Gaincline Bi-Amp / Active Crossover - work in progress

gainphile · 29th December 2007, 07:57 AM

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

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...

Nuuk · 29th December 2007, 09:21 AM

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!

gainphile · 29th December 2007, 09:29 AM

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...

Nuuk · 29th December 2007, 10:30 AM

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!

gainphile · 30th December 2007, 12:02 PM

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 ...

Nuuk · 30th December 2007, 01:21 PM

Quote:

They are the exact same design except changing the R from metal film to carbon ...

That won't make any difference!

AndrewT · 30th December 2007, 03:44 PM

I'd like to place a wager that the grounding is arranged differently.

sukyone · 5th January 2008, 09:24 AM

very nice chipamp .
hmm how about VA of transformer to do this?.

gainphile · 5th January 2008, 10:49 AM

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 ?

AndrewT · 5th January 2008, 10:57 AM

hi,
a 4channel 60W could be run from a 200VA to 500VA transformer.

29th December 2007, 07:57 AM	#1
gainphile diyAudio Member Join Date: Dec 2007 Location: Melbourne the sunny city!	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 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... __________________ http://gainphile.blogspot.com

29th December 2007, 09:21 AM	#2
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

29th December 2007, 09:29 AM	#3
gainphile diyAudio Member Join Date: Dec 2007 Location: Melbourne the sunny city!	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... __________________ http://gainphile.blogspot.com

30th December 2007, 12:02 PM	#5
gainphile diyAudio Member Join Date: Dec 2007 Location: Melbourne the sunny city!	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 ... __________________ http://gainphile.blogspot.com

30th December 2007, 03:44 PM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I'd like to place a wager that the grounding is arranged differently. __________________ regards Andrew T.


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5th January 2008, 09:24 AM	#8
sukyone diyAudio Member Join Date: Jul 2006	very nice chipamp . hmm how about VA of transformer to do this?.

5th January 2008, 10:49 AM	#9
gainphile diyAudio Member Join Date: Dec 2007 Location: Melbourne the sunny city!	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 ? __________________ http://gainphile.blogspot.com

5th January 2008, 10:57 AM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	hi, a 4channel 60W could be run from a 200VA to 500VA transformer. __________________ regards Andrew T.

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