Magnepan Capacitor Confusion

[HR8938Cephei]

Hey folks, apologies if this is the wrong subforum, I'll be happy to delete or relocate.

I inherited a pair of original Magnepan MG-II speakers, but in the rushed process of moving, foolishly disconnected them without taking photos of their wiring arrangement. Magnepan themselves were unable to help, so here is my first stop in my journey of figuring out how the hell to get these working again.

There are the two speakers, each with the positive and ground connector on the back, but wired between these and the receiver/amp were these cylinders which I assume are electrolytic capacitors, with an AGC fuse holder running either between them or to one of the speaker connectors, however I have no idea which, or how to determine which. Wondering if anybody might have a better idea what might want to connect to what, or where I would do best to ask about this sort of thing? I'll happily accept whatever tips anyone has to offer.

Images attached, in hopes of providing helpful context.

 

[Joe Smith]

Magnepan folks were not able to answer? That surprises me. Did you talk to them by phone?

 

[kevin gilmore]

for some reason, and i have seen this in the distant pass, and probably depending on which amplifier the speakers were hooked to,
the fuse one per speaker and the capacitor one per speaker are wired in series with the + input terminal on the speakers.
done to keep dc out of the speakers, and generate some low frequency filter. with modern equipment, the cap for sure is unnecessary but
if the amp is a lot more power than the speakers can handle the fuse is a good idea.

 

[HR8938Cephei]

Magnepan folks were not able to answer? That surprises me. Did you talk to them by phone?

I did, I was told that as it sounded like an aftermarket modified setup that they would be unable to offer any advice on how to wire things back together. I also contacted them via email, and although they were able to provide what appeared to be some original wiring diagrams, I said they did not match the arrangement I'm looking at here and they told me roughly the same as they did by phone, that they couldn't be of help.
I can wire up a GFCI receptacle and solder copper wire to copper wire but that's about as advanced as my electrical know-how gets. As best I can gather, these capacitors + the fuse are meant to function as a crossover, however I have no understanding of how that works or what that means as to how to connect these things to one another without blowing up something that could be impossible or astronomically expensive to repair.

 

[HR8938Cephei]

for some reason, and i have seen this in the distant pass, and probably depending on which amplifier the speakers were hooked to,
the fuse one per speaker and the capacitor one per speaker are wired in series with the + input terminal on the speakers.
done to keep dc out of the speakers, and generate some low frequency filter. with modern equipment, the cap for sure is unnecessary but
if the amp is a lot more power than the speakers can handle the fuse is a good idea.

I should probably have mentioned that there are two pairs of capacitors, I only included a photo of one. There are two pairs ziptied together. The have a + and - terminal on the tops, however I'm not sure which terminal needs to be connected to which corresponding terminal on the sibling capacitor, which terminal(s) the speaker wires need to connect to, or where the fuse connector needs to connect at either end. (I'm simply laying this out, not backhandedly insinuating that I expect you to magically figure all this out for me)

 

[G|force]

If the caps negative terminals are tied together, you effectively have a bi-polar capacitor array that can pass AC- a first order (6dB/octave) high pass filter.

Pure speculation, but I'd imagine the negative terminal on the amp was wired straight to the negative on the Maggie. The negatives on the caps tied together. Then the + on the amp tied to one + on a cap, and the other cap + tied to the fuse, and in turn to the Maggie +

You can probably do away with all of this while retaining LF protection if you are using an amp that isn't too powerful and DSP that has a HPF.

 

[kevin gilmore]

depending on how those electrolytics act, 3900uf and 6 ohms is a high pass filter with a 7 hz corner. which is typical of a filter that removes turntable rumble.
likely no longer applicable with modern equipment.

 

[timindy]

If you have a facebook account, I suggest joining a Magnepan forum there for info. I'm a member of a group called "Magnepan and modified Magnepan speakers." I've asked a couple questions there, and got answers pretty quickly.
Magnepan

 

[solderdude]

@kevin gilmore gave the correct answer.

When you want to wire it as it was:
+ output amp > fuse (only needed when you have a too powerful amp) > + (cap 1) > - (cap1) > - (cap2) > +(cap2) > + speaker > -speaker to - output amp.

The 2 polar caps become a single bi-polar cap of half the value of a single cap.

Depending on the value it could serve as a high-pass (for usage with a sub).
These caps are not original and is simply what the previous owner used for reasons he seems to have had.

