QSC PLX v. Crest Audio CA Series

[boogiebass]

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

Thanks for weighing in on the weight issue, Jim!

 

[ganttbos]

Thanks to Jim Bergantino for sticking his neck out on this issue. Although this point has been made many times by "lesser mortals" who lack the clout to be heard, perhaps Jim's post will cut through the BS. The weight/sound trade-off is not to be taken lightly (no pun intended) though. I presently have my PLX 2400 in my gig rack and not my Crown PT3 - for weight only. If I do a straight rock gig with a hard-hitting drummer, the Crown comes outta storage and the QSC recognizes its boss and steps aside.

 

[Fuzzbass]

Awesome. Thanks, Jim.

I use a lightweight amp because my back has more political clout than my ears when it comes to making gear decisions (I really do have a back problem). So, I accept the tradeoff.

 

[r379]

I have been hearing the same things that Jim said from players I respect for a couple of years now and it always made sense to me. It's nice to hear Jim confirm those opinions. The notion that better tone is available for the penalty of a few pounds (and maybe saving a few bucks in the process) seems a small price to pay.

If a heavy power amp is a cross to bear I will do so cheerfully. If the weight becomes an issue for some, rack the power amp separately from the preamp/tuner/what-have-you and go on about your business.

 

[PlayTheBass]

Thank you, Jim, for that beautiful explanaion. The whole "equal volume means equal sound" argument just never made sense to me as an absolute rule, since every circuit an audio signal goes through affects that signal in a manner unique to that circuit.

To me, saying that signals going through two very different circuits come out the other end sounding the same so long as they're at the same volume is like saying a piece of sheet metal that goes through the Chevy assembly line comes out the same as one that went through the Ferrari assembly line -- as long as they're the same color!

 

[secretdonkey]

Threads like this, and members like those who have contributed to this thread on all sides, are what makes TB such a great place and resource.

 

[pickles]

Ignorance is bliss, eh?

Well, not so much ignorance as just an understanding that the light power amp sounds "good enough" and is a long way from being the weak link in my sound. Usually, the weak link in my sound is the room I'm playing in!

I've said before that I think my old Eden WT-1000 sounded slightly better than my PLX1602(though I don't have them side by side), but its important to pick the low hanging fruit first! Did you change your strings this week? Did you practice?

 

[KJung]

Per Jim's comments.... we (TB'ers) had a back and forth a while back on 'digital' amps. There was quite a bit of disagreement per my comment that the 'bottom' of the Walter Woods Ultra is a little thin versus more traditional 'analog' power supply amps. A number of people disagreed. Again, it's not that the Walter sounds bad at all...it's my favorite amp head of all times, and I use it on 90% of my gigs. HOWEVER, in very large rooms at high volume playing 'bottom heavy' music (like old school slapping on 70's tunes), the low end of the Walter tends to disappear a little bit. That's why I always have a high wattage 'traditional' analog amp in my collection.

Jim made a great comment about the low end dropping off a number of feet from the source. That's been my experience with the Walter.... it's not the amount of low end that's lacking, it somehow seems to be the quality of low end in a performance situation.

 

[kringle77]

I agree with Pickels. For guys who gig several times a week, the light amps are good enough sounding and save on your back in the long run. 99% of the people in the crowd can't tell the difference anyway. Yeah, it's true. Also, playing two different amps with a band at a gig usually won't sound a whole lot different out front. So, gas is usually caused by sitting at home in front of your amp without a band where you can hear every little thing that the crowd can't at a gig. I wish that I would have realized this years ago!

 

[KJung]

I agree with Pickels. So, gas is usually caused by sitting at home in front of your amp without a band where you can hear every little thing that the crowd can't at a gig. I wish that I would have realized this years ago!

Man, is THAT THE TRUTH!!!! For basses, amps, etc. I find that when I'm gigging 3 or 4 nights a week over extended periods, I become totally happy with whatever I'm playing. If I'm sitting on the couch woodshedding for a week, I notice every tiny 'deadspot' on the neck, and every subtle 'lack' of low or hi end presence in an amp or cab. Great point, although it's still fun to nit-pick

 

[Bob Lee (QSC)]

Easy there, Jim. The real bottom line is, listen to the amps at equal volumes and double blind, and you won't have an easy time telling them apart, even in the low end.

Power amps with soft supplies (even conventional ones), from high impedances in the supply circuitries, have really high dynamic headroom. In fact, the more cheaply made the power transformer is, the higher its winding resistances, and the higher its dynamic headroom will be because of the increased supply rail sag under heavy current draw. Dynamic headroom is essentially an indicator of power supply rail sag; this is not a bad thing, but really high numbers can be a nice way to paint real deficiencies.

