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QSC PLX - 1602, 2402, or 3002/3402?

Discussion in 'Amps and Cabs [BG]' started by GRoberts, Jan 24, 2003.


  1. GRoberts

    GRoberts Supporting Member

    Jan 7, 2003
    Tucson, AZ USA
    I am assembling a Preamp/Power amp Bass rig to complement my Roscoe LG3005 5 string bass (Bartolini's with Aguilar 18V 2-way active Electronics) feeding a Bergantino 322 bass cabinet. (1x12, 2x10's and the famous Bergie Horn). I play mostly Blues/R&B/Funk/Motown/Jazz.

    My preamp decision is yet to be made. I'm following the preamp threads in that regard. Choices are down to Demeter VTBP-201, Kern 777, EBS Classic or maybe a used SWR Grand Prix or an RBI to save some money for now. I’m still undecided at this point.

    I'm trying to decide which make and model of Power Amp to choose. How much power is the best match for the 4-ohm Bergantino cabinet without going overkill?

    I've read a few TB'ers are using the QSC PLX 2402 (2400W Bridged - 4 ohms). Some are even using the QSC 3002/3402 series. Yikes! That's some serious headroom! (3000W - 3400W @ 4 ohms bridged mono!) At the normal volume levels I play at, would I notice any sonic performance differences if I chose the QSC PLX 1602? (1600W @ 4 ohms bridged mono) versus the higher powered QSC amps like the 2402 or 3002/3402? I'm leaning toward the PLX 2402 if the PLX 1602 is not quite enough headroom for the Bergantino. Is it unnecessary and overkill to go from the PLX 2402 to the 3002 or 3402 Series QSC's? At this point, I'm not interested in paying for more power than I need if it only amounts to 'bragging' rights. If there is however, a sonic difference, that would be noticeable, I'd like to know which QSC PLX amp you recommend for the Bergantino 322 cabinet.

    My desire for serious power is about tight, focused low B-string transient response with good punch across the entire frequency range at normal band volume levels. I don't play at "stupid" volume levels. (Anymore that is. Sigh. I don’t miss the ringing in my ears) It's bad enough putting up with all the voices in my head ...but I digress. ;-)

    Lastly, someone told me that he thought the PLX series amps were a bit skewed to the low end on behalf of DJ"s who prefer the QSC PLX amps because of a pronounced low/mid bass sonic bump. He said that the Stewart World amps (1.2, 1.6 or 2.1) are more sonically transparent. Any comments on whether there is a sonic difference between QSC PLX amps versus Stewart World amps?

    I also heard the World amps have been a bit less reliable. I'm strongly leaning toward the QSC PLX based on feedback in this forum from fellow working professionals. Your comments are most welcome. Thanks TB'ers!
     
  2. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Hi there,
    although the PLX's are capable of some scary output when run bridged, I'm using my 2402 in stereo.

    I'm currently using a single EA CXL 112 with my PLX 2402. The 112 can handle 350w, and my power amp is capable of up to 425W per channel @ 8 ohms. When I add another cab later, I know I'll have control over both cab volumes individually and still have a decent amount of headroom.

    In your case, your Berg 322 can put out 700w (mercy!) and it has 4 ohm impedance. If you were planning to never add another cab, you could make do with the plx 1202 which would give you 1200w @ 4 ohm in bridged mono mode. That's some headroom!

    But if you wanted to add another 322 (uncle!) or just A.N.Other cab at another date, you might want to look at the 3002 as that would be capable of delivering 900W per channel @ 4 ohms.
    The 2402 could theoretically be used to drive both channels fully at 700w in stereo, but this would have the amp at max output.

    Nice to see you've narrowed it down to 5 choices! ;-)

    I can relate though, I've already tried out Alembic F-1X, SWR IOD, Demeter HBP-1, Ampeg SVP-PRO. Out of these, I still have the Alembic. As someone said: "It's a bit of a one trick pony, but it's a very good trick".
    I'm also planning on trying out the Aguilar DB659, Kern and Warwick Quadruplet.
    Musicians Friend very generous 45 day return period has helped with a lot of this evaluation :)
    Anyway, I'll stop here lest I turn this into a preamp thread...
     
