Converting Magnepan 1.7 planars to a DSP Crossover

[HAL]

New connector plates wired for 3-way use for the Magnepan 1.7 speakers.

Disconnected the original passive crossover in the 1.7's and will install the new connector plate in the speaker with the open super tweeter for testing.

Attachments

[HAL]

The DC resistance of the planar drivers for the 1.7 are supposed to be:

Woofer=4.5 Ohms
Tweeter=3.5 Ohms
Super Tweeter=1.0 Ohms.

Looks like it is time to try a current output (transconductance) amp on the super tweeter instead of a voltage output amp. Just need to high pass the amp input for super tweeter power handling limit. Absolute max power is 16watts when the fast blow fuse opens.

DIY Audio has a design by Joe Rasmussen the "Trans-Amp" that uses the same IC as the Pizza Box V1 amps. Time to resurrect two chip amps and mod them.

[HAL]

Both 1.7's have been modified to use them as active 3-way planars. Removed the passive crossover boards and wired up a the new 3 pair 5-way binding posts directly to the 3 planar drivers.

The right speaker is the one with the open circuit super tweeter quasi ribbon. That will be a good weather project as it needs acetone and isopropanol to clean off the glue to remove the old foil. Use Super77 spray glue to attach the new foil and rewire the connectors.

Attachments

[Cogito]

Rich,

In your journey, you should have experimented with different slopes of active crossover.

Can you give small write up on the slopes you are using and why?

[Roscoe Primrose]

I would probably close off the hole where the xovers used to be....

Roscoe

[Cogito]

I would probably close off the hole where the xovers used to be....

Roscoe

Are you playing with Lowthers?

[Roscoe Primrose]

I would probably close off the hole where the xovers used to be....

Roscoe

Are you playing with Lowthers?

No, why?

[Cogito]

I would probably close off the hole where the xovers used to be....

Roscoe

Are you playing with Lowthers?

No, why?

I though you are referring to full-range speakers.

[HAL]

I would probably close off the hole where the xovers used to be....

Roscoe

Hi Roscoe,
Yes, I plan to cover the holes. I have a piece of thin plywood and will be cutting the two pieces to screw on.

Magnepan used cardboard over the area where the fast-on connector are to cover over that area. That was gone on the speaker that has the bad super tweeter.

[HAL]

Rich,

In your journey, you should have experimented with different slopes of active crossover.

Can you give small write up on the slopes you are using and why?

Cogito,
I have experimented with different slopes for the DSP crossover. I do not use the original style filters that Magnepan developed since they are series mode filters. Triamping these with DSP is the way to go after the experiments with the MG10/QR's.

I like either 4th order or 8th order Linkwitz-Riley since they are 0 degrees at crossover. That is either an acoustical or electrical alignment depending on the driver. I typically use 8th order, as it allows the planers to have more power handling in band. I also high pass the planars and time align them to th subs. That solves the typical planar problem of sounding congested when trying to reproduce low frequency signals. Easy enough with the DSP.

Rich