Crest CA-9 vs. QSC PLX2502 (PLX2 Series)

[Bob Lee (QSC)]

Thanks for the link. I enjoyed reading these. If you wade through a few, the author properly credits Dr. Floyd Toole for his pioneering efforts in this area. I was fortunate enough to participate in several of these tests when Dr. Toole was based here at the NRC and conducting tests in the anechoic chamber. When the (acoustically transparent) curtain was lifted at the end of the testing, it was always astonishing to discover that those tiny Yamaha studio monitor speakers were shaming refrigerator-sized Tannoys in double blind tests (for example), as determined by a majority of listeners. Anyhow, I'm drifting off topic here so I'll wander off in search of some coffee...

Dr. Floyd Toole is one of my audio heroes. He and his colleague, Sean Olive, have long pioneered meaningful listening test methodologies and evaluations of audio quality both at the NRC and at Harman International (Dr. Toole retired from Harman at the end of January this year).

 

[oddio]

Dr. Floyd Toole is one of my audio heroes. He and his colleague, Sean Olive, have long pioneered meaningful listening test methodologies and evaluations of audio quality both at the NRC and at Harman International (Dr. Toole retired from Harman at the end of January this year).

Hi Bob...

Thanks very much for the update. You and I have discussed Dr. Toole's work in the past, but I didn't realize that he had finally retired from Harman for a well-earned rest.

Hope all is well with you.

Cheers,
Andrew

 

[Bob Lee (QSC)]

Hi Bob...

Thanks very much for the update. You and I have discussed Dr. Toole's work in the past, but I didn't realize that he had finally retired from Harman for a well-earned rest.

Hope all is well with you.

Cheers,
Andrew

I saw Floyd most recently at the memorial for John Eargle about two months ago. He's as kind and personable a gentleman as ever.

 

[psemeraro]

I hope I can add something here and not just "stir the pot."

I am an audiophile and a pro sound user and sometimes there are MASSIVE differences in sound quality between amps of each discipline even though the specs might be similar or identical. Take a CA9 and an RMX and plug them into a good set of speakers (B &W 802, wilson Puppys, etc.) match your 1k tone to within .1 dB, and you will absolutely hear different presentations. Compare both of those amps to a Krell or a Bryston and your jaw will drop. Listen to a solo piano recorded in a nice hall. Pay attention to the hall sounds, the reverb lengths, the stereo width. Listen to well recorded percussion - congas, tympani, snare drums and pay attention to their "snap" and resonance. As customers we have to be realistic about what we get versus what we pay. I have an RMX 850 that I bought for $100. Listened on the B&Ws and heard absolutely quiet, full range powerful audio. It was also conjested sounding, had a very narrow stereo image and didn't reveal much of the room sound. I put Nichicon "Gold Tune" caps in all 8 of the parking spots for power supply caps, replaced the electrolytic coupling caps with film caps and upgraded the opamps, bypassing everything properly. The sound changed completely. BUT if QSC offered an "audiophile" version of the RMX 850 it would be 4 times as expensive. It would sound similar to the Bryston and cost about the same.

I believe what everybody is hearing but can not quantify is the "sound" of the amps power supply and various passive components. That power supply is in the signal path and it's quality is audible. It's why a PLX sounds marginally better than an RMX. A large overbuilt, well filtered power supply will help compensate for differences in line voltage quality including noise on the power line and sagging voltage. A "lead sled" will cope better with sagging voltages than a non regulated smps supply. Faster, lower esr filter caps will give a "punchier" sound and clearer transients and a more detailed sound. On your JBL SR's it might be hard to tell the difference but on good speakers it is very obvious. None of that will be reflected meaningfully in a signal to noise spec or a thd spec. It's well known that on bass Crown amps have a "tight" sound, Crest amps have a "full" sound and PLX amps have "clear" sound that's maybe a touch light. It's not just about the watts, its also about how the amp deals with the impedence of the speaker and the quality of the incoming AC line power.

Mastering studios don't buy expensive gear just because they like to waste money. Again, we have to be realistic about how much we spend on gear then pick our poison with weight vs quality vs cost.

