Ampeg Bass amp help.. please..

[jgcable]

I just bought an Ampeg SVT-3Pro to replace the GK 800RB that crapped out on me. The Ampeg is a rack mount bass amp. I have a problem that I can't figure out. On the GK, there is a biamp feature that has jacks for 2-4 ohm cabs and jacks for standard 8 ohm jacks.
The Ampeg only has 2 speaker jacks on the back of it.
I have 2 bass cabinets. One is an 8 ohm Bag End with a 15: EV in it. The other is a 1x18 that I am pretty sure is either 2 or 4 ohms. The problem is this.
If I plug in the 1 x 15 8 ohm cab the amp sounds fantastic. If I plug in the 1 x 18 in the other jack it sucks the life out of the amp. Do I need some sort of a crossover?? With the GK I would plug the 15" cab into the 8 ohm speaker out and the 18" cab into the 4 ohm speaker jack and it sounded killer. Am I missing something here??

[mwm70]

Re: Ampeg Bass amp help.. please..

Is the Ampeg set up to biamp? What I mean does it have two separate power amps with a built in crossover? If it does not then all you are possibly doing is running the cabs in parallel, if that is how the jacks in the head are wired. Which raises another question, what is the minimum impedence the head is capable of? An 8 ohm cab and 4 ohm cab run in parallel gives you an impedence somewhere around 2.6 ohms. While it usually does not effect the sound running below the minimum ohm rating it will eventually smoke the head. Also Ampeg and GK make entirely different sounding heads. GK is known for a clean or what some call sterile sound where Ampeg is known more for a tube-like grit. I would definitely check the impedence restirctions and make sure you are not running below them (usually it is 4 ohms on most bass amps). Good luck.

[mwm70]

Re: Ampeg Bass amp help.. please..

I should have done this first, Checking the owners manual on the Ampeg site, The SVT 3 Pro has a minimum impedence of 4ohms and the jacks on the back are wired in parallel so hooking an 8 ohm cab and a 4 ohm cab into them will eventually smoke the head. Again good luck.

[thebisch]

Re: Ampeg Bass amp help.. please..

A couple of things going on hear...First off, the Ampeg isn't a bi amp setup. Second, I find 18s suck the life out of most rigs, unless you have super high power, which the Ampeg isn't. Also, if your mystery cab is 4 ohms, you are running a 2.6666...ohm load, and if it is 2 ohms you are running a 1.6 ohm load. The Ampeg is rated down to a 4 ohm load. You are probably just running out of current supply from the amp. I doubt you will blow up the amp, it should shut down before any damage occurs. IIRC there is a thermostat controlled fan in those also, which should kick on as well. I do know from experience, however, a common failure of these amps is the fan doesn't come on when its supposed to. A common fix is to wire the fan permantly on. The SVT3pro is a great amp, but you are asking way too much of it most likely. The problem is you bought the wrong amp for your needs

[RickStar]

Re: Ampeg Bass amp help.. please..

dude go to the ampeg site and they have a forum like this that can answer anything you will ever need. my buddy uses it for his svt 4 pro