New Duetta I at home: a few questions!

[jperel]

Happy owner of a pair of a C Minor pair for 20 years, and of a pair of Stage not really installed for 15 years (they are still in their original package in a building that I am gradually renovating, it takes time), I have just purchased for a few hundred euros a pair of Duetta 1st generation (#SN 3069). I bought them from their first owner who had acquired them in 1990.

There was a repair in 2003 on the low ribbon of the right panel, repair carried out by the dealer, one of the few stores in France that sold Apogee at the time (and always has...).

The MRT ribbon of one of the panels was working randomly (hence the low price). So, I disassembled the corresponding panel (right): removal of the front panel (cover), of the sock for direct access to the MRT ribbon contacts. Just a loose connection, since by moving the return "wire" of the ribbon a bit (the one connected to the blue wire of the terminal), it works. This problem seems to be solved (or at least it is identified). I took the opportunity to note the filter diagram, a simple 1st order filter at 6dB, with a series coil with the bass and some capacitors for the mid-high, plus an LR impedance correction filtering. Nothing very sophisticated.

Now, I notice several things:

- The MRT ribbon is quite loose (euphemism).
- The foam surrounding the woofer has turned to dust (almost 40 years old).
- No buzz heard even at a certain volume. I also dare not turn the volume too loud yet.
- The foam which is damping the front panel has also turned to dust.
- The foam preventing excessive flapping of the MRT ribbon is in very poor condition.

Next, several questions:

- Can I "tighten" the mid-high ribbons by loosening the small Allen screws of the top and bottom metal squares that maintain the ribbon tension, slightly tighten the ribbon and then tighten the screws? All this with infinite precautions, needless to say. I am aware that this is not equivalent to buying new ribbons from Graz, but as they are, it is already very satisfactory, and I am not in a hurry to refurbish them, as the quality of what I listen to is already good (very good).
- I do not intend to replace the bass membranes anytime soon, because it is still - for my finances at that time - a certain cost (compared to the MRT membranes which are at a cost even more acceptable as I will probably do it myself. Is it so bad to infiltrate very low-density silicone into the space left by the disintegration of the foam on the sides of the bass ribbon? Even just to prolong the life of these precious membranes?
- The filter is very simple. Is it too simple? Can it be improved at low cost? Encapsulate the coils in epoxy? Add a small MKP or paper/oil capacitor of high quality as a bypass to the 5 original Sprague capacitors of 10µF? Replace them all? Replace the resistors with non-inductive ones? Remove the switch (2 positions, normal/high) and keep only the "normal" mode? Switch to active filtering?
- I power the Duetta with a Mark Levinson ML-9 (theoretical 100W, in practice rather 200). We can say it works. But not really better than with a Bryston 2B (50W) that I repaired a few weeks ago, or with a Cello Encore (also 50W). One can feel that from a quarter of the volume (on my Jeff Rowland preamplifier, 50/200), the amp is not as imperial as below this volume even though the volume is not very high. Are the Duetta as power-hungry as that?
- Can a Duetta I be transformed into a Duetta II or a Duetta Signature simply by modifying the filter, or is it imperative to replace the membranes?

Finally, I am thinking of soon:

- Redoing the covers of the panels. Even in fairly good condition, I am not a big fan of anthracite. I imagine an off-white, maybe a vintage white or butter cream. From a car body shop or house-made, to be seen.
- Building metal feet (steel? Aluminum?) which raise the panel a little while stiffening the whole. Spikes? Wheels? To be seen.
- Taking the filter out in a dedicated box. Easier to make modifications if necessary, or to switch to active.
- Replace the MRT when necessary.
- Replace the bass ribbons when required.
- Selling my Centaur Minor, but keeping my Stage...

I thank everyone who has made it this far and even more those who will have an opinion, advice, or a warning to give...
And I will soon post photos and diagrams.

Hello from France (and I apologize for my not-so-good English writing)

Jerome

[jperel]

Here are them in the kind of barn I'm rebuilding as a music room. The left one is still dressed.

Duettas in situation

Duetta 1.jpg (248.64 KiB) Viewed 22489 times

[jperel]

And below, a quick schematics of the crossover present in the speaker. Nothing fancy there, just a low-pass series inductor with the woofer and a high-pass caps bank for the MRT plus an impedance compensation LC circuit, if I'm not wrong. Values surprise me a little, and don't fit well with standard calculations for a cover at around 500Hz. Correct me if I'm wrong.

(edit: I wasn't totally sure of the values I measured for the coils, the big one is corrected on the schematics)

Duetta I original Xover

Duetta I original xover.jpg (56.01 KiB) Viewed 22483 times

[jperel]

Here is a close shot of the (original) crossover. A classical and simple arrangement.

