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earlier XLS 402 questions


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#1 Aw_dee_o

Aw_dee_o
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Posted 03 February 2006 - 04:16 PM

The bass player in a band that i work with recently purchased an earlier version of the XLS-402 for use with his actively crossed bi-amp bass rig.  After initially putting it into use with one channel working full range and the other idling, we've run into some problems.

First of all, the amp seems to clip phenomenally hard when overdriven.  That is, the sound breaks up horribly i.e. cracking with a very slow recovery time.  We were running the one channel into two high sensitivity 15's in a vented cabinet ( higher efficiency ), yet with a 4 ohm load and a supposed 400+ watts rms playing in his living room, the amp was clipping.  On top of that and in order to minimize over-excursion and "slapping" of the ( poorly ) vented drivers, i had the EQ set flat with a -12 dB drop at 20 Hz.  Using another "bass guitar amp" of 400 watt rating ( ha ha ha ), we never experienced this problem.  While i know that reducing the bandwidth that each channel sees via the 24 db electronic crossover will increase amplifier efficiency and available headroom in the "real" set-up, the horrendous recovery time when clipping in the "trial" set-up really has me worried.  

For sake of reference, i was running the high pass filter on the back of the amp at 15 Hz and the "limiter" set to on.  I was under the impression that the "limiter" would act as some sort of "soft clipping" circuit, but judging by what i'm hearing now, i must be wrong.  Given that i don't have a manual for this unit and the info on the Crown website pertains to a newer model without these features, i'm kind of operating in the dark on this aspect of operation and what to expect.  

As such, i'm wondering what i can do to this amp in order to help alleviate this problem.  I know that i can increase power supply reserve in order to minimize sag under peak and long term conditions, but i'm thinking that this may not be enough.  Is it possible to easily modify the existing circuitry to add a "soft clipping" circuit in the negaitve feedback path?

As mentioned, our initial impressions of the amp are based on single channel full range use driving two fifteens and this is completely different than what we will be using the amp for.  I could be freaking out over nothing as we'll have another channel with an active crossover to reduce the load, but being the "perfectionist" that i am, i'd rather be safe than sorry.  I helped this guy pick out this gear and now it's going to be my bag to make sure that it delivers as promised.

Rig that the amp will be driving is as follows:

Peavey MI-1 two channel Musical Instrument Preamp

ART 351 31 band EQ

ART 310 24 dB active crossover

Crown XLS 402

11 gauge low inductance speaker cabling

Two custom built cabinets.  Each cabinet contains two 10" drivers and one 15" driver in sealed chambers with a Q of appr .7 or so.  Was planning on crossing at appr 320 - 450 Hz or so, depending on what sounds best.  

Any and all help / comments appreciated.  Sean
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