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Beet Farmer 03-22-2019 05:54 PM

Magnepan 20.7 midrange resistor experiments.
The last post about resistors was a number of years ago. For 3.7 Maggies.
I thought I might write about my experiments with the midrange resistors for Magnepan 20.7 in particular. I have been playing with them for a number of months.
The midrange resistor mainly changes the TONAL BALANCE of the mids. No resistor, brighter, adding resistance warms up the midrange sound, plus bringing it closer to a seamless connection to the bass panel.
I tries and immediately discarded the stock ceramic one ohm resistor. It is terrible.
I bought a variety of Mundorf 10 watt wirewound. From 0.33 / 0.68 / 1.0 / 1.5 / 2.2 ohm pairs, and some quads, so I could used parallel and other resistances.
I felt with the Mundorf parallel to get 0.75 was good to start with, and also tried the 1.5 ohm alone. The 1.5 was clearly 'too much' leaving the sound rather muddy and dull. With other changes, particularly adding a lot of Furutech AC duplex, the balance seems to favor back around the one ohm level.

After awhile I decided to 'go for it' and bought some Duelund CAST.
I placed a 5watt Duelund CAST 0.75 on the tweeters, along with a home made version of the "Al Sekula choke tweak"* (a choke) on a dowel with 30 turns of Kimber wire. This has been the tweeter mainstay since. I really have no complaint using it. (and actually place it inside soldered in place, I feel that confident it is right)
The midrange I have varied from below one ohm (0.90), to 1.05 ohm (pairing a 2.0 and 2.2 CAST) , then 1.1 ohm (using two 2.2 ohm Duelund CAST.

One sad discovery is one cannot safely 'hang' Duelund resistors by the resistor wire from the Magnepan 20.7 midrange holes. The leads being highly angled off the long resistor body, and stressed, may break off right where the wire enters the resistor, rendering the resistor useless and not repairable (the very fine pure silver wire of the Duelund is easily work hardened, and soon will just seem to let go) . So I made a little 'carrier' of a dowel and some wire so the weight of the resistors wrapped onto and carried by the dowel, and by some 18g wire held on the dowel. This is particularly helpful with multiple resistors.

The sound improvement using the Duelund resistors is a real upgrade in clarity. Finding the exact right impedance.. Hovering near one ohm, but I am finding I like the 1.1 ohm. I am going to further try 'three resistor' combinations. Which will allow 1.067 ohm, and 1.085 ohm values. I find the differences to be noticeable, and worth investigating to find just the right balance.
The multiple resistors also allow greater current flow.. Two parallel seem better for this than one. So I will find out if three does more? or two are just as good.
The sound mainly seems to be the lower mids which gain from the slightly over one ohm. Below one ohm (like 0.90 ohm) the upper mids gain ascendancy.
The higher value Duelund are on their way as I write.. So perhaps next week I can see how they perform.

* the "Al Sekula Choke tweak" can be found by Googling the words.

Added: I had a few odd Duelund Cast laying around, so I made up a set using (1.3 ohm parallel with a 10 ohm to give) 1.15 ohm total. I decided to make it and install them. First impression more midbass, which would be expected. Just put them in, so need some break in time to decide if want to go 'more' higher impedance? or somewhere less, between 1.1 ohm and 1.5? I also can go as high as 1.2 ohm..

crwilli 03-22-2019 07:19 PM

You got ‘it’ bad, in a good way!

timm 03-25-2019 10:55 PM

Curious beet farmer. How would you characterize your room ? Bright / damped /big / small. I ask because I don’t feel the need to muddle with the resistors on my 20.7. Now I consider my room fairly damped with carpeting/pad/acoustic tile in the ceiling / dry wall in a 17x30 basement room.

Beet Farmer 03-26-2019 08:53 AM

The desire for the resistor adjustment was partially brought about from AC upgrades. As i cleaned up the AC, the system became leaner sounding. Over the years, and well before I owned the 20.7 Magnepans (I previously owned 3.6 Magnepan) I was balancing the sound between sounding a bit too lean vs wanting more clarity. All with AC conditioning, power cords...
So IMO the room has nothing (at least to my needs) to do with the sound.

On the other hand, one should realize the resistor is 'part of the Magnepan speaker'. It is not there as some sort of 'band aid'. The owner's manual says point blank it is a tone control (at least as revised 2019 version) I understand the desire to be a purist on the resistor thing. My generally being an iconoclast makes it easy to ignore such desires.

