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Pre/Power Setup Question: almost too silly to ask

Discussion in 'Amps and Cabs [BG]' started by yoss, Aug 12, 2005.


  1. yoss

    yoss

    Oct 1, 2003
    This is probably going to sound pretty silly, but here goes.

    I'm switching to a preamp/poweramp setup for the first time (once the units arrive) this week and I have a question on how everything connects together. I'm sure the manuals will explain, but I want to try to have all the right cords I'll need ready and waiting.

    So here it is...I'll have a Sansamp RBI and a QSC RMX 1450 with an Avatar 410 and 115. I'll probably want to run it bridged mono to ensure proper headroom against the two guitarists with their full stacks. Exactly what sorts of cables would I need to purchase to set everything up correctly? I'm clueless about "speakons" etc. as I've never had to use them or have owned anything with them. From what I've gathered along the way in reading various posts that mention them they're a bit different from the usual 1/4" inputs. Or are they?

    Sorry for the newbish question. But I'm entering a new realm of amplification here. Any advice or suggestions on setting this up, or alternate configurations is appreciated.
     
  2. rockstarbassist

    rockstarbassist Banned

    Apr 30, 2002
    The Woodlands, TX
    Endorsing Artist: HCAF
    I'll give this a shot, but others chime in and correct me if necessary!!

    From your pre to power amp, all you'd need is some sort of 1/4" or XLR speaker cable. I had an older Monster Speaker 1000 cable lying around, and use that to go from my Demeter to Peavey amp.

    If you're bridging mono, you need to get, find, or have one made, a mono bridgeable speaker cable. It will have 1+,2+ connections instead of the 1-,1+. I get mine from Pro Cables 'N Sound, and it might be a good place to start. I can hardly ever find them in most music stores. From there, just run Channel 1/A to your first cab (which should be 8 ohms if your amp's bridging at 4), and then a regular cable run from the Out on your first cab to your second one. You should be pullin' full juice in no-time! :)
     
  3. TheChariot

    TheChariot

    Jul 6, 2004
    Boston, MA
    Your going to have an awesome rig :)

    Alright... so first step is going from the preamp to the power amp. You need to run from the preamps output into CHANNEL 1 of the RMX. It should be in the upper left corner in the rear of the amp. You can use a standard cable. You'll obviously prefer a short one.

    AFter that, you'll have to set your power amp properly to run bridged mono. There's these teenie tiny little switcher doodads in the back of the RMX, and it thoroughly explains how to switch it for what you need.

    You cannot use standard 1/4" speaker cables on an amp this powerful.... but its not as horrifying as you think. Speakon cables are cool because they LOCK into the jack they're in. However, there's a catch. To run in Bridged Mono with a Speakon cable, you have to rewire it so that is bridges the two power amps. Standardly, speakons come ready to run in the regular (stereo) mode. But.... if your weary over screwing around with rewiring.... you can just buy a Banana Plug cable with a Speakon on the other end. That's what I did :smug:. No, it doesnt lock in, but its just as good really. If you use a speakon, plug into Channel 1 of the power section. If you use Bananas, You plug it into the 2 red banana inputs... they're clearly labeled for mono-bridge usage. Then you run the other end into the speakon jack of the top cab. After that.... you take a 1/4" speaker cable, and run it from the first cab, and into the second cab. And you should be all set... and very very loud. ;)
     
  4. Dr. PhunkyPants

    Dr. PhunkyPants Guest

    Aug 11, 2002
    USA
    Also, please confirm that the two cabinets you ordered are each 8 ohms, which will be a 4 ohm load when paired. Most power amps, when run bridged, shouldn't be pushed below 4 ohms. It they aren't 8 ohm cabs, you may want to return them. Alternatively, you could run a single cab off each side of the power amp.

    Can the amp do it? Probably. Should it? Probably not.
     
  5. yoss

    yoss

    Oct 1, 2003
    Thanks for the great replies so far!

    Sorry, forgot to mention that both cabs are indeed 8ohms. Here's a follow up question:

    Do I just use a regular instrument cable (short of course) to connect the preamp to the poweramp? Or do I use a speaker-type cable? Or is there something else?
     
  6. Dr. PhunkyPants

    Dr. PhunkyPants Guest

    Aug 11, 2002
    USA
    use a short (1'-1.5') instrument cable. You can find them at the music store. It is important for this cable to be short because it reduces the length of exposed to the power amp and back of the speakers, which can result in additional unwanted noise. Do not/not use a speaker cable.
     
  7. TheChariot

    TheChariot

    Jul 6, 2004
    Boston, MA
    Yep.... plain old instrument cable... short enough for you to use to connect a couple of distortion pedals together.
     
  8. If you use banana plugs you won't have to rewire your Speakon plugs.

    Banana plugs can be "stacked" if you get the right type. Get the open back type and plug one banana plug into the other. Then insert this whole thing into the (Bridged Mono (yes, they're really red) jacks on the amp. Make sure the switches are set as described above.

    (2) 10ft cables with appropriate connectors will run you about $45 @ GC.

    I know this because I just did a rig similar to this, albeit with a BBE preamps into an RMX850 power amp into (2) 2x10s. Sounds great! :bassist:

    My cabs have 1/4" inputs (only), so I got banana->1/4" cables. Make sure you get the correct ones for your cabs.

    -- Sam
     
  9. BigSky Bass Guy

    BigSky Bass Guy

    Apr 15, 2005
    Yeah, just watch your ohmage.

    That rig is going to be all-out awesome. Probably won't even need that 15" cab.
     
  10. So to summarize.... some conflicting info earlier,

    DO NOT USE SPKR WIRE to connect pre to power amp. that should be short audio cable (xlr if you have them at both pre-out and pwr in), or 1/4" is fine if its instrument level and shielded, NOT spkr wire...

    If you have spkon connectors on pwer amp for bridged output, get the spkon NL2 connectors (grey plastic outer shell), not the NL4 connectors with blue outer shell with metal latch. On my SWR amp, the newer #4 connectors won't even fit, its on purpose to prevent hooking up bridged output wrong I think. Not sure if other pwr amps are the same, possibly true if they have seperate bridged output spkon jack. If the speaker has 1/4" inputs, make sure if the 1/4" plug going into the spkr doesn't have an insulated outer shell, you wrap it in electrical tape. Running bridged, that metal cover is not ground, it is hot. If it comes into contact with something grounded, Shock potential. Shorted output of power amp potential. Banana jacks are the next best connector to use after spkon, followed by 1/4" as the least desireable.

    Randy