B&W DM70; rebuilding an Icon

[i2Paq]

I have had many type's of speakers.

From High-end (Dutch brand Hepta) to Bose, B&W, Leak, Rogers, Acoustic Research, IMF, KEF, Tannoy etc. ect.

Many are still on my list but I will probably never own them.

One I knew I would: The B&W DM70!

There where 2 models.

De Standard, model ‘60.
https://s-media-cache-ak0.pinimg.com/564x/db/c2/1c/dbc21c2b35599d853096edc49170f894.jpg

De Continental, model ’70.
http://www.eraudio.com.au/ESL_Repair_Kits/B_W_DM_70_Kit/a_B_W_DM70_pic02.jpg
http://www.mats-enterprise.co.uk/DM70page/images/DM70C_main.jpg

I've looked at a few Continental sets in the past but as the were dark brown veneer I never bought them.
The second reason was I did not know where to go if I needed repairs to the Electrostatics.

There is but one “expert” I now of who repairs/rebuild these DM70, based in Germany: Shackman Electrostatic Loudspeakers Repair Service (http://loudspeaker-repair-service.reromanus.net/refurbish_DM70.htm)

After an ad on a Dutch website I was contacted and offered a set Continental that needed some work and was missing parts.
But the price was good and by now I know where to look for parts and/or help.

So last Friday I wen on route an picked them up.

Pictures!
Fronts; I've now cleaned them as it is mostly dirt what you see. They do need new paint.
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02703.JPG

Back:
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02704.JPG

Inside:
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02705.JPG
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02706.JPG

Power Unit, original and another bought by the seller.
As my model is the latest model, DM70c, the other unit will never fit.
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02707.JPG

Electrostatics:
Original:
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02701.JPG
Second set bought by seller. They look to be in 100% condition.
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Org/DSC02702.JPG

So it's missing the woofers and stands but as this is de DM70c it has woofer adapters which means I can buy flat woofers instead of the more expensive curved ones.
They are also missing the stuffing.
As I bought a pair of the model Standard I thus have woofers and stuffing + filter/Power unit spairs.

The plan:


New paint - This week I'm seeing several people for this job
Woofers - I bought a technical 100% set Standard which I will use for woofers and stuffing
Rebuilding Power Units and Filters - This will be done by a friend
Finding original stands - I'm getting drawings and detail pictures and a friend (metal constructor) has offered to built me new ones
Transfering the Brown Electrostatics into the White housing - I will go to Germany to do this


First thing will be getting them a repaint while a friend rebuilds the Power Units and filters.
The second pair of Power Units will be used for spare parts.

When the stands are ready for use I will start rebuilding the DM70c with all the parts I have.
If needed I will travel to Germany to get help. I will take my wife along to have some day's together while we wait for the technician to fix what needs fixing.

I will update this topic as I go along.

[struth]

A lot of work but sure it will be worth it. Interesting design

[walpurgis]

Good project Norman. It'll be interesting to watch as you progress.

Yes. I did spot what looks like an AR4xa sitting at the back! :D

[i2Paq]

Good project Norman. It'll be interesting to watch as you progress.

Thanks!



Yes. I did spot what looks like an AR4xa sitting at the back! :D

In this picture there are restored AR3a's in the back :ner:

[walpurgis]

In this picture there are restored AR3a's in the back :ner:

Ah. Very similar in appearance. It's hard to judge the size.

[i2Paq]

Ah. Very similar in appearance. It's hard to judge the size.

Yep, they are!

They all sound amazing, it all depends on room-size.

[ReggieB]

Great little project. I look forward to seeing the end results.

[Barry]

Great little project. I look forward to seeing the end results.

So do I! :)

[i2Paq]

Next week, 16 March, I will deliver the electronics at my friends house for a rebuild.
This will take about 1 or 2 weeks as I'm looking for spare-parts (I found them but they are pricey).

March 17 the speakers housing will be dropped of at the painter. This guy paints the speakers for Hepta, a Dutch speaker brand, so they will be in good hands.
RAL9010 is the color according to the painter, I thinking about RAL9001 myself.
They will be in satin, not gloss as I think they where in satin originally.

[martian sunrise]

Hi Norman - how are you getting on with this?

[i2Paq]

So it has been a while since my last update.

The Power units are still being restored. I had some difficulties finding the schematics but thanks to a Dutch guy over at the http://www.vintage-radio.net/forum I got a copy.
Next was finding the right (physical) 800 Ohm resistors; this is still a work in progress.

The stands have now being made, all by hand and (almost) to original size / specs.
They still need to get a layer of mat black paint.

http://cupofcoffee.nl/media/audio/i2paq/DM70c/voet1.jpg

http://cupofcoffee.nl/media/audio/i2paq/DM70c/voet2.jpg

The cabinets have been freshly painted with RAL9010 and here are some images with the new stands.

http://cupofcoffee.nl/media/audio/i2paq/DM70c/beiden.jpg

http://cupofcoffee.nl/media/audio/i2paq/DM70c/kast-en-voet.jpg

In two weeks I will drive up to Germany to have the Electrostatics renewed.

