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Comparisons between Crest and QSC

Discussion in 'Amps and Cabs [BG]' started by bucephylus, Feb 22, 2006.


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  1. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    There have been several threads comparing the performance of the Crest CA9 and the QSC PLX over the past few months. Aside from experience opinions (which matter a lot), it seems difficult to separate the wheat from the chaff.

    1st question: is the difference in performance due to differences in the input sensitivty?

    If so, shouldn't we be comparing the performance between the CA9 and a PowerLight which includes an Input Sensitivity adjustment capability?

    If not, is it just simply the mass of the output transformers.

    I can't tell whether everyone is trying to be diplomatic or just don't know the answer. However, given the weight considerations, this seems like a pretty important issue to get square on (if possible).
     
  2. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Neither brand of amp has output transformers.

    When comparing amp sound quality, it is important to match the gains, not necessarily the input sensitivity.
     
  3. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    Thanks Bob.

    However, for bass use, I have generally maxed out the preamp to drive the tubes just into saturation and then use the power amp gain (and my fingers) to control stage volume. Is this incorrect? From a tonal perspective, it made the most sense to me.

    In this case, the power amp gain is whatever it needs to be for a given volume.

    Some of the previous threads seemed to suggest tonal differences between the power amps at the same volume. Since I don't have 8 different power amps to A, B, C,... I thought I would try to understand what such a perception would be attributable to.
     
  4. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    There are two camps of opinion (much of which is very educated):

    camp A: all good power amps sound the same ... like nothing. What you put in is what you get out only louder. If you think one sounds better than the other, then your test probably wasn't set up correctly (one was louder than the other).

    camp B: I don't care what camp A says, I hear a difference and I'm sticking with the amp I like better.

    Having used both, I'm in camp B, the two amps you are looking at sound different ... neither is better or worse, but definately different. If you can find any way to try them out, side by side, with your band ... thats your best bet. In my experinece, every resistor, transistor, capicitor or piece of cloth lint that gets between your hands and the audience contributes (for better or worse) to the sound. And power amps have LOTS of those parts.

    If weight and features (high pass filters, speakon connectors) matter to you more than any sonic differences there may or may not be, then the QSC is the clear winner. But I suggest listening to them.
     
  5. bugbass

    bugbass

    Apr 8, 2004
    Norway
    IMO the PLX sounds rather thin comparing to the CA9. The CA9 is a monster with headroom to spare
     
  6. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    One man's thin is another man's tight.
     
  7. Horny Toad

    Horny Toad Guest

    Mar 4, 2005
    NJ

    +1000

    I owned both. I now own one. I couldn't agree more with what pickles has said.


    [​IMG]
     
  8. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    Thanks guys. I've read your previous posts carefully and appreciate your experience. That matters a lot.

    I'm just trying to figure out if the same is true for the more expensive PowerLight series which have the input sensitivty adjustment; or if that doesn't matter.
     
  9. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    Also, in my experience, some power amps and some cabs get along better than others. Its the total recipe that matters, so when you demo amps make sure to use your cabs.

    Or when you demo cabs make sure to use your amp.

    Or make a big stack of gear and try every possible combination until you find the one that "pops". I just finished doing that, and it was very interesting. The results were not what I expected and I found some great sounding combos!
     
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It's fine to use your amp gain control to adjust volume. It's just that when you compare them, do it at the same gain. Otherwise, the lower gain one will tend to sound thinner with a given input level, even they are exactly the same amp.

    This is a psychoacoustic phenomenon that's been known for decades, except in many parts of the music world. ;) See equal loudnes curves below.
    [​IMG]
     
  11. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Actually, here is a third camp: Good power amps tend to sound alike when compared at the same gain. Even good power amps will sound different at different gains.

    What's your experience with different components? Are there any particular ones that you find contribute for better or worse to the sound? In my experience, at least equally important to the components used is the actual circuit implementation.
     
  12. pickles

    pickles Supporting Member

    Mar 23, 2000
    Ventura, CA
    Thats camp A.

    What I meant about components was that a power amp is not just a black box that magically makes things loud. Of course, circuit design will effect the sound even more than components! Even if the engineers of an amp shoot for (or even claim) zero coloration, they will likely not achieve it due to the complexity of the device.

    I'm not going to post anything more on the topic (since these usually turn into flame wars).
     
  13. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    No, camp A by your description doesn't fit the third camp I mentioned.