To me the only problem is the poor quality of the stock OEM resistor, which if added really degrades the quality of the sound.
Mundorf 10 watt, or the 20watt (if the rivets are removed) are a cheaper compromise that sound OK. But I have to say the Duelund CAST are the ones to get (once the approximate value one wants is determined). Even though the Duelund are rather problematic to work with.. due to the way the lead are made, and how the silver they are made with is unfortunately easily work hardened. Plus they must be 'carried' and not just hung on the back via the leads.. MY curent way of caring for that is really ugly looking, though practical. Would be nice to have some simple clean little case to enclose the resisotrs to releve any stress on them...
At this moment I am trying a Duelund resistor 1.15 ohm combination.
(I am pretty much certain the tone I want can be had with a midrange resistor somewhere between 1.0 ohm, and 1.2 ohms.

One point I would make is my particular adjustment would probably not be valid in some other system with 20.7 Since so many other parameters are different. (there is no 'one size fits all')

As for my actual room, 11' 8" wide. 27' deep Speakers at narrow end, 18" from side walls, 42" and 54" from rear angled in a lot, tweeters 'in'
suspended floor, back wall brick, large window. to sides behind speakers back heavy lined drapes, to back sides bookshelves floor to ceiling.carpeting on pad. I sit closer than halfway in room, Equipment rack to left behind me.

Slightly more reverb than I would lie from the wall behind peakers. I need some diffusers.. Probably will eventually make some 'skyline' type for back under window, over window and at least something in window like planters? or similar (Some residential restrictions on what is allowed in windows...)

Beet Farmer 03-27-2019 04:42 PM

Thought I would add a comment about changing to the meidrange fuse value of 1.15 ohms.
The sound was/s slightly heavy the way I had everything. So I CHANGED A POWERCORD. The cord in question on the Furman REF20 conditioner. from a cord made with DH LAbs $8ft wire and Furutech '28' Rhodium plugs, back to a cord I had on it before, and still laying right next to the DH Labs cord! a Pangea AC14XL .THe XL is clearer/brighter sound than the DH Labs.
Naturally this adjusted the slightly heavy 'dark' sound of the midrange resistor 1.15 ohm.

The way I would describe this is a race car analogy. In an ordinary car, with folks driving to work at rush hour, a difference anywhere from 40psi down to 15psi in the tires could easily be overlooked. Not even noticed. The difference of ! psi in a race car tire on a race track, might mean the difference between winning or top three, or crashing, or just plain losing.
Same thing listening to a 'high strung' AC setup in a stereo system.

While thinking over the days events before sleep, it dawned on me to swap the Furman AC cord...

The only reason for posting this is to say there are plenty of ways to arrive at the same destination...

SteveJ 04-21-2019 08:51 PM

Hello Beet Farmer,

I hope you are well.

I read your OP with great interest. I am one of those that will experiment as you have done.

As much as I appreciate the great sound and value of Magnepan speakers, it stands to reason that their may be opportunities to improve their sound with changes such as you have suggested. I do not fault Magnepan. I have been in the design and manufacturing world for quite a few years and have seen some of the decisions that have been made and the reasoning behind them. Also, some of what you have done may be tuning you Maggies to your listening environment. Something not to be overlooked. You may have described the best way to do so.

If you would, please explain what you meant by "The multiple resistors also allow greater current flow." The purpose of a resistor is to reduce current flow. Do you have reason to believe the resistors, if used singularly, reduce the current more than the resistor value would indicate?

I looked up the Duelund CAST resistors. The ones I found were 5% tolerance. The differences in resistance value you cited between combinations of resistor pairs would be only slightly greater than the cumulative tolerance. If you used 3 resistors, the 5% would be greater than the difference between two values you indicated. It would still be possible to arrive at the values you indicated but you would want to measure each grouping.

This is not to negate in any way the work you have done. I appreciate it very much. As one who works with resistors on a daily basis I might be more attuned to some of these considerations and wanted to bring them to your attention.

I Googled the phrase "Al Sekula Choke tweak" but it did not return anything I recognized as being useful. Would you be so kind as to post a link?

Best regards,


Beet Farmer 04-22-2019 11:25 AM

I am not an 'expert' in electrical circuits. I have no technical abilities and training to 'explain' the question you are having with what I am doing using multiple resistors (three, with three times the resistance, so the result is equal to one resistor with more current flow. Beyond saying it is helpful, theory is going to have to come from someone with more schooling in electronics. If I tried it would just be made up from the small (tiny) amount I know of electronics theory.
What I can say is: The fact each individual resistor can carry TEN watts. (a measure of power) Three in parallel means the total three resistors can dissipate THIRTY watts (without heating up). Thirty is bigger than ten. A larger safety allowance. Curiously it also allows more detail, faster attack.

