B&W DM70's - top end lacking

Looking at the B&W crossover it should be very easy to split the high/mid and bass to allow bi-wiring or bi- amping.

I could then get the best out of my 15/25 watt tube amp and use my Unico  for the bass. The Unison Unico has 70 watt from MOSFETs and should drive the bass easily.
My Conrad Johnson has two outputs to make this easy.
Level matching could be done using the volume on the Unico.

I should receive my super tweeter today, but think that I should still check out the power supply.
I would have thought that the resistors should be checked first.
B&W claimed that they used NO electrolytic capacitors, but how long do diodes last.
Perhaps the B&W claim only related to the crossover and anyway the paper in oil's may also need replacing.

Anyway, I will do what I can bit by bit.

The Leak Sandwich drivers have already improved the bass after I removed half the speaker stuffing.
I checked the original bass units and see that they both need replacement surrounds but one makes a metallic pinging noise which is not so good.

I will send them both to Wembley Speakers to have them checked out.

Iscm
I have heard mixed reports about the results of subs with ELS57’s?

Yes. If your subs are across the room, near the main speakers, and one listens to different genres of music, high and low SPL levels, IMO, one needs to have remote DSP management. A remote control that allows you to control phase, crossover level and db levels from your listening position.
The Dynaudio brand version that I have looks like

this.

Once one has used a remote DSP you can’t go back to a Sub with controls only on the box.
I have detailed the Quad 57 and subs experience on my virtual system page and my Quad 57 review page. See my post here from the Quad 57 review.

https://forum.audiogon.com/discussions/review-quad-57/post?postid=1324755#1324755

The B&W DM70 ESL’s are probably the rarest known speakers I can think of in North America. I assume more common in Europe. Here is a speaker that cost more to make than what it sold for !
Unheard of today - B&W became a bean counter company (post - John Bowers era - RIP). They are definitely worth the time to restore.

The B&W DM70 ESL’s are probably the rarest known speakers I can think of in North America. I assume more common in Europe. Here is a speaker that cost more to make than what it sold for !

I was told that only about 2500 set were made in total including the Sony versions which were basically the Continentals (SS7000 - same as DM70c - curved front).

One of my friends has a pair and I have been offered another at a fair price complete with spare bass units (the original units need new surrounds). They have Leak Sandwich 13" bass units in at present (like mine)

There is also a pair of Sony’s (SS7000) on eBay just now.

I just took out the two power/ energiser units and was surprised to find that there were many voltage selections (250, 240, 230, 220, 115, 105) and that they were set to 250V.
When this was changed to 230V which is the nearest to my mains ay my current address, the treble units came to life and now produced output up to 14kHz. That is still not as it should be, so the next thing is to send the units to One Thing who repair these (Change all the diodes and whatever else may need doing).

If the sound is still not correct I will get the Panels repaired by One Thing, who say that they have made a jig for these.
I do wonder if the panels were last repaired with too thick a membrane and I do also know that if it is too thin there can be a bit of a gap between mid and bass. It may be for this reason that they always had a falling response above 16kHz.

Regarding the bass, I have now stuck a door mat to the rear panel of the main box (inside). This seems to have tamed a resonance in the upper bass, so now I will do the same with the other unit.

ct0517, I hope you are enjoying yours

Iscm

from the manual.

Impedance
Nominally 8 ohms but rising throughout the mid frequencies to some 20 ohms, falling at 20 khz to 4 ohms.

The manual specifies the following for frequency response.
better than plus or minus 4db - 50 hz to 15khz
plus or minus 5db - 40hz - 20khz

This tells me they need really good setup or people will hear 50hz - 15khz (or less) with an average setup..

The manual also states the ESL panel has a removable pad to control the rear radiation pattern. Make them more dipole. This would be very important for a full midrange and keeping them a few feet at least from the front wall. You don't have a lot to work with - its a small panel. Everything helps. 

My feeling is if B&W kept producing them, the ESL panel would have grown in size - taller, as ESL Panels become more efficient with size. Interesting that the Quad 57 treble & bass panels are vertical. The DM70 mid/treble panel is horizontal. From what I remember the DM70’s have a bigger sweet spot over the 57’s when the 57’s are kept on the ground on their stock feet.

Mentioned earlier I was thinking of taking them out of the stored spot and setting them up. But this needs my son’s lifting help so maybe when he visits. The power supply finding is interesting. Will check the setting on mine before they do get turned on again. I have multiple dedicated lines in the house and live in the country so the demand is not high - Its a solid 121 volts. So the 115 setting it is, and it is low.