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Crest CA9 or Stewart 2.1
- Thread starter atrapp
- Start date
Here's the other edge of that sword. An engineer acquaintance (he modded a guitarist friend's stompboxes) could not understand why anyone still used tubes. To paraphrase: "tube technology is obsolete; good tube amps are heavier and more expensive than their solid state counterparts". I'm thinking he didn't understand the difference between "production" and "reproduction"! Bottom line is that tube emulation has become pretty good lately, but still doesn't beat real tubes.
I'm also grateful to those guys, Bill Fitzmaurice, and others: I've unlearned much misinformation here at TalkBAss. In this case: I think Bob *might* be correct about gain matching, but I'm still not convinced. I've seen nothing more than anecdotal references to double-blind testing that supports his point. Hey... unlike other debates (fingerboard wood, anyone??), at least there's SOME science. Even so, I just don't think there's enough for anyone to claim the scientific/better-educated high ground.
I think you are missing my point (first I'd never argue tubes vs. emulation!). I hear the same differences between the two amps that everyone else hears when the gains aren't matched. When I took the time to measure the signals and match the gains I no longer heard a difference. I don't know if someone else would hear the difference, but the three bass players in the room that day went from hearing significant differences "at the same volume" between the amps to not hearing any differences when we set them up for a fair fight (it wasn't a double blind test though so am I just telling myself there is no difference? Maybe!).
I think Dr. PhunkyPants and Vic are on the better conversation now, which is the design choice's impact on the marketplace. No reasonable purchaser is going to gain match these amps to test drive them and no reasonable purchaser is going to pick the QSC over the Crest based solely on sound if they aren't matched (plenty may pick QSC on weight or other factors). Don't knock the QSC's design from a technical standpoint, question it from a marketing perspective. I'm sure QSC has made an informed choice about why they want their input sensitivity as high as it is and why not to try to compete with the gain provided by the CA9. I'm sure it is based on selling more of these amps for use in pa systems than as bass amps.
Vic, to address your point, I think you are neither stupid nor ignorant. My post was written late last night after a long day at work. If my point was lost and you took me to be criticizing you, I'll take the blame on that one and offer my apology.
That's what I was gonna post. I'm sure the vast majority of QSC's sales go towards PAs and not bass rigs. Any half decent piece of pro audio gear will be able to properly drive the QSC amps.
The question now is, why don't bass preamp manufactureres make their pres with hot enough outputs to properly drive pro audio amps!?!?
BINGO!.............. Whodaknown. I prolly would have kept the 2402 then, but I had no advice as to the input sensitivity on it.
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
I suppose QSC and others should revamp their lineups so that a ridiculously low .5 volts or so will fully drive them (better make new lightweight but heavy-looking faceplates too, with a macho look that just screams POWAH!). That way people who just don't seem to realize they just need to run their preamp's post gain high enough to push the amps into mild clipping on peaks can just leave the post knob where it always is and be driving that amp to the brink and beyond so often that the particular amp is hailed as being the loudest/fullest sound around ; }
That's one good thing about heads: they often are designed so that their preamp section has totally driven the power section by the time their knobs have been turned halfways up. A lot of players put big stock into "My knobs are only up to 3 and this thing is rockin!'" and seem unable to embrace pro sound practices, so perhaps power amp designers need to be aware of that mindset and accomodate it (even though in some cases the needs of those interfacing them with pro SR gear will be derailed).
</sarc>
I really appreciate this comment, and to give you your due, I really can understand your position (and Bob's, and some others... yeah, I also have a degree). So if anything, what I think it all boils down to is this... is real life with all kinds of different stuff attached really exactly like the specs and test results show across a 50-10KHz sweep? Some, such as yourself, feel there's really no room for lattitude here, and the answer is yes. I'm still not convinced, but rather than get too mired in acedemics, I'll just continue to do what we all should do... buy and play what works best for me... for whatever the (real) reason.
