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Acoustannoy 16th January 2011 09:05 PM

Acoustat 1+1 high sound level limits
As most of you in this part of the forum, I love the sound of ESL. But my Acoustats have only one defect : they cannot stand high pressure levels.

As i'm cautious (I live in France, so I cannot afford me to blow the panels), I'm using 2,5A fuses, plus the 1+1 are filtered 6db/oct with a 0.04ĩF capacitor at the power amps in. The low frequencies are given to a 46cm JBL subwofer with separate amp and active filter.
I tried bigger fuses (5A), but the big MK121 resistor almost melted, and I was afraid for the pannels.

Each time I'm listening loud, the fuses are blowing.
And if I've got a party with dancing music, I buy 10 fuses before, because they blow everytime... Now i use a pair of JBL for the parties.

But it make me a little bit frustrated on lyrics, high female voice levels make the fuses blowing too. Is that something unavoidable with these speakers ?


bear 16th January 2011 09:44 PM

Sounds like you are clipping your amplifiers.

The 1+1s do have an SPL limitation, but you also need a LOT of voltage swing from the amp.
A 200 watt amp will get you to pretty darn loud, but if you have a large room and stuff it with people and try to crank out dance tunes, ur probably going to exceed the limits... I took the fuses out of mine years ago and have never melted anything... but I never tried to blow my eardrums out either - otoh I have played live rock via a mixer with no limiting and we monitored our playing (E-drums, bass, two guitars, vocals) only with a set of Acoustat 4s... more cells than the 1+1 by 100%, but still... (the room is/was 30ft x 14ft x 8ft ceiling)

The power level at 2.5amps is P = I ^2 * R which is P = 6.25 * 6ohms = 37.5 watts. The impedance of the Acoustats tends to be about 6 ohms... so at 5 amps you have 25 * 6 = 150watts. (if it is 8 ohms you made 200watts)

So, if you want to reach the 200 watt equivalent voltage swing you need more than a 5 amp fuse in there... fwiw. Of course if you are clipping the amps, best to not put more in...

ALSO, the speaker is a moderately capacitive load, so the amp needs to also be stable and able to drive such a load, not all can - especially cheaper amps and receivers...

I suggest a solid, real world 200 watts plus amplifier - you need the voltage swing, not so much high current.


casper21 17th January 2011 02:09 AM

I join this topic for a slightly different problem, sorry.I use Spectra 11 speakers with Caso S80 tube amp. I can't exceed about 1/6th of the volume (very dirty sound at higher level), well a lot of power available... With my old Perreaux 200w solid, I used to listen at full amp level . Is there any improvement for these speakers? Maybe could i add a subwoofer but without another amp. (how,wich one?). Trying to reach high sound levels, the low frequencies are damaged first, then the mid range.

PS: Mathieu I will send you pm

Calvin 17th January 2011 07:27 AM


what fuses? At the inlet of Your amp, In the supply lines of the amplifier circuits? From what Bear writes it might also be some fuses in the input of the ESL itself?
Anyway Bearīs calculation describes the best case, a power calculation into a resistor as load. In this case power is lowest. As soon as there is a inductive or capacitive part in the load, the power is higher, because besides the īrealī power which is usable for acoustic output thereīs a imaginary part. The amount of the imaginary part increases with the phase shift it introduces. At 45° of phaseshift real and imaginary part already equal.
This means that the amplifier has to deal with 41% more power than the speaker could translate into acoustic power. Now if You look at the impedance plots of ESLs many of them feature the highest phaseshift and rather low ohmic values in the upper midrange, just in the freq-range of high pitched female voices. This might lead to overload when driving the amps hard.
A second factor might be as Bear already suggested the amps capability to remain stable under capacitive loading. It could well be that Your amp is right at the rim, close to the onset of oscillation. It canīt follow the signal as precise as required, but adds some post ringing.
A amplifier driven close to its limits will sound harsh and stressed.
Choosing a fuse bigger doesnīt improve things in such a case but asks for serious defecting of the electronics.
Choosing a stable working amplifier is the best safety and sonic measurement....or a different speaker if You want to party.


bear 17th January 2011 02:17 PM

Google does not reveal what a Caso S80 amplifier might be.

I think you are confusing the position of the volume control for the power output of the amplifier - they are not related at all.

Calvin, the Acoustat interface fuses the speaker input line... fyi. They also fuse the PS.

The other possibility is that the HV multiplier string that produces the bias voltage for the cells has malfunctioned. This would cause lower output and distortion when driven harder.

