[Beardy]

Hi folks,

I am seeking guidance from the people who have gone down the active path...

I have just had an epiphany with the recent evaluation of the MMGs from Magenpan; I had forgotten how much fun it is to listen.  I am currently using an OPPO BDP-103 directly connected to an Emotiva XPA-200 amp (2x 240W into 4ohms).  The OPPO has volume control and I am not using a preamp.  To my unqualified ears it sounds great, so I am keen to get `more' as long as the law of diminishing returns doesn’t hit too hard…

I intend to buy either 12s or 1.6s (Wife doesn’t want to go larger!!?!).  I have also just acquired an LPA-1 Emotiva amp; (6x 225W into 4Ohms).  I would like to build a stereo pair of open baffle subs in H or W frames and use an active crossover and drive with 6 channels of amplification.  That leaves me a couple of spare channels.

I have read as much as I have been able to find in the last few weeks and was planning to buy something like a Rane  AC23 or similar (DBX or cx3400…).  There seem to be plenty on ebay.  I think I will probably have to make up some interconnects as most of these active crossovers used balanced or ¼” plugs and the cd player uses RCA o/p.  Other than that can it be as simple as connecting it all up and then trying it (at low volume)?

Do I need to put a cap in the tweeter circuit?

This is a lot of money (for me) to spend on audio stuff, so I am keen to try to keep this to a budget.
I have seen 1.6s at about 1k and MG12s for a little less – are these reasonable prices for speakers in good condition?

I can solder and diy and will likely make better frames at some point, but I don’t have an SPL meter and don’t want to get in so deep that I have to throw a lot of $ at solving problems I hadn’t anticipated, so I am keen to avoid these by leaning on the experience of others….

Any guidance you can give would be most appreciated.
Thanks
Beardy

[jk@home]

Not an expert here, but AFAIK it's not correct to use crossover settings as is employed in the standard analog low-end pro crossovers on Maggies. You have to go digital like the Behr. DCX2496 or MiniDSP, and set it up properly for best results (whole other subject).

I would use the pro crossover like you describe above between the Maggies and subs, but to crossover in the Maggies themselves, the other (cheaper) option would be to look at a diy passive line level crossover design. There are other folks here that can help you design that.

Here's one example, for the MMG, from member Davey. Quite simple:

http://home.comcast.net/~dreite/MMGPLL.htm

Just remember you most likely will also need some EQ for the subs, so you have to take in account where that will happen. The digital crossovers can also do EQ.

Currently I'm not actively crossing over my MMGs on the line side, instead using the speaker level series design. In my system, I have the EQ (Behr. DEQ2496) in the digital front end before the DAC, then cross over the lows from the MMGs to IB subs after my preamp, using a simple analog DBX223xs. But I still run the MMGs full range, to keep their signal path out of the DBX.

[Davey]

An active crossover like the AC23 (or similar) is not the best choice since they're constructed with 4th-order state-variable filters.  You completely lose any flexibility regarding slope rate, asymmetry, separate filtering frequencies for the sections, etc, etc.  This type of flexibility is especially important with speakers like Maggie's that have electrical filtering which varies signficantly from "textbook" curves.
You could try the Rane unit, but you'll find the result is much-too-much midrange which totally unbalances the speakers.  A low-Q correction notch filter with adjustable parameters could be added before a generic active crossover, but that's a DIY (or DSP) project.

If you want to do it on-the-cheap there's nothing better than the PLL approach linked by jk.  However, many variables need to be considered and the design is probably not "transportable" should you change preamp/amp(s) combinations.

Integrating dipole woofers adds another wrinkle to the problem since there are no commercial, active, analog crossovers set up for the EQ required.  Some of the DSP-based units would be suitable.  If an analog solution is preferred this becomes a DIY project with some complexity.  I built my own and it yielded the best sounding MMG-based system on the planet. 

