I recently picked up a pair of Martin Logan CLS II but their interfaces have been replaced with the Acoustat MK-121-2A. I also own Maggie MG-IIIa, Maggie MG-3.5R, Apogee Scintilla, and Wilson Watt Puppy 5.1 and I have to say, they may be the best sounding on the list. The previous owner (now deceased) was quoted as saying the Acoustat interfaces are considered better than the original ML interfaces. Have you ever heard of these being installed on CLS? Also, those speakers are supposed to go down to 35hz or so, but they sound a little thin in the bass. It looks like there are 3 taps in the interface selectable for 2,3, or 4 panel electrostatics. I wonder if this is set wrong for the CLS but I have no idea how many "panels" the CLS II have. Any insight would be appreciated!
I owned a set long ago and found them to be very good in the midrange but not in the lower end. Also found that they easily breakup when played loud. I also don't know if these can handle the high voltage the Acoustat PSU delivers. This needs to be checked as well.
The settings on the transformer can be changed to a lower setting (2 panels) if you want more bass (less panels more boost). As the more panels you have more bass will be given by nature....
As said earlier it can happen that the CLS will not be able to handle the higher voltages or the foil will touch the stators.
The settings on the transformer can be changed to a lower setting (2 panels) if you want more bass (less panels more boost). As the more panels you have more bass will be given by nature....
As said earlier it can happen that the CLS will not be able to handle the higher voltages or the foil will touch the stators.
Last edited:
I have 3 pr of the older CLS ...one pr stock work sound like new, best sounding esl i have ever had,mine dont play as loud as my acoustats or sound lab but cls best over all,i have ran the CLS panels with the MK121 acoustat interfaces but the ml stock sound better...well to me.
If the one on youtube are the one you have thay rocking
5k bias is what the older CLS ran at....i have had the Cls 2. an 2z never like there sound
thay also drop the bias on the new ones.
If the one on youtube are the one you have thay rocking
5k bias is what the older CLS ran at....i have had the Cls 2. an 2z never like there sound
thay also drop the bias on the new ones.
I have tried the CLS with Acoustat interfaces - the high 5kv voltage caused the diaphragm to collapse to one stator, so I used a Variac to dial down the voltage, and landed right around 3000v - right where ML has their interface Bias voltage (how about that!).
But I was not impressed with sound, but these were badly used panels, I eventually opened up the CLS panels to clean them off and recoat and ended up tearing the mylar...I installed new mylar and used the Hand Soap for coating (Sodium Lauryl Sulfate), and again, diaphragm kept collapsing, even at the lower bias, until I realized my tension was way too high at around 14 pounds (I don't know where I got this number from) - I think Quads are more like 3 pounds...
Anyway, that's where the project stands - from 7 -8 years ago - in my closet...maybe when I get the current crap on my bench done, I will revisit this project...
But I was not impressed with sound, but these were badly used panels, I eventually opened up the CLS panels to clean them off and recoat and ended up tearing the mylar...I installed new mylar and used the Hand Soap for coating (Sodium Lauryl Sulfate), and again, diaphragm kept collapsing, even at the lower bias, until I realized my tension was way too high at around 14 pounds (I don't know where I got this number from) - I think Quads are more like 3 pounds...
Anyway, that's where the project stands - from 7 -8 years ago - in my closet...maybe when I get the current crap on my bench done, I will revisit this project...
One of my 3 pr cls are the first one that ml made with the big green,black,red panel feed wire,they were higher bias 5k then they drop to 3k400.so they say ....but i would like to see in side the beez kneez mk121 interfaces,sounds like hes made some changes i think... i get a littel bass over lode ,his seems to miss...his play louder...Wow rocking
As far are stands...been there did that....that sounds not for me...lose to much bass an mid.....but i have all my speakers out into the room, if your setup right on the back wall it my work....have fun
As far are stands...been there did that....that sounds not for me...lose to much bass an mid.....but i have all my speakers out into the room, if your setup right on the back wall it my work....have fun
First well need a big thanks to techpurch with this post an his Beez kneez CLS with Acoustat MK121 interfaces that you can hear an see on youtube here....
Lavishness513 Martin Logan CLS Mod Acoustat MK-121-2A The BEEZ KNEEZ Onkyo M-506RS Stereo Amplifie
All you need is a pr stock Acoustat MK121 a,b,c, interfaces, an a pr of good working ML CLS panels, for my CLS panels I change nothing in the Acoustat 5k bias.
