My MartinLogan Descent amp developed a problem. Everything still "works" but it produces very little volume with minimal excursion of all 3 woofers.
ML says that the amp is dead and they no longer have the part (the entire back plate). Anyone know how to repair this or have suggestions? Here are some pics of the back plate which includes all the electronics and amp, and I've attached the service manual and schematics provided by ML.
This was a really nice sub despite its age, would be a shame to dispose it.
ML says that the amp is dead and they no longer have the part (the entire back plate). Anyone know how to repair this or have suggestions? Here are some pics of the back plate which includes all the electronics and amp, and I've attached the service manual and schematics provided by ML.
This was a really nice sub despite its age, would be a shame to dispose it.
Check the speakers with a meter, and the power supply voltages.
Pre amp is TL082, power amp section can be easily replaced with LM1875 or similar, based on the supply available, or a Class D module.
If it is an SMPS, those are not easy to repair, too many part number changes.
Also, consider making it passive, with an external amplifier driving the woofer, that is depending on your choice.
Pre amp is TL082, power amp section can be easily replaced with LM1875 or similar, based on the supply available, or a Class D module.
If it is an SMPS, those are not easy to repair, too many part number changes.
Also, consider making it passive, with an external amplifier driving the woofer, that is depending on your choice.
The woofers are servo controlled, not sure if it's easily convertible to passive.
How difficult is it to replace the amp? I don't even know which part is the amp. Is there someone here who can repair it for me for a fee?
How difficult is it to replace the amp? I don't even know which part is the amp. Is there someone here who can repair it for me for a fee?
I'm actually in Singapore but I will be in Vegas for 3 weeks from May 7 to 26. Maybe I can send it to you then? The amp is currently set for 220V but ML says it can be configured (I will find the details).
Would I also need to send you one of the woofers so you would be able to test? Each of the woofers have 2 leads, I believe one is for servo feedback.
I am in India...KL / Bangkok would be closer.
A decent technician with soldering experience can do the repair, except the servo.
What is the source?
A decent technician with soldering experience can do the repair, except the servo.
What is the source?
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Ok I will see if I can find someone local to fix it. If not I'll contact you.
What do you mean what is the source?
What do you mean what is the source?
The signal source, that means the home theater or whatever device which provides the audio signal.
The net tells me it is 3 units 10 inch speakers, 250W RMS power...the inside photos do not look like that, maybe I looked at a different model.
Unless the speakers are blown, not too difficult.
Shipping will be expensive, and chances of damage are there, stick to the nearest competent service center, ask around, find out how good they are.
Maybe you can check the speakers using a meter?
The net tells me it is 3 units 10 inch speakers, 250W RMS power...the inside photos do not look like that, maybe I looked at a different model.
Unless the speakers are blown, not too difficult.
Shipping will be expensive, and chances of damage are there, stick to the nearest competent service center, ask around, find out how good they are.
Maybe you can check the speakers using a meter?
Ah, the source is my PC home theatre using LFE input. I replaced the subwoofer and the source is fine.
Yes it is 3 10-inch woofers, 400 watts total. You can see specs here https://www.martinlogan.com/en/product/descent
Thanks for your advice, I will try to find a local technician. I had sent a video to MartinLogan and they informed me the amp has gone bad.
Yes it is 3 10-inch woofers, 400 watts total. You can see specs here https://www.martinlogan.com/en/product/descent
Thanks for your advice, I will try to find a local technician. I had sent a video to MartinLogan and they informed me the amp has gone bad.
All speaker drivers have two wires, plus and minus.
Check with a meter set at x1 ohms, a cheap one is only about $5.
If they are okay, the unit can be rebuilt, shame to scrap such a nice unit otherwise.
Even the speakers can be rebuilt, with new coils, so don't worry about it.
Check with a meter set at x1 ohms, a cheap one is only about $5.
If they are okay, the unit can be rebuilt, shame to scrap such a nice unit otherwise.
Even the speakers can be rebuilt, with new coils, so don't worry about it.
If you look closely at the picture of the woofer, each woofer has 2 pairs of wires. The pair on the bottom below (thicker pair of black and red wires) are for the power and the pair on the top (thinner pair of black and grey) I believe are for the servo feedback. The subwoofer uses servo feedback to compensate for distortion etc.
@bchow,
According the the schematic you posted, you should find an ICE 1000A amplifier module underneath the main circuit board attached directly to the back plate with bolts circled in red.
I'm guessing this is what Martin Logan thinks is wrong and is no longer being manufacturing.
They show as "no longer available" pretty much everywhere on line. For example:
https://icepoweraudio.com/buy/a-series/1000a/
https://www.parts-express.com/ICEpo...Amplifier-Module-1-x-1000W-326-202?quantity=1
But I did find one place that still showed them available. You would have to contact them to see if they actually have any.
https://shop.ampman.co.uk/icepower-1000a-amplifier-module-2061-p.asp
If you can't get a replacement 1000A module, you have might consider replacing it with a 500A module which is still readily available and has the exact same input/output connections. It is slightly smaller so you would have to drill one new attachment hole in the back plate for mounting.
https://icepoweraudio.com/buy/a-series/500a/
https://www.parts-express.com/ICEpo...-Amplifier-Module-1-x-500W-326-200?quantity=1
According to the schematic, the filter capacitors of the main power supply for the amp module are rated at 63V, so this should put it well within the allowable voltage range of the 500A module.
You would want to measure to confirm, but it is in line with the 400W RMS rating for the output power in the manual.
Another alternative is to ditch the Martin Logan backplate completely and replace it with something like a YUNG 500W plate amp.
https://www.parts-express.com/Yung-...oofer-Amp-Module-w-6dB25Hz-301-514?quantity=1
You would need to measure the impedance of the woofers to make sure driving 3 in parallel will be ok.
