Magnepan 1.7 dspNexus 2x8 DSP Crossover project

[HAL]

My nephew wants the Magnepan MG10/QR speakers system with the dspNexus and two 2x12 servo subs, so was looking for another pair of planars to replace them.

Found a pair of original Magnepan 1.7 speakers on FB Marketplace in the area for $100 for repair.  This was the first Magnepan speaker to use all quasi-ribbons for planar drivers when it came out.  One speaker has an open super tweeter quasi-ribbon.  Magnepan sells a repair kit for the aluminum foil quasi-ribbon speakers, so ordered a kit.  You purchase Acetone separately to remove the old glue to detach the quasi-ribbon material to install the new material for repair.
Will pick it up in MN since I am here to visit Danville Signal this week. 

Measured the correctly working speaker setup for measurement with the original passive crossover and here is the frequency response plot on center of the vertical tweeter axis. Once I have the second speaker repaired, will do a comparison frequency response plot.

This is a 3-way design with a woofer/mid planar, a tweeter planar and super tweeter planar.  The tweeter and super tweeter crossovers are connected in series.  My understanding is that the super tweeter is a 1 Ohm load.  This is perfect to try a current output power amp for that planar, instead of a voltage output amp. 
Amps like the Acoustat TNT200 and modern Hafler Transnova amps both designed by Jim Strickland are transconductance amps designed to drive electrostatic speakers.  These are highly capacitive loads that go to very low impedance at high frequencies.  Sounds like a good fit for this planar super tweeter.

This will add the Magenpan 1.7 to the dspNexus 2x8 upgrade library.

[Nick B]

Rich,

Rebuilding those sounds like a fun project and a great deal too for your nephew 👍

Nick

[S Clark]

????  Measured on the tweeter axis, and output from 250 to 1000 was significantly higher than higher ranges.  Just looks odd to me.   Also, was that 1 watt at 1 meter?  If so, that's going to take a lot of watts to drive it well.   

[P.I.]

????  Measured on the tweeter axis, and output from 250 to 1000 was significantly higher than higher ranges.  Just looks odd to me.   Also, was that 1 watt at 1 meter?  If so, that's going to take a lot of watts to drive it well.

There you have the reasons I've never been a fan.

[HAL]

This is why Hi Rez DSP is a great way to correct the response of the Magnepan planars as the low end needs less power once correctly filtered than the high end due to the higher sensitivity and easy to correct when multi-amped.  You cannot do that passively as you loose to much sensitivity.  The mids and tweeter need much less power than the woofer with music content, so easier demands on the amp, so higher level drive is fine.

The MG10/QR's sounded much better with the DSP crossover than the passive original.  Lots of EQ in the crossover like the Magnetar planar speaker setup I had at Lone Star in Dallas in June.  Just wished I had built a switching box to swap between passive and DSP crossovers.  The differences were not subtle at all and much flatter on axis with DSP.

My '80s Maggie MGIIB's always needed help and now I could do it.  I know, as I just measured a pair of restored MGII's.

 



 

[HAL]

Modified the new connector plates with the Superior Electric BP30-10 5-way binding posts.

Next is to rewire the fuses to the tweeter and supertweeter planars for protection.

Hard to find the black 5-way connectors, so went with yellow for the negative terminals.

[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.

[HAL]

Have the 1.7 passive crossover disconnected to remove it and install the new triamp connector plate.  This also lets me get the driver ready to replace the open super tweeter foil.

The super tweeter driver is the left most two foil traces on the diaphragm.  The DC resistance when working is 1 Ohm.  With the 4A fuse that means that the max input power is 16W rms before it opens.  A big amp is not needed.  Yes, you could series it with the tweeter foil, but that has been done, so time to try something different for direct drive.

This is a case where a transconductance amp like a First Watt F1 or F1J amp would be an idea.  You can also DIY one with Chip Amps.  These are current output amps not voltage output amps like any typical audio amp mostly available.

[HAL]

Both passive crossovers in the 1.7's are now removed and replaced with each planar driver having a pair of Superior Electric BP30-10 5-way binding posts on the connector plate.  Wired with 14awg Belden 1309A wire to the fast-on's.

I still have to wait for warmer weather to take the one speaker with the open circuit super tweeter outside to chemically remove the old glue and install the new aluminum foil for the super tweeter on the diaphragm.  Acetone and Isopropanal are recommended for the task.

At least with one speaker fully operational, I can now make farfield measurements of it to complete the DSP crossover.  I have a model of the original crossover design to see what makes sense for improvements.

[HAL]

Finally getting back to these speakers.

The three pairs of 3' 14awg speaker cables with locking banana plugs is complete. 

I am beginning to test the three pairs of Orchard Audio Starkrimson monoblocks that were in my room during the ground water problem.  See some residue on the chassis, so time to open them up and check.  Most of the original SMPS took on water, so bought the 300W GaN replacement SMPS to use with them.

