# Remove/disable internal crossover on monobloc amp



## ninetysix (Dec 6, 2009)

Im using a pair of soundstream Picasso nano PN1.450D monobloc amps to power a pair of sealed alpine type R 8" subs on the floor in front of the seats as midbass drivers, and the amps internal crossovers are getting in the way. There is no "off" switch and dial only goes up to 250hz and it's a 12dB/octave Butterworth filter. I had my heart set on a steeper slope as I have a bit of a dip at 200hz. The phase shift is proving a little tricky to sort out too, everything would be so much easier with a 24db slope....

Sure the amps are meant for subs, although soundstream list the FR as going up to 30kHz... Kinda hard to get past 1kHz with a permanent 250hz 12db filter! It would be so much nicer if my DSP could handle all the crossings over. I've compared measurements of the same drivers powered by a 450w AB amp and the sub amp starts rolling off above 150hz, exactly the same as when I set a 250hz 12db/BW filter on the AB amp.

I haven't looked too closely at the board, but does this sound doable? Either disable it completely or perhaps changing the pot to a different value, so that the internal crossover is up around 500-1000hz and out of the picture?


Cheers


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## Lycancatt (Apr 11, 2010)

I would like to know about this too. been looking at doing a very similar thing as your doing but I think your right the permanent lowpass might be an issue.


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## ninetysix (Dec 6, 2009)

Hmmm, just had a thought.. If I set my DSP to a 12db/octave Butterworth low pass at 250hz, and the amp also does the same, does that not then become a 24db/octave linkwitz-riley filter? Which is probably exactly what I need any way. So DSP set to 12dB/BW low on midbass and 24dB/LR highpass on the midrange, all set to 250Hz and it should be in phase and sum to 0dB gain at crossover. I think. Neither driver is (naturally) rolling off by 250 anyhow.

Though I'm still keen to kill the amp xo if I can, I'd hate to find myself thinking "sounds like I'm a few degrees out of phase between 247-250hz" because I'm relying on the pot on an amp and the setting in the DSP to be the same :blush:


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## Justin Zazzi (May 28, 2012)

ninetysix said:


> Hmmm, just had a thought.. If I set my DSP to a 12db/octave Butterworth low pass at 250hz, and the amp also does the same, does that not then become a 24db/octave linkwitz-riley filter?


Yep, that's how it works.


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## ninetysix (Dec 6, 2009)

Jazzi said:


> Yep, that's how it works.


Cheers mate


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## ninetysix (Dec 6, 2009)

OK just a quick update, if any body else is interested in doing this, don't. At least with these cheap soundstream Picasso nano monoblocs, I finally figured out why I just couldn't find a good setup... These babies are clipping their ass off in the midbass range, strong as an ox if you low pass them around 120hz BW-4, but 60-200 the amp is hot as hell and the woofer is making awful mechanical clicking noises


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