But like john65b said ML did drop the bias, I was told by ML 3.4k but the 5k work on the only two typs ML ended up with of CLS panels! No i dont have the first one with only horizontal bars.
All you do to get what i thinks is some of the best sound out of the ML CLS panels ever.... is just bypass the two 50k res. on the mixer board!!
I found no other need for any changes to the stock mk121 interfaces with my CLS panels!!
Thats right you end up... runing the bass transformer secondary strat to the panels
NEVER REMOVE the stock 1 ohm 30watt res on the bass trans neg input!!
Have fun....long live Acoustat Parts
Lavishness513 Martin Logan CLS Mod Acoustat MK-121-2A The BEEZ KNEEZ Onkyo M-506RS Stereo Amplifie
All you need is a pr stock Acoustat MK121 a,b,c, interfaces, an a pr of good working ML CLS panels, for my CLS panels I change nothing in the Acoustat 5k bias.
But like john65b said ML did drop the bias, I was told by ML 3.4k but the 5k work on the only two typs ML ended up with of CLS panels! No i dont have the first one with only horizontal bars.
All you do to get what i thinks is some of the best sound out of the ML CLS panels ever.... is just bypass the two 50k res. on the mixer board!!
I found no other need for any changes to the stock mk121 interfaces with my CLS panels!!
Thats right you end up... runing the bass transformer secondary strat to the panels
NEVER REMOVE the stock 1 ohm 30watt res on the bass trans neg input!!
Have fun....long live Acoustat Parts
speaking of NEVER REMOVE the stock 1 ohm 30watt res on the bass trans neg input!!
These res are 30 years old now, with this CLS setup the one ohm should a 50watt heat sink to the case or biger push these panel an these 1ohms get Hot, that 1ohm res is all thats keeling the bass trans a live.
always trad offs...
These res are 30 years old now, with this CLS setup the one ohm should a 50watt heat sink to the case or biger push these panel an these 1ohms get Hot, that 1ohm res is all thats keeling the bass trans a live.
always trad offs...
John65b
"I have tried the CLS with Acoustat interfaces - the high 5kv voltage caused the diaphragm to collapse to one stator, so I used a Variac to dial down the voltage, and landed right around 3000v - right where ML has their interface Bias voltage (how about that!)"
Sounds about right...So working with the CLS2 panels i pulled the stock working interfaces, an there bias it just above 3k....But the bias feeder res 30meg not like the Acoustat 5k bias feeder res it 500meg
So what i thought was the Mk121 over loading the panels with the 50k res in....not bypassed, was the 500meg res. in the 121s mixer board, was the need to be lowered to 30 meg an with the 50k res back in the mixer board theres no overlode now.
So it looks like the bias 3k drop, an bias feeder res at 30meg are the only changes thats s needed with the Acoustat mk121 interfaces to run the CLS2 panels.
I think that because these CLS panels cant store a charge like the Acoustat panels the 500meg let the CLS panel run out of bias with big bass hits...that cause the panels over lode
But still say the 1ohm res on the bass trans neg input needs to be up greadedto 1ohm 50-100 watts..it our life saver
all one mans finding....if others try this let know your findings
"I have tried the CLS with Acoustat interfaces - the high 5kv voltage caused the diaphragm to collapse to one stator, so I used a Variac to dial down the voltage, and landed right around 3000v - right where ML has their interface Bias voltage (how about that!)"
Sounds about right...So working with the CLS2 panels i pulled the stock working interfaces, an there bias it just above 3k....But the bias feeder res 30meg not like the Acoustat 5k bias feeder res it 500meg
So what i thought was the Mk121 over loading the panels with the 50k res in....not bypassed, was the 500meg res. in the 121s mixer board, was the need to be lowered to 30 meg an with the 50k res back in the mixer board theres no overlode now.
So it looks like the bias 3k drop, an bias feeder res at 30meg are the only changes thats s needed with the Acoustat mk121 interfaces to run the CLS2 panels.
I think that because these CLS panels cant store a charge like the Acoustat panels the 500meg let the CLS panel run out of bias with big bass hits...that cause the panels over lode
But still say the 1ohm res on the bass trans neg input needs to be up greadedto 1ohm 50-100 watts..it our life saver
all one mans finding....if others try this let know your findings
Last edited: