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Old 29th December 2007, 08:57 AM   #1
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Default Gaincline Bi-Amp / Active Crossover - work in progress

I've taken the plunge to remove all passive crossover and build an active one. The circuit is 24dB/octave Linkwitz-Riley based on the design at http://sound.westhost.com/project09.htm. For a $50 project it's a tempting gamble

Click the image to open in full size.

The system was previously based on 1st order passive crossover so the phase coherency was already good. However upon powering up the active system there is much much improvement in transparency of the sound. Everything sounded 'easier' the bass even reminded me of my open baffle setup, but much..much power

At the moment i'm using 2 channel LM3875 build and a spare dared gainclone with tube stage (to drive the tweeters). But tonight I'm going to add additional channels using similiar LM3875s ... we'll see how it sounds...
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Old 29th December 2007, 10:21 AM   #2
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What speakers are you using? Be warned, changing from passive to active crossovers may require a change in the size of the box, particularly if it is a ported design!
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Old 29th December 2007, 10:29 AM   #3
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I wonder why I need to change the box size?

It's a pair of Jensen SPX-7. The original crossover was pretty crappy, simple 1rst order with no Fs compensations and sounded pretty harsh. Managed to upgrade the crossover to proper cutoff frequencies, but did not like the inefficiencies of notch filters...
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Old 29th December 2007, 11:30 AM   #4
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Quote:
I wonder why I need to change the box size?
It's to do with removing the passive crossover and changing the alignment of the whole box+crossover. It may not make enough difference to hear but is always worth remembering if you want optimum performance!

In the case of a speaker I went active with, box volume changed from 27 litres to 32 litres before it sounded its best!
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Old 30th December 2007, 01:02 PM   #5
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Ok... managed to cram 4 channels of 3875 amps into this little box. Believe me this thing SINGS

However I'm pulling my hair as the new pair of amps have hums. It's also running noticeably hotter than the old pair They are the exact same design except changing the R from metal film to carbon ...

Click the image to open in full size.
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Old 30th December 2007, 02:21 PM   #6
Nuuk is offline Nuuk  United Kingdom
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They are the exact same design except changing the R from metal film to carbon ...
That won't make any difference!
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Old 30th December 2007, 04:44 PM   #7
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I'd like to place a wager that the grounding is arranged differently.
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Old 5th January 2008, 10:24 AM   #8
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very nice chipamp .
hmm how about VA of transformer to do this?.
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Old 5th January 2008, 11:49 AM   #9
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It's 160VA and does not seem to strain even when playing loud ... not sure what the correct requirements for 4x 3875s though... anyone have any ideas ?
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Old 5th January 2008, 11:57 AM   #10
AndrewT is offline AndrewT  Scotland
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hi,
a 4channel 60W could be run from a 200VA to 500VA transformer.
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