There is always room for latitude. I just don't hear it in this case. By contrast, I have recently taken up building tube amps as a hobby. I can't build two amps to sound the same. I can use the same circuits, components, etc., but there is just too much latitude in layout and tolerances and wiring to get exact matches. I believe that there are differences between every single electronic device, even within a product line, I just think I can't hear the differences between these two products. I would rock the **** out of either of them!
I will say one thing, however, I'm going to keep my eye out for a good deal on a PLX1802 and try them again. I love my Stewart, but I'd rather have something that would fit in a shalow rack, and also not have the 1 minute delay if A/C is cycled.
Well maybe we need to clearly define something: what exactly do we mean by gain matching? Are we talking about the matching the nominal output of the pre-amp to the input sensitivity of the amp? Crest CA-9 have .775V input sensitivity. (It can be adjusted to higher values, but this is the factory default.) The input sensitivity of the QSC PLX2502 is 1.15V. I understand this to mean that the QSC needs twice the input level to get similar output levels. This is the minimum voltage input needed to drive the amplifier to full output. Do I understand this correctly?
So what does this mean in terms of the typical bass pre-amp? What is the voltage output of my Kern IP-777? I thought it put out as much as +24 dBu or 12Vrms. Is this not correct? Does the IP-777 not have enough voltage to drive these amps? What am I not seeing here?
Also, I thought +4dBu, (1.22V), is the industry standard for a line level signal. This appears to be enough for either amp.
(I picked the QSC PLX2502 because it's power rating for '8Ω 20Hz-20kHz 0.1% THD', 1400 watts, is most similar to the CA-9, which is 1600 watts.)
So what does this mean in terms of the typical bass pre-amp? What is the voltage output of my Kern IP-777? I thought it put out as much as +24 dBu or 12Vrms. Is this not correct? Does the IP-777 not have enough voltage to drive these amps? What am I not seeing here?
Also, I thought +4dBu, (1.22V), is the industry standard for a line level signal. This appears to be enough for either amp.
(I picked the QSC PLX2502 because it's power rating for '8Ω 20Hz-20kHz 0.1% THD', 1400 watts, is most similar to the CA-9, which is 1600 watts.)
Here's what I did. I used a recorded bass sample to set the levels. If I remember correctly we started by picking an input voltage of approx. 0.25 for the Crest which based on the gain ratios is equivalent to an input voltage of 0.54 for the QSC (0.25 x 86.5 = 0.54 x 40). These were well under the input max for both amps. We listened to the recorded bass and played our own basses through the amps. We varied the levels up and down a bit making sure to again match the levels. Nothing was double blind, there was no ABX switching, it was completely non-scientific. It "proves" nothing, but it made me pretty comfortable with what I was hearing.
Someone more deeply knowledgeable about these issues can correct me if I am wrong, but I believe the only reason to look at input sensivity would be to find out the input required to drive both amps to max power. When matching the gains, it is better to simply deal with the gain of each amp. In this case, the QSC has to get a signal that is more than twice as hot, but if you feed it that signal, you get, to my ears, a matched output.
I know nothing about your Kern, so I will let someone else field those questions.
bongomania
Commercial User
IMO it would have been nice for Bob to have provided us with some of this information, instead of just saying "those who know, know" and then telling us "that is how power amps work". 
IMO it would have been nice for Bob to have provided us with some of this information, instead of just saying "those who know, know" and then telling us "that is how power amps work".
To be fair to Bob, I think he's done just that in several different threads and has gotten beat up over it every time. He may be a bit battle-wary.
I guess the bottom-line here is that one cannot compare these different amps by driving them at the same levels. It is not a deficiency of the PLX amp that it requires more input signal from the preamp, but I would be curious to know if that need is a function of the type of amplifier, and if there are any benefits to that from a design standpoint. Not from the perspective of which is the better amp, just curiosity.