You may also see on the bass foil the repair that has been made in 2003. A simple copper braid soldered on the foil. The foil was probably broken on that place? Not very aesthetic but working ever since.

xover close shot

Apogee Duetta I xover close view.jpg (238.28 KiB) Viewed 22483 times

[Vansloneker]

Congratulations with your purchase!

On my Centaurs I have achieved very satisfying results by replacing the caps and resistors for better ones and potting the coils.

[jperel]

Hi Vansloneker, thanks for your interest and response.

I've been reading thoroughly your experiments with your Centaurs, and you're the one who made me think about potting the coils
As you know, even if you tried hard to help another forum member with his C minor crossovers upgrade, this particular C minor has its crossover very well stuck and hidden at the back of the woofer case. It's quite uneasy to dismantle it and take it out of the speaker for experiments, that's why I didn't try it on mine. So I've got no experience on modding any Apogee xover.

My Stages are still in their original packing, I get them out from time to time just to admire them but never opened them (I mean "to get inside"). The room in which all that stuff is kept (speakers, electronics and so) is more or less a 30 sqm room in a separated building in my yard, where I also do some wood work or small repairs of different objects. It has got no heating yet so I do not spend much time there for long listening sessions when winter is strong and harsh.

On the contrary, I had to open the Duetta's (the left one at present) to check the MRT ribbon for continuity. That's why I've got pictures and small knowledge of what's inside the xover. Plus, I've been visiting regularly this forum since 2005, when I get the Centaurs, to learn a bit more about Apogees... and when I got this rare opportunity to buy the Duettas, I was more interested than ever into reading about them, since I never thought I could afford such speakers one day. They don't show up very often here in France, or at prices I can't reach (for Sigs mainly).

Right now, I can say that they are very satisfying just as they are, even if they clearly can be bettered with new foils (from Graz). No infamous buzz, and even if the MRT ribbon is somewhat flapping, they produce a beautiful sound and image from well recorded CDs. A good test - for me - is that I can hear very quickly the difference between multitracks recording's lack of natural and the live jazz or classical perfect positioning of instruments and vocals...

If necessary (when necessary?), I can go active bi-amplification rather easily, just have to build a new active crossover with the correct crossover frequency and slope(s). I can keep that for later, since modding the passive xover can be a satisfying option without spending €€€ right now.

Replacing the MRT ribbons will be a not too expensive task that can bring to a much better quality, so I plan it this year. Just have to get accustomed to "how they're made".

I'll keep you informed!

Greetings from France!

[Vansloneker]

Actually, I had in mind you can also replace the components of the Duettas. I have a pair of Calipers with sagging ribbons and stashed a set of AmpOhm caps for them.

For as much as I know the ribbons can not be tightened. Technically they can of course, but they will not sound better. When I acquired the Centaurs the seller proudly explained how the ribbons had been tightened by "an expert". Even at the sellers place I immediately heard they were just shot and needed replacement.

I'm pretty sure the Kapton ribbons last longer than Mylar equivalents, and Graz' ribbons longer than the original Apogee ribbons. But in the end it's a free hanging and moving piece of plastic that will degrade over time.

Kapton is a very high quality plastic by the way and used by Nasa as a sunshield membrane for the James Webb Space Telescope: https://webb.nasa.gov/content/about/inn ... ating.html

[jperel]

You mean, replace crossover's components (all of them or just some bypass caps of good or excellent audio quality and a resistor or two) or the ribbons (maybe both!)? The crossover on that Duetta I has got very few components, even less if I'm to consider only the normal position for MRT...

For sure, the sagging MRT ribbons will be changed as soon as I can, and it should improve the sound quality of the speakers by a large margin. Rather surprisingly, my C Minor's ribbons behave well (very well indeed) and are straight as they should. On the Stages too (same ribbons actually).

I had a quick look on the way the ribbons are set on the small bars inside the metal frame. It doesn't appear to be as simple as I had thought before. I think I'll learn more about this when I'll see the new ones in real. Till that time I wouldn't dare doing more than having a deep look at them. Don't want to ruin anything...

Do you run both Centaurs and Calipers?

Good evening

[Vansloneker]

There are different roads you can go with the crossover filter components.

It is my point of view the original parts, particularly the caps of the crossover now are old and worn, and from a lower quality as a good cap from today.

Adding a modern high quality small bypass cap to the existing caps should already give an increase in sound quality, taken that the old ribbon can reproduce that.

Replacing all caps and resistors for newer and better should definitely give a better sound. That is what I will do with my Calipers.

The choice of caps may give different accents in the experience of the sound. It does to me, while others have reported to them it didn't make much difference. Each of it's own there.