  3. FWIW, I own two 3002, and one 1202.

    The 2402 and higher models have the more efficient output stages. The PLX has an ever-decreasing input sensitivity as you go up in power. The 1202 is 1.0 v required input to drive it to full amplification. The 3002 requires 1.7 volts. This topic has been beaten to death here... use the Search functions.

    The 1202 is the most capable of tolerating full power 2-ohm loads. Evidently the same amount of cooling and heatsink capacity is common to all power ranges, so the 1202 has the highest ratio.

    Unless you get real lucky, PLX trade for substantially higher than 66% of new-discount price, on eBay. If you buy new, check out Lord Valve for great pricing and fast shipment. LV can also do the input sensivity modification for a modest fee.
     
  4. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    I have the PLX 2402 & 3002 with a Demeter pre, I never run them bridged because there is plenty of head room on either side. If your going to run the amp Bridged, the 2402 will probably be great for you with tons of head room. You can talk to Jim Bergantino about your needs.....he really knows what goes best with his cabs. Sounds like a great rig your putting together.......I wish they had the HT322 when I got my Bergies.....even though it's hard to imagine me being happier with my tone as it is now;) I heard from a lot of people the the 322 just rocks!!!!!!
     
  5. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    I have a PLX 2402, driving a pair of 4 ohm Acme Low B-2s in parallel mono mode. When I first added the PLX to my rig, it seemed to lack deep bottom compared to the RMX 1850HD it was replacing. But then I got an SWR Grand Prix, and the deep bottom is back. I really like this combination - the Grand Prix sounds great, offers a wide variety of tones, and has two XLR balanced outputs among its numerous ins and outs, and the PLX has ample power for my Acmes.

    I now think the weak bottom was due to the old preamp, which wasn't designed to drive the low input impedance of a PLX with the inputs paralleled. (The Grand Prix is - I've seen the schematic.) The old preamp works just fine with the RMX in my backup/practice rig. I'm a happy camper both ways now. :)

    In any case, I don't think the PLX adds any more coloration than other power amps in its class.

    One reason to pick the 2402 over the 1602 is that the 2402's class H output circuitry is more efficient than the class AB output in the 1602. The 2402 uses less electricity than the 1602 to make the same output power levels. This can help on gigs where the wiring is marginal. It also means the 2402 will stay cooler.

    I consider operating an amp in bridge mode, or at its lowest rated load impedance, as a last resort. It definitely stresses the output transistors more, and the sonic quality usually suffers as well. Yeah, the pro sound guys do this with subwoofers all the time, but they're trained pros, and the subs' narrow bandwidth masks any high-order distortion products.

    Unlike David, I don't see anything wrong with driving a pair of 4 ohm cabs with a PLX 2402. Speaker power ratings don't have anything to do with the demand they put on an amp - that's a function of speaker efficiency, speaker impedance curves, and your desired volume levels. If you actually pumped 700 W into your Berg for more than a fraction of a second, it would become toast pretty quickly.

    I do agree with David about leaving yourself options for adding a cab later. It doesn't hurt anything to leave one channel of a modern stereo power amp idle.
     
  6. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    BTW.....I also recomend Lord Valve for QSC products. Great prices and service....he really knows the QSC line! I've seen his prices comparable to E-bay......and alot more reliable.
     
  7. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Thanks for the info, I'm a relative newcomer to the pre/power/cab setup having been pretty content with combo's up until recently. I obviously still have some learning to do!
     
  8. rok51

    rok51

    Sep 2, 2002
    Crawfordville, FL
    I have an Alembic F-1X/PLX 1602 combo that I love. That said, if I were to do it again, I'd opt for the 2402 because of the class H output.

    Kim
     
  9. VicDamone

    VicDamone

    Jun 25, 2000
    Once again...ditto bgavin.

    That little tidbit you were told about the PLX's voicing. I'm not Bob Lee but I would doubt very much that they voiced in a mid bass hump for DJ's. I recently had my PLX in a very reveling high end hi-fidelity stereo system as well as my own and have never experienced any such hump.

    If there are any differences between the PLX and the Stewart (other than the fan noise) those differences would be very small. Don't forget the QSC offers you many switching, limiting, filtering options which become very handy when running and balancing dissimaler cabinets.