    There will always be some alteration of a signal in a circuit. That's called distortion. We're fortunate that modern amp circuitry can achieve extremely, extremely low distortion, both in linearity, phase, frequency response, etc. That's good, because it means that high quality is actually a goal--the proverbial straight wire with gain analogy--and not just a hit-or-miss random occurrence.

    I was interested in knowing more about your component experience, though!
     
  14. inazone

    inazone

    Apr 20, 2003
    Colorado
    Actually, here is a fourth camp. Ive yet to see a bass player, local or national, bring testing gear and match gains at a show. They use what works best for them (or I guess what their paid to use). Wait, thats still camp B.:smug: :)

    I do have to say though, that some basses just dont sound good with some amps, and the other way around. IMO.
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    No, obviously you would do your comparisons somewhere other than at a show, unless you're trying to bore your audience.

    Using what works best would also fall into the third camp category, too.
     
  16. inazone

    inazone

    Apr 20, 2003
    Colorado
    :p just pointing out that matching gains and all is fine and may be a good point but what matters most to the customer (and me) is that it works great when we take it out of the box and plug it in. It may be fun to do all the A/B ing but at the end of the day, its what works best.
     
  17. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    True. Most players never get to really compare a couple pieces of gear, so for most what works best is really just what works, period. (Maybe that's why there's so much uncertainty about how things work, and why there's so much GAS?)
     
  18. Fuzzbass

    Fuzzbass P5 with overdrive Supporting Member

    This leads to another point. Forget about power amps for the moment. We bassists do a lot of A/B-ing with basses, preamps, consolidated bass heads (pre+power), speaker cabinets, etc.

    Very important: all of these pieces of gear can vary tremendously in output level. But we bassists take great pains to compare them on an equal footing. Plenty of us prefer passive basses, even though output level is less than actives. Let's talk high-end speaker cabinets: this is a better example because they are relatively flat in response. Cabinet efficiencies can vary tremendously, but many prefer low efficiency speakers such as Acme. I don't see evidence that we favor gear with higher output when it comes to judging tone alone. (Some do prefer higher output gear when the goal is to increase overall output level, drive a device into distortion, etc.)

    So, I don't buy the assertion that power amps can only be compared fairly in a fancy double-blind environment, and that everyone who hasn't A/B'd them this way is a victim of psychoacoustics.


    Another 2 cents: when I compare amps, I don't consider the positions of the volume knobs because I fully understand that those positions do not correspond between Brand A and Brand B. I simply set them for what I think is equal volume. Sure, there's a chance I won't set the volumes equally... but there's a 50-50 random chance of which amp will be louder than the other. So, if I perform many tests at varying volumes, then it'll be a wash: neither amp will have unfair advantage in the long run. Also: most of us do understand that it's unfair to compare tone when setting one amp to a volume that the other cannot achieve.

    So again, I believe users here are entitled to have valid opinions that one power amp sounds better than another. Doesn't affect me any: my back insists that I stick with my lightweight power amps even though a heavier one might sound better. And I have absolutely no opinion on QSC versus Crest; I'm simply interested in the lightweight/heavyweight amp debate.
     
  19. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    In fact, I did not intend to focus on these two brands so much as address what I saw as some unresolved factors from previous threads involving them.

    So, I agree that the interesting discussion point is to try to resolve questions related to tone vs. weight, regardless of brand.

    Regrets if this was not apparent.
     
  20. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    No, not always; only in a flat, linear system.

    Loudspeakers, even "flat" ones, have variations in frequency response (and therefore, tone) that are orders of magnitude greater than frequency response errors in most other parts of a system, and therefore actual differences in tone among them can be easily apparent at various levels. As the equal loudness curves show, even a flat system is not perceived by our ears as flat, and they deviate further from flat at lower sound pressure levels, especially in the frequencies we bassists are interested in. That's why boosting a signal, say, 10 dB might make the mids seem 10 dB louder to us but the bass could seem 15 dB louder. That's also why many stereos have a "loudness" switch that boosts the lows and extreme highs at low volume settings.

    I used to be in "Camp B" years ago, but I began to realize that it just didn't make much sense, especially since I was aware that the human ear's own tonal response varies with SPL and I could see that these power amps weren't altering the signals passed through them in any significant way. So I investigated it, discovered double-blind testing, and learned that most good, competently designed power amps tend to really do what they're supposed to do.

    I saw a bunch more defectors from "Camp B" at a power amp "shootout" two years ago in the SF Bay Area that a few guys from the Live Audio board (www.live-audio.com) put on. ;)
     



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