Electronic crossover modification - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th January 2007, 10:23 PM   #1
qguy is offline qguy  Canada
diyAudio Member
 
Join Date: Mar 2005
Location: Burnaby
Send a message via AIM to qguy Send a message via MSN to qguy Send a message via Yahoo to qguy
Default Electronic crossover modification

cross posted in loudspeakers ...

WARNING ....not an electronics expert.. not even an electronics amateur...

but I just built an electronic subwoofer crossover from a kit, I simply soldered and prayed a lot It has a volume gain pot but it has no cut-off frequency pot, it has a DPDT that switches from 50 or 70 hz. Is the default 50 or 70 hz setting based on the values of the resistors and capacitors ? Does the two IC thats built into the kit play a role in the cut-off frequency. My goal is to change these to 30 and 40 hz, as I can still localize the position of the sub on the 50 hz setting.

Click the image to open in full size.
__________________
na
  Reply With Quote
Old 4th January 2007, 11:52 PM   #2
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
The actual filter is the section in the middle, it's a new topology on me, but at a quick glance it looks like it is only a first order crossover as I can only see one pole. Of course, I reserve the right to be completely wrong.

This means you only have a 6dB slope, so no wonder you can still localise the sub. Changing caps or resistors won't help much I'm afraid, you need a much steeper slope. Where did that kit come from? Do you have any references?
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 5th January 2007, 12:47 AM   #3
qguy is offline qguy  Canada
diyAudio Member
 
Join Date: Mar 2005
Location: Burnaby
Send a message via AIM to qguy Send a message via MSN to qguy Send a message via Yahoo to qguy
its from a local electronics store.. unfortunately, its the only one available...how about daisy chaining two of these ?
__________________
na
  Reply With Quote
Old 5th January 2007, 01:04 AM   #4
diyAudio Member
 
Join Date: Jun 2003
Location: Menlo Park, CA
Quote:
Originally posted by pinkmouse
The actual filter is the section in the middle, it's a new topology on me, but at a quick glance it looks like it is only a first order crossover as I can only see one pole. Of course, I reserve the right to be completely wrong.

This means you only have a 6dB slope, so no wonder you can still localise the sub. Changing caps or resistors won't help much I'm afraid, you need a much steeper slope. Where did that kit come from? Do you have any references?
IC1B is an inverting buffer, gain = 16.8. You'll need to turn down your sub-woofer volume 24.5dB compared to what you had before you tried to use the low-pass filter. Replacing the 500 and 510K resistors with a single 15K part will get you back to unity gain.

IC2D is a second order Sallen Key low-pass filter with unity gain.

With SW open, F0 = 50Hz and Q0 = .73
With SW closed, F0 = 70Hz and Q0 = .69

A third pole is added at 153 Hz before IC2C.

IC2C is a unity gain non-inverting buffer. You should have a resistor (try 196 Ohms) in series with its output to limit short-circuit current and avoid oscillation problems driving capacitive loads.

With calibrated output level (Measure with an SPL metter. Try pink noise a couple octaves wide in the sub's pass band and main speakers') no port noise, no rattles, and low distortion the sub should not be localizable.

Integration with the main speakers may be a problem.

http://en.wikipedia.org/wiki/Sallen_Key_filter
http://www.linkwitzlab.com/filters.htm#2
  Reply With Quote
Old 5th January 2007, 02:43 AM   #5
qguy is offline qguy  Canada
diyAudio Member
 
Join Date: Mar 2005
Location: Burnaby
Send a message via AIM to qguy Send a message via MSN to qguy Send a message via Yahoo to qguy
Hi Drew, thanks for the inputs.. to summarize

1. Replace the 500 and 510 K resistors with a 15K part
2. add a 196K ohm resistor in series with the ic2s output' , that would be before the 2.2K ohm resistor right ?

the new circuit would look like this right ?

Click the image to open in full size.


After doing all these what would the effect on the sub be ? did I just lower the crossover point ?

thanks]
__________________
na
  Reply With Quote
Old 5th January 2007, 03:52 AM   #6
F1 FAN is offline F1 FAN  Canada
diyAudio Member
 
Join Date: Jun 2006
The changes Drew suggested only change the gain to unity ,the crossover points won't change.The resistor he mentioned is actually 196ohms not 196K ohms and it should be at the output of IC2C pin14 not before the 2k2 resistor.The crossover actually has an 18db per octave slope.If you want to lower the crossover frequency you can do this by changing 3 resistors with larger values ,or by increasing the value of the .47uf and .22uf caps either by replacing them or paralleling new ones with them.
  Reply With Quote
Old 5th January 2007, 04:18 AM   #7
qguy is offline qguy  Canada
diyAudio Member
 
Join Date: Mar 2005
Location: Burnaby
Send a message via AIM to qguy Send a message via MSN to qguy Send a message via Yahoo to qguy
Quote:
Originally posted by F1 FAN
The changes Drew suggested only change the gain to unity ,

Gain to unity ...hmmm what could this mean ? help !!!

you can do this by changing 3 resistors with larger values ,or by increasing the value of the .47uf and .22uf caps either by replacing them or paralleling new ones with them.

lets say target is 30 hz...should I change them to 20 ohms instead ? is there a simple formula that an idiot could use - thanks

__________________
na
  Reply With Quote
Old 5th January 2007, 04:35 AM   #8
F1 FAN is offline F1 FAN  Canada
diyAudio Member
 
Join Date: Jun 2006
Unity gain means that the signal into the unit will not be boosted by the circuit at all.With the original resistors(500k,510k) it would boost the signal 16.8 db which is way too much for a sub crossover.

If you were to double the value of either the resistors or the caps in the filter section you would lower the crossover to exactly half the frequency.For instance doubling the two .47uf's and the .22uf you would then have a crossover point at 25hz (instead of 50hz) and 35hz( instead of 70hz.)
  Reply With Quote
Old 5th January 2007, 04:43 AM   #9
qguy is offline qguy  Canada
diyAudio Member
 
Join Date: Mar 2005
Location: Burnaby
Send a message via AIM to qguy Send a message via MSN to qguy Send a message via Yahoo to qguy
Quote:
Originally posted by F1 FAN
Unity gain means that the signal into the unit will not be boosted by the circuit at all.With the original resistors(500k,510k) it would boost the signal 16.8 db which is way too much for a sub crossover.

If you were to double the value of either the resistors or the caps in the filter section you would lower the crossover to exactly half the frequency.For instance doubling the two .47uf's and the .22uf you would then have a crossover point at 25hz (instead of 50hz) and 35hz( instead of 70hz.)

THANKS !!!
__________________
na
  Reply With Quote
Old 5th January 2007, 04:46 AM   #10
F1 FAN is offline F1 FAN  Canada
diyAudio Member
 
Join Date: Jun 2006
Your welcome
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help with modification of QLN crossover Cyberkul Multi-Way 2 3rd October 2008 08:46 PM
Rane Crossover Modification kbasaran Parts 7 18th September 2008 02:01 PM
crossover L-pad modification Theli Multi-Way 7 26th January 2007 05:31 PM
electronic crossover modification qguy Multi-Way 5 4th January 2007 11:54 PM
Crossover Modification Jim McPherson Multi-Way 1 1st October 2005 05:05 AM


New To Site? Need Help?

All times are GMT. The time now is 02:16 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2