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QSC PLX v. Crest Audio CA Series

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#42
Jim, I respectfully disagree. What you say may be true for current product offerings, but it is a false generalization of switching power supply technology. Perhaps it’s that current switching supply based amps have focused too much on weight, not output current capability, but there is no way that a conventional supply will out perform a properly designed switching supply.

- John
 
#44
I'm sorry if I offended you, Jim. The proof in my pudding is different from the proof in your pudding, and I outlined my findings about test conditions. As I mentioned, I have frequently seen preference for conventional supply amps in sighted listening tests, and yet in double-blind tests, these same listeners could not tell them apart. I have also seen preference in listening tests between identical amplifiers for the one that's turned up louder. My conclusions don't match yours; that is all.

I used to work for one of the other amp companies mentioned. One of the major reasons I quit was because the company owner insisted that I put bogus power specs ("Heavy Metal Power," with numbers picked out of the air) in the spec sheets. A major reason I came to QSC and stayed is that the company has always kept things above board.

Regarding dynamic headroom: it is not about sustained current, but about dynamic conditions--i.e., short term output voltage compared to sustained output voltage under load. Because switch-mode supplies tend to have lower impedances and therefore rails that do not sag much, their dynamic headroom is not as great as in an amp whose rail voltages decline significantly with current demand.
 
#45
Since it looks like I'm going to be stuck with my lightweight power amps for a while, is there some way I can make them ballsier by EQ-ing differently? I don't know if I can handle any more bottom end. That little Stewart skakes the floor and the walls pretty good. And I'm not even running a preamp. In fact, last week it shook something loose in the back wall of the house. I thought there was something buzzing from a blown Stewart, but it was just the house shaking apart. :eek:
 
#46
pjhandlin said:
What do others observe? Is it possible to improve the sonic differences of switching technonogy by increasing the number of sheer watts?
Click to expand...

As Jim said, I got much better results when bridging a switching amp than when running single-channel: I would've thought that 650 watts was enough for a certain application, but 2100 watts turned out to be much better. Those are the numbers with my Stew 2.1, but I observed the same testing a PLX.
 
#47
Fuzzbass said:
As Jim said, I got much better results when bridging a switching amp than when running single-channel: I would've thought that 650 watts was enough for a certain application, but 2100 watts turned out to be much better. Those are the numbers with my Stew 2.1, but I observed the same testing a PLX.
Click to expand...

One thing to keep in mind, Fuzzbass, is that you also get 6 dB more gain in bridged mono because the two channels' output voltages are in series.
 
#48
Bob Lee (QSC) said:
Regarding dynamic headroom: it is not about sustained current, but about dynamic conditions--i.e., short term output voltage compared to sustained output voltage under load. Because switch-mode supplies tend to have lower impedances and therefore rails that do not sag much, their dynamic headroom is not as great as in an amp whose rail voltages decline significantly with current demand.
Click to expand...

I sure dont want to get in the middle of this but isnt sustained current and sustained voltage under load the same thing?
 
#51
Bob Lee (QSC) said:
One thing to keep in mind, Fuzzbass, is that you also get 6 dB more gain in bridged mono because the two channels' output voltages are in series.
Click to expand...

Yes, of course. :) I was just surprised that so many watts were needed to get the desired result.

I wasn't just referring to improvement in tone, I was also referring to available headroom. The application I referred to was a rehearsal... a loud rehearsal, but in a garage rather than a bar or restaurant. Back when I was using heavy metal amps to play heavy metal music, I don't recall needing so much power for nearly identical (or louder/roomier) situations. No, my opinion isn't scientific, but without hard data, no one here has anything more than opinion.
 
#52
Fuzzbass said:
Yes, of course. :) I was just surprised that so many watts were needed to get the desired result.

I wasn't just referring to improvement in tone, I was also referring to available headroom. The application I referred to was a rehearsal... a loud rehearsal, but in a garage rather than a bar or restaurant. Back when I was using heavy metal amps to play heavy metal music, I don't recall needing so much power for nearly identical (or louder/roomier) situations. No, my opinion isn't scientific, but without hard data, no one here has anything more than opinion.
Click to expand...

Was the amp clipping before you switched it to bridged?
 
#53
Regarding opinion, i.e. proven versus unproven pudding: I would still like to see hard data on ABX testing of the amps we've been discussing. Many times we've seen anecdotal referrals to such tests, but I'm waiting for detailed published results from an independent source, including specifics on how the testing was performed, etc. The more, the better.

Given that no such hard data exists (that I've seen), no one can claim the scientific high ground. Jim and Bob are entitled to their opinions, but so are Josh and Tom and the rest of us. I say read 'em all, and use your own ears if possible. And even if you're not shopping, this is a cool discussion IMO. :cool:
 
#54
Jim, I can’t say that I do know of specific switching supplied amps that perform better than conventional supply counterparts, and I won’t even argue that they exist at this time. My only point is that switching supplies not only have the ability to provide comparable amplifier performance to conventional supplies, that have the ability to provide superior performance.

Bob brought up a point that I was going to make, and said another way, may be that switching supplies are already much better than conventional supplies (in terms of output impedance). I suspect that the sonic difference is likely the extra headroom afforded by a conventional supply, rather than the switching supply’s inability to deliver current. This doesn’t tell me that amps with switching supplies are inherently inferior to conventional designs, but rather their switching supply may not been designed in a way to get maximum sonic performance. However, a great thing about switching supplies is that you can design them to have almost any output characteristics that you want. Normally a designer tries to get as stable an output voltage as possible, but that may not be ideal for supplying a power amp.

As an aside, a few years ago I designed a PLX into an industrial application that had extremely demanding performance requirements. In the process, I thoroughly checked the amplifier’s transient load capability, output impedance, max output power, stability with various impedance loads, etc., and found that it easily met all published specs. It’s output at low frequencies was rock solid, and did not taper off at high levels. If a PLX is not delivering as solid bass as another amp, I am fairly certain it is due to a difference in usable output power capability.

- John
 
#55
pickles said:
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?
Click to expand...

Great points, Pickles! It's all about compromises, and as is being wisely pointed out in this thread, it's just smarter to make informed decisions, so you know the tradeoffs.
 
#56
It is, to me, important to maintain economic perspective. In an earlier post I mentioned that several players I respected had told me that old-style amps performed better (based on their experience) than switching amps. One of the other things they mentioned was that (in their opinion) a switching amp would be suitable if you were willing to buy a switching amp with TWICE the watts rating of a conventional amp. That point was, I believe, also mentioned earlier in this thread. That gets expensive and for that kind of money I can live with a few extra pounds.
 
#57
Somebody (including our very own Bob Lee) did do a poweramp shootout on ProSoundWeb, here:Link Removed


They measured actual output power and did some listening tests. Whilst Ill be the first, and certainly not the last, to tell you that numbers arent everything, there must be some relevance to the power at 20hz numbers.

It seems that both Crest and QSC came out very well though!
 
#60
Hey Pickles! Thanks for backing me up. I've been on a streek of playing every friday and saturday night......sometimes on sundays too and noticed that I am completely happy with my set up. All that at home practice is the real killer. But, I will most likely be a gear whore for the rest of my natural life so....... :p I use an aguilar AG500 and a pair of Avatar 2x10 cabs with my Billy sheehan attitude basses. Can't beat it. I totally commend these amp guys for presenting their well thought out opinions on this forum. It really shows some class how they conduct themselves also. Thanks. Oh yeah, get out of the house and play some gigs and don't worry so much about your gear! You'll never hear me say that again....right nickleseye?
 
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