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Old 15th July 2006, 05:11 PM   #1
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Default Active crossover questions

While I'm waiting on my ZV9 boards, I'd like to start thinking about building an active crossover. I've read mention of an article that describes DIY opamps, but I cannot locate it. Could someone please send it my way?

Also, is this still the way to go or have opamps improved to the point where this isn't necessary? I want this crossover to be as sonically benign as possible.

Finally, was the High/Low Pass ever finalized? If so, if someone could point me to that, I'd be grateful.


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Old 15th July 2006, 05:23 PM   #2
steenoe is offline steenoe  Denmark
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Paul, here is the article on DIY opamps:
I dont think that Opamps have improved much since that article, so they propobly only measures a 100 times better than a DIY
If I were you, I would try to take a look at BobEllis's PCB GB
Nope, the High/low was never finished! Or, I mean it was never published If it was finished, I have no idea

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Old 15th July 2006, 05:55 PM   #3
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Geez, I must have looked there 10 times!

I will look at the GB.

Thanks, Steen!
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Old 15th July 2006, 06:41 PM   #4
steenoe is offline steenoe  Denmark
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Hey Paul, dont even worry We all made that somewhere
Dont hesitate to ask further questions!

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Old 15th July 2006, 10:06 PM   #5
BDP is offline BDP  United States
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Here is a thread about MOX active x-over.

MOX - active crossover

Do a search on MOAMPS.
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Old 17th July 2006, 09:39 AM   #6
moamps is offline moamps  Croatia
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Here's the latest (somewhat improved and more compact) MOX version, for those interested:

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Old 18th July 2006, 05:40 AM   #7
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Beautiful Mox
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Old 13th August 2006, 05:46 PM   #8
BillWW is offline BillWW  United States
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Default Opamps?

I thought I would ask this over in the pass labs forum since it regards his amps.

Which opamp would not degrade the quality of his amps such as the Zen v9 or Alephs?

I have always thought of active as inferior to passive low level cross overs due to the active opamps.

However, I bought some of Bob Ellis's cross overs that will end August 18th on the group buy.

I have seen a lot of opamp mentioned there, but what about a class A opamp that would match the quality of an Aleph amp or jfet amp?

I hate to degrade the quality of the signal.

I believe Bob's cross over uses an 8 pin dip opamp.

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Old 13th August 2006, 06:35 PM   #9
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Bill -

You are correct - the group buy XO is configured for DIP-8 dual op amps. The spacing is too tight to use the MOX group buy discrete op amps without extraordinary measures that may cause other problems.

IMHO, OPA2134, OPA2132 or LM6172 will be totally transparent. Of course others are free to disagree

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Old 13th August 2006, 09:06 PM   #10
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It depends on your system.

Do you need to biamp?

Unless you can re create the exact voltage drive of the passive crossover the results of an active crossover maybe inferior irrespective of the theroretical gains or any potential for impurities in the signal pathfrom using additonal active stages.

I spent a lot of time building a mox active crossover and comparing it to other active crossovers. Others have compared chip active crossovers on the Lansing Heritage forums.

Under critical listening conditions there are audible benefits using discretre opamps biased into class A. Biamping using chips offers a firmer more detailed bass but there can be a dendancy to loose some of the nuances of the music. The effect of veiling of a chip based active crossover was noticed on a system using the X150.50 and an X250.

I would suggest attemping to bias the chip opamps into class A which is not difficult too do.

Building an active crossover thay is totally transparent is a real challenge. I discovered that the layout and earthing is really important to minimise any induced noise and simplicity works best. The power supply was a key element like so many Pass designs.

You could also try a simple Jet follower such as that referred to on the Borbely articles for the buffer depending on your needs.. Least is best....

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