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A year ago September I purchased a pair of T IVa's. A friend picked them up and 'stored' them for me until Saturday. I finally got them into my living room yesterday. :)
I have searched but didn't find anything regarding upgrading the crossovers. Does anyone have a schematic for 'improved' crossovers, external or internal?
Has anyone upgraded the crossovers as in retuned or has it just been part for part, value for value replacement with better quality components?
MG's!
Follow Ups:
Here is the stock T-IVa XO schematic:
As you can see from the FR:
... it could do with a bit of tweaking, for a smoother FR. :-))
I would suggest a better SQ will be achieved by:
1. combining the internal & external XO sections into 1 external box, allowing you to remove the ribbon HP filter from the 'embrace' of the 75uF cap in the external XO.
2. minor adjustment of the roll-off points, to achieve a smoother overall FR.
This leads to the following XO schematic:
Having this FR:
Choose the best components you can afford for the passive filters - eg.:
* 12g ribbon inductors
* good film caps - eg. Jupiter.
Unfortunately, though, doing this doesn't allow you to get rid of the level difference between the bass panels and the mids & ribbons.
The only way you can do this is by replacing the external passive XO with an active XO and using one amp on your bass panels and another on your mids & ribbons.
This would give you the following FR:
Good luck,
Andy
Andy-
I'm building new crossovers for the Tympani IVa's. The images you posted above are too small to be completely legible. Could you post the crossover schematics in larger format?
Thanks,
Mike
Send me your email address and I can send you some better pics than the format I am allowed to use on the Asylum.Andy
Edits: 02/24/21
Andy, is it not the electrical response of the crossover you show us? I think you have forgotten the series resistor for the 2 Ohm ribbon tweeter. If you run without it, there will be an increased level of the tweeter and it may also be hard for some power amplifiers to drive that load.
Please note, that if you separate the two coils, it will change the transfer characteristic somewhat.
The acoustic response is more linear, see below. I think the peak around 1 kHz need to be tweaked.
Sure, Roger, it's the electrical response of the crossover I showed (the output from lspCAD).
There was no 1 ohm series resistor on the ribbons, in the T-IVa mid/ribbon panels that I bought for my 'Frankenpans'.
In my 3-way active Maggies, I used a ribbon amp that could cope with 2 ohms. (Now I have swapped them for 3 ohm ribbons, this amp has an easier time of it! :-)) )
Andy
I had these for a year and used the 0.5mH inductors that I use on my MG-IIIas in the tweeter attenuator on Steve's IVas. Since I need them for my IIIa I left Steve with a place for something. To get started he can easily jam a chunk of speaker wire into those two spots and bolt it down.
Would folks consider using the inductors as was discussed here a decade ago? I know I like the change it made in the sound of the IIIa taking the shrill out of the tweet.
As to the III/IIIa crossover vs. the IVa crossover, if Steve wants to upgrade the parts on the external crossovers, I'm damn sure he will use the values of the components in his boxes and not the ones in the how to that I suggested he look at to see what a crossover upgrade is.
The stock crossover for the IIIa is from the rebuild
18dB/300Hz Low Pass
12dB/500Hz High Pass
12dB/2500Hz Low Pass
12dB/4400Hz High Pass
The IVa has from the diagram an incomplete list not specifying the complete tweeter LP/HP combo
18dB/250HZ Low Pass
12dB/400Hz High Pass
12dB/2700Hz
It is obvious that some cap values will be different and inductors might change but really it ain't rocket science and Steve can decide if he wants to get better parts and use those instead of the bulk buy parts Magnepan used to build the crossovers 30 years ago.
make changes based on the internals you have. This will get you good parts. For small changes to the crossover, I don't know where to look.
It is always a good thing to get famliar with these speakers as they are before doing anything to them. I would advice to have the mid/tweeter panels detached from the bass panels (require extra feet).
I would replace the external crossover with an active crossover. You will need two more channels of power amplification. You can use something like a miniDSP and play with various setups of the crossover. If you want an analog solution, you may need to customise the slopes as Magnepan use non-textbook slopes.
Not sure about the internal crossover, it is unusual to place the coils that way, they will interact. If you pick the coils out and place them "as they should be", I think the crossover characteristics changes. In other words, if you build the crossover externally the values may need to be changed.
Schematic: http://www.integracoustics.com/MUG/MUG/tweaks/mikebarney/Tympani-4a_xo.gif
Do you know what ribbon tweeters yours have? The original were 3 Ohm bit often failed due to the very thin foil. Second version were 2 Ohm + a 1 Ohm resistor.
I believe the tweeters are the newer version. There looks to be a place to put an external resistor.I have 17' so enough room to separate the tweeters from the mid base panel. What sort of spacing from the wall to the base panel, tweeter to mid and tweeter to tweeter? Should all the panels be parallel or angled?
I have some speaker wire and interconnects on order which should be here in a few days. It will take me a few days to get the turntable and motor control system assembled. I may have it up and running this weekend.
Longer term I will replace the mid panel with a B&G RD75 and will look at bi-amping. I have a Marchand XM44 active crossover for that and I may try to find a Pass/First Watt B4.
Edits: 01/19/21 01/19/21 01/19/21 01/20/21
Tymp IVa ribbons are the same as the later MG-IIIa ribbons - ie. 2 ohmsAndy
Edits: 01/19/21
Well, the original ribbon that I have is 3 Ohm without any resistor. Was the T-IVa released before the MG-IIIa? I also have the replacement ribbon, the 2 Ohm, as this is the only spare Magnepan have for these.The external crossovers are not identical for MG-III/IIIa and the Tympani IVa. The T-IVa is crossed over lower.
