some questions about power/pre setup

themattacaster · #1 07-13-2010, 08:50 PM

So I am in the market for a new amp and have been doing a bit of research but am still new to the idea of a power/pre amp setup rather than a head that has the two packaged together.

I have an Aguilar S810 that is rated at 1000 watts (4 ohms) but i only really need around 500 maximum for my band. From what I understand: power amps generally have two separate power sections and can be bridged to combine the power sections and essentially double the output. For example the QSC GX3 runs at 250 watts/channel therefore bridged it would run at 500 watts at 4 ohms.

PLEASE CORRECT ME IF I AM WRONG!

So my question is what limitations to selecting a preamp would there be depending on the poweramp or the other way around? In other words: is there any reason why I couldnt match ANY preamp with ANY power amp? and if so how do I determine these restrictions?

-Matt

sawzalot · #2 07-13-2010, 08:59 PM

I've used separates for many years now, and I don't think they depend on each other very much, in my experience. You want a good sounding preamp, the choice of which is guided by your ears and signal processing needs. But as long as the preamp is capable of driving the power amp, you should be fine. Power amps are somewhat standardized regarding how much input signal it takes to produce full output, and I think most preamp designers keep that in mind.

So my advice is, pick the preamp that sounds great to you and lets you do what you need to do with your signal, and pick a rock-solid, reliable power amp. You should be good to go at that point.

Tom

bassplayerbob · #3 07-13-2010, 09:09 PM

If your thinking of using the GX3 as your amp, dont try to bridge it! I own the GX5 and the are designed to run as a 2 channel amp with a 4 ohm min load per side. I mention this because you used that amp as an example,

themattacaster · #4 07-13-2010, 11:17 PM

Quote:

If your thinking of using the GX3 as your amp, dont try to bridge it! I own the GX5 and the are designed to run as a 2 channel amp with a 4 ohm min load per side. I mention this because you used that amp as an example,

I was actually thinking of using this but that was just the first thing that had caught my attention. If you have any suggestions for a power amp that would put somewhere around 500 watts into 4 ohms that would be very helpful?

also I forgot to ask earlier how do you go about bridging a power amp? (how do you connect the cables?)

Sten · #5 07-14-2010, 02:35 AM

Not all power amps allow bridging, check the user manuals to check. Also it iw wrong to assume that bridged output is double the separate, this can or cannot be the case. Also, the minimum allowed impedance increases with bridging (e.g. if both channels can run 4 ohm minimum then bridged you can run that amp 8 ohm minimum).

One thing to consider is the output level of your preamp and the input sensitivtiy of the poweramp. For best results the output of the preamp should be higher than the input of the poweramp (e.g. in my case my preamp has 1.0V output while the poweramp has 0.75V input). You can safely run your pre into a poweramp with sensitivity of 1.25V or 1.4V aswell, but the sound can get degraded. Again, consult user manuals.

Also, check that the poweramp you are looking for has the input and output sockets that you need.

For 500W I would recommend Peavey IPR1600 (or similar) and use only one side at a time. The other side serves as backup or can be used to drive a second cab if needed.

More info on preamps:
http://www.ovnilab.com/articles/preamp.shtml

lbwdog · #6 07-14-2010, 06:20 AM

Quote:

Originally Posted by themattacaster

If you have any suggestions for a power amp that would put somewhere around 500 watts into 4 ohms that would be very helpful?

also I forgot to ask earlier how do you go about bridging a power amp? (how do you connect the cables?)

There are plenty of choices but if you're just looking for more power, any conventional integrated bass amp would be more practical IMO. MarkBass and Genz Benz both have 800w/900w (@ 4ohm) micros (I'm sure there are others). G-K has the 1001RB-II at 700w and 22 lbs., and there are plenty of others.

themattacaster · #7 07-14-2010, 12:24 PM

Quote:

Originally Posted by lbwdog

There are plenty of choices but if you're just looking for more power, any conventional integrated bass amp would be more practical IMO. MarkBass and Genz Benz both have 800w/900w (@ 4ohm) micros (I'm sure there are others). G-K has the 1001RB-II at 700w and 22 lbs., and there are plenty of others.