The EA dspNexus 2x8 with the AK4499EX DAC's is here and getting it setup with the one working speaker for testing. 

The weather is almost warm enough to take the one speaker with the open super tweeter outside to begin the replacement.  Going to be interesting.

[HAL]

The Magnepan 1.7 with the dspNexus 2x8 DSP crossover is now running.  This is the one speaker with all three planars working for measurements. 

From the passive crossover design and first measurements, the DSP crossover is working.  Now to make individual driver measurements to fine tune the crossover.   This is nothing like the original passive crossover in design.

The three Orchard Audio Starkrimson Monoblocks with the 300W GaN SMPS are triamping the planars with the 2x12 in servo sub on the left.  Had to replace the original SMPS as they were in the room when the water problem occurred and soaked in water and failed when tested and the amps survived.

The super tweeter is padded with a resistor since its resistance is 1.4 Ohms.  This makes it an easier load to drive for any amp. 

The EA dspNexus 2x8 with AKM AK4499EX DAC's is here and will be testing it soon with the speakers.  To begin, this is using my original prototype unit with AK4493 DAC's.

[Nick B]

The Magnepan 1.7 with the dspNexus 2x8 DSP crossover is now running.  This is the one speaker with all three planars working for measurements. 

From the passive crossover design and first measurements, the DSP crossover is working.  Now to make individual driver measurements to fine tune the crossover.   This is nothing like the original passive crossover in design.

The three Orchard Audio Starkrimson Monoblocks with the 300W GaN SMPS are triamping the planars with the 2x12 in servo sub on the left.  Had to replace the original SMPS as they were in the room when the water problem occurred and soaked in water and failed when tested and the amps survived.

The super tweeter is padded with a resistor since its resistance is 1.4 Ohms.  This makes it an easier load to drive for any amp. 

The EA dspNexus 2x8 with AKM AK4499EX DAC's is here and will be testing it soon with the speakers.  To begin, this is using my original prototype unit with AK4493 DAC's.

Rich,

Looking good so far 👍 Is the EA dspNexus 2x8 with AKM AK4499EX DAC a finished product? I believe it was in the works or being considered or am I not remembering that correctly?

Nick

[HAL]

Nick,
The AKM AK4499EX DAC boards are finished.  I am testing them now.  These are a purchased upgrade to the system.

They will be released at the same time as the ADSP21569 dspBlok when the firmware is ready.  The plan is to release them both by AXPONA 2024 in April.

All the EA dspNexus 2x8 owners will get the ADSP21569 dspBlok as part of their original purchase price.  They will be stock in the full production system.

All these are plug-in replacement boards into the motherboard for the upgrades.  Everything is upgradeable.

Pricing is:
Production dspNexus 2x8 with AKM AK4493 DAC's is $3000.00 + shipping/handling (same price as the EA dspNexus 2x8 system)
Production dspNexus 2x8 with AKM AK4499EX DAC's is $4000.00 + shipping/handling
AKM AK4499EX DAC boards upgrade is $1500.00 + shipping/handling for either the EA system or production system originally with AKM AK4493 DAC's.

Rich

[Nick B]

Nick,
The AKM AK4499EX DAC boards are finished.  I am testing them now.  These are a purchased upgrade to the system.

They will be released at the same time as the ADSP21569 dspBlok when the firmware is ready.  The plan is to release them both by AXPONA 2024 in April.

All the EA dspNexus 2x8 owners will get the ADSP21569 dspBlok as part of their original purchase price.  They will be stock in the full production system.

All these are plug-in replacement boards into the motherboard for the upgrades.  Everything is upgradeable.

Pricing is:
Production dspNexus 2x8 with AKM AK4493 DAC's is $3000.00 + shipping/handling (same price as the EA dspNexus 2x8 system)
Production dspNexus 2x8 with AKM AK4499EX DAC's is $4000.00 + shipping/handling
AKM AK4499EX DAC boards upgrade is $1500.00 + shipping/handling for either the EA system or production system originally with AKM AK4493 DAC's.

Rich

Thanks, Rich. Glad things are moving along with the Maggie’s and dac boards.

Nick

[HAL]

The Magnepan 1.7's are playing music.

The super tweeter ribbons are disconnected since the one in the left panel is open circuit.  Running the tweeter panel 400Hz and up.  Sounds pretty good to me even without it for testing.

The speaker is EQ'd for flat response.  That can be varied to taste. 

The planar woofer to tweeter time offset is corrected as is the servo subs to the planars time offset. 

The dspNexus with the AKM AK4493 DAC's are running now.  Just updated the firmware in the EA dspNexus 2x8 with the AKM AK4499EX DAC's and will be swapped in tomorrow for listening trials.

This is the fun part!  🙂