QSC PLX v. Crest Audio CA Series

[metron]

Ha! You think so now, but wait til you actually start trying to move that SVT from point A to point B. A 50lb CA9 feels light by comparison. I know, I used to own one...and it's amazing how fast your bandmates seem to vanish when it's time to move the SVT.

a 50 lb power amp in addition to my 20 lb preamp closes part of the weight gap. either way bandmates definitely disappear!

 

[alexclaber]

Just popping up to say that my PLX 3002 puts out significantly more bottom when near clipping than my Mackie M1400 did. Not a fair comparison but it's nice to save 25lbs haulage and add some extra fatness (and loudness).

Maybe the CA-9 and others sound a bit better at the limit (but I won't believe it totally until I hear some blind tested results because the brain does weird things) but the weight difference makes the argument irrelevant for me. JMHO.

Alex

 

[Eric Moesle]

My BACK loves the sound of my PLX 3002, and frankly if THAT amp doesn't have enough headroom for a bass rig, you need a different profession before you go deaf.

I haven't personally played through the CA-9, but I've played through many others and really didn't notice any difference.

I lug my rack around several times a week, and my rig (though large and loud) is still just for stage volume and we rent big PA's to handle the front. Frankly, I can't see giving up the lightweight and reliability of my PLX for anything, even if it might sound marginally better.

 

[geshel]

I think it's time to put this whole arguement to rest. There is a huge difference between a switching supply amp and a properly designed conventional power supply amp as far a low frequency reproduction is concerned. That difference is in the ability to deliver instantanaus and sustainable current to the load (i.e. speaker). It is not a gain issue as one certain individual likes to continually mislead you on, nor is it a matter of blind vs. double blind vs. "totally blind" listening tests. In fact one would have to be completly deaf not to hear the difference between the two. Conventional amps, with their larger cored transformers and longer windings act as a current resovoir. Speakers are very low impedence devices and needs lots of current. That is where the switching amps "fall" on their faces, as they do not have the reserve current (also know as dynamic headroom) to "finish" off the note. It's not a volume issue, it's a quality issue. You can hear the difference in the quality of the bass. You get a fuller, weightier, warmer ,"girthier" bass which projects into the room. It doesn't sound thin, anemic, and fall off 3ft in front of the speaker. The fact is, amps such as the Crest CA series, Crown micro/macro tech amps, and even the now discontinued QSC MX series of amps can "eat" the lunch of every switching power supply amp as far a low end performance goes, every day of the week and twice on Sundays! It's not even subtle! I can understand the quest for lighter gear. Just understand the trade off. Less performance for less weight. There are no free lunches here. One has to balance the trade-offs (performance vs. weight) and determine which is the best option for them. Just as a side note, I talked to an industry "insider" recently on this very subject and their take is that it would be upwards of about 10 years before the technology advances to a point where the lighter weight amps will be able to achieve the same low end perfomance as their conventional power supply amp counterparts!

Jim Bergantino
Bergantino Audio Systems

Jim, I for one wouldn't mind hearing your technical rationale behind these assertions. Stating the results that you've subjetively heard is fine, but I know that the fact that you are Jim Bergantino will give the impression to people here that there is some actual engineering knowledge behind these statements. So it would be good to be clear about it (either way).

Bob Lee, and others, have gone into technical detail on numerous occasions as to why some of the reasons given why switching power supplies have the problems you describe are misunderstandings.

For instance, some of the assertions you make baffle me: "It doesn't ... fall off 3ft in front of the speaker. " How exactly do you suppose the supposedly inadequate current capabilities of a switching power amp would affect the acoustic dispersion qualities of the loudspeaker?

The other thing I don't understand -- if there is any difference in the output between two amplifiers, it can be measured. To a very high degree of accuracy. One of the amps is reproducing the input more faithfully. As Bob has pointed out numerous times, if the manufacturers' specs are to be trusted then any difference values listed for THD do not adequately describe the sound differences attributed by people like you.

 

[Folmeister]

Well, I did it. I got the DB750. Again, Bob - your PLXs work great in my PA and will never be replaced. Jim - your NV 425 is now my main cab and it is awesome! Tonight is the real test, and I can't wait. And, yes, Jim, when I need to run more than one cab, I will get a Crest! Thanks again Juan, you are a GREAT person to deal with. Dave B., you get kudos too, you know! And, I'll miss you most, Scarecrow!

