Karaoke Forums

I thought I would share my amp strategy and get some input from the guys who have been in the business for a decade longer than me.

Also, I just bought two JBL SRX728S subwoofers, which have two 18" 800/1600/3200 drivers in each box. I got a killer deal on these things and could not pass them up. None of my amps are powerful enough to drive a 1600w RMS cabinet, however JBL has made it easy to open up the speaker and remove the input jack paralleling jumper so you can power each driver with its own amplifier. They must have had me in mind when they designed the input panel.

So I own (3) XTi 2000, (2) EP2500, (1) RMX2450, (1) EPX3000. Only the EP2500s and RMX2450s are good on subs, the others are switch-mode and I truly think all light-weight switch-mode amps suck on subs because of the way they are designed, unless you have a professional power distro box and a large-gauge feeder.

My plan is to rearrange my two amp racks so when I need a lot of power for one job, I can use one rack per side of the stage; and otherwise I will have one rack that is suitable for a small job, and one for a medium job with four monitor mixes.

Medium rack: (2) XTi 2000, (1) EPX3000, (2) EP2500 ~ 110 pounds net
Small rack: (1) XTi 2000, (1) EPX3000, (2) EP2500 ~ 95 pounds net
Spare: (1) RMX2450 ~ 45 pounds by itself, which is why I don't want more

And since I am modifying the SRX728S inputs for discrete operation, I will build some NL4 to 2xNL4 splitter cables so I can still parallel the 728s using a single amp in bridge mode when I need to.

I think most people would go buy much larger, more expensive amps for boxes like the SRX728S, but then they would need a very large and expensive spare. I think my plan saves me a lot of money. Three RMX4050HD amps (one spare) would cost about $3,300 vs four EP2500s and the RMX2450 cost me a little under $1,500; or a savings of $1,800 for nothing more than making some adapter cables. Plus my setup is more flexible for doing 2 jobs at once.

_________________
Jeff Wheeler, moonlight DJ/KJ

Sorry I can't help you --I just looked up those speakers...THEY ARE SOME SERIOUS SUBS.... Good luck with you plan !!! That must be one heck of a system you got !

Jeff, I have good news and bad news for you. The bad news is your planned configuration is not a good one. The SRX cabinets are 4 ohm when running in parallel. When you split them and go discrete, that's now 8 ohms for each input. Both the EP2500's and the RMX2450 are only capable of 500W/channel @ 8 ohms (you'd want a minimum of 800). So you'd be seriously under powering those subs if you went that route.

The good news is you're wrong about the capabilities of your amps and you don't need to mess around with discrete mode input or anything like that at all. You said have two EP2500's. Each one can deliver 2400W @ 4 ohms in bridge mono (same for the RMX). That's enough power to drive a 1600W cabinet. So that's what I'd do if I were in your situation (even though running a serious JBL cab with a Behringer amp makes me shudder a little). Run one EP2500 in bridge mono for each SRX cab in parallel input mode. Too bad you don't have another one of those QSC's, that'd be a much nicer amp.

Now off topic, but I got to know, what in god's name do you need over 3000 Watts of sub-low for? I'm hoping you do a lot of festivals and other such outdoor gigs or else you're running Karaoke for 300 person crowds.

_________________
DJ Tony
Let It Rip Karaoke

I don't think I explained my plan well. I was going to bridge 1xEP2500 into each SRX728 cabinet at 4Ω when I have one amp rack out, or 1xEP2500 into each driver at 8Ω when I have two there. However, your comment made me do some math and figure out if there was really any advantage to this; and you are right (of course) the difference works out to 98V bridged into 4Ω or 101V bridged into 8Ω, so I may as well just use one amp for each SRX728.


Indeed. I bought the one for $300 and if I find more crazy deals like that I will be getting more.


It's about a 150 person crowd on weekends, but my partner will be at a new bar down the street soon, and I don't know if they are doing a house PA or if he is bringing his mobile system. Either way, I am pretty sure 525s over 728s with reasonable power will be better than whatever they do down there; and my goal is to remain the best karaoke sound system in town.

Also, since my rig is at the bar on band nights anyway, I am using it for the bands once in a while. I had a rock band on my Kustoms over Peaveys Friday & Saturday and it was fine, but I want bands and their techs to feel confident about the gear, and 525s over 728s will give them confidence. I also bought 4 more wedges and have extra subs and 2x15s I can use as drum monitors if needed.

I mixed the band for about half the night Saturday, and I felt a little limited by my subs (EDIT: the 728s won't be here for a week or two; this was the Peavey subs.) I think part of the issue may have been the band tech who disabled the 100Hz HPF on every channel instead of just the appropriate ones, so a ton of out-of-phase energy was getting into all the drum mics and a fair bit of bass guitar into the bass player's vox mic. I asked him why he did it and he said it was his preference, so I did not change it, though I sure wanted to.

_________________
Jeff Wheeler, moonlight DJ/KJ

Yeah I can definitely understand if you're using it for bands why you'd want something larger (also explains how you can justify the cost, which I was wondering about too). Also you mentioning the Peavey's reminded me about the pictures you posted of the club you're playing. In that setting I can see using those SRX boxes, should be real nice!!

_________________
DJ Tony
Let It Rip Karaoke