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Or just tired of typing the same stuff in over and over just to get more of the same... I've been told SEARCH works now ; }To be fair to Bob, I think he's done just that in several different threads and has gotten beat up over it every time. He may be a bit battle-wary.
Well, I know the original PLX series all give 32 dB worth of input gain, so I'd assume they all have the same input circuit design - and that's for everything from the PLX1202 which can be driven to rated power by 1.0 volts for 8-ohm loads, to the 3402, which requires 1.9 volts to do the same. Any decent pro sound gear can deal with that span and do more besides, and a lot of bass preamps can too - if people don't assume that their preamp's post-gain/volume control should stay glued to the same position it is in when driving an amp that only requires .75 volts to, er, reach climax.
bongomania
Commercial User
Ah, good. Let's say I came to this freshly, and had read multiple posts claiming that a CA9 sounds different than a PLX. Assuming I don't already know that they require different input voltages, what search terms should I be expected to use to determine the truth of those claims?
We've been down this road sooo many times.
In my experience, the Crest Audio CA-9 is a far better power amp for bass than a QSC PLX. (I owned a PLX.) For the mids and highs in a PA system, I would not hesitate to use the QSC PLX.
I agree 100%
Case in point: I was using a PLX2402 when I received my pre-production model Read Custom Purity preamp. I instantly had problems getting enough volume without my 2402 clipping like crazy. I called Jack Read about what was happening. We talked about my setup and he felt my QSC amp required more input voltage from my preamp. I shipped my Purity back to him to have it's output voltage adjusted. When I got my Purity back, Jack had even went the extra mile and installed a variable output knob on it's back panel, just in case I ever bought a different power amp with a lower input voltage requirement. I still had the clipping/lack of headroom problems, especially on my lowest notes, but running the preamp's output voltage knob wide open increased my overall volume a bit, yet my PLX still clipped, mainly when I played my lowest notes.
Wanting better low end reponse from my Roscoe's B-string I researched a few different brands of speaker cabinets here on TB. I eventually bought a Bergantino HT210 and a Bergantino HT115. I called Jim a few times and during one of our conversations I mentioned my preamp/power amp setup and the problems I was experiencing. He recommended a few different "lead sled" power amps, I decided to give a Crest CA9 a try.
I know nothing about matching gains, and very little about electronics. I also respect Bob Lee. He's always been very nice when I participate in these threads. So Bob, without beating me up
, please explain why my CA9 was the "better" of the two amps, or how I was running my PLX2402 incorrectly after reading this:IME when comparing the overall volume of my PLX2402 and my CA9, with the front panel outputs of both amps all the way up, my CA9 was much, much louder. The CA9 also had no clipping problems, even when I played my lowest notes hard. When I bought my Demeter HBP-1 preamp I tried the same "tests". Once again, the Crest was clearly the "better" of the two amps in regards to low end headroom and overall volume without clipping.
I switched to the CA9 and I kept my PLX2402 as a spare. Later, my band required subs for a gig. We used my PLX2402 that night to power our subs, but it was practically clipping the entire first set. My old drummer owned and ran our P.A.. None of his P.A. gear is low or mid-priced stuff. He has worked as a repairman in the audio field for close to 30 years and I consider him to be very knowledgeable about electronics and sound reinforcement. He was concerned about the PLX clipping, so during our first break we switched my CA9 over to power the subs and the PLX2402 to run my bass cabinets. The CA9 didn't clip once during the night. After the gig, my drummer commented on how well the CA9 did. And as a matter of fact, my CA9 was used to power our subs a few more times after that without a hitch.
I've since sold my PLX2402. I preferred some of it's features over my CA9, like speakon outputs, etc., and it's light weight, but it didn't do what I needed it to do nearly as well as my Crest does. BTW, I didn't notice any tonal differences between my QSC or my Crest. The differences I noticed were overall volume and clipping.
Just my 2 cents.
-Art
