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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
iscm OP
38 posts
 
At 19:30 the sound seemed a bit off so I measured the mains voltage.
It came in at 233V.
I will measure again later.
These days 233V is in the centre or the range, so it will be interesting to see if it gets nearer to 240V later.
It may be that the power supply on my electrostatic units are a bit weak after all these years and exaggerate the effects of any voltage drop. I am not sure whether the 3000V polarising voltage applied to the electrostatic panels is regulated or not. 
Perhaps a change of capacitors is due here.

233V should really be OK.
Of course it may be a problem with dirty mains which can affect any good hi-fi.
iscm OP
38 posts
 
20:45 - 236V
Tested again as sound seemed a bit better and more lively.
Could 3 Volts make much difference or could it just be that the supply is cleaner at this time?
iscm OP
38 posts
 
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.
iscm OP
38 posts
 
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.
ct0517's avatar
ct0517
1,798 posts
 
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

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