I realize it is probably more realistic that I am going to just get an integrated head but I wanted to at least explore this option instead of completely writing it off

brotherbassj · #8 07-14-2010, 12:33 PM

QSC sound states to power a cab with 2.5 x the RMS wattage of the cab.......this is for sound.............I used a qsc rmx 2450 with an avatar 4x10 and it sang like a bird! NOW.......all the technical guys can tell you that I never really used the full wattage and had I done so would have fried my speakers.....but they can explain that to you..........I used the setup for over a year, every weekend..........mono bridged into 4 ohms.........so in theory 2400 watts to a 1000 watt cab.........there is no obvious or audible damage to the cabinet.....I ran the power amps WIDE OPEN.................not an expert but had a great year running that setup......with an avalon U5 as my pre

BassmanPaul · #9 07-14-2010, 12:41 PM

There is nothing wrong with using a pre/power rig. I've done so since the Sixties. It's a very versatile set up.

Bridging is accomplished usually by operating a switch or flipping a couple of links or DIP switches. If the amp is stable with 2Ω per channel you can bridge into 4Ω.

A preamp can be anything that has the output voltage sufficient to drive the power amp. Some pedals can do so. You can use a microphone channel strip with great success or one of the bass specific pre-amps.

Paul

emohair · #10 07-14-2010, 01:02 PM

I have been really happy with a pre-amp/power amp rig for years. It's versatile, and you can get used power amps on the cheap. Swapping out different pre-amps is pretty fun, but can get costly if you aren't shopping around. I would suggest getting something like a QSC PLX 1602, it puts out 1800 watt at 8Ohms, which in reality would not blow up your cab as long as you aren't running it at 11

Sten · #11 07-15-2010, 12:33 AM

Quote:

Originally Posted by brotherbassj

NOW.......all the technical guys can tell you that I never really used the full wattage and had I done so would have fried my speakers.....but they can explain that to you..........I used the setup for over a year, every weekend..........mono bridged into 4 ohms.........so in theory 2400 watts to a 1000 watt cab.........there is no obvious or audible damage to the cabinet.....I ran the power amps WIDE OPEN

I do not doubt that you ran your setup like this with success, but I still doubt that you pushed your cabs with 2400W constantly. First of all, power amps are meant to be ran wide open. Still, it will output 2400W only if it is given the maximum input it can handle and even then you would probably have to be vigorously playing low B. You could try measuring the output RMS power with some device if you can do it safely (reminds me of the TC Electronics video where they power a chain saw from output of RH450

)

Still, I agree that a higher powered amp usually works very well together with a lower power handling cab, and with 1000 or 2400W at your hands you don't need to push it to clipping area where RMS figures really have no meaning

johnk_10 · #12 07-15-2010, 01:15 AM

i'm using an Avalon VT737SP channel strip with my crown xti2000 bridged mono at 4 ohms (2K watts) into an accugroove whappo jr. cab ( rated at 800 watts) with no problems whatsoever. i've run it super loud, but i don't think that i've ever run the full 2K watts for any real length of time, but i'm sure that it would blow the speakers or the crossover if i did.

Son of Bovril · #13 07-15-2010, 02:23 AM

unless you are looking for like over 1000watts or you specifically want the ability to swap out your preamps I would advise rather looking into the newer lightweight heads... I don't see much reason to start looking at bridging a bulky poweramp just to get 500 watts. There are many brands available (SWR even does a tiny 400watt poweramp - though ovrpriced IMO) in the lightweight category at the moment and you could still use other preamps by just going straight into the fx return if you prefer

BassmanPaul · #14 07-15-2010, 11:29 AM

Quote:

Originally Posted by Son of Bovril

unless you are looking for like over 1000watts or you specifically want the ability to swap out your preamps I would advise rather looking into the newer lightweight heads... I don't see much reason to start looking at bridging a bulky poweramp just to get 500 watts. There are many brands available (SWR even does a tiny 400watt poweramp - though ovrpriced IMO) in the lightweight category at the moment and you could still use other preamps by just going straight into the fx return if you prefer

This is the reason I no longer use the pre/power rig. I couldn't find a light weight power amp to replace my ailing Carvin DCM1000. It took a tumble in its road case and channel two became intermittent. I bought the Carvin BX1500 and am pleased as punch with it. I don't use any of the bells and whistles - it's just run flat. It sounds superb. First bass amp I bought since the Sixties!

Paul