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MG3A external crossover capacitor refresh / upgrade

111.90.220.19
Posted on June 21, 2023 at 19:47:57
mondial
Audiophile

Posts: 886
Location: S.E. ASIA
Joined: January 14, 2007



Hi guys ,

I would like to replace the capacitors in the external crossover box of my factory rebuilt MG 3A . When I listen to it full range using the stock Magnepan MG 3A crossover box driven by my high powered tube amp ( ARC REF 610T monoblocks w/ KT 120 upgrade 840W / channel ) it sounds crap . It's so bright , mids has a lean texture , bass has no body . Maybe a parts upgrade of the caps in the external crossover will improve its performance .
When I listen to the MG 3A in biamp ( driven by a pair of ARC D79B's all tube power amp ) configuration using an active crossover ( ARC EC21 crossover) the system sounds sublime . Here is a picture of the contents of the MG3A external X over network .
Thanks in advance .

Mondial

 

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RE: MG3A external crossover capacitor refresh / upgrade , posted on June 22, 2023 at 08:53:38
josh358
Industry Professional

Posts: 12285
Joined: February 9, 2010
 Are those the original electrolytics? They may have failed with age.

You could use Sonicaps or another good cap but they're physically large, they may overflow your XO box.

If you replaces old electrolytics with new electrolytics, you want to bypass them with a high quality cap.

That said, there are a lot of variables here, not the least of which is that you're using different amplifiers. There's also the active crossover. It may give you a different crossover curve, but beyond that, Maggies really like to be biamped. I have a feeling -- it's just a suspicion -- that the improvement has to do with damping of the out-of-bandwidth resonances - in some crossover topologies, the amplifier doesn't "see" anything outside the passband, so there's no electronic damping. With an active crossover, the amplifier sees the driver across the whole frequency range.

 

RE: MG3A external crossover capacitor refresh / upgrade , posted on June 22, 2023 at 10:05:35
Roger Gustavsson
Audiophile

Posts: 2002
Location: Huskvarna
Joined: February 12, 2010
 Replacing the electrolytics with film caps may be expensive. For lower frequencies there is not much to gain in fidelity. You can replace them with fresh bi-polar electrolytics or with polyester film caps (if they fit inside the enclosure).

 

Even then... , posted on June 22, 2023 at 12:23:18
E-Stat
Audiophile

Posts: 36182
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 electrolytics have lower effective series resistance (ESR) than do film types. When I did that with New Advents, the results was an overly BRIGHT presentation. You would need to add some resistance to provide the same tonal balance.

Or, parallel an electrolytic with a smaller "bypass" film for equivalent total value. That's what I did with the Advents. Replaced a 13 uF with 12 uf NP electrolytic and 1 uF film. That still improved overall transparency without significantly changing frequency response.

 

RE: MG3A external crossover capacitor refresh / upgrade , posted on June 22, 2023 at 23:49:17
mondial
Audiophile

Posts: 886
Location: S.E. ASIA
Joined: January 14, 2007
 Thanks for the reply Josh, Roger and Estat , I will keep in mind your in sight's & suggestions .

 

RE: MG3A external crossover capacitor refresh / upgrade , posted on June 23, 2023 at 16:47:17
neolith
Audiophile

Posts: 4819
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 Before modifying the crossover, I would do two things. First verify the polarity of your setup ie switch the leads on just one speaker. Two, buy a calibrated microphone (about $80 from Parts Express) and install REW5 on your computer. This will give you all sorts of info not only about the crossover but also placement of the speakers.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: MG3A external crossover capacitor refresh / upgrade , posted on June 24, 2023 at 04:24:15
andyr
Manufacturer

Posts: 12495
Location: Melbourne
Joined: September 2, 2000
 As you've discovered ... replacing the external bass/mid-ribbon XO box with an active XO - improves the sound no end.

From my own experience, the improvement is due to active vs. passive; using the highest-quality inductors & caps in the passive XO ... won't reach the level of the active!

Using your D79 on the mids & ribbons and a powerful ss amp for the bass panels will make it sound even better! There are quite a few amp possibilities for the bass panels - Class D as well as AB.

Making it 3-way active will improve it further. :-))

 

Maybe, Maybe Not, posted on June 24, 2023 at 13:55:35
Barry
Audiophile

Posts: 965
Location: PA
Joined: November 24, 1999
Contributor
  Since: January 18, 2009
 >>Using your D79 on the mids & ribbons and a powerful ss amp for the bass panels will make it sound even better!>>

I realize this has been argued before, but be careful. You may or may not like this combination on extended listening.

For over 25 years, I have used at least 6 different pairs of unmatched amps bi-amping the 3.5s and 3.6s. I've used test equipment and REW to check levels and experiment with many active crossover settings. I spent $$$$s upgrading and modifying the passive and active crossovers used as well as the speakers. I never achieved great, seamless integration bi-amping these speakers until I used matching amps. Using different amps works well with add-on subs at around 100Hz or less, but not so well at levels between 200-300Hz where your hearing may be (should be?) more sensitive. I'm not alone in this view.

If it were me, I'd stick with the pair of D79Bs. I bet that does sounds terrific.

 

RE: True but ...., posted on June 25, 2023 at 04:25:53
andyr
Manufacturer

Posts: 12495
Location: Melbourne
Joined: September 2, 2000
 My view is that a D79 simply doesn't have the power to drive the bass panels optimally.

If there is a 200w or 250w 'big brother' of the D79 to use on the bass panels - then that would be a different matter!

 

RE: Maybe, Maybe Not, posted on June 25, 2023 at 07:18:41
dumpingground
Audiophile

Posts: 254
Joined: February 23, 2011
 Kind of an extreme example of different Amps for biamping (on my maggie 1.6's). But I did try it with an Parasound HCA-1000A Class AB and Panasonic XR Class D AVR. The AVR had measurable differences in latency which defiantly caused a change in sound in the crossover region. You can see the measurement plots here:

https://db.audioasylum.com/mhtml/m.html?forum=mug&n=251596

I am presently using a Pass Labs clone Aleph 3 Class A on the tweeters and Buckeye Hypex Class D amp on the woofers. This combination works much better giving me a nice airy sound on the tweeters and very controlled power on the woofers.

So in my case an example of different amps on the twt/woofer that works and one that did not.

 

RE: MG3A external crossover capacitor refresh / upgrade , posted on August 23, 2023 at 22:27:43
pictureguy
Audiophile

Posts: 22438
Location: SoCal
Joined: October 19, 2008
 First? ALL 4 inductors facing exactly the same way / orientation?

Should all be at right angles to one another to minimize interaction. I'd start there.....
Too much is never enough

 

RE: MG3A external crossover capacitor refresh / upgrade , posted on August 24, 2023 at 04:20:07
jubal62
Audiophile

Posts: 92
Joined: December 9, 2012
 Problem is you say you just had them rebuilt so they will need to broken in all over again just like if you had bought them new.

 

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