The reality is that a switching supply amp that "falls on its face" with low end reproduction just isn't designed well. In fact, to the power supply, it doesn't care whether the frequencies are 40 Hz or 4 kHz--it refreshes the rails plenty of times each cycle, so sustained current draw is not a problem.

 

[pjhandlin]

Jim, welcome and thank you for sharing your thoughts here at TB!

So what about Joshua's comment:

"perhaps the sheer number of watts allows the amp not to lag on lower notes"

What do others observe? Is it possible to improve the sonic differences of switching technonogy by increasing the number of sheer watts?

 

[Bob Lee (QSC)]

I've seen the proof in the pudding as well, and I've also spent a couple decades searching for reasons behind them. I maintain my stance that any time someone says that one amp sounds fuller, richer, etc., than another, it's worth looking into whether they were listened to at the same sound level. That critical information is usually missing from the stories.

I do know that the PLX amps are among the most linear and accurate on the market, and they are ruler flat in frequency response (aside from the switchable low frequency filters), so unless the clip LEDs are lighting or the input section itself is being overdriven, the amp is putting out an extremely faithful analog of the input signal and is in fact not decreasing the bass frequencies or committing any other anomalies. Most sighted listening tests that I've witnessed coincide with your findings, but all the double-blind tests (based on sound alone) that I've witnessed coincide with mine. So my disagreement is based on my experience … my proof in the pudding.

 

[Folmeister]

Whoah! I sure opened up a can of worms! I want to thank everyone who contributed to this thread! Jim, Bob, please go to your respective corners. O.k., here is what I have learned: my PLXs are going back into my PA, where they do a wonderful job and keep my back from completely coming unhinged. For my bass rig, I need a specific tool to carry my low signal. My final decision is to go buy an Aguilar DB 750. Juan, warm one up for me, cause I'll be there Thursday!

 

[ganttbos]

If I had the motivation to search out and collect/post links to the various threads on TB that have gone this way, there would be several. I have posted in most of them because this is an interesting topic to me. As a 57 year gigging musician - old ex-rock and roller who has gone from a rig in the 60's consisting of two SVT heads and four 810 cabs to my present set-up of a couple of Schroeder 1210s, a Read Purity and a PLX 2402, I have some miles on me. But I rank quite low in the TB pecking order because I post infrequently and mostly just lurk in the shadows, although I read TB almost every day. When Jim weighed in on this thread, I got a smile out of it. I agree with Jim's posts 100%. I have a friend in New Orleans who owns a pro sound store and we talk about the power amp issue all the time. He LOVES to get prospective customers in for a power amp demo in which he AB's a switching power supply with a conventional one, going from moderate sound levels to thunderous. You can tweak all you want, cheat by turning up the switching amp louder than the conventional one, whatever - the result is obvious to anyone without an agenda. The conventional amp (he likes Crown, and I do too) slams the switcher (QSC PLX). And remember, I use and LOVE my PLX every weekend. This is not about discrediting QSC. But I carry my Crown (or hire someone to carry it :^) when I wanna be a bad boy bassist in a rock setting.

 

[Chef]

I really like the fact that two bigshots can present their views here, so thanks!
I used to use a big heavy crown. I recently switched to a much lighter similarly powered qsc/plx.
I guess I'm deaf, cause I don't hear a loss of quality, happily
I don't have to push the low frequnecies of any of the three pre's I use to get rich full bass sounds thru either a schroeder 410, or an swr henry 8x8. Maybe just dumb luck on my part, maybe I'm just dumb, I dunno.
But I don't prefer a thin sound, and I am a happy qsc/plx owner. I was a happy crown owner too, just not in terms of weight. I feel I've lost nothing but wieght in the switch. YMMV, and I have enjoyed this thread a lot, thanks!

 

[Joe Beets]

I've had my eye on that RMX5050. Hmmmmm.........

 

[pickles]

I sure hope you guys don't have the 30 or 50hz filters enabled when you are A/Bing!

 

[tombowlus]

You can tweak all you want, cheat by turning up the switching amp louder than the conventional one, whatever - the result is obvious to anyone without an agenda. The conventional amp (he likes Crown, and I do too) slams the switcher (QSC PLX). And remember, I use and LOVE my PLX every weekend. This is not about discrediting QSC. But I carry my Crown (or hire someone to carry it :^) when I wanna be a bad boy bassist in a rock setting.

Thanks for posting. My personal experience closely resembles yours in this regard.

Tom.

 

[tombowlus]

I sure hope you guys don't have the 30 or 50hz filters enabled when you are A/Bing!

Good point. For the record, I did not have the filters enabled when I did my experimenting.