Active crossover questions

[Paul Ebert]

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.

Thanks.

Paul

 

[steenoe]

Paul, here is the article on DIY opamps:
http://www.passdiy.com/legacy.htm
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

Steen

 

[Paul Ebert]

Geez, I must have looked there 10 times!

I will look at the GB.

Thanks, Steen!

 

[steenoe]

Hey Paul, dont even worry We all made that somewhere
Dont hesitate to ask further questions!

Steen

 

[BDP]

Here is a thread about MOX active x-over.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=27651

Do a search on MOAMPS.

 

[moamps]

Here's the latest (somewhat improved and more compact) MOX version, for those interested:
http://www.moxtone.com/mox.htm

Regards,
Milan

 

[macka]

Beautiful Mox

 

[BillWW]

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.

Bill

 

[BobEllis]

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

Bob

 

[macka]

Bill,

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....

Ian

 

[Paul Ebert]

Re: Opamps?

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

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'm in the same boat, except that I'm probably going to have a three-way or even four-way setup and use most of the EQ and notch filtering capabilities of the Active Filter 4. So, I'm looking at a lot of opamps in the chain.

At a certain point I realized that and thought "Doh, how unzenlike". I may try LM6172s, though I'm concerned about oscillation (I'm a newbie, so I will not know how to deal with it if it arises).

I'm going to stick to the plan of the filter feeding Z9s, but it will be fairly incongruous.

I've thought about starting a thread on a Zen discrete opamp. It sounds like it would be difficult to make it fit the filter PCB, however.

Maybe I will need to rethink my speaker design...

But, hey, it's DIY so it's all good

 

[Paul Ebert]

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

When you say 'chip opamp' are you refering to an OPA2134 and the like as opposed to a discrete opamp?

If so, I'm really curious how you would bias one to operate class A. I don't see how you bias one in any direction.

Please fill me in about this.

Thanks.

Paul

 

[kristleifur]

When you say 'chip opamp' are you refering to an OPA2134 and the like as opposed to a discrete opamp?

If so, I'm really curious how you would bias one to operate class A. I don't see how you bias one in any direction.

http://www.tangentsoft.net/audio/opamp-bias.html

To bias an op-amp into class A, you simply put a current source from the op-amp's output to one of the power rails. Everything else is details. This article is about those details.

It's pretty clever

Edit: also note the links at the bottom of the referred article at Tangentsoft.net - and browse the rest of Tangent's website while you're at it! It's truly a goldmine of information.

 

[macka]

That pretty well covers it and by all accounts it makes a difference.

Just check the power dissipation ratings for the various chips.

macka

 

[BillWW]

Possibly 4 way

Bill,

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....

Ian

I am currently using a 3 way horn plus a stereo sub. I would like to keep the signal path as pure so like the idea of keeping it simple. I have found in the Aleph's that biasing in class A makes a huge difference in stereo spaciousness. So, perhaps the opamps could benefit likewise.

If the cross over sounds bad in the highs or less transparent, perhaps I should keep it on the bass and subwoofer only?

I guess I could try through listening tests to see if it is transparent enough or not? I think for the bass or subwoofer, it may be okay since an inductor seems to rob the power from the amp.

So, which opamp can handle the greatest biasing? I think that has been the trick to my alephs sounding wonderful. I also prefer a jfet opamp on the input.

Further ideas on which opamp would meet my criteria of heavy biasing?

Bill

 

[macka]

I would start with the opa2134 and review the data sheets and consider the opamps mentioned above.

If you like send me an email and I will scan a whole TAAS article by Paul Stammer on getting the best out of opamps for you.


Macka