I've posted this before, but the short version is that you need to be able to solder, mark the position of the diode's polarity on the board, then remove the diodes, remove the caps and replace with suitable HV units. You want >3kv (5kv+ ideal) diodes (low amps ok) and >5kv+ ceramic NPO caps (although Z5U will work ok). The value of the caps is printed on the caps, you can go +100% and -25% on the value no problems at all. Replace them all unless you have a way to test. Will cost you about $30USD per channel worst case. Any decent Electronics repair shop can do this job for you if you present them with the HV boards from the interfaces. (open the interface, and make a drawing of the wiring to the board, desolder, remove...)

Post a picture of the interface inside if you are unsure what is what...

The Acoustat HV boards often fail now that they are >25yrs old.
The caps get leaky and kill the diodes, drag the voltage down...
If you could troubleshoot, you could replace just the bad parts, but the parts are cheap enough, and easy enough to replace... a clue is that the channels are not equal output, although that may not always happen...


Acoustannoy 17th January 2011 09:45 PM

2 Attachment(s)
It looks as if I met the right people...
First, I try to answer about Casper question : I tried a Cary tube amp, without any success. It work now with Magnepan speakers in a bi-amping configuration (in the mid-upper frequencies). Not enough current for acoustats. I tried 7 amplifiers with the Acoustats, sadly burned 2 lovely Carver PM1.5 ... :bawling:
As says Bear, impedance is a key point when considering ESL. As a coincidence, I had a perraux 200W amp, together with the perreaux SM3 preamp. This is a good choice for ESL's, it heats up to cooking some eggs, but never failed.
4 years ago I found two Electrocompaniet AW180 fot a 'decent' price :rolleyes:. I sold the Perreaux. But with a good preamp (try AR SP14) the Perreaux can be a good chice for Acoustats. If I can give an advise, look for a good second hand solid state amp with strong, clean bass, and put your monney in a very good preamp. You will not regret it.

Now if You look at the impedance plots of ESLs many of them feature the highest phaseshift and rather low ohmic values in the upper midrange, just in the freq-range of high pitched female voices. This might lead to overload when driving the amps hard.

[! Bear ! Thanks for this info. This explains why fuses are blowing mostly on female voices.
I'm thinking about bi-amping of the 1+1. This would ease the amplifier work. What is your opinion, and do you know how to connect the MK121 interfaces for bi-amping ?
Secondly I will take your advise into consideration,and will change the diodes. I already changed the caps (see photos) for MKP ones with a very good result, but could'nt find the diodes. Can you advise me the references and a supplier ?

Many thanks !!!

bear 18th January 2011 03:11 AM

Wrong caps - but the ones you changed MUST be of VERY HIGH VOLTAGE or they will break down. Did you save the old ones? Note the ratings - iirc like 15kv or so!!!

The caps you want to change are the ORANGE ones. Do those first, then the diodes, or both at the same time... never the diodes first. The caps failing kills the diodes... although the diodes failing might kill the caps too... :D

The impedance of the Acoustats does not fall like most ESLs... the interface is patented and that is part of the point of it.

In the second image the big series resistor seems to be overheated and has some burn spots, hard to tell from the pix...

Biamp? Not a plan - the Acoustat does not have a "xover" as you expect - it does not have highs coming from one transformer and lows from another, they overlap by several octaves! One could bi-amp but it would be slightly tricky and it is unclear what advantage you'd have... there might be one, but it is somewhat unclear, and in the event one amp was inverting and the other wasn't you'd have real problems until you figured that out...

For the diodes try looking at an electronic distributor in your part of the world, or if you mail order from afar, almost any major USA (or British, probably German too) distributor will have diodes of a suitable PRV... you can series two diodes to get the required PIV in a pinch...


Acoustannoy 19th January 2011 08:19 PM


- Original caps are 0.01mF-6000V. I replaced tham with a serie/parallel arrangement of 4000V caps.
- You are right, the big resistor is somewhat burn... Needs repair...

- I'm not very familiar with the Diodes, ebent less in the high tension field.
What should I look as spares ? Nothing is written on theses...

Many thanks,

bolserst 19th January 2011 10:35 PM


Originally Posted by Acoustannoy (Post 2439359)

- Original caps are 0.01mF-6000V. I replaced tham with a serie/parallel arrangement of 4000V caps.

Be advised that the original Acoustat cap is rated for 6000VAC.
Your series/parallel arrangement of WIMA caps are rated for 4000VDC, but only 1400VAC.
These capacitors need to withstand the high voltage audio signal produced but the step-up transformers.
Maybe this is why you have been blowing fuses?

You might contact Moray James as he sells Polypropylene caps to replace the Acoustat Polyester caps with the proper AC voltage rating.

bear 20th January 2011 04:48 AM

the diodes are simple just find "high voltage" diodes. You want PRV or PIV of 5kv or more, that is all you need. Current is low. So any diode that is not expensive with that spec will do fine. The current is very low, so a 1amp rated diode is more than good. 0.5A is good too... check the usual electronics distributors. As I said you can series two 3kv diodes too... CHANGE THE CAPS!! :D

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