Later MGII (>1975) had a 3A (normal blow) fuse in the back the older ones (1973-1975) did not and the owner probably added the fuse. Should be 3A (3.15A)

The caps aren't really needed for any decent amp with protection though.
Best to simply connect the speaker directly to an amp (or via a 3.15A fuse).

 

[HR8938Cephei]

If the caps negative terminals are tied together, you effectively have a bi-polar capacitor array that can pass AC- a first order (6dB/octave) high pass filter.

Pure speculation, but I'd imagine the negative terminal on the amp was wired straight to the negative on the Maggie. The negatives on the caps tied together. Then the + on the amp tied to one + on a cap, and the other cap + tied to the fuse, and in turn to the Maggie +

You can probably do away with all of this while retaining LF protection if you are using an amp that isn't too powerful and DSP that has a HPF.

Thank you for the detailed explanation. I was actually able to find a couple of images I'd forgotten I'd taken, evidently after I'd begun to disassemble the speaker setup but after I realized "damn it, I have no idea how these are supposed to be wired up."

I will say I am 99% confident I did not reattach anything that I might have hastily detached, which leaves me with this setup, which appears to differ from your and @solderdude 's recommendations. There appeared to be a length of wire as a jumper from the positive+ to the negative- of one capacitor to the other, then the fusible link (with a 3A fuse as you suspected) running from its loose wire end at the capacitor's positive+ to its spade connector end presumably having gone to the speaker's positive+.

The amplifier in question is a Yamaha HTR-5550, at risk of information overload I'll attach the output section listed in the owner's manual, which if I understand correctly indicates the output should be 8 ohms? They ran flawlessly for a good 16 or so years with this amplifier, so I assume the 8 ohm rating is not an issue for the speakers' 5 ohm rating, though I don't know if the capacitors were intended for that use. They are clearly decades older than the Yamaha amp, which as best I recall was gifted to my dad c.2004.

 

[HR8938Cephei]

If you have a facebook account, I suggest joining a Magnepan forum there for info. I'm a member of a group called "Magnepan and modified Magnepan speakers." I've asked a couple questions there, and got answers pretty quickly.
Magnepan

Thank you for the suggestion, I'll have to take a peek over there as well.

 

[solderdude]

There appeared to be a length of wire as a jumper from the positive+ to the negative- of one capacitor to the other,

Then they wired it wrong originally.
It SHOULD be wired as I stated.
Has worked even when wired incorrectly in the past because there won't be much voltage across the caps but as it is a 16Hz high-pass (-3dB) filter but it would be better for the caps to use them in anti-series.
The caps sole purpose here is DC protection it isn't a filter.
When the connected amp has been known to fail and put DC on its output and have no protection against it the caps can protect the speaker.

 

[HR8938Cephei]

Then they wired it wrong originally.
It SHOULD be wired as I stated.
Has worked even when wired incorrectly in the past because there won't be much voltage across the caps but as it is a 16Hz high-pass (-3dB) filter but it would be better for the caps to use them in anti-series.
The caps sole purpose here is DC protection it isn't a filter.
When the connected amp has been known to fail and put DC on its output and have no protection against it the caps can protect the speaker.

I went ahead and forwent the capacitors and wired up the speakers directly to the receiver/amp (with the 3 amp fuse inline), and so far no explosions. It's been 5 years since I last heard them but my gut feeling is they sound qualitatively different, perhaps in the upper frequencies--I wonder if that's why the capacitors were used, although given they were seemingly wired incorrectly, who knows? All the same, it's a start and a joy enough on its own to hear them in action again after so long, and I thank you and the rest of the contributors for your knowledge.

I suppose next is the daunting debacle of whether to leave well enough alone, attempt a teardown, inspection, and potential refurb on my own, or pay the eyewatering costs of shipping them up to MN and having them reconditioned professionally.

 

[solderdude]

Different room, 'false' memories of what once was are the most likely cause of this gut feeling.

I am fairly confident the treble (nor bass, nor mids) cannot possibly be different when using the capacitors.
This would be very easy to test.
Wire them in series with the speaker and have someone 'short' the capacitors now and then when you are playing.
When you do hear differences these very old polar caps that were not intended for AC usage without a DC bias voltage might be totally dried out and do not act as they are supposed to act.
There should be absolutely no difference in sound with or without them.

Just enjoy the speakers.