It is true the resistors are relatively high tolerance. 5%. it is possible to check them and use them in a way where the variation works out to be pretty even.
If it worries you, and you do not have the ability to check them (since really small impedance can be hard to measure. Other quality resistors, like Path Audio are also good, and available in 1% tolerances. (I have just ordered some of the Path resistors, Though they are said to have a long 100hr breakin period! I am determined to try them too.)

Finally my experiments are just experiments. Other folks who might try to just copy exactly what I am doing may not end up happy. The resistance which works in other Magnepan based could be very different than what works in mine.(in conjunction with their own electronics, and taste)

As you found, Google search is becoming worse every day.. trying to become all things, it fails to do the basics.
I did a more refined search, and can offer links:
And there is a whole pile of threads at the link at bottom of that page for more responses to the choke tweak
Those should allow you to delve further if you wish

I would say unless you feel comfortable with the tweak do not do it! Basically it is limiting the ultra high frequency.. Since the Magnepan ribbon works at frequencies well over 50,000 Hz*, reducing the current at those frequencies may, or may not improve the sound at normal audio frequencies, Since it also depends on the amplifier connected to the speakers.And the ultra HF signal that amp may, or may not be passing along to the speaker.

* reported in Stereophile 3.3 review, measurements and test results. graph of the frequency response out to 50,000 hz shows the Magnepan ribbon tweeter still good and response not dropping off at the limit of the test equipment at 50,000 hz. (this is basically the same ribbon in the 20 20.1 20.7 and 3.7i Magnepan speakers.)

ADDED: Just wanted to mention... Today, for first time in awhile (two months?) Played Decca collected Count Basie (3CD) sound was much better. Never before seemed so real. Definitely the attack, and general 'thereness' was exceptional (compared to last time played it a couple of months ago, otherwise same system.)

timm 04-22-2019 10:09 PM

This is awesome! Congrats! Kick back and enjoy. :)

Beet Farmer 04-24-2019 01:25 PM

For any folks who may try this resistor stuff.
For The Duelund, break in experience: (just so you know)
At first, right away, and first couple of days the sound is darker (than it will become after break in)
Then for a few days it starts to brighten up. So much so it seems a little tilted to the treble. And after say ten days.. finally settles down (no longer bright or heavy) to the real sound.
Natually this is a bit subtle. But you guys would hear it...

Reminds me of the way Rhodium plated plugs break in.

I have some Path Audio resistors on the way. SO I will be also trying those. So if you have not jumped into the pool... You might want to wait!
I have no idea if the Path will be same, different better of worse.
But I bought a pile of them to find out.
The Path are shaped like an AA battery, but 1cm longer. Where the Duelund are like a pencil .. long and thin. Both types are 10 watt rated, and come in a lot of small values perfect for this sort of tweaking.
For folks wanting to stay on a smaller budget, Parts Connexion now also have 10 watt/12 watt Mills and Jantzen in many small values, beside Mundorf
( I'm getting my Path Audio from them too, plus many of the Duelund are still on sale there, though the supply 'on hand' (on sale) seems to be thinning out)(( so if they run out, there is always the Path Audio type))

Beet Farmer 04-27-2019 08:16 PM

Installed a trio of the Path Audio resistors, similar to the Duelund set, but slightly larger resistance.
Did it fast.. so left off the little coils in the wires since the were on the hanger needed to help the Duelund. The Path are just hanging off the wire. They have that ground for the shell, I used a small eyelet and stuck it on the banana plug negative terminal on the speaker wires.
First did a dual set which I plan on sticking in the treble, but wanted to see how they sound, and what they sound like with no break in. (Folks say the break in takes a hundred to one-fifty hours!) The sound was OK so no horror assault on the ears, like some brand new stuff! So after a few hours I made up the triples and stuck them on. Like the Duelund, a trio of resistors seems to be a bit more 'magical' than one or even two.
Actually I have four, three main 3.9 ohm each, and trim resistor of right now 39 ohms. With no trim the resistance would be 1.3 ohms. as is it is 1.258
The Duelund were at 1.251
The sound is very good right off with the trios, not as perfect with the short term in use duo.
If they get better as reviews say.. Whoo hoo.
Since that is supposed to be 100 to 150 hours, I will say no more and report back in ten days... (I play music 10 to 12 hours a day...)

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