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Calvin 12th November 2004 10:34 AM

Polarising Voltage on older Sequel II

Id like to know what the nominal value for the Polarising Voltage of an older MartinLogan Sequel II is (10-14 Years old). My candidat just puts out 1.1kV and 0.9kV in the different positions of the HV-switch. Presumable thats far too low? The Transformer seems to put out such a stray field that the Bass is constantly humming (Coil in the crossover picks up the strayfield). The HV-board has bcome quite dirty throuh the Years, so my guess is, that the dirt has established a leakage path for the HV and the transformer is always running into saturation whlie trying to keep up the Voltage.


tim pattinson 2nd December 2004 12:05 AM

I'd highly recommend the Martin Logan owner forum, which I don't currently have the URL for, and also M-L's aftermarket support is second to none.

Calvin 2nd December 2004 06:57 AM

Hi Tim,

thanks for Your re.
Meanwhile I measured a second paur of Sequels and found out, that the 1.1/0.9kV is the standard value of HV . From 1.5kV on You can hear first popping noises from small flashovers. So 1.1kV is really ok.


tim pattinson 2nd December 2004 07:30 AM

nice speakers.

Calvin 2nd December 2004 02:15 PM

Hi Tim,

well Im building ESls my own and have made plane panels with wire stators like Audiostatic and am now building curved transducers like the MLs. Very very fine panels the MLs indeed and the technical solution is to the point, but the quality of the audiotransformer is very low. This costs efficiency (the crossover and frequency correction cost around 10dB!) und sound.
The Sequels I measured had to get maintenance and repair.


coolhandluc 22nd September 2006 12:01 AM

Martin Logan Sequel crossover schematic ?
Hi Calvin from Australia,
I was wondering if you have a circuit schematic for the original Martin Logan Sequel, I have the newer SL3 panel fitted to mine but want to see what I can do to improve the crossover (other than better caps), also the later models had the facility to bi-wire and a bass attenuation switch which I want to retro fit...I just know that they can sound much better with a few tweaks !


Calvin 22nd September 2006 07:02 AM


here it is ;-)

I did extensive tests with different trannies, crossovers and crossover parts. For e.g when the panel alone was connected to the excellent Amplimo-tranny (1:75) the panel showed better linearity and more HF accentuation. Still though the panel itself could show better HF-response when fitted with a new and thinner membrane. The 12m thick film ML uses already attenuates the HF response. With a very thin film of ~4m You can gain up to 3dB at the upper end and better overall linearity. Besides a slight enhancement of the higher frequencies the resolution of details is clearly better.

The original tranny is a remarkable cheap and dirty piece of thing :dead: Its this bad tranny that makes such a complex crossover a must. Every try to make an crossover with lesser part count failed.
With an excellent tranny You can get away with a simple dampened second order filter and notch on the ground resonance. As a result You have better linearity all the way down to 250Hz and a way better efficiency of well above 90dB/2.83V/1m!! But Youll need a new bass part of course that can cope with that high efficiency or You omit the passive stuff all at once and drive the ESL actively!

Things alter when the crossover is connected! The good Amplimo tranny doesnt show any significant advantage any more. So You should stay with the original one in this case. All the good of the panel is swamped by the tranny and the crossover. The crossover itself is perfectly engineered to correct for the trannys failures and to match the low sensitivity of the bass to the high sensitivity of the panel. So any tweaking is up to the parts and values of the crossover parts.
Of major importance are the values C2, R1 and R2. A change of values here will effect the sound of the speaker much more than changing Cap X from foil A to foil superduper ;-)
C2: tilts the HF-response, with 10F 1dB less HF, with 20F +1dB HF
R1: influences the range from 300-500Hz. R1=0.39Ohm gives +2dB, R1=2Ohms = -2dB
R2: changes the complete range below ~3kHz. R2=8.2Ohms -1.5dB, R2=3Ohm +1.5dB
Id suggest to try different values of these 3 components before starting to throw money at more expensive parts.
Happy tweaking :-)


coolhandluc 22nd September 2006 02:57 PM

Thanks Calvin !
But can you tell me if the details your have provided are the same for the original Sequel (Series I)...mine are the ones with the ported bass enclosure and I was under the impression that the characteristics of the crossover were somewhat changed for the later sealed cabinets which have different bass drivers and curves ??
Also curious, it would appear that ML didn't use ported bass drivers on any other model since this one.......I must say that the bass produced by this model is phenomenal, and I don't notice any obvious crossover point to the esl panel...even my "stacked Quad 57" owning buddy is quite impressed by this early model Sequel, although the mid band on it does not even begin to approach the 57's absolute clarity...but what else does....!

MJ Dijkstra 22nd September 2006 03:42 PM

Hi Calvin,

Is it possible to make a simple active crossover (6 dB/octafe), without notch, and feed this to the sequel2 panel? Maybe you already tried it.

Calvin 23rd September 2006 05:59 AM


of course is a simple 6dB active filter possible ;-) Just size the input cap of Youre amp apropriately :D
Sonically itll very probabely be a disaster though apart from crossover frequencies well above 3kHz.
All visually open panels exhibit a quite strong ground resonance (+10dB is rather common) with which You have to deal with. Thats what the notch is for. In togetherness with a notch You might get away with a 6dB-filter, though my experience is that 12dB+notch work best with panels of an ML-style.


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