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Rackmount Power Amps

#41
pbassnut said:
Bassballs27 … Funny you should mention Aguilar preamps as I have their DB659 preamp which, in conjunction with my SWR Stereo 800 and my Schroeder cab(s) is like the voice of God. I call it my "poor man's" DB750/DB751. The preamp and tweeter-less 15s of my 1515L have plenty of old school woof and the Stereo 800 adds a degree of clarity that works with my P-Basses (particularly my flatwound strung ones) like bread & buttah. BTW, have you tried plugging an external preamp into the poweramp-in jack on your DB751? The power section on that bad boy is going to be about as good as anything on the planet, IMHO.
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Very cool. I've heard a lot of good about the DB659. I had one chance to play one and it was ironically through a Schroeder 412. It sounded good, but didn't grab me the way the DB680 did. I'll have to try one through my current rig one day.
I'll see how the DB751 sounds like with the DB680 connected to its return jack. I might be in for surprise. I think I tried using the DI out of the DB751 into the QSC one time too. Hmmm, time for some more experimentation. Thanks for this post pbassnut.....it's got even more gears turning!
 
#42
Anyone had an experience with a Crown K2?

I've heard great things about this amp too.

In fact, I've heard a lot of great things about Class A/B power amps from back in the day.
Many of the old Crown Macro techs.......I remember those monster 5002 units. Holy crap, tanks!

It's funny that the PLX 1202 and 1602 are both Class A/B where the 2402, 3002, and 3402 are all Class H.
Class H is just a more efficient version of A/B..........but it's funny how the entire series is still the same weight. Interesting.
 
#43
In actuality, there are some weight differences between the PLX-1202 and 3003/3402, about 2 lbs.
 
#44
agedhorse said:
In actuality, there are some weight differences between the PLX-1202 and 3003/3402, about 2 lbs.
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Not that much of a difference actually. It's more like about 4 or 5 ounces. More parallel output devices and associated components, step circuitry, and such. It's a significant number of parts but they don't weigh much.
 
#47
Bob Lee (QSC) said:
The heat sink population is the same for all five models: four of the CH-000102-00 heat sinks (outputs) and two of the CH-000104-00 heat sinks (power supply).
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Ok, which amps am I thinking about? Is it the RMX-800 that has the shorter heatsinks compared with the larger models?

I hate it when this happens, I just can't recall where I saw it. Grrr ;)
 
#48
agedhorse said:
Ok, which amps am I thinking about? Is it the RMX-800 that has the shorter heatsinks compared with the larger models?

I hate it when this happens, I just can't recall where I saw it. Grrr ;)
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The RMX850 and RMX1450 have relatively shallow depths and short tunnel heat sinks. The (discontinued) RMX1850 and RMX2450 have deeper chassis and longer tunnel heat sinks. The RMX4050 and RMX5050 bump up to 3 RU height, a big fan, and a big transverse heat sink.
 
#50
Well, I finally got to test my DB751 with all my cabs and even ran the DB680 through the DB751.

The DB751 has WAY more output than the QSC PLX 2402 running in Stereo at 4 ohms.

My DB810 and DB412 sounded incredible with the DB751 running at 2 ohms, which is 975W.
The QSC should be running at 700W per cab, isn't that 1400W total?

I guess by cranking the gain, I could get more output out of the DB680 into the QSC PLX 2402……but it's almost not worth it.
The DB751 barely needs to be turned up past 9 o'clock with the master at 12 o'clock. Sounds amazing.

The DB751 sounded really loud with my Bergantino HD410's too. Big difference and a slightly different flavour than the QSC PLX 2402.
 
#51
Knob position means absolutely nothing when comparing maximum output.

Knob position depends on factors independent of rated power. Including the designer's desire for a particular impression of more power. What really matters is absolute power. If you aren't hitting the clip/limit LEDs on the PLX, you are not achieving rated power. Period.
 
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#52
agedhorse said:
Knob position means absolutely nothing when comparing maximum output.

Knob position depends on factors independent of rated power. Including the designer's desire for a particular impression of more power. What really matters is absolute power. If you aren't hitting the clip/limit LEDs on the PLX, you are not achieving rated power. Period.
Click to expand...

I agree that knob position isn't a fair comparison of maximum output between two separate amplifiers from two totally different manufactures.

I believe the issue is gain. I know Bob Lee has told me that the PLX series has the exact same gain structure in each model.
So if this is the case, and from where you're coming from, you have to drive the PLX series pretty hard to make them loud. My DB680 obviously needs to be cranked to achieve this.

Now I know for a fact that the DB751 does not sound exactly the same as the DB680 / PLX2402 rig. The DB751 seems a little more smooth to my ears and the 2402 seems a little more clear and precise.
Both are great though.
 