    Most importantly it may be one of the most reliable products used here. But who could say for sure?
     
  10. I am driving my PLX 3002 with an Alembic F-1X and while my tone is sweet and rich, I am having serious clipping issues. I use a side to drive one of my EBMM HD212's and whenever I start to push the serious dub-style lows my amp runs outta headroom and goes >CRACK<......Lovely. So, no problem with sensitivity at least not with the F-1X. Big problems with headroom however. Guess I'll have to try bridging.
     
  11. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    You sure that's not the drivers bottoming in the cab? Low-frequency clipping usually sounds like flatulence. Careful with that volume knob!
     
  12. Yeah, it certainly seems the exception and not the rule. How 900w's wouldn't be enough is beyond me. Unfortunetly, the clipping LED is definitely alight whenever that nasty sound occurs. It's less "flatulence" and more a nasty, staticy, electrical >CRACK< Could this be due to my cabs impedance changing at different frequencies? It only clips with the deeeeep dub lows.
     
  13. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    Hey Mad....do you have the clipping limiter switch engaged on your 2402? I've seen the clip light on my 2402 but I didn't hear any nastiness from my speakers.
     
  14. Yes I do..all limiters and roll-off switches engaged. I don't get it. I'd think that it could be the cab if it wasn't for the fact that the clip lights are blazing away as well. Is there possibly something wrong with my PLX? My old Mesa was only 600w's and it never clipped once. You'd think with the QSC's limiter's engaged that I wuldn't be having this problem. I've purchased a Rane DC24 (in transit) so we'll see if that helps as well.
     
  15. Jeff Haley

    Jeff Haley

    May 17, 2001
    Atlanta, Ga.
    I'm in the same situation. I have a Bergantino 3-10 and I am leaning toward a Kern-777 and a QSC plx 2402. I hope this will be my dream rig. I play Fender RB 5 and it is a great sounding bass. I've been searching for the right rig. Good luck.
     
  16. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    I'm still betting it's the speakers bottoming out, Mad Sub. Ported cabs like the MM HD212s (and most bass cabs, for that matter) don't have any control over driver excursion below the tuning frequency - and the frequency response drops off like a rock, so you have to really crank the bass boost to get any response at all down below that. That's a dangerous combination.

    The fact that you're clipping the amp doesn't mean that it's the clipping itself making the noise.

    I think the cab is rated for 40 Hz, below that you're taking your chances.
     
  17. The impedance is lowest at the tuning frequency. This means the most power draw. But it is also the point where the drivers have maximum cone loading, and the minimum amount of movement.

    The clipping LED is a sure sign for running out of head room. Then again, I run my 3002 at red line constantly while trying to keep up with a guitarist with his 30w tube screamer. I don't have any nastiness from the amp at full clipping, and I also have enough speakers in the circuit that I'm not over driving them. I have two subs in one channel of the 3002 operating at a total of 4 ohms, drawing 900 watts. The driver combined total is 2,000 watts, so I'm not thermally limited.

    I suspect the cracking noise is over driven speakers.
     
  18. Ok, thanks guys.
     
  19. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    PDX
    Even if you've got your own 15 A wall circuit for the bass rig, doesn't that give you about 1800 watts max? How would you get more than that without blowing a fuse somewhere?

    I need to understand this. :p
     
  20. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    That's a fair question. In fact, because no amp is 100% efficient, you can't even deliver that much power continuously. Class D might be 90-95% efficient at best, but most of us are using Class AB or H amps that are less efficient. You might be able to get 1200 W continuous out of a typical Class AB amp before popping the breaker, maybe a little more from Class H.

    The answer is that music has big peaks on transients, but the average power is much lower - typically a factor of 10 or more. You need the peak power capacity for headroom, but the amp spends most of its time putting out less than 10% of its capacity.

    For example, if you're getting occasional clipping on a 1500 W amp, and you aren't using a lot of compression, you're probably pushing around 150 W on average.

    That's how you can get away with a 1500 W (or larger) amp on a 15 A circuit breaker. That's also why Class H is a win for big amps, because it reduces the power consumption (and heat dissipation) in the power range where the amp spends most of its time.