Niles Si2100 for LR? At the very basics of learning here...
 
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anmpr1

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They will not test well compared to latest tech. Amir's tests have debunked that myth.
If you are talking the DAC section of the Luxman you are no doubt correct. My guess is that the analog sections will test in the average range. Which would not be bad for a 35 year old product. FWIW, Len Feldman (Audio 9/87) obtained these measurement:

171 watts at 1KHz (8ohm) with 0.03% THD.
156 watts at 20 Hz
159 watts at 20KHz.

240 watts (4ohms) 0.007% THD.

THD/Noise is graphed, but my scan is not totally legible. Performance here however appears to be good into both 8 and 4 ohm capacitive and inductive loads.

Downside? FR was volume control dependent. -1dB @ 26KHz unless it was set on full gain.
 

Champster

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Great review! I used a pair of Crown DCI 1250n amps. How does the circuitry and testing compare to this Crown amp? I would imagine, they are test pretty similarly but I’d love to hear the OPs thoughts.
Thanks
Paul
 

Head_Unit

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Damping factor...all you are doing is specifying the Thevenian equivalent source - which is identical to simply adding a very small additional series resistance to the circuit. Given you already have 8 ohms in that circuit, the additional tiny resistance is essentially meaningless.
That's true in the resistance world, but then again speakers are not resistors at all. Neither are amp guts...so the Thevenian should be complex? (I'm a loudspeaker engineer and only worked with amp engineers, didn't design myself, so that's just my feeling).

In the case of amps, we kind of use low impedance power output increase as a vague proxy for how strong the amp will be into actual speakers, due to lack of more comprehensive data. Maybe in a similar way damping factor vaguely correlates to actual amplifier control over the moving transducer's time-variant impedance? All these measurements are steady state but music is not; perhaps we need to move into an area of transient testing! And maybe someone can come up with a lower cost PowerCube type device...hello Parts Express, are you listening?
 

Francis Vaughan

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That's true in the resistance world, but then again speakers are not resistors at all. Neither are amp guts...so the Thevenian should be complex? (I'm a loudspeaker engineer and only worked with amp engineers, didn't design myself, so that's just my feeling).

Sort of. A negative feedback amplifier, which is so much the vast majority of amplifiers we may as well take it as read, simply acts to reduce the intrinsic impedance of the output stage by the feedback factor. You can look at the output stage - which is basically the output devices and any series resistors - used for power sharing and degeneration - and get an output impedance. It is going to be so close to pure resitiive that you will be hard pressed to find any reactance at audio frequencies. Divide by the feedback factor. Now feedback reduces as frequency rises, this is a mix of the nature of the output devices, and requirements for amplifier stability. This is simply because the amplifier gain is designed to drop with frequency. But this drop is very slow, and doesn't impact on things in the audio band. The upshot is still that within the audio band, for all useful purposes, a conventional amplifier is a pure resistance, with almost no complex component. The addition of an output inductor to help avoid instabilities into capacitive loads adds a tiny bit of reactance, but compared to what one sees in loudspeakers, it can be ignored.

As a speaker designer you can and should design with the assumption of as near perfect voltage source as you desire.

There are times when this isn't a sensible assumption. If you design speakers for tube guitar amplifiers you will see wild variations in output impedances. So much so that you can't reason usefully about response without taking the amplifier and speaker driver as a single unit. (Hint, that output impedance setting on the back of an amplifier is almost certainly not indicating anything to do with the amplifer's output impedance. You can see 10:1 variations in output impedance trivally. Some amplifiers have output impedances of about 30 Ohms. So damping factors can be well under one. Others open the feedback loop entirely when overdriven, and the output impedance will change acording to the input signal.)

Ultra silly high end audiophile amplifiers have similar issues. SET (singe ended triode) with no feedback, amplifiers have been a darling ofcertain parts of the fraternity. You will see very significant output impedances here. Even then, largely resistive. You see the plate impedance reflected through the transformer. There will be some parasitic reactance, due to such things as inter-winding capacitance and leakage inductance. These would normally be reduced by the use of feedback. So designing for the lunatic fringe will get you into amplifiers where output reactance matters. But for the rest of us, it really doesn't.
 

Tips

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amirm, you gotta try LabGruppen IPD1200 (or 2400).
In Europe they are known to demolish high-end amps for mega bucks!

Just two things when using it:
-it has to be fed signal via AES/EBU (and not analog XLRs) and it has to be 'true' AES/EBU and not 'fake one' (desymetrized optical - which some companies do). So it has to be steady 110Ω and below 3.0V or else IPD will clip
-one has to VERY careful when first setting up IPD and its settings on the computer (for example it is easy to fk this up and use IPD in mono mode).

Also, Monacor's STA-2000D has outstanding Pascal modules (STA-2000D) which are said to be the most musical Class D modules - even better than Hypex. It also has 4 channels so one could use it for bi-amping which brings amazing results and much better than bi-wiring.

Any chances on reviewing and measuring these please amirm?

ps. someone told me that this Macrotech line was the best Crown. I wonder how Macrotech would compare to current XLS line tested here. I also know from an owner of Macrotech that the fans on it are pretty loud unfortunately.
 
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