QSC or Stewart or ???

[mrbeezroom]

Does anyone out there have any opinions (not here, noooo)or preferences for a poweramp in the $600-$700 price range? I'm looking at the QSC PLX series or the Stewart WORLD series and it looks like I can afford either the PLX1202, PLX1602(maybe), WORLD 1.2, or the WORLD 1.6(maybe).

[palembic]

Choose the fastest one (highest damping ratio) for the highest wattage.
 
Paul the bad one
 
 
geeeeee ...I CAN be short!

[wayne]

I use a PLX1602 and love it.  Before I bought it, I actually traded emails with an engineer at QSC that worked on the PLX design team.  He bought an F-1X from Alembic to use in the final testing stages to be sure the PLX would be suitable for bass guitar amplification.  That sold me.
 
I've heard that the Stewarts are great if you go with the higher powered, 2 rack space versions.  I tried a small one and it didn't work at all for bass (great for home stereo, though).
 
Talk with the guys at Bass NorthWest.  They have experience with the Stewart line.
 
C-Ya..............wayne

[effclef]

Wayne, does that apply to the whole QSC line or just the PLX ones? I was thinking about the RMX line.
 
The RMX damping factor is 300 - is that good or bad compared to other direct stereo amps?
 
Input impedance is 10K unbalanced - how does that compare with the 1/4 unbalanced outputs of the Alembic rackmount gear?
 
100 dB signal to noise, nice THD numbers, and a variable speed fan. Hmm! Looks very tempting.
 
The above were for the RMX. PLX is probably even better. Looking at all the discussion on the Board it seems like a lot of people find that their dedicated bass heads stay at flat as far as tone controls go, so many folks are leaning towards using SF-2 or F-2B/F-1X for tone shaping and just using a straight amplifier afterwards.  
 
Seems like a great way to simplify your rack and I do remember someone on the Yahoo Alembic club saying the SF-2 and Stewart 1.2 was the best combination he had ever wound up building.
EffClef

[palembic]

What I read about: the PLX is faster: 500 or 600 damping factor!

[dnburgess]

Paul TBO: You are thinking of slew rate - damping factor is the ratio of load impedence to ampifier impedence and is used as a rough gauge of how well the amplifier can control bass speakers. There is a great article here: http://www.classic-audio.com/marantz/mdampingfactor.html
 
The slew rate is measured in volts per microsecond and tells you how quickly an amplifier can respond - it gives you a rough guide to transient response.
 
Real world speaker behaviour and psychoacoustics are far more complex than the test bench - so, as with everything else musical, its important to use your ears (or the ears of others you trust).

[bob]

David,
 
I suggest it's a bit risky (or perhaps risque?) to speculate on what exactly Paul TBO is thinking of :-)
 
In this case, my guess is he was responding to an earlier comment about 'faster', but I think if you substitute the word 'tighter' in both places, then damping factor is probably the most important differentiator (other than raw power or current delivery).
 
Unless you are primarily interested in finger and fret noise, my guess is that most reasonable quality bass amps will have a more than sufficient slew rate to provide adequate transient response, which I believe is generally evaluated in the higher frequencies.
 
For bass in particular, control of the speakers is critical to producing a tight, articulate response. I only skimmed the article you referenced, but it seems to be aimed more at hi-fi reproduction than live bass amplification. While I freely admit to having limited experience in this area, I'll throw out some numbers in case others wish to enlighten us: I think a damping factor of 100-200 is okay but mediocre, 5-600 is quite good, and if you can get into the thousands then go for it (for example, Crown claims over 3000 for their K-Series).
 
-Bob

[palembic]

Well brother bob ...it IS good to have someone who knows you! LOL!
 
David and Bob ...I was referring to my believe that damoing stand for an number that indicates how fast a amplifier can move the amplitude of the speaker cone back to it's initial position.  
The Dynacord (Electrovoice in US) I'm using has minimimum 300. A QSC-PLX has a minimum of 600 (If I remember well). Working with a Crown (minimum of 1000) stands on my long term longing-to-list!!!
 
Paul TBO
 
...***sigh*** I KNOW I am notr always THAT clear

[kmh364]

As a Hi-Fi nut for almost thiry years, I've learned that equipment spec's mean sh*t: you can not accurately predict what something will sound like via spec's alone. The best measuring stuff usually sounds the worst. Our Aussie Mate Dave already said it: Use your ears...if it sounds they way you want it to and will drive the intended speaker cabinet loads, buy it. Having said that, there are electronics designers out there that realize this and have attempted to quantify and qualify what they measure versus what they hear (Ron Wickersham, for one).

[David Houck]

According to the manual, the damping factor of the QSC PLX is greater than 500 at 8 ohms.

[dnburgess]

Correct me if I'm wrong - but I thought valve amp.s generally had quite low damping ratios compared to modern transistor amps - but you don't hear too many complaints about Mesa's or Aguilar's ability to control bass speakers.
 
Anyway, doesn't most of the superhigh damping factor disappear after speaker cable resistance is taken into account? e.g. DF 500 @ 8ohms implies amplifier impedence of 0.016 ohm. Now add 2 metres of cable with a resistance of, say 0.04 ohms. The speaker is seeing an impedence of 0.056 ohms which implies a damping factor of 143.
 