Edits: 01/20/21
"The T-IVa is crossed over lower." All else being equal, is that more or less protective of it's ribbon? I've blown my ribbon's 2.5 ohm fuses (mostly by unintentionally switching to a source set to play too loud) dozens of times. When the original Radio Shack was still in business I bought enough packs of both 2.5 and 3.0 ohm which hopefully would have lasted my lifetime, but I was forced into buying even more from eBay.
Fortunately my IV-A remains the same as the day my Magnepan dealer delivered them ~40 years ago, wired them up and played them. (Something I think he did to protect himself from possibly being accused of providing a damaged product.) I moved everything including those IV-As to my present dwelling 28 years ago.
When you live right 'nothing can possibly go wrong.'
Aah, OK - that is very interesting, Roger ... the ribbons in the T-IVa mid/ribbon panels that I bought 10? years ago were 2 ohm.
Recently replaced (as I blew one) with the current (slightly longer!) 3 ohm ribbons.
Andy
The very thin original 3 Ohm ribbons were very fragile. Even though mine survied the Atlantic crossing, one of them ripped later. I bought the replacement kit from Magnepan, the 2 Ohm+resistor+glue+shims etc. (see below) Me too, have an additional par of the recent ribbons.
"It is always a good thing to get famliar with these speakers as they are before doing anything to them. I would advice to have the mid/tweeter panels detached from the bass panels (require extra feet)."
As shipped from the factory the IV-A was designed to have the M/T panel to be separated from the Bass panels, coming with all the feet required to do that. It's the two B panels (low and high bass) which are attached by hinges, and also being connected to one another electrically. I'm sure you knew all that before I did, (at least I hope so).
Well, I bought mine as used and I think there was hinges on all panels but eight feet.
I thought what we were discussing was the Tympani IV-A, which interests me because I listen to it.
Do III/ IIIA relate to it? Are the out board X-O boxes between these models interchangeable? (Certainly the number or feet provided don't.) If not why bring then into this conversation? IAE you yourself as well as other philes, contributed to what can be found in the MUG, and it doesn't represent Magnepan's word or suggestion.
Correct, MUG doesn't have just Magnepan suggestions in their files.
I mentioned the MG-III/IIIa because there is a rebuild of the external crossover and Steve is more than capable of doing that and selecting the right value parts to maintain the crossover as T-IVa crossover instead of making an MG-IIIa crossover out of it. There are some differences in crossover frequencies.
As to what Magnepan would approve of, Steve, as you remember was going to take Josh's place as a mouthpiece for Wendell but that is not something the asylum wants, but it indicates he has access to Wendell that many of us do not. So he is in a position to get help from the manufacturer if need be.
Norm, I think the mention of "III/IIIa" is in reference to the original 3-seies models - the MG-III/MG-IIIa. Not Tympani IIIs.
So all of the 'tweaks' posted on MUG are completely useless because they are not posted by Magnepan? Of course they aren't Magnepan's suggestions; Magnepan makes the basic product ... enthusiasts get to work on them, to improve their performance.
You appear to have led a sheltered life and haven't heard of motoring enthusiasts who improve the stock models they buy - not only from GM ... but also Mercedes. (AMG used to be an after-market 'tweaker' of Mercedes cars - then (AIUI) it got bought out by Mercedes Benz.)
Don't forget that Magnepan have survived for 50 years by being frugal with their components; they use 'normal' parts - not 'boutique' parts (which can sound better).
Andy
"Don't forget that Magnepan have survived for 50 years by being frugal with their components; they use 'normal' parts - not 'boutique' parts (which can sound better)."
And might you not forget that in the Carver/Stereophile challenge BC installed NON-boutique electronic parts into his tweaked mid-priced SS (M1.0t), and 3 Stereophile Editors couldn't distinguish its sound from that of a boutique CJ tube amp costing ~30X more.
'Andyr', thanks for your reply.
Everyone can benefit from a hobby (or two). Needless to say others' hobbies may not be the same as mine. Using a IV-A, topics such as room placement, speaker wire their termination and attachment, electronics used to drive their IV-As (SS vs. tubes, Class A, A/B, D, etc.) their power capabilities, bi-amplification and necessary X-Os interest me.
I've noticed that Magnepan's "boutique" 30.7 use the same (at least external fuse assembly, although seemingly gold plated) as do their lower cost speakers.
I'm quite satisfied with my speakers (and car) both running as they did originally. Presently my major hobby is trying to run as I did originally.
Of your list of T IVa related items the only thing I have settled are the electronics and the room to put them in and that took me years. LOL
Hopefully, with the help of people here, I can make faster progress with speaker placement, room treatment and cables.
BTW, if you end up bi-amping using your active Marchand XM-44, the outboard Tympani IV-A XO boxes are NOT used, so you needn't be concerned with the quality of their parts.
That will be down the road a bit when I get another amplifier. In the meantime I'd like to experiment with the Xovers I have. One of my hobbies.
As we are discussing the Tympani IVa not the MG-III or MG-IIIa, maybe we should let them out here. Magnepan does not use textbook filters like 18 or 12 dB/octave.
About the T-IVa being crossed over lower. That was in comparsion with the MG-III and the MG-IIIa. In this case it was the external crossover taking care of the bass to mid transistion.
If you have problems with blowing fuses of the ribbon, it does not relate to the external crossover. The ribbon in the T-IVa is crossed over at a higher frequency than in the 3-series, except for the 3.7/3.7i.
The III and IIIa are very similar in that they have a similar external crossover and there is a full blown upgrade how to for that crossover. There will be some internal differences because the crossover characteristics are slightly different but not so much that Steve can't figure out what I'm talking about.
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