Pre-Amp / Power Amp Woes

Your amp requires a large amount of signal to drive it fully. Your pre may not have that much output on its own. As long as your speakers are not sounding like they are going to die, you are fine. I would recommend turning your amp up all the way and controlling the volume from the output on your pre.

 

I'm guessing this is your problem:
XTi 2002 Sensitivity (for full rated power at 4 ohms): 1.4 Vrms

A quick look at the Ampeg manual makes it look like the omitted the output spec for the unit, but I'm guessing that you're probably getting about half that.

 

Whenever I see a post like yours I immediately suspect use of an improperly wired bridging cable. Are you 100% positive that you have a cable wired 1+ and 2+ on the amp end and 1+ and 1- on the cab side?

 

You would either need something like the ART Tube MP, or similar.

 

You only need the specially wired cable if running in bridge mode -- I assumed you were doing so because you mentioned the expectation of 2000 watts.

 

Its hard to truly know that that's the problem without much in the way of specs, but if I were you I'd take that preamp and test it out with a power amp that has a .775 input sensitivity and see if that does it for you. I don't think the 'clipping' light on the Ampegs are designed as a 'warning light' and are intended to show that you're saturating, so getting it lit isn't a danger, but still.

Take the preamp to a local store (or a GC, whatever) and 'shop' a couple power amps with .775 input sensitivity (Crest, Peavey, some QSC) and see if that fixes your problem. If it does, you know what to do.

 

One of those Ampeg pres didn't have a lot of juice at the output but I don't remember which model.

Yes, an additional gain gadget like the TubeMP or other will fix it if that is indeed the problem.

The amp may also be able to be modded to accept lower input voltage as well.

 

Question? Why do you need to run 2000w?? I run my system in parallel mode (into 2 cabs) and I have plenty of wattage. If I need more volume, I'll add my 2x12 4ohm cab on one side and the 2 single 12's on the other pushing 500 watts to each side. I run the amp wide open and control volume from the preamp. Also see if that amp has an input sensitivity switch (some do).

 

put an ART tube MP between the pre and power amp. This worked wonders for my rig, totally transformed it. AS was mentioned earlier , a lot of bass pre amps just don't have a strong enough signal to properly drive the power amp. The tube mp is less than $100.00 and worth every penny, it also has a high pass filter that may be useful. I don't really see it as adding any "tube" sound its really just about hitting your power amp with a good strong signal.

 

Try the XLR balanced outs of the pre into the amp instead of the 'preamp out' jacks. You'll probably get a much hotter signal(and be able to adjust it) that way. Plus you can run the cabs stereo with one dirty and one clean.

 

Hi m.pisa,

I did a search as well to see if your pre-amp is properly matched w/the "Crown xti 2002" and as 'CrazySkies' has stated, the amp's 'full output' requires a line input of 1.4V (+5dbu); and Ampeg does not give gain output specs on their "SVT-BSP" pre-amp. But I also noticed on the Crown spec sheet that this amp will only deliver it's full rated output at 2ohms stereo or @4ohms bridged. So at 8ohms/ch (stereo) you'll only see 475W/ch. You'll only see a full 2000W if you 'Bridge' the amp at 4ohms; not sure if you did that! Here's the spec sheet:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&sqi=2&ved=0CCwQFjAC&url=http://www.crownaudio.com/media/storagebk/amp_htm/xti2files/XTi2%20datasheet.pdf&ei=BlWwVKiuNMycNunjg_AE&usg=AFQjCNGEATJN1pleVm3a8APLhJLMagVO3w&sig2=bMYr7IHl8tlenZ_nJ-1ZDA

Worst case scenario, get a "Line amplifier" (line out booster) $30 bucks from amazon!

Best to you!

 

Not without a specially wired bridging cable, you're not, as Passinwind pointed out.

 

I'm no wizard at this kind of stuff, but maybe you pres output impedance and your power amps input impedance. Happens with pedals sometimes,a buffer is the solution!

 

Okay, here's an easy way to do it:

*You need a bridge speaker cable which can be accomplished via either banana plugs spanning the two center "red" terminal posts or Speakon plug wired +1, +2 inserted in output #1. As I understand it, both enclosures are 8 ohm and daisy-chained with a resulting ~4 ohm load.

*When connecting the preamp, use 1/4" output marked "Clean/Mix" just to keep things simple. Avoid the DI / XLR outputs as these are more appropriate for sending signal to the mixer / FOH.

*I hate this particular amp based solely on the input configuration: XLR only, no 1/4". Even my Crown XLS Drivecore 1500 / 2500's offer a 1/4" input. Since you're stuck, you'll need to snag a 1/4" T/R/S (balanced) >< 3 pin XLR cable to make the necessary connection. Here's a handful I found @ Sweetwater:
http://www.sweetwater.com/c813--Balanced_Cables_XLR_to_TRS

A balanced cable should work even when the preamp's output is not.

*Double check your Crown's set-up for bridged mono operation...it's easy to goof up if not careful. I don't know if the the XTi is anything like my Drivecore but my units require little if any attenuation for best performance / optimal gain structure.
http://www.crownaudio.com/media/pdf/amps/143060.pdf

*There's a really good chance you will not need to add any peripherals (boosters, etc) if you follow the above first. You'll be out the cost of the TRS / XLR cable and you can return that if the results are less than satisfactory.

Riis