ReQuest Melted Crossover Inductor

[Asepguy]

Hi all, new member here. I purchased a set of used ReQuests from a vintage audio shop. They were purchased new by the previous owner who still had the original shipping boxes and they are serial numbers 6 and 7 which I thought was cool. I went to set them up and they both play music, but one channel seemed to be more pronounced than the other. At first I thought it was just speaker placement needing tweaking but when I used a setup disc that played on each channel individually I could tell a distinct difference between the two in clarity. Ron at ML has been helping me trouble shoot and I just sent him my most recent findings - I suspect he won't be working over the weekend so I figured I might post here just to see if anyone had seen this before. I did a search but didn't find any similar posts/issues.
It appears the crossover shorted and got VERY hot. lots of burnt insulation, even melted foam inside, charred wood, and discolored paint on the exterior after I looked closer.

 

[Robert D]

Many of the guys here will probably advise you to just disconnect the crossovers and use an external one. Hopefully thats all that is wrong. I have a set of Prodigy speakers but am still using my internal crossovers, but guys on here say that the externals sound much better, so youll be fixing your problem as well as upgrading. It doesnt have to cost much either. Im pretty sure many guys use a Crown amp with built in crossover on it. Youd just need to get one I think. I believe that they are 2 channel. The crossover has 2 amps and will also power your woofers. Hopefully one of the guys will come on here. If you do a search, youll find some good threads on it here. One member that does it is named Brandon I believe.

If its just the crossover then its an easy fix by doing that. If the problem goes deeper, then you have more problems.

 

[Asepguy]

I’ve read the posts on the active bass conversions. I have 2 concerns with that: 1) for users who already have a capable amp with plenty of headroom - it’s a downgrade. 2) In a situation like mine where the crossover is damaged - it won’t work. The crossover is still needed to filter low frequencies out of the electrostatic panel.

I’m more interested in hearing if this sort of damage has been seen by anyone else? Was a new crossover panel available from ML?

 

[ih82lose]

Based on the pictures, I would suspect one or both of the resistors next to the inductor are the issue. I have seen and replaced a few of these resistors on quest/request speakers I’ve picked up second hand. If the matching crossover from the other speaker is in good condition, you could read or measure the resistance/specs and order replacements.

As far as why these resistors fail, some will say aging panels are the culprit- users adjusting EQ or pushing more power to a panel that has become less sensitive over time, but I can’t say I have data to verify that.

 

[Robert D]

I’ve read the posts on the active bass conversions. I have 2 concerns with that: 1) for users who already have a capable amp with plenty of headroom - it’s a downgrade. 2) In a situation like mine where the crossover is damaged - it won’t work. The crossover is still needed to filter low frequencies out of the electrostatic panel.

I’m more interested in hearing if this sort of damage has been seen by anyone else? Was a new crossover panel available from ML?

Good point about the panel. I was thinking the external eq handled the panel frequencies as well but probably not.

 

[JonFo]

I’ve read the posts on the active bass conversions. I have 2 concerns with that: 1) for users who already have a capable amp with plenty of headroom - it’s a downgrade. 2) In a situation like mine where the crossover is damaged - it won’t work. The crossover is still needed to filter low frequencies out of the electrostatic panel.

The crossover in these older ML's is basically two completely independent things; one is a high-pass XO for the panel, and the other (the one with the big coils) is the low-pass XO for the woofer. The speaker will operate just fine if you completely disconnect the low-pass passive XO and get an amp with a built-in XO.
And no, not a downgrade at all, quite the opposite as shown with measurements and a bunch of us who've done it can testify, it sounds much, much better.

 

[Robert D]

The crossover in these older ML's is basically two completely independent things; one is a high-pass XO for the panel, and the other (the one with the big coils) is the low-pass XO for the woofer. The speaker will operate just fine if you completely disconnect the low-pass passive XO and get an amp with a built-in XO.
And no, not a downgrade at all, quite the opposite as shown with measurements and a bunch of us who've done it can testify, it sounds much, much better.

And from those pictures, it looks like it's the bigger coil that is fried.