Take a look here:  (near the bottom)

http://home.comcast.net/~dreite/MMGframe.htm

The w-ASP circuit boards from Linkwitz would be an excellent solution for a project like this since they allow complete flexibility of integration between Maggies and dipole woofers.

http://www.linkwitzlab.com/Pluto/woofer-asp.htm

Cheers,

Dave.

[josh358]

Davey is the go-to guy on this. I'd just add to what he said (which is far more informed than what I could have said) that I'd recommend the 1.6's over the 12's (the 12's are excellent, but the 1.6's moreso), and I'd keep it simple to start. There are several reasons for this. You want to get the 1.6's set up optimally in your room and familiarize yourself with their sound before you start fiddling with crossovers and adding subs. And it's easy to experiment with placement too when you're just feeding a single signal to the speakers. Once you've done that, the first thing I'd do with the LPA is passive bi-amping, that is, using the speakers' internal crossover but with two channels of amplification, one driving the tweeter, one the woofer. That's the easiest way to make use of the extra power. Then you can move on to external crossovers and H-frame dipoles. Re the H-frames, when you integrate them you really do want an SPL meter. It will save you a lot of time and the Radio Shack SPL meter is dirt cheap, easy to use, and fine for setting bass. Integrating a sub is a tweaky business, much harder to do by ear than with a meter.

Finally, the big issue with older Maggies is delamination. The adhesives they used were moisture sensitive and on some of them, the wires are coming loose from the diaphragm. Magnepan sells an economical repair kit or fixes them for a few hundred dollars, but obviously you want to avoid that. So make sure your 1.6's or 12's are relatively recent production, made after Magnepan introduced the new adhesives which don't delaminate. After 2005 I think should do it. You can call Magnepan with the serial numbers to verify that they are newer production. Otherwise, problems are rare.

[Beardy]

Many thanks,

I take the point that it makes sense to get the placement right before messing with the active crossovers. 

I have read that in general the SQ might be better using an analog approach.  Its clear that there are people here who could design the PLL circuit and if so this would be my preferred approach.  I dont anticpiate changing the setup much once i am happy.  Is the necessary information available to do this for the 1.6QR?

Is it likely that I would need a preamp after the PLL to compensate for the insertion loss?

Any comment on the typical price range for 1.6 Maggies?

Cheers

[Davey]

Is it likely that I would need a preamp after the PLL to compensate for the insertion loss?

No, a good preamp with low output impedance 'before' the PLL is the preferred setup.

In order to design one you need to know output resistance of the preamp and input resistances of all power amps and their voltage gains.

The price range is not much.  Usually just twenty bucks or so.  Gold-plated RCA connectors and a small enclosure are the most costly items.

Cheers,

Dave.

[jk@home]

...Is it likely that I would need a preamp after the PLL to compensate for the insertion loss?...
Cheers

Yeah, that's the only downside to PLL x-overs, they have to be designed for the specific equipment you will be using. In other words you size it for your power amp's input impedance, etc. If you switch amps with a different rating or throw another component before or after, you have to start over.

Dave was graciously going to help me build a PLL a few years ago, but I bailed partially because I was using old Aragon amplifiers, didn't know how much longer they would last. Of course I'm still using one now

If you are using your Oppo as the gain control, is the output impedance constant or variable? I use a passive attenuator as a preamp, but have a tube buffer downstream to lower and stabilize the output impedance to the power amp.

Although an added expense, if I went for a PLL now, I would think including  buffer circuits in it, like the Pass B1, would make it more upgrade proof. This way the PLL is sized for the buffer(s), then different equipment can be used downstream. Is this correct, Dave?

[Beardy]

A buffer circuit would require an OpAmp and some power supply right?  A fully passive circuit has an attractive simplicity despite its specificity.  Once I know what equations to crunch and have seen it done once, I could probably handle a change (he said with naive optimism).

If I went with a PLL for the Maggies, for which values could be guessed at with some accuracy given that information already exists on the existing crossover, could I use something like Outlaw's ICBM for the bass?

thanks
Beardy

[jk@home]

Maybe Dave can post the generic formula for the 1.6, to make it easier to plug in the numbers and go forward. How about it Dave?