On the newly capped crossover, it is possible to add a little 'flavor' in the form of a e.g. top notch bypass cap. This similar to the use of a tiny bit of truffles in the kitchen.
It is my experience though the added bypass cap comes at the price of a slightly less 3-dimensionality of the sound. I guess for the simple reason they are different from the base caps. Anyway for my Centaurs I have accepted this. My plan for the Calipers is to keep it at one single type of caps.

Here is a nice site with comparisons of caps. Take with a grain of salt and as a rough guide. Your experience with a cap may be different. After all, only you have your pair of ears.
But e.g. after reading I applied a Jantzen Superior bypass in the crossovers of the simple Mission speakers I use with my TV-set and I fully agree with the author they are dead neutral.


Currently my Calipers are still crated. All kinds of issues, tragedies and priorities have kept me from getting them done so far.


With your Duettas you are incredibly lucky to have acquired them leave alone for that money. Long time ago my own stupidity kept me from getting a pair in about the same circumstances as you got yours.
Many sellers overestimate the value of Apogee speakers because they look good and have a reputation and they don't want to see how the parts have deteriorated and ignore the costs of getting them back into a good condition.

I can hear very quickly the difference between multitracks recording's lack of natural and the live jazz or classical perfect positioning of instruments and vocals...

I also like jazz and many recordings have been direct mastered and that is what adds to the natural sound they have.

If you hear those differences you have a good pair of ears and a wonderful pair of speakers worth saving up to having them restored to their very best standard!

About the measured values of your Duetta crossover, I think to know old Apogee wasn't always very precise with what they put into it.

[jperel]

taken that the old ribbon can reproduce that.

That's right ! No mod in the actual crossover won't be hearable till I replace the ribbons, probably. But I can work in advance since it's not very difficult nor expensive to play a little with the components.

I've been visiting humblehomemadehifi for a long time and I've never been able to compare as many caps as this fellow does, of course. I didn't pay attention to those Sprague 730P which upon him are rated an 8, since I never encountered such caps before. There are 5 of them in series with the MRT ribbon (50µF measured, high-pass filter), and I'm pretty confident that they are still good at measures, at least. I've got at home a couple of Jantzen Audio Superior Z-Cap 3.3µF that I could use to bypass the Spragues. Without replacing one of the 10µF original by a smaller one (let's say 6-7µF), this would make the electrical frequency cutoff decreased from 30Hz which is not totally insignificant. I've got to think about this. I can also buy a very small one in the same league and have no change to make. I like the image of truffles in a dish, even if I don't eat truffles often...

I'm sure you'll get an opportunity to take your Calipers out of their crate someday. Going from hybrid Centaurs to full "ribbon" Calipers must make a difference. I was very satisfied with the sound produced by the small Minors, particularly after I replaced the old 6,5" Vifas by Dynaudios (old as well, but widely better). The Duettas come home (almost by accident, this was not anticipated at all) before I am too old to make the most of them. Life can be short, specially when you get older.

[Vansloneker]

In the past I've had a pair of Stages. They are different from the Calipers and onwards, but also very good. And I have listened to my Calipers, love them but after a while the limited ribbon performance gets annoying. I have heard full ribbon Apogees in good condition, I know how they sound.

[jperel]

There was a time when I was young, and student too (read plenty of time and poor), where I spent a lot of time in a hifi shop in Paris. Presence Audio Conseil (was its name) sold the first Mark Levinsons in Europe (Mark himself was a regular visitor), then Cello, and all sorts of high-end stuff, like large Beveridge and Acoustat electrostatics, Audiostatic and Martin Logan, AND Apogee. FR, Grands, Divas etc.

I never thought I could afford that kind of stuff someday, but nevertheless I could buy in the nineties a pair of wonderful Audiostatic (from your country;), plus an YBA pre and a hybrid Moscode amp. Then I changed the latter for a Cello Encore, from the same shop, and that was it. I was very satisfied with my system. But the foil of Audiostatic is not eternal, and its replacement price was too expensive for me, so I was lucky to find a pair of C Minor that I loved. Paired with a small REL bass subwoofer, it was good, very good. A few years later I bought from the same person I had had the C Minor from a pair of Stages, which was an improvement, for sure. But as you wrote for yourself, different life events prevented me to get them in place out of their original crate where they are kept silent.

