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MGIIIa's up and running

174.28.236.170

dnm

Just happened to acquire a set of IIIa's that needed some work. Desocked them to begin the diagnosis. As it turned out, the tweeters needed to be soldered in correctly and now are working. I was able to confirm continuity of each transducer with an ohmmeter, and all three of the respective (bass, mid, ribbon) resistances match right to left.

The minor downside is that the bass panel wires are in the beginning stages of delam with up to 2 inches of banana peel. A few are completely OK, a few have up to the 2 inches, and the rest average about one inch of the delam. I know how to fix it, and have done some delam work on other Magnepans already, I just need to get a morning set aside to tackle the task. With the exception of the ends, the bass panels are in surprisingly beautiful shape with their middles only very slightly tacky. The mids appear to be flawless with the minor exception of two individual three inch runs in one panel that appear to have stretched, or something, and are laying oddly out of alignment. Maybe the panel took a hit and those two wires got pulled over, but they appear to be anchored in the adhesive, and for now I'm going to leave them alone. No oxidation whatsoever on any part of the drivers (Yes!).

These are my first sessions (just beginning today with initial repairs complete) hearing Magnepan ribbons being driven by my system. I already have MG1.6's and SMGa's. Although my initial impression is that these IIIa's can run a bit "hot" in the treble sometimes compared to what I'm accustomed to (depending on the material) -- the ribbons are sweet sounding, entirely unfatiguing, and offer extension not available in the standard wire tweeters or the QR's. Looks like I need to order a couple good quality 0.5 ohm resistors, but there is no huge hurry.

The SACD of Beethoven string quartet Op. 18 No. 5 (Quartetto Italiano -Pentatone) and Goldberg Variations (Vinikour - Delos) sound very very good. The solo harpisichord on the Delos recording is really something....

I'll probably be wanting to pick some folk's brains about their favorite IIIa tweaks at some point.... new caps, biamp, wood frames, etc. But, I'm very pleased with these first hours with the ribbons!

Best Regards!! - DNM

Follow Ups:

RE: MGIIIa's up and running - neolith 13:01:35 02/06/12 (7)
Before going to an attenuator resistor, I would recommend the 10 uH choke. It may tame your tweeters and also give you better resolution.
I have an LP of Trevor Pinnock's Goldberg Variations on the harpsichord that was recorded in 1980 and it is one of my favorites. Murray Perahia's (CD - recorded 2000) rendition on the piano is also superb and rivals Glenn Gould which has long been held as the "standard".
�

On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
- RE: MGIIIa's up and running - Roger Gustavsson 07:30:38 02/08/12 (4)
  neolith wrote:
  
  "Before going to an attenuator resistor, I would recommend the 10 uH choke. It may tame your tweeters and also give you better resolution.
  I have an LP of Trevor Pinnock's Goldberg Variations on the harpsichord that was recorded in 1980 and it is one of my favorites."
  
  I think 10 �H is not doing very much until above 40 kHz.
  
  Roger Gustavsson
  - RE: MGIIIa's up and running - dnm 12:47:21 02/11/12 (0)
    I applied the 5522 chokes and have to say that the effect is positive. It does tame the high end a bit. but without seeming to give up much if anything. Smooths the whole presentation offered by the IIIa's.
    
    Also, prior to receiving the chokes, I experimented a bit with the jumper. When I first hooked them up I used a simple piece of 10ga copper wire. Switched to the 1.2 ohm attenuator resistor just to see what would happen, and that suppressed the highs too much. Then, I tried the Magnepan steel jumpers, they were less bright than the copper, and introduced what I would describe as "grit" - didn't like 'em. I also have some 5502's that I can monkey around with just to see what they will do. As some have observed, paralleling them provides more options.
    
    With the chokes, I can run the system a bit louder which helps wake up the bass a bit. Overall, an improvement.
    
    Thanks for urging me to try this!
  - Not doing much until above 40kHz - neolith 15:13:40 02/08/12 (2)
    In terms of attenuating audio frequencies, you are right, as the fc for a 10 uH coil into a 4 ohm load is ~63 kHz However as, the late Al Sekela pointed out, RFI seeping back into the amplifer can cause stridency and harshness to the upper end.
    �
    
    On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
    
    Edits: 02/08/12
    - RE: Not doing much until above 40kHz - Roger Gustavsson 01:53:21 02/09/12 (1)
      In some cases the poweramp sees a very low impedance at high frequencies, the red line of this diagram, dropping to 0.25 Ohm at 10 MHz:
      
      http://www.lts.a.se/pub/artiklar/hogtalarkabel/karimp.gif
      
      In can be cured by a suitable loudspeaker cable, one with a caracteristic impedance that matches well. A RC link at the end of the cable (or inside the speaker) and the amplifer sees the impedance of the blue line. Many amplifiers have a similar RC link (Zobel network) at their outputs.
      