The downside to this approach is you lose the distortion reduction advantage of the servo feedback system built in to the Martin Logan electronics.
Feel free to contact me off list if you need additional guidance measuring the power supply voltage or woofer impedance.
According the the schematic you posted, you should find an ICE 1000A amplifier module underneath the main circuit board attached directly to the back plate with bolts circled in red.
I'm guessing this is what Martin Logan thinks is wrong and is no longer being manufacturing.
They show as "no longer available" pretty much everywhere on line. For example:
https://icepoweraudio.com/buy/a-series/1000a/
https://www.parts-express.com/ICEpo...Amplifier-Module-1-x-1000W-326-202?quantity=1
But I did find one place that still showed them available. You would have to contact them to see if they actually have any.
https://shop.ampman.co.uk/icepower-1000a-amplifier-module-2061-p.asp
If you can't get a replacement 1000A module, you have might consider replacing it with a 500A module which is still readily available and has the exact same input/output connections. It is slightly smaller so you would have to drill one new attachment hole in the back plate for mounting.
https://icepoweraudio.com/buy/a-series/500a/
https://www.parts-express.com/ICEpo...-Amplifier-Module-1-x-500W-326-200?quantity=1
According to the schematic, the filter capacitors of the main power supply for the amp module are rated at 63V, so this should put it well within the allowable voltage range of the 500A module.
You would want to measure to confirm, but it is in line with the 400W RMS rating for the output power in the manual.
Another alternative is to ditch the Martin Logan backplate completely and replace it with something like a YUNG 500W plate amp.
https://www.parts-express.com/Yung-...oofer-Amp-Module-w-6dB25Hz-301-514?quantity=1
You would need to measure the impedance of the woofers to make sure driving 3 in parallel will be ok.
The downside to this approach is you lose the distortion reduction advantage of the servo feedback system built in to the Martin Logan electronics.
Feel free to contact me off list if you need additional guidance measuring the power supply voltage or woofer impedance.
Hi Steve,
Thanks again for your reply.
So it seems like my best and most straightforward bet right now would be to try to buy the 1000A module from the ampman.co.uk site (and hope it's available)? Replacing it should be very straightforward right?
Thanks again for your reply.
So it seems like my best and most straightforward bet right now would be to try to buy the 1000A module from the ampman.co.uk site (and hope it's available)? Replacing it should be very straightforward right?
Yes, if you can get a replacement 1000A module, the swap out should be straightforward screws and connectors.
I see that the 1000A is rated at 1000W at 4ohm (https://icepoweraudio.com/buy/a-series/1000a/).
Yet ML lists the Descent at 400W RMS, 800W peak (https://www.martinlogan.com/en/product/descent).
Why is that? Kind of surprised if ML underrates the power. It certainly feels more powerful than a 400W subwoofer.
Yet ML lists the Descent at 400W RMS, 800W peak (https://www.martinlogan.com/en/product/descent).
Why is that? Kind of surprised if ML underrates the power. It certainly feels more powerful than a 400W subwoofer.
Congrats on your successful outcome. 
I am not sure why ML decided to use the 1000A instead of the 500A for this subwoofer. It is possible that the limited bandwidth of the 1000A made the servo control loop easier to stabilize than it would have been for the full-range 500A. Or, it may just have come down to $$$, in that they may have used the 1000A for several different models with varying power requirements and it was cheaper to just stock one amp module.
I am not sure why ML decided to use the 1000A instead of the 500A for this subwoofer. It is possible that the limited bandwidth of the 1000A made the servo control loop easier to stabilize than it would have been for the full-range 500A. Or, it may just have come down to $$$, in that they may have used the 1000A for several different models with varying power requirements and it was cheaper to just stock one amp module.
Has anyone replaced the Servo? What part or values does that have if it is not the amp?
The short video in my Dropbox folder, 2023-07-27 14.31.57 descent, shows a Descent problem with one of my five Descents. I am hoping to obtain a replacement part or be directed what values the part has and what it is.
The Descent mounted directly under the sub in the 12 second video does not have that rattle, but sounds typical of a Descent handling a low frequency. They were both fed the same xlr, with the same settings on the front panel, and played the same low frequency at the same output levels of the preamp, but only one Descent at a time.
Does anyone have the spec on the Servo so that I may have my electronics helper find one of identical value? There are times when we take apart any of my legacy products the parts may not be adequate labeled or researched to determine on our own. There is no liability on your part for anything I decide to do. I would sign any disclaimer you wish. I am going to do this work with or without your help.
https://www.dropbox.com/scl/fo/gbljolu2l5m74iont69z8/h?rlkey=uuq8ysunbi4i2csxa7ee1c16f&dl=0 is the link to the 12 second video. The video is in the Descent folder.
The short video in my Dropbox folder, 2023-07-27 14.31.57 descent, shows a Descent problem with one of my five Descents. I am hoping to obtain a replacement part or be directed what values the part has and what it is.
The Descent mounted directly under the sub in the 12 second video does not have that rattle, but sounds typical of a Descent handling a low frequency. They were both fed the same xlr, with the same settings on the front panel, and played the same low frequency at the same output levels of the preamp, but only one Descent at a time.
Does anyone have the spec on the Servo so that I may have my electronics helper find one of identical value? There are times when we take apart any of my legacy products the parts may not be adequate labeled or researched to determine on our own. There is no liability on your part for anything I decide to do. I would sign any disclaimer you wish. I am going to do this work with or without your help.
https://www.dropbox.com/scl/fo/gbljolu2l5m74iont69z8/h?rlkey=uuq8ysunbi4i2csxa7ee1c16f&dl=0 is the link to the 12 second video. The video is in the Descent folder.