In the meantime, I started to be interested in repairing vintage amps and electronics. I still do that as a hobby (sometimes I even get paid for it), and could afford devices I wouldn't buy if I wasn't able to fix them. As I'm a keeper, I usually don't sell them, so it starts to be too much. I've got several tuners and CD players and amps and usually I know them from the inside. I've been for a long-time a reader/writer in diyaudio.com... last amp I fixed is a Bryston 2B amp which appears to deliver one of the most satisfying watts and amperes to speakers, even if their power is limited. Initially I thought I'd sell it, but after having listened to it on the Duettas, I'm willing to find a 3 or 4B at a fair price. Very good surprise for me. Krell and Levinsons and Rowlands are not the only ones to feed an Apogee.

Well, I think that after I've repaired my wife's Prius, I'll take the XO out of the speaker, and see how I can play with it. Maybe try the Duetta II filtering which is a little bit more sophisticated than the one on the model 1. And spare for the next move: buy and install new MRT ribbons from Graz...

greetings!

[jperel]

And a small picture of my summer "workshop"... during winter, it's on the living room table!

atelier.jpeg (209.76 KiB) Viewed 22448 times

[Vansloneker]

It's a pleasure communicating with you!

[jperel]

Shared!

I wouldn't want to make this thread too much personal of course! It is basically meant to give/gather information about a pair of wonderful speakers. But I like to write/read about our passion, music and its reproduction systems... as I like to meet new people sharing the same interest and possibly different views, to expand our collective knowledge and experience.

And I play guitar too. Not well but I love it!

Good evening

[jperel]

With the Duettas, I never heard "Things behind the sun" like that before...

Incredibly present, and there. I've got the feeling to be in a room with Nick Drake and his haunting and delicate, fragile voice. The guitar is very natural, dry and musical altogether. Hearing all small details in a whole.
Beautiful. Happy to share that.

[Vansloneker]

I had my friend over and let him listen to a few tracks on the Centaurs with the Big Amp. Already with the first, an MP3 (I was not able yet to get that track in CD quality) he was like "I've never heard it like this before!".

[jperel]

I see what you mean, Vansloneker.

I've got a friend in my village who owns a pair of bi-amplified Beveridge Model III, the large ones (more that 2m high, and 60cm wide, electrostatic MRT and 2 woofers)...
He bought King Creosote and John Hopkins Diamond Mine album after he heard it at home.
When you hear "John Taylor's Month Away" (you can have a glimpse of it on YT easily, but mp3 alas...), there is a bass sound in some parts of the track which can be physically felt with the Duettas, of which I had only a partial perception with the small REL subwoofer I had with the Minors.

I saw him yesterday and he told me that he could not hear that physical bass on his Bev.
That's like that.

[Vansloneker]

Currently this pair is for sale. The seller has tried for a long time to sell them for over €2000 and now is asking a more realistic €500.
The text says they were in playing order while put aside but nothing guaranteed, buyer has to move them from 2nd floor, and screws from feet are missing.

[jperel]

Hi! I hope you're the one who reserved them? It's a really fair price for a pair of Sigs, AFAIK.

I paid a little more than that for a Duetta I pair (not II nor Sig). They seem to need some cosmetic refurbishing, screws are not an issue at all. The question is about the need for a bass ribbon replacement or not. I'm happy that mine don't need such a fix, at least right now as I can't hear any buzz (and I can play them rather loud). So 500€ is more than a realistic price, I'd say it's a good price, here in Europe where those speakers are rather scarce.

Nice end of Sunday to all.

[Vansloneker]

I had to pass, too many other expenses. I take it these will need a full restoration. Then there is the issue of transporting them.

[Scinemaniac]

The main difference between Duetta ! and Signature is in the crossover (so I heard).
Since you are considering upgrading the crossover, why not fit current quality capacitors with values taken from the schematic of the Signature crossover (I don't have the schematic unfortunately).

[jperel]

The main difference between Duetta ! and Signature is in the crossover (so I heard).

Thanks for the input @Scinemaniac. I've heard a different tune considering differences between Duetta I and Sigs, in particular about the foils and (maybe?) the magnets disposition. But I might be wrong since the Duetta I are not as "popular" among Apogee owners than Sigs and not as many information is available.

Nevertheless, as the bass foils on mine seems OK (no buzz at least, and really beautiful slam and depth), I'll probably keep them (and both my wife and my banker push me to do so). As the MRT ribbons are rather "flappy", and since their cost is almost WAF+, I'm thinking about a replacement some day. Even if their sound seems perfectly OK to my ears.

Then remains the question of the crossover, as I wrote earlier. I've got some kind of schematics for the Sigs to which I could give a try. Actually I found a few schematics for the Sigs Xover, not knowing if there's one better than the other or more recommended... But because components can get really expensive as trial/error process asks for new capacitors or foils, I could be tempted to go active, not making it simpler but - at least - cheaper. Undecided yet.

Thanks to all for reading and views.