[Pharos]

If they are mild steel do use a Hammerite or similar for bonding and anti rust; that is a lot of work to sabotage.

[karma67]

I like the picture of the lambretta, my guess is a model d :)

[walpurgis]

I like the picture of the lambretta, my guess is a model d :)

Horrible things!

[Arkless Electronics]

Horrible things!

Yep. Land fill at best!

[struth]

Looking great Norman

[Barry]

I bet those electrostatic tweeters and moving-coil woofers are producing a nice, clear and transparent sound. :D

[i2Paq]

I bet those electrostatic tweeters and moving-coil woofers are producing a nice, clear and transparent sound. :D

Yep, very "open" :D

[i2Paq]

I like the picture of the lambretta, my guess is a model d :)

Nope, it is a model B.

I used to have a few Lambretta's. Love them!

[i2Paq]

Time for another update!

Filters and High Power Units have been reworked to specs.

HPU
http://cupofcoffee.nl/media/audio/i2paq/DM70c/IMG_7445.JPG

Filters
http://cupofcoffee.nl/media/audio/i2paq/DM70c/IMG_7446.JPG

We have also tested them with the spare Electrostats that I have.

Little nervous to power them on after being without power for years.

But they switched on without issues, tone generator generated a nice tone with no disturbing noises or deformation.

http://cupofcoffee.nl/media/audio/i2paq/DM70c/IMG_2301.JPG
http://cupofcoffee.nl/media/audio/i2paq/DM70c/IMG_2303.JPG
http://cupofcoffee.nl/media/audio/i2paq/DM70c/IMG_2304.JPG

It is a shame that the aluminum fronts of the Electrostats are damaged and that replacement is no where to be found.
I've decided I will use plain aluminum on the Electrostats and woofer to have a overall look.
They will be painted (muffled) in black and I think it will be perfect.

https://www.mcb.eu/d79e95f5086d7f1dd7474190851b1c81/output/png/size/370/sys-master/s3public/h9f/h37/8801348583454/mcb_plaat_geperforeerd_rond.png

The woofers from the donor pair are removed form their cabinets.
The stuffing is completely deteriorated and cannot be used so I have to find some other.

Both woofers measure 6.3 Ohm.
The're different in model looking at the magnet, probably one has been replaced under warranty.

http://cupofcoffee.nl/media/audio/i2paq/DM70c/Woofer-1.JPG
http://cupofcoffee.nl/media/audio/i2paq/DM70c/Woofer-2.JPG

[farflungstar]

Hows the project going?

[i2Paq]

Hows the project going?

We are waiting on the return of the Electrostatics.

I'm going to use BAF-wadding for stuffing.

[farflungstar]

I've never had the pleasure of hearing these iconic speakers - but have airways wanted to. How would you describe their sound, in comparison to today's best?

[i2Paq]

I've never had the pleasure of hearing these iconic speakers - but have airways wanted to. How would you describe their sound, in comparison to today's best?

2 weeks ago I got a call from someone responding to my AD on marktplaats.nl where I'm looking for parts.

He had a set which, as it turned out, had been restored by it's previous owner.

He lived on the other side of The Netherlands but the coincidence was that I needed to be there just 3 days after we spoke.

So I was invited by him to come and listen.

There they where, in a great, large, living-room, beautiful house and a very nice and proud owner.

We listened to a large amount of different kind of music, jazz, Dutch pop etc.

The sound?

Wauw, I mean, everything was there and it all fitted perfectly.

Bass, mids and highs were all in balance.
At least, to my taste.
Yours could be completely different :)

They sounded amazing, and if this is what mine will sound then I'm over the moon.

This was the first set that I have heard that were "as new", all other sets were still original.

[agk]

Gorgeous speakers that I'm quite sure will sound as good as they look.
They fall into the final, end of the search speaker category for me Norman.

[drSM]

2 weeks ago I got a call from someone responding to my AD on marktplaats.nl where I'm looking for parts.

He had a set which, as it turned out, had been restored by it's previous owner.

He lived on the other side of The Netherlands but the coincidence was that I needed to be there just 3 days after we spoke.

So I was invited by him to come and listen.

There they where, in a great, large, living-room, beautiful house and a very nice and proud owner.

We listened to a large amount of different kind of music, jazz, Dutch pop etc.

The sound?

Wauw, I mean, everything was there and it all fitted perfectly.

Bass, mids and highs were all in balance.
At least, to my taste.
Yours could be completely different :)

They sounded amazing, and if this is what mine will sound then I'm over the moon.

This was the first set that I have heard that were "as new", all other sets were still original.

did u not take any pics?

[i2Paq]

did u not take any pics?

Nope, he did not want me to.