[Davey]

I think the ICBM (if you have one) would be fine for a typical (conventional) bass integration with Maggie speakers, but it lacks the necessary EQ for dipole woofers.

Regards the PLL.  As I said, you need to know the input resistance of both amps and voltage gain difference (if there is any.)  The preamp needs to be fairly low output resistance and have decent voltage gain in the line-amp portion.
The formula is just the standard formula for capacitive reactance.
This is the basic starting point for textbook responses, but doesn't work well for actual configurations:

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

Cheers,

Dave.

[josh358]

Many thanks,

I take the point that it makes sense to get the placement right before messing with the active crossovers. 

I have read that in general the SQ might be better using an analog approach.  Its clear that there are people here who could design the PLL circuit and if so this would be my preferred approach.  I dont anticpiate changing the setup much once i am happy.  Is the necessary information available to do this for the 1.6QR?

Is it likely that I would need a preamp after the PLL to compensate for the insertion loss?

Any comment on the typical price range for 1.6 Maggies?

Cheers

How are you feeding them? If your sources are digital, I'd go with digital filters, if economically feasible. If analog, many people are reluctant to digitize the signal, although at least as many say that the quality and versatility of the digital filters makes it worthwhile. A PLLXO is definitely the cheapest approach, though, just a handful of components and a box.

Average price on the Audiogon bluebook is $1050, last sale was $960.

[Beardy]

Maggie 1.6QRs are here!
I am enjoying them as I type.
Significant upgrade to the MMGs I have on evaluation.  The MMGs were an eye opener for me, and these just offer "more".

Happy Holidays.
Beardy

[SteveFord]

Merry Christmas for you!

[Beardy]

What is the concensus opinion on the miniDSP?

cheers
Beardy

[josh358]

What is the concensus opinion on the miniDSP?

cheers
Beardy

I've heard varying things about it, some positive reviews, but also a review or two that said it doesn't sound very good.

[Davey]

I think the best evaluation method for most of the DSP units is to configure them for no processing and introduce between your amp/preamp and listen for a while to your system and then take it out and listen some more.

Make sure levels are matched since some of these units aren't unity when programmed to be unity.  The miniDSP is a good example as the output level is slightly lower than the input level. 

If you don't find the A/D, DSP, D/A conversion objectionable, then it's probably worth further consideration.

Cheers,

Dave.

[dm]

I did go the minidsp route with my magnepan 1.6's.  You can read about it here:
http://db.audioasylum.com/mhtml/m.html?forum=mug&n=184970&

Although at present I am in the design phase with significant help from Davey to implement a PLLXO (passive line level crossover) or ALLXO (active line level crossover).  I am happy with the sound of the minidsp, but I just want to try the experience of tweaking them with the PLLXO approach.

[Beardy]

many thanks
I am familiar with the postings you have made and read them with interest.   I look forward to hearing how things progress, perhaps I can piggyback on your trail blazing...
:O)

thanks
Beardy

[dm]

I did go the minidsp route with my magnepan 1.6's.  You can read about it here:
http://db.audioasylum.com/mhtml/m.html?forum=mug&n=184970&

Although at present I am in the design phase with significant help from Davey to implement a PLLXO (passive line level crossover) or ALLXO (active line level crossover).  I am happy with the sound of the minidsp, but I just want to try the experience of tweaking them with the PLLXO approach.

If you check the *other famous planar forum you will see that I have posted about my current PLLXO experiences......

[jk@home]

I'll say it again, very nice job and write up. Good "cheap and cheerful" idea with the all metal junction box. When I built my last project, I sprung for one of those expensive Hammond enclosures. All the panels were nicely powered coating for a tough finish.

Only problem was the paint insulated the panels from each other, which I had read on the net could cause hum or shielding problems. So I had to go in there with a Dremel tool and grind grounding spots on each piece.