 

[StimpyWan]

That's an ugly failure. Hopefully, ML Support will help make it right? Just in case, if you need to order new inductors, from the schematic, Erse Audio is back in business, as U.S. Coils. A very decent range of available gauges and values.

https://uscoils.us/

 

[DanR]

Thank you for posting that, JonFo. I’m not sure where the basis for that downgrade comment came from but as you point out it is completely wrong. Your explanation of the low quality passive crossover in these older hybrid Logans is spot on. Yes I modified my Odysseys too and do the active crossover and the IMPROVEMENT in the sound of the speakers was not small believe me. And in this case here it maybe the only thing outside of replacing that complete crossover that will make this speaker functional again because that crossover look cooked majorly. That speaker was not far at all from going up in flames good thing it lost electrical energy when it did. The fact that any sound is produced from that speaker is pretty amazing, I'm guessing the low pass crossover is completely disabled now and only the panel is producing sound so the owner is already halfway there to going with the active crossover and it also may be the lowest cost option as well.

 

[Brandon Hartwick]

I'll guarantee the traces on the crossover boards are damaged as well, I had this exact issue on a speaker I worked on a while back and the boards were pretty much toast.

Time to toss the passive crossover and go active, regardless of how capable your amp is it would still be an upgrade. The passive bass crossovers suck the life out of the speaker.

All new Martin Logan speakers use a class D amp for the bass with active crossovers so just keep that in mind.

 

[Asepguy]

Thank you for posting that, JonFo. I’m not sure where the basis for that downgrade comment came from but as you point out it is completely wrong. Your explanation of the low quality passive crossover in these older hybrid Logans is spot on. Yes I modified my Odysseys too and do the active crossover and the IMPROVEMENT in the sound of the speakers was not small believe me. And in this case here it maybe the only thing outside of replacing that complete crossover that will make this speaker functional again because that crossover look cooked majorly. That speaker was not far at all from going up in flames good thing it lost electrical energy when it did. The fact that any sound is produced from that speaker is pretty amazing, I'm guessing the low pass crossover is completely disabled now and only the panel is producing sound so the owner is already halfway there to going with the active crossover and it also may be the lowest cost option as well.

The basis for the downgrade comment is that these mods are all using amps/crossovers intended for PA use - not critical or even in home listening. If you are using entry level equipment to begin with, then sure it might be an upgrade. But if you are using higher end/capable equipment begin with, then a PA amp is would seem to be a major downgrade to me.

 

[Brandon Hartwick]

The basis for the downgrade comment is that these mods are all using amps/crossovers intended for PA use - not critical or even in home listening. If you are using entry level equipment to begin with, then sure it might be an upgrade. But if you are using higher end/capable equipment begin with, then a PA amp is would seem to be a major downgrade to me.

False

These are Hypex based class D amps, many people use them for critical listening with great results. The amp only needs to play 350hz and down anyway so they perform fantastic for the application.

If you're absolutely dying to spend way more money than you need to you can always get an external processor and another matching amplifier, but it's not going to make a difference.

 

[Brandon Hartwick]

Using this logic all new Martin Logan speakers should sound worse than the old passive models. This isn't the case though because the panel and woofer both present totally different loads to the amplifier, when you seperate them your power amp will only see the capacitive load of the panel and not the combined load with the woofer. Your amplifier will thank you.

 

[Asepguy]

I'll guarantee the traces on the crossover boards are damaged as well, I had this exact issue on a speaker I worked on a while back and the boards were pretty much toast.

Time to toss the passive crossover and go active, regardless of how capable your amp is it would still be an upgrade. The passive bass crossovers suck the life out of the speaker.

All new Martin Logan speakers use a class D amp for the bass with active crossovers so just keep that in

False

These are Hypex based class D amps, many people use them for critical listening with great results. The amp only needs to play 350hz and down anyway so they perform fantastic for the application.

If you're absolutely dying to spend way more money than you need to you can always get an external processor and another matching amplifier, but it's not going to make a difference.