Not quite as pithy as Kevin - but I'm in the same camp. Engineers only measure what they know how to measure. Kind of reminds me of the early days of CD. The engineers swore blind that the spec.s exceeded the resolution of human hearing. Whereas anyone who listened knew something was wrong. It wasn't until much later that they were able to quantify what was causing the psychoaccoustic effects. But I digress...
 
Back to the original QSC vs Stewart question.  
1. Whichever amp, buy the most powerful you can afford - there is no substitute for headroom when it comes to bass amplification.
2. QSC is very reliable and user friendly. Also a lot of hire companies have them - so if you do have a breakdown or need a larger amp for a big gig it is easy to get hold of one on short notice.
3. There are conflicting reports about the reliability of the non-fan cooled Stewarts. OTOH the fan on the QSC is bloody loud, which makes it not really suitable for domestic use.
 
David B.

[kmh364]

David,
 
Good on ya', Mate. You hit the nail on the head with the CD analogy..the perfect sound forever, LOL!. I call it the Stereo Review Magazine syndrome. Everything the infamous Julian Hirsch ever reviewed measured awesome and, therefore, sounded great (i.e., he never met a component he didn't like). When you went to listen to it, it sounded like crap. My ex-father-in-law met him at the Las Vegas CES trade show years ago and confirmed why his reviews were always so positive: he was virtually tone deaf, and used his test bench 'scopes to write the review for him, LOL!

[bob]

Gee, guys, I really didn't mean to come off as a measurement freak - I'm actually pretty close to the fringes of the subjective camp on this stuff: trust your ears, and don't let anyone tell you that you can't :-)
 
As an example, I had a marathon session this afternoon where I tried seven different sustain blocks in my bass (really). Now, part of me thinks it would be interesting to look at the effects on a spectrum analyzer or something, but I immediately have to ask myself what I could conclude from that. How would I know which curves or distributions actually sounded 'better', whatever that means to me?
 
Yes, Hirsch was a bozo (or maybe, Bose-oh?). Yes, 20 years later people are still figuring out how to get better sound out of CD's, and still can't figure out how to quantify it. And yes, I wasn't the one to mention measurements in the first place...
 
At the same time, there are some things we seem to have a fairly good understanding of. For instance, if we agree on the testing conditions, it appears we can generally produce reliable and useful measurements of amplifier power. So if you show me one amp that comes fairly close to doubling output as it goes from an 8 to 4 to 2 Ohm load, and a second amp that does only a little better into 4 and is not recommended for 2 or perhaps specifies a minimum of 2.8 or something - then all other things being equal, I'll take the first one, thank you.
 
Damping factor seems to be a somewhat less precise measurement, but there does seem to be fairly strong subjective correlation between significantly higher numbers, and tighter bass reproduction. Personally, this is a number I would look at, but not trust as much as a carefully specified power measurement.
 
And I agree completely that there are other really critical factors - I couldn't possibly tolerate a fan, for 'domestic use' (which is all I care about at this time).
 
-Bob

[kmh364]

Bob,  
 
Actually, while with regards to all that is music I let my ears decide what is right, I do believe that there is a place for quantitative and qualitative measurements. I just don't let  them take precedent over what I hear: if it sounds the way I want it to (like actual music is supposed to sound) and it can work harmoniously with the other components it will be utilized with, then that particular piece of equipment is for me.  
 
In the Hi-Fi realm, the anti-Hirsch is a fellow named J. Gordon Holt (of Sereophile magazine fame) who has spent his entire life trying to scientifically quantify/qualify with the best technical equipment available what he hears versus what he can measure. In many instances, he's had to invent test equipment, procedures and measurements that heretofore did not exist in order to identiify what he is hearing via the scientific method. He has advanced to a point where he can develop a scientific picture of sorts as to why a particular component sounds the way it does (especially for sonic anomalies ala digital audio, i.e., cd's). What he does realize is that no matter how many test are invented and performed, it is still only part of a whole picture of what it is that makes up the sound that ears ultimately hear.  
 
I'm a degreed Electrical Engineer (Power Systems) who is a High Tension specialist. I have had frequent instances in my career to use some highly sophisticated testing equipment in order to commission and/or troubleshoot high-voltage/high current electrical power distribution system equipment. While this equipment must be used, it is up to the Engineer (I am also a senior Code official) to decide if the measurements taken are within specifications and/or if they are indeed are actually valid. I have had instances with equipment where all the industry standard commssioning tests were satisfactorily performed, the gear was satisfactorily installed and inspected, and yet the equipment experienced an electrical fault upon initial energization. When asked why, I try to explain to those not in the know that testing only provides a part of the whole picture as to an electrical systems health and cannot account for every variable that makes up said systems.  
 
My whole long-winded point with all this was to illustrate that I don't just whole-heartedly discard scientic measurement with regards to audio/musical equipment. They certainly have their place in the grand scheme of things, especially when performed ala Holt. I just don't let them superceed the best test equipment available to me: my own ears. Unlike test equipment, They never steer me wrong, LOL!  
 
Cheers,  
 
Kevin  
 
   
 
(Message edited by kmh364 on May 09, 2004)

[dnburgess]

Bob - we promise not to call you Bob TMF (the measurement freak).
 
I'm dying to know what you found out about sustain blocks - no measurements required.