B&W DM70's - top end lacking


I have a pair of DM70’s.
They sound really good with vocal, blues and opera.
The bass is overblown with complex orchestral or progressive.

I am already replacing the bass units with Leak sandwich, as I found that the original units had not been repaired correctly.
They had some sort of home made surround made of thick paper with a 12 inch foam surround stuck on top.
The leaks seem to solve some of the bass issues.
I will get the bass units professionally repaired at some point.

Now to the treble units.
The mid and lower treble seems great, but things like symbols seem muted.
I was told that the electrostatic units had been repaired by One Thing, but now I am not so sure.

I am driving them with an Art Audio Quintet fed from a Conrad Johnson PV9a pre.
My CD is a Unison Unico and I am using a Focus One turntable just now.
Cables are from Chord. (Yes they do help a bit)

These are frustrating speakers, as when at their best, they sound so good.
First I need to know what to expect (especially from the treble).
Then I need to know how to fix any issues.

Sometimes they sound so so good and other times . . .
iscm
23:00 - now 238V and sound seems a lot better.
That is near as dam it to 240V
Could it just be my imagination?

Now 23:30 and voltage bang on 240V
Best sound so far
It is like the noise floor has dropped and the treble is better defined.
They just sound less like speakers.
ct0517:
Have you ever had you treble panels repaired?
If so, where did you go and what was the difference?
I know about One Thing, but they are quite expensive and I have heard that their place is a tip. There is also a German man, but I have had mixed reports about him and he is VERY expensive plus there is international post.
My ideal would be somewhere that I could drive to easily from Somerset.
Friends who had Quad ELS units serviced have said that the sound comes 'alive' with the repaired speakers.

I may look at the energiser units as well, as I am sure that small fluctuations in mains voltage should not make so much difference to the sound. 
Perhaps I am being hypercritical as I know that higher end equipment can show up other issues and that all equipment tends to sound at its best late at night.

I have ordered some ribbon super tweeters and it will be interesting how they work.
Hi iscm

I acquired my DM70 ESL already refurbished.

here is a link that shows a pic of the woofer as well as an experiment with the Quad ESL. The experiment did not go well as the B&W crossover Woofer to ESL Panel is 400hz.

https://photos.app.goo.gl/jB2ocyZ1sMjUI86X2

It is using silver wiring.

If there are periods when they sound great, and other times when not so, that tells me the ESL panel may be ok and I suspect the ESL power supply / capacitors. So I would be tempted from your posts to have the capacitors / power supply checked out and recapped. I am pretty sure the DM70 are using electrolytic capacitors versus the polypropylene film capacitors of the 800 matrix series.

The manual recommends that they not be closer than 8 feet apart.

Owners manuals can be found here.

http://bwgroupsupport.com/manuals/bw-archive#ID_DMSeries

Service manuals can be found here.

http://bwgroupsupport.com/manuals/bw-service#ID_DMSeries

ct0517: The service manual is a great hep.
I had no idea that it could be accessed and as it is from 1970 there is a good chance that it is correct for my early versions of the DM70’s.

One thing that I notice straight away is that I have a missing pin A to one of my HF units. This is the Ground connection which is also connected to the centre tap of the audio transformer.
This may explain why I do not get an even treble across the whole panel. I could either get hold of a new plug or remove one of the redundant pins from the other speaker, as only 4 pins are used out of the seven.
First I will try to get a spare if at all possible.
The pin may have fallen out when I first transported the speakers. The seller was not keen for me to remove the HF panels, but I was not happy to transport them in one piece.

After the above I will check the electrolytic capacitors and the resistors.
I am working my way through the wiring replacing with Chord Odyssey as I go.
This is the cable that I use for the speakers and I use Chord for the rest of the system interconnects.

When you bought your speakers did the seller say anything about their restoration.

Thanks again
I just noticed a slight buzz in the right speaker.
When I checked, I could see that some of the filling was pushing very slightly against the cone.
I corrected this and now the sound it much cleaner.
These speakers rely on being totally filled, so it is hard to stop this happening.
In future I may try a different type of filling around the area of the bass unit to prevent this kind of ingress happening again.

I have also raised the speakers by two inches using two 2 * 3 between the speaker and the stand.
This has also made the bass much better (less volume and better definition).
Later I could turn the wood to make the extra lift 3 inches.