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Best power amp for pre/power rig

#41
Kudo's to everybody for sticking to their guns. It makes for interesting reading.

Kudo's to all the providers of hardware (the Bob Lee's of the world, etc.) for all their valuable input. That's what makes TB the best board on the internet.

Bob I really appreciate the yoeman's work you do here. I always enjoy your post... :)

Peace

SuperT
 
#42
paulraphael said:
That's a clever and condescending way of putting it. It also ignores that a speaker (unlike a fixed impedance test load) presents a reactive load to the amplifier. Speaker impedences change in complex ways in relation to signal frequency and amplitude. So an amp is going to respond in very different ways to different speakers (and will respond to all of them in different ways from the simulated loads used on the test bench). It's possible for a particular set of speakers to illuminate a difference between two amplifiers that truly didn't exist in a lab environment with a speaker simulating load.
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It ignores nothing. If that difference exists, it will show up as a difference in the signal.
 
#44
barthanatos said:
One disadvantage I see to the Crown MA-2400 is that it does not have Speakon outputs. I need an amp with two of those.
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I wouldn't let that be a deal breaker. It's easy enough to make a speaker cable with speakons on one end and spades or banana plugs on the other. You can do it yourself or have an audio shop put it together.
 
#46
paulraphael said:
I wouldn't let that be a deal breaker. It's easy enough to make a speaker cable with speakons on one end and spades or banana plugs on the other. You can do it yourself or have an audio shop put it together.
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Okay, but when someone damages the cable and I need a replacement in short order? Plus... I just don't like spades/banana plugs.
 
#47
paulraphael said:
So you're talking about measuring the signal from the amp while it's driving an actual speaker? I'd be interested in seeing tests like that.
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Measuring it or looking at it or analyzing it.

Damping factor is one very basic but marketing-friendly way of stating an amp's tendency to interact with the loudspeaker load.

If you'd like to see such tests, visit a good power amp manufacturer. Unfortunately, Crest is no longer located in your general area (they used to be in Bergen County, NJ).
 
#48
barthanatos said:
Could we get back on topic here? I'm interested in the results of this discussion. (Not that Bob and paulraphael's discussion isn't interesting)

One disadvantage I see to the Crown MA-2400 is that it does not have Speakon outputs. I need an amp with two of those.

I'd also like something light.

Currently my eye is on on the QSC PLX-1804, or if I get to feeling really frisky, maybe the 3602.

I'm looking to match that up to an Avalon U5 as a preamp, a Whappo Grande and El Whappo cabinet (but looking at the specs, it doesn't look like those two cabinets have the same impedance, so I don't know what the deal is with that).

Also, please don't just state, "______ power amp rules!". That's not really helpful. Please justify.

Thanks!
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Do you have a local dealer that will let you try out an amp?
 
#49
Bob Lee (QSC) said:
Damping factor is one very basic but marketing-friendly way of stating an amp's tendency to interact with the loudspeaker load.
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Marketing friendly, but as you've pointed out in the past, not very meaningful in most cases.

Bob Lee (QSC) said:
If you'd like to see such tests, visit a good power amp manufacturer.
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Does QSC have any publishable test results? It would be most interesting to see comparisons between different amps in identical conditions.

Have you had time yet to look at Bob Atkinson's test bench results in those Stereophile links? I think it's interesting that even in the unrealistic, controlled environment of a test bench with a speaker simulator, all these very high quality amps measure differently, especially in terms of harmonic distortions and frequency response.
 
#50
paulraphael said:
Marketing friendly, but as you've pointed out in the past, not very meaningful in most cases.
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Exactly. "Damping factor" is tailor-made to exaggerate the minuscule; higher and higher damping factor figures represent inverse-exponentially smaller and smaller differences in output Z.

Does QSC have any publishable test results? It would be most interesting to see comparisons between different amps in identical conditions.
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We have all kinds of data, from development and qualification tests--typically hundreds of pages for each model--to analyses of competitive products, which are less comprehensive. I don't know how much of it is publishable, or even what would be comprehensible out of context. If you're interested in knowing more you'd probably want to talk to engineers who do the testing and discuss what the tests are, what they reveal, what they mean in sound quality, etc.

Have you had time yet to look at Bob Atkinson's test bench results in those Stereophile links? I think it's interesting that even in the unrealistic, controlled environment of a test bench with a speaker simulator, all these very high quality amps measure differently, especially in terms of harmonic distortions and frequency response.
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I haven't yet but hope to later today. A lot of things can measure differently on "spec sheet" parameters but not make an appreciable difference.
 
