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Old 13th September 2008, 10:59 PM   #1
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Default Rane Crossover Modification

Hello everyone,

I had abandoned my hi-fi system about a year ago when I got too busy with work, school etc. A few weeks ago I began my diy efforts again and built the system back, this time as bi-amp. The sad thing was I didn't have much time and I could not build a diy crossover. I bought a Rane SAC 22 which came cheap and installed it as the crossover on my hi-fi system.

Now I feel like a sinner putting a pro audio device with balanced connections in my link. I want to modify it with some better parts. Then perhaps I'll feel better

The crossover works with TL072 opamps and selection of the crossover frequency is done by a voltage controlled amplifier SSM2164. I'm planning to change the electrolytic caps in the signal path and maybe the opamps with better ones. Rane offers the schematics of the board in its website which is pretty cool.

I'd be glad to hear any comments on this subject.
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Old 15th September 2008, 10:13 AM   #2
Mooly is offline Mooly  United Kingdom
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Hi,
Had a quick look at the circuit. I don't really think you will gain much trying to mod this. The TL072 is suprisingly good -- better than most folks give credit for. The current consumption of the TL0's is low -- something to bear in mind when there are a lot of them. Having said that OpAmps do have a subtle "character" but so much depends on how good the rest of your system is-and what your trying to improve.
As to the caps, if they are reasonable quality "commercial grade" parts then again IMO I don't really think you will hear much difference. You might feel better swapping them but that's another story.
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Old 15th September 2008, 09:29 PM   #3
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Hello Mooly,

I think you're right about changing parts from the crossover. Changing parts with similar ones do not offer much improvement. But there's lots of room for improvement in acoustics. I'll try to eq the Rane now

My system has a dip at around 170Hz. I've found a peaking filter circuit from http://mysite.verizon.net/vze3xvxs/id1.html. I'm not sure what is the proper way to add it to the signal line but I think I will add it before the C46 and C52 coupling caps on the SAC 22. I may add a 1.5K resistor to the input of this filter circuit. I'll use an OPA2134.

Here's the picture of my peaking filters. Not soldered but setup

What do you think?
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Old 16th September 2008, 06:28 AM   #4
Mooly is offline Mooly  United Kingdom
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Couldn't find the circuit of the filter you mention but what you propose sounds OK. Trying to correct room response problems is never going to be easy. I think you will have to experiment a bit.
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Old 16th September 2008, 02:06 PM   #5
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Here's the link:

http://mysite.verizon.net/vze3xvxs/s...our_manual.pdf

I've done my tests with foobar media player equalizer. Boosting 170Hz 6dB Q=0,9 and adding the treble unit about 1dB gain will very much improve the vocals and body of the sound. I expect to have good results - if it is OK to add this peaking filter to the SAC 22 on that location.

I have the measurements of my speaker response measured from about 1m at http://keremdiy.blogspot.com .
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Old 16th September 2008, 02:28 PM   #6
Mooly is offline Mooly  United Kingdom
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Hi,
I really think your going to have to experiment with this. This is an area I've never worked on -- trying to equalise room response problems. I can't see any problems with inserting the filter where you intend. The "peaking" filter looks as though it uses an OpAmp to simulate an inductor (Gyrator) to obtain the very steep transfer function.
Not really my thing I'm afraid, I prefer the more direct signal approach.
Good luck with it all
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Old 17th September 2008, 10:09 AM   #7
kepa1 is offline kepa1  France
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Reading that review might be useful :

http://www.audioxpress.com/reviews/m...01verhagen.pdf
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Old 18th September 2008, 02:01 PM   #8
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Thanks kepa1 that helps.

This article will lead to some new work for me. First of all it's written for a AC 22 not a SAC 22. Secondly, the part codes on the schematics have changed on the AC 22 since then. I'll need to find the infrasonic filter and output caps on the SAC 22 and modify it accordingly.

I'm also puzzled there's so much difference in the THD ratings of AC 22 and SAC 22. THD is 10 times higher in SAC 22 though it's a simpler model. I guess it's the opamps and the design of the output stages.
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