Alan Moss ESLs

[nautilus]

Hi Guys,
I have recently picked up a pair of Alan Moss ESLs.
There was a previous post way back on this forum about them....
Well they are in pretty good nick really. Both bass drivers are excellent and one ESL is excellent.
The second one not so.
I have tracked down the fault to the connection of the HV bias to the Mylar diaphram. Has anyone had any experience with these speakers?
I am loath to pull them apart without checking whether somone else here has done it before.
I look forward to any replies.
Other pics to follow......
Matt

[chinsettawong]

The speakers are really beautiful.

Wachara C.

[Calvin]

Hi,

really beautiful? The build quality seems rather poor to me. Your HPs look much more professional.

jauu
Calvin

[arend-jan]

Well, the are 'handcrafted', Calvin

[The Saint]

Hi Matt

Alan Moss is a very good friend of mine.
I had the pleasure I spending many hundreds of hours in front of those loudspeakers at his Riverside home.
You are very lucky to have a pair of those loudspeakers.

I can put you in contact with Allan if you like and he can help you
very likely to fix them.

[otto88]

Hi Matt

Alan is quite elderly now, long retired from the business and I believe not well. I also have a pair, which had what sounds like the same problem.

I didnt fix them, as I was a tad wary and knew a technician who has worked on ESLs here in Melbourne. I have these notes on the treatment, and some clarifying emails:

* NO SOUND FROM A MOSS PANEL *

It is very unlikely to be a UHT power supply problem (it never happened in over 15 years). What is most likely is that the contact with the membrane has been lost. This happened with one of the panels and a repair performed.
If it is with this panel the problem has occurred, then just relocating the wire, foil and foam to a slightly different position will regain membrane contact.
But if it’s with the other panel, here is what to do:

TESTING
1. On the UHT board, locate the thin blue wire connecting to the membrane. It connects to a strip at the bottom left of the panel.
2. Solder another thin wire to that point on the UHT board.
3. Strip a very small section of the insulation away from the other end.
4. Poke the wire through one of the perforations on the front metal grid stator, so it just touches the membrane (take care not to perforate the membrane and have very little bare wire exposed or there will be sparking as it shorts with that front metal).
If you now get music, the fault is with the contact strip to the membrane.

THE REPAIR
1. Remove the cloth cover completely and disconnect the mains, or unplug the power pack.
2. Remove the black cloth tape along the right side and across the front of the panel (purchase some more wide tape as this will need to be replaced)
3. Carefully lift up the front perforated metal at the bottom right, so you can slip in the items listed below.
I did cut out portion of the front stator on the panel I repaired, but later found this was not necessary if you follow these 3 steps - but it is an alternative to gain access to the membrane.
4. The aim is to duplicate the metal strip contact, which has become corroded and lost conductivity to the membrane. Just placing a wire there is no permanent cure (tried that).
What is needed are
1. a wire bared at the end as in the test above
2. a piece of al foil to rest on top of the bared wire, to give a greater contact area,
3. a thin piece of foam to act as insulation between the aluminium foil and the front metal grid, and provide some pressure to secure the wire and foil with contact to the membrane, when it is all put back together again.
5. Slide the wire, foil and foam into the bottom right of the panel between the front perforated metal stator and the membrane.
6. Reconnect the power and be prepared to experiment with foam thickness. Too thin and the wire and foil will not make good contact with the membrane. Too thick and the membrane will be pushed to the rear stator so it shorts out.
7. When the correct foam thickness has been discovered, press the front metal stator back and secure with black cloth tape at the sides and front
8. Reinstall the cloth cover

> I gather the membrane is internal, and the stator is internal; to be certain: which colour
is the membrane?
No, not quite. The stator is the external metal mesh you can see and touch on the outside.
There is another similar Stator (but with different charge) constituting the metal mesh on the back. The setup is
• METAL STATOR (on the front)
• plastic metal coated membrane (in the middle)
• METAL STATOR (on the back)

> black cloth tape?
Hardware shops carry it. Get the widest cloth tape available - 5 cm should do, but more would be helpful. To ensure the tape sticks firmly, it might be a good idea clean gunk off the area you are going to tape with methylated spirits.

Another thought - if the faulty speaker is the one I repaired previously, it might be that the tape cloth I put on has lost its grip and so the tension on the foam etc has been reduced -> loss of contact with the membrane. Not likely, but just a thought


> If or when you are talking to Alan, if he has a copy of the EHT circuit diagram, that would be much appreciated.
I'll see what I can do, but Alan is a bit strange about "giving away trade secrets"

A couple of other things -
1. Use soft foam plastic for the repair - it will give you more flexibility in getting the best usable thickness
2. On the made up EHT board I have no idea what the bias setting would or should be.
I suggest that the screw be set in the middle. Adjust it until you hear a crackling in the membrane and back it off from that. Similarly with that board I made up - I did not check the setting on that either.
Adjust the bias to bring sensitivity to be the same for both speakers.


Before finally putting on the grill cloth, use a cardboard tube (used for posting rolled up items) as an ear trumpet to locate exactly where any buzzing problem could be happening.
This buzzing could be due to one of two causes -
(i) a particle of gunk has entered through the stator and is touching the membrane - cure is to vacuum the front to suck it out before putting back the cloth
(ii) a small section of the membrane has become fatigued and is moving too freely so it is touching the stator - cure is to inject a small amount of Silastic through the front. This has already been done in places and could be contributing a relative drop in sensitivity to one speaker over the other.

I hope this helps.

They dont have a great finish, but with their curved wide panels, I found they have a much wider dipersion pattern than many 'stats.


Cheers

[nautilus]

What a fantastic reply!
Thankyou.
I will have a crack at the repair as I am pretty sure that it is the connection to the diaphram.
Do you know whether Alan is still in contact with anyone on this forum?
I also live it Tassie and it would be a shame not to have a few people that can rebuild/repair these panels.
Also mine did not come with any crossovers. Do you have any information on the type and crossover frequencies that are used?
Cheers
Matthew

[The Saint]

Matt

I think you might have missed my post, I was with Allan when he was designing the very speakers you have.
The panels where crossed over at around 100hz
The panels by default from memory rolled off naturally at that frequency. I can phone and and have a talk with him, to verify my comments.

What part of Tassie are you from?

[otto88]

Hi Anthony

Are you sure the XO was as low as 100 Hz?

Tho' they are biggish panels

Were there different models??

Thanks

[The Saint]

Hi otto

Yes I am quite sure they rolled off at that frequency.
They were a number of models made of these panels.
The ones that matt have were the standard issue so to speak.
There was also a 2/3 height version of the main production models.
Long before Alan intergrated the sub woofer with the panels we use to listen to much larger panels, from memory they were over 6 feet in height and sounded quite excellent without any sub.
The sub of course added that extra depth to the bottom end.
A few times we visited a chap named John Coulson in Dilston.
He had a pair of the 12 foot models, 2 x 6 foot panels stacked on top of each other like totem poles, with a pair of very large transmission line subs sitting behind each set of panels.
Alan also use to make heaps of amplifiers to drive these panels, ranging from OTL valve amps to MOSFET SS and MOSFET/Valve hybrid amps and we got to listen to quite a number of high end commercial amplifiers borrowed from a number of Audiophiles and shops around Australia.

Matt before you attempt any repairs be sure that the voltage multiplier is working OK, it should be putting out around 3kv so you will need a high voltage probe connected to your multimeter to check it safely. Does the red LED light up on the Multiplier board?

Anyway I hope this helps.