Acoustat Answer Man is here

[AcoustatAnswerMan]

Originally Posted by hella356

Thanks, Andy. I learned a lot about my various Acoustats from your site. Did you ever experiment with a tube front end on the Servo amps?

Sorry, no. I did do some service work on the Servocharge Amps, but never used them in my own system. Never cared much for their reliability or danger-value, so I always preferred transformers. Admittedly many of the reliability problems were addressed by later mods at the factory, and those done by Mike Savuto of Analogue Associates.

[AcoustatAnswerMan]

Originally Posted by SY

Thanks, Andy- I had them apart once before (replaced diaphragms), but that was a very labor-intensive process; that time, the wires were intact. This time, they're not... sounds like I may want to just do a scratch build of new ones. Any particular wire recommendations?

The wire was custom made, 24-gauge fine-strand OFC, with PVC insulation, 100% tested to 10-kV. Jim Strickland did a lot of experimentation with wire insulation types, and found that PVC had the best combination of high voltage resistance and yet was 'leaky' enough to provide the right amount of resistance in the electric field (Jim's White Paper explains it better than I ever could!).

[bolserst]

Originally Posted by AcoustatAnswerMan

The 'C-Mod', introduced after the initial use of Medallions, was actually suggested by David Hafler (quite the expert in transformers himself). It involved changing the input crossover network to the hi-freq transformer, resulting in a smoother freq transition and less likelihood of core saturation.

Thanks for the info on the Medallion transformers. I had often wondered if the push for the transformer upgrade was mainly a reliability issue.

Your mention of the 'C-mod' brings up another topic I have been wondering about.
If you compare the Acoustat 'C-mod' interface schematic to the Soundlab Model A-1 interface schematic, they are nearly identical.
Do you happen to know if Strickland or Hafler was involved in developing the Soundlab transformer crossover network?
It seems their network should have been covered under Strickland's patent US4323736.
The 'C-mod' (and Soundlab) crossover networks do add a shunt resistive load across the primary of the HF transformer to reduce tendency for core saturation, but other than that, the basic circuit is the same.

[planet10]

Originally Posted by AcoustatAnswerMan

The conductive coating was a proprietary mix of carbon black, plastic compounds and solvents for bonding to the diaphragm. It was applied with a brush. Good luck in your attempts at Acoustat panel repair - if successful, please share your results.

Moray James is/has built replacement panels from scratch so it can be done.

dave

[AcoustatAnswerMan]

I know that Jim maintained communication with other manufacturers of ESL's, most notably (Harold?) Beveridge, and he was never reluctant in sharing his expertise, but I am not aware of any actual design work that was done for other companies. Any similarity in circuit designs was coincidental, unless there was some 'copying' done, but I'm not making any accusations. Since Acoustat was somewhat the pioneer in making affordable, reliable ESL's (and in my humble opinion, never surpassed in those respects), designs that followed were bound to take advantage of lessons learned at Acoustat. As Jim was fond of saying "You can always tell the pioneers - they're the ones with the arrows in their back".

[bear]

Afaik, based upon actual tests - 20+ years ago now - and iirc, the HF xfmr has a different turns ratio in the C medallion version, the HF coupling caps were also changed. I wrote it down, and it is probably in a folder marked Acoustat, if I'm lucky.

Afaik, and I could be wrong, the PVC wires seemed to be attached with polystyrene dope, not epoxy. But on this I am only going by appearances.

There is/was an article in Speaker Builder years ago called "Amber" which was a DIY clone of the Acoustat panels in most regards.

The wire was essentially similar to "test lead" wire, except it was copper, not tinned (certainly on the later ones) and the PVC insulation was not as fat as standard test lead wire. Where one would get such a thing today is a good question, since it's not a standard wire afaik. If it made 10kv test, I'd be very surprised, but certainly better than standard PVC wire...

If you go with a very high ohm coating then it's unclear that the insulation is going to be much of an issue. In other threads on the Acoustat people have said that using a lighter diaphragm and lighter coating results in better HF performance and overall sound. At least that opinion was voiced, iirc.

Now, here's a question - there was an outfit in Florida that was making replacement transformers, do you know if they or someone else is still around??

Welcome to diyaudio!

_-_-bear

[bolserst]

Originally Posted by bear

Now, here's a question - there was an outfit in Florida that was making replacement transformers, do you know if they or someone else is still around??

I believe Russ Knotts from JustRealMusic can make replacements.

Here is a link to his repair website showing a burnt up coil from a LF Acoustat transformer.
gallery

Here is a link to his main website:
Home Page

[hella356]

Andy, any info on how Acoustat tested regarding the angles of the panels, particularly the 4 wide speakers? Also, how important it is to mix 8" & 9" panels vs just going with 9 inchers in a Model 8 / 4+4 type? I'm planning to build such a speaker with all the extra panels I've got. Thanks!

[AcoustatAnswerMan]

Originally Posted by bear

Afaik, based upon actual tests - 20+ years ago now - and iirc, the HF xfmr has a different turns ratio in the C medallion version, the HF coupling caps were also changed. I wrote it down, and it is probably in a folder marked Acoustat, if I'm lucky.

Afaik, and I could be wrong, the PVC wires seemed to be attached with polystyrene dope, not epoxy. But on this I am only going by appearances.

There is/was an article in Speaker Builder years ago called "Amber" which was a DIY clone of the Acoustat panels in most regards.

The wire was essentially similar to "test lead" wire, except it was copper, not tinned (certainly on the later ones) and the PVC insulation was not as fat as standard test lead wire. Where one would get such a thing today is a good question, since it's not a standard wire afaik. If it made 10kv test, I'd be very surprised, but certainly better than standard PVC wire...

If you go with a very high ohm coating then it's unclear that the insulation is going to be much of an issue. In other threads on the Acoustat people have said that using a lighter diaphragm and lighter coating results in better HF performance and overall sound. At least that opinion was voiced, iirc.

Now, here's a question - there was an outfit in Florida that was making replacement transformers, do you know if they or someone else is still around??

Welcome to diyaudio!

_-_-bear

You are correct that the original 'glue' used to attach the wires to the panel was a home-made brew of styrene pellets dissolved in MEK. The MEK actually melted the panel slightly, allowing the wire to 'sink into' the panel. I suggested epoxy since it is readily available and would probably work fine for spot-repairs. But for building a new panel - probably not.

I know there WAS a company in Florida making replacement transformers for Acoustat - at a handsome price - but not sure if they are still around or offering that service. I believe they were a successor to the original Southeastern Transformer, who made all of Acoustat's transformers except towards the very end of Arizona production.

I cannot confirm nor deny your suggestion that the turns ratio was changed for the Medallion HF tranny. However, there was NO difference in transformer from B Meallion to C Medallion - only the passive network changed.

The wire that Acoustat used was most certainly rated for 10-kV, and was 100% tested by the manufacturer for pinholes and other sources of leakage.

[bear]

Andy, I just said that I was surprised that the wire would handle 10kv...

_-_-bear