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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
ct0517's avatar
ct0517
2,041 posts
 
iscm -  I found the panels sounded best at ear level and by raising the speaker to achieve this, the bass improved as well. I have a device that gives voltage readout. Plugging components into it also shows how much voltage they are using. Any voltmeter can be used to check AC voltage on the mains. When it sounds good and when you notice a problem. If there is a difference that tells you something is up with your main. But if the mains voltage is good both ways, I would suspect an issue with the power supply in the cabinet so it should be looked at. That is not a difficult repair.      
iscm OP
40 posts
 
ct0517. Tonight everything sounds good, although I still think that the treble is a bit recessed.
Did you make your own super tweeter?
I was thinking of using a ribbon crossed over at around 8 kHz with some sort of pot for adjustment. I presume that the effect should be subtle. 
ct0517's avatar
ct0517
2,041 posts
 

Did you make your own super tweeter?

iscm

the one in the linked picture is a simple dome tweeter. On the (plus +) side of the line there are 6 or 7 resistors.  I add / subtract resistors to get the desired effect, if needed. Very subtle. The curtains that can be seen in that room can be slid open to reveal pine walls and drywall, removing damping as needed. I have tried both the Music Reference RM10 and Rm9 Tube amps with them, as well as an assortment of SS amps. They were quite a load for the Rm10. They sound great with the Rm9. Well, everything sounds great with that amp.

My DM70 are not hooked up right now but your thread is making me want to hook them up, upstairs. :^)


iscm OP
40 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
40 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?
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