What specifically are you claiming is false? Please give me a link to a thread using the amps you are referring to and/or a link to the product information. The ONLY examples I have seen of this mod give the make and model of the amps being used and they are all Behringer or Crown "professional" (PA/live music) amps.
To your point on "dying to spend more money..." you are missing my point entirely. I'm not advocating a mod at all, but instead advocating for those who have already invested in quality equipment to begin with - which negates the purpose of modifying at all. As I stated...if someone does not already have high end equipment then this mod may very well produce the results that are being discussed here. But the mod is a downgrade if you already have in your system, high quality and capable gear. I am keeping an open mind and discussing both sides here, but the only comments I seem to be getting in return are ones that leave no room for using proper critical listening gear. Don't get me wrong, I'm not saying PA amps are total garbage and never ever have a place in home stereo systems - but I am absolutely saying they are no replacement for proper gear - ESPECIALLY when it is already in place.

I keep getting comments saying that I should immediately jump to this solution because there is no hope for my crossover...What on earth are those comments based on? I have already repaired the crossover for pennies on the dollar compared to modifying this way. I also see lots of disdain for the original Martin Logan crossovers. Why?

 

[Asepguy]

Using this logic all new Martin Logan speakers should sound worse than the old passive models. This isn't the case though because the panel and woofer both present totally different loads to the amplifier, when you seperate them your power amp will only see the capacitive load of the panel and not the combined load with the woofer. Your amplifier will thank you.

You are only proving my point here...As I have stated several times - using entry level equipment would mean the amp may not be powerful enough to fully drive the full range of the speaker and in those situations a mod like the one discussed here may give improvements. My entire statement is focused on listeners who have high end and capable amplifiers that do not struggle to push the full range of the speaker. Individuals with this type of equipment would be downgrading their equipment by inserting a PA amplifier to drive the low end and high end amp power would not be needed/used to only drive the mids and highs in the ESL portion.

 

[Brandon Hartwick]

It's not a matter of having an amplifier capable of driving the entire speaker, it's the effects the passive crossover has on the interaction between the panel and woofer. Unloading the panel amp from the woofer is just a bonus.

Your mind is made up and I'm not going to try and change it. We must all just be wrong.

 

[Russr]

You are only proving my point here...As I have stated several times - using entry level equipment would mean the amp may not be powerful enough to fully drive the full range of the speaker and in those situations a mod like the one discussed here may give improvements. My entire statement is focused on listeners who have high end and capable amplifiers that do not struggle to push the full range of the speaker. Individuals with this type of equipment would be downgrading their equipment by inserting a PA amplifier to drive the low end and high end amp power would not be needed/used to only drive the mids and highs in the ESL portion.

What specifically are you claiming is false? Please give me a link to a thread using the amps you are referring to and/or a link to the product information. The ONLY examples I have seen of this mod give the make and model of the amps being used and they are all Behringer or Crown "professional" (PA/live music) amps.
To your point on "dying to spend more money..." you are missing my point entirely. I'm not advocating a mod at all, but instead advocating for those who have already invested in quality equipment to begin with - which negates the purpose of modifying at all. As I stated...if someone does not already have high end equipment then this mod may very well produce the results that are being discussed here. But the mod is a downgrade if you already have in your system, high quality and capable gear. I am keeping an open mind and discussing both sides here, but the only comments I seem to be getting in return are ones that leave no room for using proper critical listening gear. Don't get me wrong, I'm not saying PA amps are total garbage and never ever have a place in home stereo systems - but I am absolutely saying they are no replacement for proper gear - ESPECIALLY when it is already in place.

I keep getting comments saying that I should immediately jump to this solution because there is no hope for my crossover...What on earth are those comments based on? I have already repaired the crossover for pennies on the dollar compared to modifying this way. I also see lots of disdain for the original Martin Logan crossovers. Why?