#53
bassballs27 said:
...you have to drive the PLX series pretty hard to make them loud.
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huh; my 3002 wakes up just fine with the output from my sansamp pedal, 1/4" unbalanced set to line level, pedal level at say 2:00 and power amp knob (whatever we want to call it) at maybe 10:00. bump the amp to noon and i could easily bounce against the clip lights (and blow my cabs up).

i did run into this sensitivity issue when i first scored some old but "real" amps for my little bar band PA, a powerlight 4.0 for subs and a powerlight 2.0 for the tops; coming off the old crown powerbase 3 i was using, the 4.0 was so "deaf" at the input that i had touble getting the subs loud enough, even though i had literally doubled the amp power to them (from 700/side to 1400/side).

i had to both refit my mixwiz and upgrade the rane EQ in line to true +4 balanced output to have enough input juice to wake that thing up!

i think the idea was that the bigger amps would actually put out the same power at a given input voltage as the smaller ones, and you needed more input level to get the bigger amps to "step up".
 
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#54
Hmmm……interesting……

I just ran the QSC PLX 2402 in Stereo at 2 ohms with the DB810 and DB412 on one side and the two Bergantino cabs on the other side.
The DB810 and DB412 on one side was perceivably louder than using both cabs on their own separate channel.
 
#55
I have a question about power amps in general for my larger rig. I'd really be interested in hearing about some knowledge out there. I am interested in purchasing one because I have so many great preamps to use. However...my plight is that I am concerned about the ohm rating on my cabs, and I want the power amp to work well with them. I use 2 Phil Jones 12-b cabs. Each have 12 5 inch drivers in them. They sound great ! My concern is that they are each rated at 6 ohms per cab. I am "ohm dumb", so any help and suggestions would be severely appreciated. Thanks in advance...Mark
 
#56
Power amps are rated for a minimum load (generally either 2 ohms or 4 ohms). For all practical purposes, you can consider your cabinets to fall into the 4 ohm catagory as far as the amp is concerned.

Most power amps can not drive less than 4 ohms bridged, therefore, paralleling 2 cabinets would not be an option for you (no big deal since there are plenty of suitable stereo 4 ohm rated amps available.)
 
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#57
Mark Corradetti said:
I have a question about power amps in general for my larger rig. I'd really be interested in hearing about some knowledge out there. I am interested in purchasing one because I have so many great preamps to use. However...my plight is that I am concerned about the ohm rating on my cabs, and I want the power amp to work well with them. I use 2 Phil Jones 12-b cabs. Each have 12 5 inch drivers in them. They sound great ! My concern is that they are each rated at 6 ohms per cab. I am "ohm dumb", so any help and suggestions would be severely appreciated. Thanks in advance...Mark
Click to expand...

You could however run both cabs in parallel to obtain 3 ohms using one channel of a QSC PLX series amp (which allows a 2 ohm minimum load)
However, for all intensive purposes……you're probably better just running them on separate channels independently.
 
#58
bassballs27 said:
Hey guys,

I figured I'd poll the audience with a more open approach, who here is still using rack mount power amps?

I've been thinking about retiring my QSC PLX2402 and going with a new power amp.
Not sure what brand or topology just yet. I really do like this Class H QSC.

At the moment, I'm working with 4 ohm cabs only, so I would like to work with a power amp that can handle 4 ohms per side and have a decent amount of power, say 1000Watts or more. I like good clean headroom on a power amp and as always they have a volume knob to turn them down (as does the preamp of your choice that you're driving it with too!)

I haven't really been liking the Class D stuff lately, but it might be worth trying a Class D Pro Level Power Amp. Any one using these?

I've also heard that the quality of certain brands of power amps have diminished over the years. Lots of people have been telling me to hold onto my PLX 2402.

Anyway, any feedback on some decent rack mount power amps (whether recent or recently discontinued) will be appreciated.
Click to expand...
The QSC PLX1804 is another excellent possibility. It's 900 watts per channel @ 4 ohms, class H, and weighs only 13 pounds. The difference of dropping the weight to only 13 pounds from a 25 lb+ amp makes a nice difference, especially in a larger, loaded rack. It is limited to a minimum 4 ohm load per channel (8 ohms bridged), but based on how you want to run your amp, that's obviously not a problem. I've been using this power amp in my largest rack rig and it's absolutely perfect, and LOUD.

p.s. - The difference between 900 and 1,000 watts is only 1/2 dB!)
 
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#59
figuredbass said:
The QSC PLX1804 is another excellent possibility. It's 900 watts per channel @ 4 ohms, class H, and weighs only 13 pounds. The difference of dropping the weight to only 13 pounds from a 25 lb+ amp makes a nice difference, especially in a larger, loaded rack. It is limited to a minimum 4 ohm load per channel (8 ohms bridged), but based on how you want to run your amp, that's obviously not a problem. I've been using this power amp in my largest rack rig and it's absolutely perfect, and LOUD.

p.s. - The difference between 900 and 1,000 watts is only 1/2 dB!)
Click to expand...

Hey, cool……I didn't see the PLX2 1804. That's a cool bonus and lighter weight.
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Hmm, I should check it out.

The one thing is still true (and what Aged Horse eluded to) is the fact that I'm really not driving my PLX2402 all that hard to begin with.
I was messing around with it again last night and really cranked the Aguilar DB680. I can see where the 700W is coming from now.
It's all in the gain!

I flipped the 2402 in Bridged mode at 4 ohms just for fun too and I really didn't care for it. It was a tad louder……but I was more worried about what would happen if I really cranked the preamp or if the preamp failed while the setup was running. I had all the limiters and filters on……but still…..it's not worth testing out.
 
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