Martin Logan Montis Power Supply Board Help

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Hello all,

Anyone have any connection info on these power supplies - I believe they are common on the tier of ML Speakers - Montis, Vantage, etc.

I have two of them and need connection info - I see two small headers with 5 -- 6 pins, one three wire connector block, and two spade connections - My guess is the spades go to the speaker inputs to for sense circuit, but other connections are in question - wanted to use these power supplies for an ESL (CLS Panels) experiment.

Dose look deff than this.....then the other I have never had my hands on this type....Spire...


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John.....looks to me your going to need more seen the CLS bias setup....
I think you have only part of the bias setup....what do I part of the CLX bias board...
good luck I hope it works


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I have not seen those supply boards before.
Did you have any pics before their were pulled from the Montis to see how it was wired?
That would certainly help figuring out how to hook them up for your CLS.

if these are similar to the Spire supplies:
- the 5 pin connector requires dual +/- 12 volt supplies to operate the board.
- you will also need to provide speaker level signal to get the HV supply to turn on
- the MOSFET on the heatsink is a limiter which you will want to make sure you don't use on your full range CLS as it would burn up the MOSFET in short order. So, need to be careful how you hook up speaker level signal to the board...or may need to just unsolder the MOSFET.

Is there a connector just to the left of the MOSFET heat sink in the first pic?
If so, can you post a pic of it?
Also, a pic of the bottom of the board would be helpful in figuring out the speaker level connections.

tyu is right about the voltage output of these boards not being as high as what the CLS was designed for. They will put out about 2.4kV, whereas the CLS was designed for about 5kV. You could add 4 more cap and diodes to get there.
Joined 2005
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The connector to the left of the MOSFET Sink says LED.

When I last connected the CLS to a home built power supply, I had to dial it down to around 2500V, or else the stator would collapse and panel would make all sorts on noises, so 2.4kv should work fine...

I can trace the two 5 pin connectors for the ones that go to ground and to rectifier diodes to see the 12VAC input...

i also noticed the two spades are connected to the two far ends of the three pin connector...which really confused me...

No pics of it connected to the speaker..
Joined 2005
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The ML PCB Board is a BCFS7HV. When I googled it I now come to a disconnection diagram of this board in a Vantage speaker...yehaw!


The two spades (Speaker Level Inputs) are also connected to the two far ends of the three pin connector...which means the two far ends of the grey three pin connector goes to the step up transformer... now we are getting somewhere...
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i also noticed the two spades are connected to the two far ends of the three pin connector...which really confused me...
Hmmm...that doesn't sound right.

Looking at the PDF you linked to:
- the 3 pin connector has HV+ on one end (red wire) and HV- on the other (yellow wire). If it is like other ML supplies, the HV- will be connected to the center point of the 2K power resistors which are connected to the spades.

- the spades are hooked to the primary of the transformer. They provide music sense signal to turn on the power supply. They also are used to connect the shunt limiter MOSFET across the primary. You will not want the limiter working. The easiest way to remove the limiter from the circuit and keep the auto-on funtionality will be to remove the bridge rectifer (small round black 4 legged component sitting right in front of the MOSFET)

- as far as the 5 pin connector, the PDF doesn't give any details on the pinout, but if it is like the SPIRE:
pin 1 will be +12Vdc
pin 2 will be ground
pin 3 will be -12Vdc
pin 4 will be ON/OFF control to power amp (same signal going to the LED connector)
pin 5 NC

You can cross-check by measuring continuity with the LM311 opamp pins.

LM311 pin 1 should be ground
LM311 pin 4 should be -12V
LM311 pin 8 should be +12V
Joined 2005
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Thanks Bolserst!!

I will have a look - there are two 5 pin connectors. the one 5 pin connector that lines up with pins on LM311 is the power connector...

"- the spades are hooked to the primary of the transformer."
You mean the step up transformer, correct?

Also, have been planning on using the CLS from 150hz and up only - I have to see what the Spires / Vantage crossover from panel to woofer is...

The Vantage has the ICEPower 200ASC amp modules in it and likely the +/-12VDC supply to this board...
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Hi, I recently replaced the PS supplies on my Clarity. A very knowledgeable forum member sent me the following circuit chart and explanation to understand the board better. Maybe it could be helpful:

Here is a typical ML high voltage board...the top left section is the music detect circuit, the input resistors and 4 diodes by the connector BB2 clamp the max music input voltage to IC1D to + or - .7 volts. IC1D amplifies the music signal and turns on Q2, discharging C6. Timing capacitors C5 and C6 give a turn-off delay, so it stays on for several minutes after the music stops, to keep the speakers charged between songs and album changes.
The high voltage section starts at the AC mains connector AC1, further down on the left, which feeds a step-up transformer, T1, then on to a voltage multiplier ladder circuit with diodes and capacitors around D15 to D20, on to four 15 meg current limiting resistors, and out to the speaker @ connector BB1.
When it detects music, C6 discharges, and the output of IC1C changes state, this puts voltage on connector BB3 to light the speaker LED, it also goes through an on-board LED D1, and turns on a triac TRIAC1. This enables the high voltage ladder circuit, and gives you the high voltage for the speaker.
Diodes D12, 13, 26, 27 form a bridge rectifier...that in conjunction with Zener diodes Z3 through Z13 clamps the maximum output voltage of the step-up transformer. By adjusting the number and voltages of the Zener diodes, you can adjust the high voltage that goes out to the speaker...(this board uses five 47 volt zeners [1N4756a], and five 12 volt zeners [1N4742a]...add them all up, and you get 295 the two .7 volt drops of the bridge rectifier diodes) = 296.4 volts max output from the step-up transformer feeding the voltage multiplier ladder circuit...(this will likely vary depending on which speaker model that the PCB gets used with).
High voltage from the ladder multiplier circuit can be from 2500-5000 volts, and the capacitors (C13 to C22) will retain that voltage for quite some time, even after power is removed. Be VERY careful working on the PCB.
Other components on the board give you the low voltage DC to run the circuitry, etc.
If there was a problem in the high voltage section of the board, the music detect portion could still work, and light the LED OK, but not give the high voltage it should.


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Note that the posted schematic is for an earlier generation of ML power supply boards.
Attached pic shows what the board looks like that matches the schematic.
Compare with your board pic from post#5

In case anybody needs it, PDF of schematic can be zoomed without losing resolution.


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Bolserst thanks....
...NO one has posted any schematic on the ML bias john has.
this schematic has been posted here for a long time...SL3 came out in 95...the board in the pic above is what I well call the best ML ever made....all the other even thought the price has went way up for the speakers....the bias setup cheaper ....gofig
Joined 2005
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Yes, the posted schematic does not match mine - maybe I will do what tyu advised and call ML and see if they will provide me with a schematic - crossfingers... I am sure they dont want those newer model PS schematics to be posted on sites like here...

meanwhile I have the recommendations from bolserst on checking the pinouts to make good guesses...
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