Dynaudio identification help required.

[USRFobiwan]

OR a few of these chips.
TPA3255 datasheet 315W Stereo / 600W Mono Ultra-HD, Analog-In Class-D Amplifier | TI.com


All jokes aside. You can find numerous Class D amp boards on ebay. Maybe even with dsp processing on board.
for example: AU TDA7498+TL072 Class D 2.1 Digital Power Amplifier Board 200W+2X100W DC24V~32V | eBay

dsp controler:
ADAU1701 Audio Control DSP board Adjust Gain Cut-off Frequency Bass and Treble | eBay

[chrisb]

Well, there's more than one way to skin this cat (sorry animal lovers), and the ICE powered DSP plate amp would certainly deliver far more system flexibility than the original, and the elegance and simplicity of no external components.

Thanks to the modern offerings of very compact class D amp boards / modules, the simpler approach of internal amp and passive XO would likely be a less costly approach, but would lack the advantages of full DSP processing, including EQ, etc

So I'd imagine the path forward depends on whether the cited miniDSP unit would fit without much modification, and if owner wants to invest in the steeper cost. If it weren't for the software's learning curve, I might have tried that already myself

[Old'n'Cranky]

Owner managed to picked up a mf a300, so were going the passive route.

Originally Posted by system7

Too nice to throw away, for sure.

Looking at the scorch marks, the electronics was insufficiently ventilated. Sort of issue you'd run into with a near prototype.

With the low price of second-hand amplifiers in junk shops, I'd think that going passive is a very real possibility. My own view, is that if you design for easy impedance, you really don't need any exotic amplifier for a very good sound.

And you do that by using an old BBC BW3 design like the LS5/9:
Rogers Loudspeakers › LS5/9

This speaker is still made, and still sounds good. It uses passive RL bafflestep and impedance correction: mh-audio.nl - Home

Just calculate for BW3 and 10R bass and 6R tweeter and 3500Hz, and the values drop out: 2-Way Crossover Calculator / Designer

But it's down to your friend really. FWIW, I believe the D28-2 is a ferrofluid design, so an oil-change might be in order.

Steve, just out of curiosity, why are you suggesting a 3.5khz xover point ?
With an 8" bass driver, wouldn't a lower point be preferable ?

Originally Posted by phase_accurate

I think I have seen this speaker in a special "speaker-issue" of the German DIY magazine "elrad".
I know that I still have all these mags but I don't know where at the moment.
Regards
Charles

Hi Charles, if you could find and post that article, that would be so awesome.
I had a look around for that magazine and article but couldn't find it.

[system7]

The reason that a highish 3.5 kHz crossover works in two-ways with big, badly time-aligned woofers is something the BBC discovered 50 years ago.

Rogers Loudspeakers › LS5/9

See with a big woofer, your time-alignment problems to the tweeter come down to about 5cms.

Well, at about 3.5kHz, it happens that the speed of sound, being about 340m/s, to be about 5cms as a half-wavelength.

Hence these negative polarity classic BBC designs: Rogers Loudspeakers › LS5/9.

I'm all in favour of good amplifiers: Musical Fidelity A300 Integrated Amplifiers reviews - Audioreview.com

BW3 and impedance correction is quite a hard concept to explain. It happens to be somewhere in-between LR2 and LR4. And therefore viable IMO.

What I can tell you is that the BW3 concept, and recessing the woofer, and flat impedance is still alive and well. Some people like it. I do.

[Old'n'Cranky]

Thanks Steve.
Time for me to go do more research

Tweeters done, woofers done, now I need to sort out the cabinets, then do some sweeps...

Why do the "it's a simple job" repairs end up a pain in the @@@@@
Oh yes, cause no one would buy the thing if it was advertised correctly.
Dog looking for cashed up new owner...

[system7]

What I can tell you is just based on Dynaudio's own measurements and recommendations:

.

6.8R and 22uF ought to do it for impedance correction on the woofer. Good luck, my friend.

[Lojzek]

The crossover frequency with such an unusual 2 way set ought to be on the lower side. Tweeter is capable of performing nicely at 2 kHz, so in that region it would be wiser to high pass it. A good compromise between tweeter power handling and off-axis response of the woofer. If you ask me.

[Old'n'Cranky]

An update for those interested, and in the interest of documenting history.

I'm still working on them, very slowly, as time and other jobs permit.

The people at Dynaudio have been able to provide some more information about these speakers.
Heres a selected copy and paste of Dynaudios email to me.
....

A gent by the name of Wilfried remembers this old model.
It was a DIY model called Jadee Active.
Dynaudio used to sell drivers and kits for DIY speaker builders but this part of the business was discontinued long time ago, around 1996 according to Wilfried.
Many of these kits are still alive out there and we frequently get requests for spare parts for these.
Unfortunately they are now so old that this is often not possible - but we always try!
The tools for the old drivers are all but gone and technology has moved quite a bit since the 1990's.
....

This is all the info that they have been able to provide.
But it's another step forward

Huge thanks to all the people at Dynaudio for their time and help.

[system7]

It's always nice when people get back on projects. 'Cause I am interested.

I did a bit of work on this today. My great inspiration on 8" plus 1" is Troels Gravesen: DTQWT TWEAKS

Now, TBH, I figured out most of this approach on my own... because I build speakers like this. o

I simmed it time-aligned on a typical 1" 88dB tweeter. And any old 8" bass. I set the tweeter back 5cms. Which flipped the polarity to all positive.

I think these sort of circuits are worth a go. The ca. 6kHz tank notch ( I'd try 0.47uF or 0.68uF with 22R) is interesting. It certainly does something to take down the cone breakup from the bass and clean up the sound. Tweeter level, as always, is adjustable to taste.

[Old'n'Cranky]

Because of the rarity ? of these speakers, I almost class this as giving back to the audio world.
A blog or historical record if you will.
Hopefully this will help others now or in the future.

Steve, you really are a gentleman.
Giving of your time and experience and ask for nothing in return.

The owner asked for a change in the cabinets appearance to better fit the waf
Once the paint and varnish has cured a little longer I will mount the drivers and do some sweeps that I will post here.
Pics will also be forthcoming.