      Roger Gustavsson
      - RE: Not doing much until above 40kHz - neolith 05:27:06 02/09/12 (0)
        
        In Reply to: RE: Not doing much until above 40kHz posted by Roger Gustavsson on February 09, 2012 at 01:53:21
        
        Yes, indeed. The choke should raise the impedance at high frequencies but because of self-capacitance the high frequency behavior is far from ideal and an RC network across the leads is the way to go. I believe that is what the Walker High Definition links are.
        BTW, I couldn't get your link to work.
        �
        
        On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
        
        Edits: 02/09/12
- RE: MGIIIa's up and running - dnm 20:07:08 02/06/12 (1)
  Just ordered the chokes - some of the Miller 5522's and the 5502's. Folks may be interested in knowing that www.newark.com has the 5502's on sale now for about $2 apiece, and a couple inmates have written that they preferred the 5502's over the 5522's. I got them from Newark because Digikey said that they were out because they were being obsoleted by the manufacturer. (so, I got a few extra of the little buggers, just in case... ) Don't know if the obsolescence thing is really true, and I hope I don't start a panic around here.
  
  Also, Mouser seemed to require UPS, which cost about $13 shipping for less than one pound of shipping. Newark had the option to ship USPS 3 day, which was 5 bucks. Not that losing $8 leaves me shipwrecked, but it is just the principle of the dadgum thing......
  - RE: MGIIIa's up and running - neolith 09:09:30 02/07/12 (0)
    Good info. BTW I am using 2301's which are toroidal chokes rated at 10uH, 20A, DCR = 0.005 ohm. I figured the toroidal's will give some protection from EMI as well as RFI. They are about 1/2 the price of 5522's as well.
    For those who are interested:
    �� L�� A�� %�� DCR ��AWG
    5502�� 10��9��20�� 0.017�� 18
    5516�� 10��16 ��20 ��0.008 ��14
    5522�� 10��20�� 20 ��0.006�� 12
    2301�� 10��20 ��15 ��0.005 ��12
    
    �
    
    On the violin: "Heaven reward the man who first hit on the idea of sawing the innards of a cat with the tail of horse."
    
    Edits: 02/07/12 02/07/12 02/07/12 02/07/12
RE: MGIIIa's up and running - josh358 05:56:36 02/06/12 (0)
Hey, congratulations!

Ribbons tend to be a bit hot in part because they have such good dispersion -- their power response is flat while the power response of a dynamic tweeter is rolled off in the treble. And most recordings are mixed/EQ'd with dynamic tweeters.

A bit of HF absorption (drapes, carpet, etc.) in the room can bring the HF balance to where you like it. IIRC Magnepan's recommendation is that if you need more than the 1 ohm tweeter attenuator to bring it in to balance, you should add absorption.

Also, the IIIa's are flat speakers rather than down-tilted ones, as you can see from the in-room power response in the link below. Some degree of downtilt, maybe 4-6 dB across the entire spectrum, is usually preferred with two channel stereo when playing large ensemble works, presumably owing to the fact that the mics don't pick up as much of the HF-attenuated hall ambiance as the human ear. Again, something that can be achieved with some combination of room treatment and tweeter attenuation, or with electronic EQ.
- IIIa in-room measurements (Open in New Window)
RE: MGIIIa's up and running - tyu 05:24:05 02/06/12 (0)
My frist 3a were in the 90s....an have a pr here now...i never could get them to sound good....hot like you say ...i pulled the ribbion out an run them with other speakers...sweet sound ..i have the MG2.5 thay sound great with no mods...it the mid in the 3a i dont like..others have put foil on the 3a mid.. this may be for you lot of info here on the 3a,s
goodluck have fun
RE: MGIIIa's up and running - stigs 22:26:00 02/05/12 (2)
I am delighted that you were able to find the speakers without too many issues. As far as your small delam problems go, I don't what you have used for an adhesive in the past, but I would highly recomend trying some Beacon 527 as it has worked wonders for me. It dries super fast and is soluble in acetone. Stays very pliable and only costs about $6.00 dollars per tube. I completely did both my MMGs over 7 months ago with no issues. Good luck with your endeavors.
- RE: MGIIIa's up and running - dnm 06:03:13 02/06/12 (1)
  Thanks for the tip about the glue alternative. I'll hunt some down. Best - DNM
  - RE: MGIIIa's up and running - Satie 14:02:44 02/07/12 (0)
    PG, who is very experienced and repairs maggies professionally, and a few others, like DAP adhesive for "banana peel" repair and other wire repairs.

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