Magnepan 1.7 dspNexus 2x8 DSP crossover

0 Members and 1 Guest are viewing this topic. Read 5442 times.

HAL

Magnepan 1.7 dspNexus 2x8 DSP crossover
« on: 14 Jan 2024, 11:25 pm »
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.





HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #1 on: 18 Jan 2024, 02:40 am »
Talked to Magnepan and was able to get a pair of used 2.7/QR speaker connector plates to rewire the 3-way 1.7 planar speakers for direct amp drive.  I can also rewire the fuses to the tweeter and super tweeter for protection. 

These connector plates will have the 6 new Superior Electric BP30-10 5-way binding posts for speaker wire connections.  :)



cheesey

  • Jr. Member
  • Posts: 8
Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #2 on: 20 Jan 2024, 06:43 pm »
The plot shown is with a super tweeter operating???

HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #3 on: 21 Jan 2024, 12:21 am »
If the speaker is working correctly, then yes. 

Just received the Magnepan 1.7 quasi-ribbon repair kit to replace the blown supertweeter.  Will know more once I have the blown supertweeter speaker apart to check. When it is working correctly it should be a 2 Ohm DC resistance.

Will be able to replace the connector panel at the same time for direct triamp drive the planars.

HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #4 on: 22 Jan 2024, 09:05 pm »
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.

The quasi-ribbon foil repair kit has arrived and have the side stiles and sock removed to work on the 1.7.  No obvious burns or breaks in the foil, so have to remove the adhesive to investigate the open foil of the supertweeter.



HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #5 on: 23 Jan 2024, 05:28 pm »
Have the side stiles off and the sock removed from the 1.7 with the open super tweeter foil.

No obvious breaks in the foil, so have the foil repair kit for the 1.7's with the other pieces needed for replacement of that winding with instructions.



HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #6 on: 25 Jan 2024, 01:23 am »
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

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #7 on: 29 Jan 2024, 09:29 pm »
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

This is going to be fun! :)

Hobbsmeerkat

  • Industry Participant
  • Posts: 2586
Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #8 on: 30 Jan 2024, 09:22 pm »
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

This is going to be fun! :)

The super low impedance of the super tweeter is why Danny wired the tweeter and super tweeter in series in his upgrade, turning the speaker into a 2-way design.

HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #9 on: 30 Jan 2024, 09:51 pm »
Hobbs,
That is also the way the original design passive crossover is done, so makes sense. 

Since the maximum current to the super tweeter is 4A (4A fast blow fuse for protection), the maximum power is 16W rms. No need for a large wattage voltage amp that would normally be needed to drive that low impedance. 

A friend that passed had home built ribbons speakers that were 0.5Ohm loads directly driven by heavily modified ADCOM GFA-555 amps with three extra power transformers, bridge rectifiers and multiple caps paralleled to drive the current since they were very large drivers.  Think of something like an early Apogee ribbon speaker.  Not really needed in the 1.7 case.

My idea is to use a low power current output (transconductance) amp instead of a voltage output amp to direct drive the super tweeter.  Nelson Pass' First Watt F1 and F1J are transconductance amps, as are a few other DIY designs are that style out output.  That style of amp will drive a low impedance load at low power.

The DSP will provide a high slope high pass filter for the amp input to limit LF from getting to the super tweeter. 

I can then use the Orchard Audio Starkrimson Class D monoblock amps for the woofer and tweeter panels as I did at Lone Star Audio Fest last June.  That makes a fully triamped system.

HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #10 on: 3 Feb 2024, 10:51 pm »
Have rewired the 1.7 with the open supertweeter to 3-way direct drive. 

The original passive crossover is removed.  Will replace it with a cut piece of board screwed into the baffle to cover the opening.




« Last Edit: 3 Feb 2024, 11:55 pm by HAL »

AK-Grwn_v2

  • Jr. Member
  • Posts: 26
Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #11 on: 13 Feb 2024, 03:19 am »
The inside edges of the 1.7…. Would those benefit from foam or something else to reduce reflections?

HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #12 on: 13 Feb 2024, 03:25 am »
Something like felt strip that is porous would be good for any edge refraction around the periphery of the driver. 

That might fit below the sock when it is reinstalled as long as it is not too thick. 

HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #13 on: 25 Feb 2024, 02:51 pm »
Back from the Florida Audio Expo and to work on the Magnepan 1.7's.

Took the second panel apart to rewire the planar drivers for 3-Way direct to the connector plate.  Removed the original passive crossover and getting the wiring to the planars connected.


HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #14 on: 25 Feb 2024, 09:33 pm »
The second 1.7 is now wired for triamping.

The dspNexus 2x8 will be driving 3 channels of Parasound A23 stereo amps for testing with Audiomatica's CLIO Pocket.   

Checked the planar resistances and they are as expected for values.  Just the first 1.7 has the open circuit super tweeter, but the tweeter and woofer are working.  With the original series style passive crossover, with the super tweeter open circuit, the tweeter did not function as well as the super tweeter.



HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #15 on: 6 Mar 2024, 02:42 pm »
The 1.7's are wired with locking banana plugs for testing the individual planar drivers. 

Will be using the Parasound A23 to drive the planars for frequency response measurements to design the DSP crossover.






HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #16 on: 21 Mar 2024, 11:39 am »
The Magnepan 1.7 with the dspNexus 2x8 DSP crossover is now running.  This is the 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 upgrade 300W GaN SMPS are triamping the planars with the 2x12 in servo sub on the left.

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. 

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


HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #17 on: 26 Mar 2024, 03:17 am »
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 delay. 

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!  🙂




HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #18 on: 2 Apr 2024, 01:58 pm »
Going to update the servo subs to 3x12's with the Magnepan 1.7's.

Did a new DSP crossover design for the Rythmik Audio A370XLR3's for AVR mode. 



HAL

Re: Magnepan 1.7 dspNexus 2x8 DSP crossover
« Reply #19 on: 27 Apr 2024, 05:38 pm »
Have the Flagship EA dspNexus 2x8 with the AK4499EX DAC's setup in the Magnepan 1.7 system with the Orchard Audio Starkrimson Monoblocks and 2x12 OB servo subs. 

This is an improvement over the standard AK4493 DAC's.  This is the final version of the AK4499EX DAC board since the first version used the single chip AK4499 DAC that is no longer made.  These are the two IC version with the digital processing and analog processing on different IC's. 

The new modular OB servo sub cabinets for the two 6x12 stacks in the picture are going to painting this week.  Then install the 12 GR-Research SW-12-16FR servo drivers and wire them up into the system.  Will be using Rythmik Audio 4-HX300-12OB servo amps for the system all controlled by the dspNexus 2x8.

Fun stuff! :)