 

[Bob Lee (QSC)]

It's not a dispersion issue, it's a projection issue. It is my finding that these switching amps are running out of current prematurely and not sustaining the note. This IMO causes the sound of the low end to fall of much sooner (i.e. closer to the cabinet), and lose the low end weight and girth of the bass, then a well engineered conventional amp such as the ones I mentioned earlier. Let me state here once again that I have no issues with the technology itself. In theory it should work as good, and actually even better than the conventionally designed ones. In fact the switching technology itself goes back as far as the 1930's from what I understand. It's just that it really hasn't been until rather recently that other technologies have caught up to help implement it. I believe at some point all powered devices, not just amplifiers will be "switching" to this technology. But as it stands right now, from the ones commericially available and reasonably affordable, it is my opinion, based on actual experience, that they are just not "there" yet in terms of low frequency performance. As for manufacturer's specs, they just don't tell the whole story. If it works for you, that's all that matters. I stand by my opinions of the technology as it stands today, although I understand Crown has a series of amps (the I-Tech series) that supposidly crosses this "barrier". The cheapest one "only" lists for $5000!

The whole point of my discussion is that I want players like yourself to make informed decisions. Not based on hype or misleading information and certainly not by a manufacturer's employee who continually taunts TBers who find other amps to outperforms theirs. He can quote all the tech specs he wants, but the only "spec" that counts is how it perfoms in a real world, live gigging environment. You can't explain away with specs and theories what a person hears. Ultimately all players will choose their gear based on tone, performance, price, portabilty, weight, etc. Some of you will be fortunate enough to find gear that suites all your needs without trading off one aspect for another. Others may have to make some tradeoffs based on what's most important to you. It's really that simple.

Jim Bergantino
Bergantino Audio Systems

So what you're saying, Jim, is that the amps are clipping prematurely after a short time? Why would the frequency of the audio signal affect it?

I'm sorry that maybe you see my repeated point that listening comparisons must be done at least somewhat fairly, at equal gains and therefore equal volumes, as "taunting." Oh well. Then again, the person you cite relies solely on tech specs, so that's not me.

In ~25 years in pro audio I've probably heard conflicting things almost any possible combination of competing products--"A sounds night and day better than B" and also "B blows A away." Maybe one's right, maybe the other, and maybe both are right depending on the situation, and maybe neither is. Thus I've learned not to put too much stock in casual comparisons, and informed buyers, or at least those who wish to be informed, shouldn't either.

The problem is that the vast majority of listening comparisons aren't done with both devices put on equal footing. If I see a Lexus drive by and then a Mercedes, would I be silly to conclude that the Lexus is faster than the Mercedes? I might well be; the cars might not even be racing; and the cars might not have started at the same time from the same starting point. But for some reason the same lack of control is okay for listening, right? I'd love to hear of some listening comparisons where people have taken the time to set them up properly, but they're few and very, very far between, and believe me, I've read the posts in this thread carefully to find such details but none have shown up. That's why when I read someone's conclusion based on a faulty test, I'll point it out. And in doing so I have defended brands other than QSC, too.

 

[tombowlus]

Just curious, Bob, but without a means of measuring the signal being sent to the output stage of an amp (for as cited above, there seems to be some difference in the input sensitivity among various amps), how do you propose that we, the end users, make a "proper" comparison, and ensure that all of our gain settings are "equal?" I can send the exact same signal into each amp, but because of the differences in input sensitivity (which I don't know is the correct term, but it's how I am thinking of it, so please bear with me for now, and correct me as need be), in some ways this is not an "equal" comparison. I can set my gain stages such that the perceived volume on each amp is the same, but that "test" might be "unfair" if one amp is (properly) rated higher than the other.

I have tried listening to amps at a variety of levels, with a variety of gain stage settings. I have intentionally listened with one amp louder than the other, then reversed my volume settings and repeated. I have used mulitiple different instruments, preamps, and cabs with the amps in question. My thoughts were to avoid falling into the pitfall of preferring whichever amp was louder. But you tell me that this is flawed, too. I'm not really sure exactly why my approach is flawed, but I would welcome any suggestions on how to make a more thorough comparison.