Bob, thanks for your great posts here helping to keep everybody straight!

Cheers, Pat, Orlando, FL

 

[Bob Lee (QSC)]

I hope I can add something here and not just "stir the pot."

I am an audiophile and a pro sound user and sometimes there are MASSIVE differences in sound quality between amps of each discipline even though the specs might be similar or identical. Take a CA9 and an RMX and plug them into a good set of speakers (B &W 802, wilson Puppys, etc.) match your 1k tone to within .1 dB, and you will absolutely hear different presentations. Compare both of those amps to a Krell or a Bryston and your jaw will drop. Listen to a solo piano recorded in a nice hall. Pay attention to the hall sounds, the reverb lengths, the stereo width. Listen to well recorded percussion - congas, tympani, snare drums and pay attention to their "snap" and resonance. As customers we have to be realistic about what we get versus what we pay. I have an RMX 850 that I bought for $100. Listened on the B&Ws and heard absolutely quiet, full range powerful audio. It was also conjested sounding, had a very narrow stereo image and didn't reveal much of the room sound. I put Nichicon "Gold Tune" caps in all 8 of the parking spots for power supply caps, replaced the electrolytic coupling caps with film caps and upgraded the opamps, bypassing everything properly. The sound changed completely. BUT if QSC offered an "audiophile" version of the RMX 850 it would be 4 times as expensive. It would sound similar to the Bryston and cost about the same.

I believe what everybody is hearing but can not quantify is the "sound" of the amps power supply and various passive components. That power supply is in the signal path and it's quality is audible. It's why a PLX sounds marginally better than an RMX. A large overbuilt, well filtered power supply will help compensate for differences in line voltage quality including noise on the power line and sagging voltage. A "lead sled" will cope better with sagging voltages than a non regulated smps supply. Faster, lower esr filter caps will give a "punchier" sound and clearer transients and a more detailed sound. On your JBL SR's it might be hard to tell the difference but on good speakers it is very obvious. None of that will be reflected meaningfully in a signal to noise spec or a thd spec. It's well known that on bass Crown amps have a "tight" sound, Crest amps have a "full" sound and PLX amps have "clear" sound that's maybe a touch light. It's not just about the watts, its also about how the amp deals with the impedence of the speaker and the quality of the incoming AC line power.

Mastering studios don't buy expensive gear just because they like to waste money. Again, we have to be realistic about how much we spend on gear then pick our poison with weight vs quality vs cost.

Bob, thanks for your great posts here helping to keep everybody straight!

Cheers, Pat, Orlando, FL

Hi Pat,

Most people, including the vast majority of "audiophiles," don't know what power amps actually do or how they work, let alone how to compare them properly. The less you know about power amps, the easier it is to believe that sounding different is the norm rather than a sign that either an amp or the comparison setup is faulty (or that power supplies are in the signal path). Even worse than the MI industry, the "audiophile" world is rife with "well known" myths about "sonic signatures" and "presentation" and stuff like that, fueled by fluffy reviews in magazines dependent on ad revenue from the reviewed items.

You can very easily make Crown, Bryston, Crest, QSC and any other good amps sound indistinguishable from one another without modifying them. You can also make an amp sound "jaw-dropping" one moment and weak or lacking thump the next, also without modifying it.

Mastering studios may not like to waste money, but they do buy much stuff based on "image" when there is no significant difference in audio performance. Fortunately for them, they can often buy at a good discount.

 

[seamonkey]

+1 totally agree

 

[psemeraro]

I do love a lively discussion! I also find it fascinating to watch engineers and audiophiles have a discussion, often they are not very long-lived. The audiophile may believe with a religious type of faith that their $2000 xlr cable improves their audio system. The engineer will insist that if it measures the same it must sound the same. I believe that the audiophile is absolutely wrong and the engineer is not always correct because measurements don't always reflect what we hear. 1% THD would "sound" very different it it was primarily 5th harmonic vs 2nd harmonic yet the total thd quantity is the same.