Wow... where to start...
1) "Entry level" and PA/Live systems are NOT synonymous. Please remember that almost ALL live concerts/performances, from Pink Floyd to St. Martin-in-the-fields are dependent upon "PA gear". And recordings made of those, are not going to improve on the source, no matter HOW much the "critical home listener" spends. ALL OF US are TRYING to approximate that live music experience, driven by those (shudder) PA Systems.
2) "Proper gear"... once again, not sure you realize it, but mediocre module-based el-cheapo amplifiers these days have statistics (signal-to-noise, etc.) equal to or better than the very highest end gear from 30 - 50 years back. And no, our ears have NOT evolved.. if anything, with everyone growing up listening to compressed MP3s and similar, I mourn the future of Hi-Fi as we have known it. If you want to be (or at least, sound) elitist, haul out the signal generator and oscilloscope and lead with verifiable, repeatable facts (sorry... you hit a nerve with "proper gear"!).

3) As Brandon pointed out, the exact path he has taken (and very thoroughly documented) in his projects is the biggest differentiator between the older ML products and their new top-of-the-line ones. Yes, the Masterpiece series have Class D amps driving the woofers. and they are "shaping" the curves using ARC.... all in the digital domain.

4) ANY (and I do mean ANY) additional circuitry results in lost efficiency and the introduction of sonic artifacts. YES, crossover circuits have been a major focus of hi-fi aficionados for about a century, but things change. Coils, capacitors, load resistors... they ALL add "issues" to the signal... a crossover circuit, by definition, is a compromise. Some of the very highest end products are swinging towards the digital domain... DACs, Filters, dedicated digital feeds to speaker-embedded DACs with separate active amps per driver. THIS is where things are going. I'm not sure if they're still around, but Gayle Sanders, founder of ML, was working on a product range at Eikon Audio doing JUST THIS... Digital control of the entire domain ( Gayle Sanders Eikon & DSP Optimization).

5) From a personal perspective, I plan to try catch up and jump on this band-wagon. I have a nice-sounding pair of SL3s (with new panels), driven by an excellent Bryston 4B-ST. I plan on tossing out the crossovers, and using a Crown amp with digital low-pass filter to drive the woofers... can't wait!

Sorry if this came across as too "rantish", but if we don't have science, we have Luddites running amock ... and heck, even Douglas Adams designed a video game before his untimely passing...

Speaking of which, here's a quote from The Luddite that helps explain a lot of this:

“I've come up with a set of rules that describe our reactions to technologies:​

1. Anything that is in the world when you’re born is normal and ordinary and is just a natural part of the way the world works.​

2. Anything that's invented between when you’re fifteen and thirty-five is new and exciting and revolutionary and you can probably get a career in it.​

3. Anything invented after you're thirty-five is against the natural order of things.”​

 

[DanR]

Wow is right here! I’m not even getting involved in this beyond saying two things and they’ll be very basic.
1) Please check your FACTS before you make statements. The OP jumps right on the class D, Hypex amps are automatic downgrades, just not true.
2) I use a Behringer KM750 on my 10” woofers, I’ve attached the spec sheet and if you will READ it you will see it is NOT a class D amp it’s a class A/B amp with a pretty stout power supply to power just 2 10” woofers from aprox 45hZ to aprox 265hZ
The bottom line is this. I know how my speakers sounded with the factory crossover and how they sound now with the factory low end (bass) section removed and run actively. And the difference is NOT SMALL running it actively sounds so much better. A d my Krell Class A amp that runs the panels sounds just great as part of a much improved speaker.

 

[Asepguy]

Wow is right here! I’m not even getting involved in this beyond saying two things and they’ll be very basic.
1) Please check your FACTS before you make statements. The OP jumps right on the class D, Hypex amps are automatic downgrades, just not true.

@ DanR, no, I never said any of what you are claiming. This group is unbelievable! You guys are a tough crowd. It's like you think I'm coming after you or something. If you read my comments, I NEVER jumped on any specific type of amp. I did ask questions of the one member who mentioned them to please share additional details which was not done. I have no issue with a specific amp technology. In fact, my primary amp is in fact a class D, but it is designed for Hi Fi listening, not throwing sound large distances at concert venues. So before you go claiming someone is spreading untrue statements and needs to check their facts - please perform your own due diligence. My statements are quite the opposite of what you are trying to claim here.

 

[DanR]

I stand by every word I said. And here is why see attachment. Both of these statements that you made are completely wrong and people are just trying to show you that they are. We’re not a tough crowd at all but Myself will not listen to blanket incorrect statements period.