[iscm]

Time for another update! . . .
. . . .
The stuffing is completely deteriorated and cannot be used so I have to find some other.


I have the Original DM70's and mine are filled with fiberglass.
It looks like yours had long fiber wool.
You could just get more of the same.
I did try to run the speakers with less filling, but I found that the bass just got more boomy. It is one of the failings of these speakers, but with careful positioning the problem can be reduced.

In another forum it was suggested that I should raise the speakers a bit.
I did this and it was better for both the treble and the bass.
It is a shame that you did not make the stands a fraction higher than original. Mind you these speakers are quite imposing anyway and you could always try spacers anyway.

As I had some issues with my bass units, I have purchased some 13 inch Leak Sandwich 8 ohm to use and must say that these seem to be quite an improvement on the side that I have done so far.
I will still get the original bass unit repaired, but will not be in a hurry to put them back as the Leaks are so good.

Next I suppose it must be the replacement of the electrolytic capacitors.
I may also split the crossover to allow bi-amping.
Could it help with the bass control?

How are you getting on with your referb?

[spendorman]

I have several pairs of B&W DM4's, some have long fibre wool in, others have white BAF wadding inside.

[iscm]

i2Paq:
May I ask who is restoring your electrostatic unit?

Mine seem OK, but they seem to lack some sparkle.
I was told that mine had been restored, but sometimes I wonder if it was done correctly. It is as if the very top of the treble is missing and things like symbols seem recessed.
The treble drops in level at 9/10 kHz and stops completely at 11 kHz.
I can hear up to 16 kHz (just) these days.
This does not seem correct to me

I already found an amazing bodge on my original bass units.
Now I am using the Leak 13 inch sandwich.
The bass speaker units had two surrounds on each of them.
One is thick paper bent into some shape and on top of that a foam surround meant for a 12 inch bass unit.
The units can be salvaged, but it is more work. At first glance they look OK.

[iscm]

I did a basic test of the high frequency response on my panels and found that the cut off is around 10/ 11 kHz.
With a normal tweeter I can hear (just) to 16 kHz.
This may explain why symbols seem so recessed and why, depending on the music, things just don't sound quite right.

It could be the power supply to the panels or the panels themselves.
As my mains is just over 230V where I live, I could try setting the selector on the power supplies to 220V to see if the treble improves.

I suspect that it it is the panels themselves that need a refurb.
We will see.

How was the response on your panels?
I would expect them to extend to at least 15/ 16 kHz if not higher.

[iscm]

So it has been a while since my last update.

The Power units are still being restored. I had some difficulties finding the schematics but thanks to a Dutch guy over at the http://www.vintage-radio.net/forum I got a copy.
Next was finding the right (physical) 800 Ohm resistors; this is still a work in progress.
.

Looking at the schematics that I have, there are 3 * 800 MEG ohm resistors in series.
Do you mean these?
There are some in the Radio Spares site, but they are not quite the correct shape.

This is where I obtained my service manuals:
http://bwgroupsupport.com/manuals/service#ID_DMSeries
via a very nice chap on another forum

NOTE: My bass crossover is not the same as in the manual
22872


I'm in the middle of restoring a pair of DM70 (in White) to original specs.
I'm looking for a pair of female connectors used in the Power Unit. The unit you connect the Electrostatics to.

I would be happy with a second hand pair, as long as they are without corrosion.
Are there shops in the UK that specialize in those vintage B&W?
I know a German address but I could be more lucky asking you guys in the UK :D


I presume that you have the connector by now.
In the UK One Thing Audio repair the electrostatic units plus the electronics
http://www.onethingaudio.org/index.php?route=common/home
and
http://onethingaudio.net/index.html
46 Siddeley Avenue
Stoke
Coventry
CV3 1GA
TEL: +44 (0)24 7627 4573

They may have parts.

Wembley Loudspeakers can do the speaker surrounds if required.
http://www.wembleyloudspeaker.com/
+44 (0)20 8743 4567
I will be using them shortly.

[koyaanisqatsi]

I did a basic test of the high frequency response on my panels and found that the cut off is around 10/ 11 kHz.
With a normal tweeter I can hear (just) to 16 kHz.
This may explain why symbols seem so recessed and why, depending on the music, things just don't sound quite right.

I would expect them to extend to at least 15/ 16 kHz if not higher.


22911

this is the frequency response graph from the original handbook

[iscm]

22911

this is the frequency response graph from the original handbook

Thanks
That is what is claimed, but what I wanted to know was peoples experience with repaired or original DM70 panels.

[iscm]

Here are links to all the reference documents that I have so far.
https://1drv.ms/f/s!AsdR4rYZVpE4sUzCKIvZoEG9f5Ag
Note that that this is my working area and there could be duplicates.

This is interesting, as it give an insight into the development of the speakers.
https://1drv.ms/b/s!AsdR4rYZVpE4sDU7GJjlvhBf1_2N

I hope the above links help