I do concede, of course, that as I have been doing all of these tests on my own, I am certainly aware of which amp is playing at a given time, so in theory the placebo effect would apply. But again, I have no preference for any given amp. I own all three (QSC, Stewart, and Crest), I plan on keeping them all, and I am endorsed by none of the companies involved (nor will someone of my meager playing abilities ever be endorsed! ). So yes, I'm not even doing single blind tests, but I would like any instruction that you could give as to how I could make the most relevant comparison between various power amps.

The only two ways that I can think of to determine if I have equal gain settings is to either measure the SPLs coming out of the speaker (but as mentioned, this is not inherently equal if the amps are not rated identically as to power output), or to find some way to test (and equalize) the level of the signal coming out of the amp's intial gain stage, but before the amp's output stage. Is there another, better way that I am not thinking about?

If you could give me detailed recommendations that I can pull off on my own, I would be happy to do my best to implement them. If possible, I will try to get someone else to come over and swap amps for me (should I make them were a blindfold, too, so that we're double blind? ), but I guess first off, I'd like to know how to improve my methodology.

Thanks, Tom.

 

[BassJunkie730]

So after reading this whole thread, I've become intrigued. What are my "conventional" amp options out there, that come with speakon outs? Are there any that are comparable to the Crest CA series - or am I just going to have to deal with binding posts and silly banana plugs. And furthermore - why doesn't a company like crest offer speakons in the CA series in the North American market?
Right now I have a PLX1602, but I'm wondering if it's the right choice for my "BALLS OUT" rock band. I want girth, but if I can get that from a cab and my p-bass (I'd rather not change my U5 out). then I'll keep the PLX.

 

[emjazz]

Bob, if I may, what's your position at QSC?

 

[the dude]

So after reading this whole thread, I've become intrigued. What are my "conventional" amp options out there, that come with speakon outs? Are there any that are comparable to the Crest CA series - or am I just going to have to deal with binding posts and silly banana plugs. And furthermore - why doesn't a company like crest offer speakons in the CA series in the North American market?
Right now I have a PLX1602, but I'm wondering if it's the right choice for my "BALLS OUT" rock band. I want girth, but if I can get that from a cab and my p-bass (I'd rather not change my U5 out). then I'll keep the PLX.

If I were you, for the kind of music your play (same as me) I would definitely check out a CA9. I definitely hear a difference (and I belive Arthur Poon and Tombowlus will tell you the same.)

 

[PB+J]

I'd just lilke to thank Bob lee and jim Bergantino, especially Bob, whoise presence here has always been extremely valueable.

I have to say I think he's right that tests need to be undertaken with care. I can hear what my wife thinks are non-existant differences--the differences between brands of preamp tubes, for example. at least, I believe I can hear them. I've also noticed that an amp setup that sounds good to me at ten am may sound terribleto me at 4 pm. My ears are highly variable with my mood

As to the bigger an heavier is better argument--it seems kind of like tube vs solid state. The two technnologiues are different and are good at different things, things that matter. I'd love to play through an SVT, but I'm not going to haul one around

I have a stewart world 600 and as QSC PlX 1202. The Stewart sounds slightly warmer, softer, and beefier to me, and I think I prefer it. But the stewart craps out all the time if it's bridged. The QSC, on the other hand, is a total workhorse and has never givien me the slightest problem. And I'm not even sure the difference I think I hear is there--my wife thinks the difference is purely imaginary, shrugs her shoulders, mutters about obsession, and walks away

 

[44me]

As a circuit designer, if there’s one thing I’d like to get across, it’s to not draw conclusions about amplifiers prematurely based technology. Sure, tube designs have less damping and tend to have more harmonic content, but the differences between various SS approaches are technically much more subtle. The mature technology always has the leg-up. In the short term, advanced technology rarely trumps evolutionary refinement in all areas. We’re arguing whether switching supplied amps have a slight sonic disadvantage watt for watt. It would be interesting to see how things looked if it were pound for pound. In the end most of us have to choose based on a variety of factors (tone, volume capability, frequency range, size, weight, and cost). The best way to make that bottom sound like thunder is to get a well designed 18” cab(s) to take care of the lowest octave or two, but wants to lug all that around? Cabs are going to effect your sound much more than subtleties between well designed amps.