I should have been more careful with my "power supply in the signal path" comment. The power supply is not in the signal path, obviously, but the power supply is what we actually hear driving the speakers. As I understand it the "signal path" is merely a control signal to modulate the power supply in a way that replicates the input signal but amplified by a specific gain driven into a resistive load.

 

[Bob Lee (QSC)]

I do love a lively discussion! I also find it fascinating to watch engineers and audiophiles have a discussion, often they are not very long-lived. The audiophile may believe with a religious type of faith that their $2000 xlr cable improves their audio system. The engineer will insist that if it measures the same it must sound the same. I believe that the audiophile is absolutely wrong and the engineer is not always correct.

I should have been more careful with my "power supply in the signal path" comment. The power supply is not in the signal path, obviously, but the power supply is what we actually hear driving the speakers. The "signal path" is merely a control signal to modulate the power supply in a way that replicates the input signal but amplified by a specific gain.

I've never known an engineer to insist "if it measures the same it must sound the same." An actual engineer would look at it as "what does it do to the signal?" and use measurements to quantify what is observed.

 

[seamonkey]

I've never known an engineer to insist "if it measures the same it must sound the same." An actual engineer would look at it as "what does it do to the signal?" and use measurements to quantify what is observed.

Hey Bob - what do you mean by "what does it do to the signal?"
Isn't this a measurement? Given the same input signal, If they produce the same output waveform would not they be the same?

By they way, It's quite refreshing and remarkable that you, as a expert representative at QSC, point out that other amps can sound the same. Except, we all know there are lots of build quality, features, and support reasons to buy QSC over an other brand.

 

[psemeraro]

"I've never known an engineer to insist "if it measures the same it must sound the same." An actual engineer would look at it as "what does it do to the signal?" and use measurements to quantify what is observed"

Feet to the fire, I love it!
I was speaking in the most broad terms I could imagine to draw clear differences in mindsets. My perspective is unusual as I go "both ways" dabbling in the audiophile world and working in the pro sound world. You will never hear me mention words like "pace and timing" or "bloom" oir whatever the press is talking about this month. BUT I can hear clarity, seperation, space and grit.

It has been my experience that comparing different capacitors for example vs a piece of wire (taking load resistance vs uf into account) will demonstrate differences in sound and in general better capacitors sound closer to the wire than cheaper ones. Different opamps also sound different (making sure of course that they are not oscilating and have proper supply voltage) and this is easy to demonstrate with two adjacent mixer channels and a y cable.

For me the bottom line is that I have racks of QSC amps (formerly Carver, then Crest, now PLX and a few assorted RMX) that I depend on and with a few simple parts upgrades they are, to my ears, virtually the equal to "boutique" amps with more power, excellent reliability and realistic selling prices. While this might make a real engineer cringe, for me it has been a very rewarding ownership experience.

I also think it would be interesting for manufacturers to publish a full battery of tests on power amps at different power levels. THD, noise, IM, crossover, rise time, etc. My guess is that different amps would show more variations at 1 watt than they show at full power. Bob, I appreciate being engaged respectfully in this slightly off the path discussion. I hope I can buy you an adult beverage some day!

Cheers, Pat, Orlando FL

 

[Chef]

Nice conversation gents; thx.

 

[billhilly66]

I’d love to be able to dump my K2 and go with a light weight amp so I’ve checked out this thread with interest. I worked at a music store 10 or so years ago part time for the discount and used the demo matrix to mess around with every amp they had. I liked the K2, Macro, and CA amps much better than the others although light weight amps weren’t really happening back then.

If all or most amps can be made to sound the same, why do some cost so much more? There was a noticeable difference in the sound of different amps playing a cd through the same cabs when I had my buddy switch amps and adjust the source for volume while I wasn’t looking. Not scientific but sure enough, the high dollar amps sounded better. The cheap Crown amps didn’t sound as good as the high dollar Crown amps and so on with each manufacturer. There wasn’t much difference in the CA, Macro, and K2. I went with the K2 only because I got it for around $600 through a B stock deal directly from Crown.