B&W DM70's - top end lacking

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.

I did a basic test of the high frequency response 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

an experiment with the Quad ESL. The experiment did not go well as the B&W crossover Woofer to ESL Panel is 400hz.

ct0517: With the Quads, I would have thought that around 200 Hz would be better.
I also have a pair of Dali Skyline 2000 and they have a great bass with the right amp and they are totally open baffle right up to their 40cm ribbon tweeter.
They get around the bass loss by using a super efficient 15 inch bass unit which is attenuated until it crosses over to the mid range.
Dali claimed a flat bass down to 38 Hz.

When driven correctly, they have been the nearest thing to Quads will balls that I ever heard, which is what made me think about using their open baffle method with electrostatics.

ct0517: With the Quads, I would have thought that around 200 Hz would be better.

Hi iscm

A 200 hz setting is much too high for the Quads. the Quads are wonderful to 50 hz with the Music Reference RM10 which was designed for them.
they needed help below that for the bottom Octave only, and to help create fill /SPL in the room.

For the experiments I placed the DM70 as shown in the picture I linked,  and did not plug them in so only the woofer was active. The woofer plays to 400 hz as designed. This was way too high and the reason it did not work well. Did not mix well with the Quad ESL bass panels. 

In room 2 I have the 57's set up with two Dynaudio BM12s Subs. The subs come with their own Class A/B amp - 250 watts each - they are set to play 60 hz and down only. The RM10 is full out on the 57's.
The preamp used in that room has two direct outputs to allow for separate connections to the RM10 and the BM12s subs. 
So the subs are filling in 60 hz and down only.