- John

 

[Bob Lee (QSC)]

Bob, I think it should be very clear where we both stand on this issue. It's time to put it to rest. You can continue to believe it's a gain/equal footing scenario, and I will continue to believe that for low end performance, a well designed conventional amp will outperform most if not all switching amps currently available today. This added performance may not be important to some due to the added weight, or for others, it may not even be noticable. But for me and everyone I've turned on to the other amps, it has been quite obvious. You can continue to support and use QSC amps, which BTW, up throught the MX series I was always a fan of and user of, and I will continue to recommend amps which I feel best suit my customers needs. All the best in your career with QSC!

Regards,

Jim Bergantino
Bergantino Audio Systems

Jim, all I ask is for rationale behind the comments, a clarification. When I make a point I try to clarify it to whatever extent necessary if someone asks.

Yes, I will continue to believe that equal gain is necessary to make power amp comparisons and will do so until someone can prove that it is not. I will also reluctantly point out that your description of flux in a power transformer applies not only to conventional supplies but also to switch-mode supplies as found in a PLX amp; the supplies really are doing the same thing, using AC through a transformer to derive different voltages, then rectify and filter the voltages to develop suitable DC. They're both converting a ~120V sine wave to DC voltages; the real difference is in the structure of the transformer and its operating frequency. As you correctly describe, a too-small transformer would cause a problem with current delivery because the core would saturate earlier than with an adequately sized one. However, what is too small at 60 Hz and too small at 110 kHz are two different things; dI/dt in the PLX transformer is 1833 times greater than it would be in a comparable conventional transformer. Therefore core flux is not the culprit if the alleged deficiency in performance actually exists. At the higher frequency, one commonly overlooked area where losses could occur is in rectification. Plain 1N4004's won't do, so QSC uses rectifiers with a very fast turn-on. With full-wave rectification, the rails get refreshed 230 thousand times per second, so whether the audio signal is 25 Hz, 250 Hz, or 2500 Hz really is immaterial to the power supply.

Maybe next NAMM show you can come visit QSC, and we'll see how audible differences between amps show up in sighted and blind listening tests. I'll continue to recommend your cabinets and some other brands to anyone who asks who makes good ones.

 

[Chef]

Again...thanks to Bob and Jim for coming here and explainging their viewpoints. I've found it very interesting. I can't remember the website audiophile amp shootout someone pointed out earlier, but it had an impact on my buying decision.

 

[tombowlus]

When I make a point I try to clarify it to whatever extent necessary if someone asks.

Any advice to me, then, on how I should be setting up an amp comparison?

Thanks, Tom.

 

[Chef]

Setting up a shootout I would think would involve a decibel meter, one pre, two amps, one cab, and a blindfold. Set both amps for same sound level, plug and play thru the same cab leaving the pre set flat. Same bass, same player, same bass line, and see if you, blindfolded hear a difference.

 

[Fuzzbass]

My point has been that we should all be allowed to draw conclusions, without being told that our conclusions must be wrong. It has NOT been proven that conventional and switching amps are equal. There may be some evidence pointing one way or another, but that is hardly proof.

Most of us are used to comparing gear that has a variety of output levels. We try extremely hard to be fair and use our ears rather than our eyes: f'r instance, by ignoring volume knob settings. Tombowlus cited an excellent example: running both amps in the green, and comparing tone at a variety of volume levels.

I'll add my thanks to both Bob and Jim for their comments.

 

[metron]

IMO there is a flaw in gain matching for real world application because most players consider overall performance of an amplifier not how amp A sounds compared to amp B at some specific gain setting. If one can sound better by turning it up then thats what players are going to do.

 

[PB+J]

You'd need to do more than just set the volumes the same--I would think you'de need to know the imput sensitivity of each amp and set the preamps so they were seeing the same relative signal level

 

[Chef]

To metron and pbj: that's why you need a decibel meter or some toher scientific method to make sure both units are putting out the same volume.

I think...