#51
Bob Lee (QSC) said:
Do you have a local dealer that will let you try out an amp?
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Well, I'm a ferry ride away from BassNW, so yes. I always feel weird about just sitting in the store trying stuff out. To be honest, they don't seem that accomodating, and I would be really uncomfortable taking the amount of time that I would want to really evaluate it (not to mention the volume). They're great, don't get me wrong... I got a great deal on my current rig there... but they're not the "paradise" people make them out to be. I mean for crying out loud, they don't even stock a variety of picks!
But, I think they would maybe let me take one home to try out for a couple days. Plus they get used stuff in there, and that's nice. On the other hand, I don't remember seeing any PA type amps there anyway!
On top of that, they don't stock the other components that I want to hear with the amp.

So in summary... it would be worthwhile to hear what people here have to say about amps.

But that does give me an idea... there's a couple power amps at my church I could borrow for a couple days...
 
#52
Bob Lee (QSC) said:
A lot of things can measure differently on "spec sheet" parameters but not make an appreciable difference.
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I'm sure that's true. The converse is also true ... there can be things that make an appreciable difference that we don't have a good metric for.

One thing that might be causing some confusion is that your definition of a good amp--one that changes little about the input signal besides gain--is not the definition used by every manufacturer. Or user. Some great amps are extremely linear and low in distortion, others are pretty far from it. What makes them great is that people subjectively think they sound great.

In other words, the qualities which could strictly be interpreted as flaws are also what make them special. The obvious example of this is the even-order harmonic emphasis of classic tube amplifiers. I have heard engineers (in other forums) go on rants about tube amp lovers being on crack--that the technology is proveably obsolete. They're not making a distinction between "good" as they learned it in school and "good" as heard by the ears of the beholder.
 
#53
wow, this is a really interesting thread. measurements, brands, etc...i tend to follow the mantra of trusting your ears (even if your ears can't be trusted). your ears are your best guide to what YOU like whether they are being honest to you or not. and what you like is purely based on your own opinions and not facts.

i find that different reference monitors and headphones which are supposed to be relatively flat and true to what the sound actually is...sound drastically different. drastically different to me...5 years ago, they may have sounded exactly the same...maybe my ears have becomed trained better to notice slight nuances or maybe my brain has become more focussed on trying to pick out differences, either way, i still hear a difference.

as for power amps...i use a stewart running through a EA CXL 112. this powers my demeter vtbp-201s. i find that the sound quality running the demeter pre directly into a protools rig is pretty much what i get running the pre through the stewart and EA cab, so i like the stewart because i feel like it does what i expect a power amp to do...amplify my tone without adding any color. i didn't try out a million power amps though, i read a lot of talkbass posts and swapped my SWR SM400 for the stewart...don't know if any others are "better" but the stewart gives the power i need and keeps the sound clean (to my ears).
 
#54
Bob Lee (QSC) said:
You can read specs, but don't expect them to tell much. They don't necessarily lie, unless the manufacturer is unethical, but they are at best only sketchy descriptions of a product that can at best give a vague idea of what it can do. I don't think the solution is "more specs" either; you can look at an engineering group's large binder full of tests on an amplifier model and still not know what the engineers were experiencing.

If power amps do respond differently to how you play, then at least one of them is defective or poorly designed. ;)
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OK you're not gonna budge. 2 differently designed amps with identical specs measured with the same proceedures must sound and PLAY alike. Some say they don't engineers say they must. I say that if there is a difference its d@mn small and certainly not night and day. I suppose that the big debate is between switching power supplies and traditional transformers and that the older technology led sled somehow sounds better than the newer lighter switching type power amp. I've compared my plx1202 to a Carvin dpc1000 and a EV dynacord and I can't really tell any difference and the EV is 250 watts bridged into 8 ohms and the other 2 are around 600. A 250 watt operating at 75-150 watts doesn't sound any different than a 600 watt amp operating at 75-150 watts. The big headroom thing (imho) is a real myth. I've used tube amps and SS amps and must say that they don't sound (to my ears) the same and I've been able to get a good sound with both. All in all I prefer SS as it generally has a tighter bottom end. When I read statments that use terms like "night and day" I wonder just what are they hearing that I'm not. If they are talking about pre-amps or guitars it makes sense but Power Amps:hmm:
 
#59
m.oreilly said:
"it" is not a "mith" (myth). i agree with bob. again, us boutique folks are a strange whiny bunch...well, maybe not me so much...i love them big transformers too.
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The myth I'm writing about is that say a 1200 watt amp operating at 50 watts will sound better than a 250 watt operating at 50 watts, they sound the same to me.
 
#60
paulraphael said:
You just hit on the idea for a small business. "High-End Logos.com"
Why spend thousands for one of these boutique amps when you can have all the perceived sound for just a few bucks?

For my next research, I'm going to see if my playing gets better when I wear a Jaco wig.
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Nah, just buy the cheapest amp possible and debadge it. :D
 

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