[Scooter-mcgavin]

Looking for a couple 10" woofers for my ff3's. Any out there?

[stehno]

Hi.  I own the fabulously musical VMPS RM-40's. I'm the second owner having owned them for almost 5 years now.  Anyway, tonight while playing music at maybe 104 db which I often do, there was some instaneous distortion (nothing sounding too bad or loud) and suddenly my 4 mid-range ribbon drivers in the right channel ceased functioning.  Woofers and tweeter seem fine which implies to me something occurred at the crossover and not the drivers but I'm guessing. 

I'm pretty much out to lunch here.  Might the crossover have one or more fuses?  If not, do I need to find NOS crossovers?  What if I can't locate an RM-40 crossover?  Or might it be all 4 mid-range drivers blew simultaneously?

Any advice is appreciated.  Thanks.

-John

[John Casler]

If you're lucky all you did was fry the L-Pad.

To check take a small screwdriver and gently turn it from one side to another. 

If it sticks, feels rough, or the sound to the Neos  cuts in and out, then you need to replace the L-Pads.

While it could be other things like a burned cap or coil, those are a lot more difficult to track down (unless they visually look burned/which they sometimes do)

[stehno]

Thanks, John.  I have 4 mid-range drivers so it sounds like I'll need to check each of the 4.

1.  When you say take a screwdrive and "turn it", I'm not sure what it is having never taken the VMPS apart.  Tomorrow night I plan to visually inspect the 4 mid-range drivers there but thus far I've no idea what to expect.  I'm fairly mechanically inclined but electronics and speaker challenged.  And soldering iron challenged.

2.  If it turns out to be L-pads, are replacement L-pads available out there and might this be something I can replace?

3.  Is it close to impossible to locate Neopanels these days? 

4.  Do you happen to know if the mid-range drivers are daisy-chained such that if one blows all cease to function?

5.  If a crossover, are there any similar crossovers available if this one can't be rebuilt?

The RM-40's have been fabulous and trouble-free until tonight and I'd hate to consider alternatives.

Very much appreciated, thanks.

[Stimpy]

Ouch!  I hope you get this sorted out.

L-pads are volume controls for the tweeter and mids.  They'd be on the rear of the speakers, near the inputs.  Look for small holes with a metal shaft.  The shaft is part of the L-pad, and allows you to adjust the volume of the drivers.  If the L-pad is OK, you should be able to turn the shaft, and it should turn smoothly.  You should also hear the volume of the driver shift too.  If not, the L-pad might have failed.  It could feel sticky and rough when turned, with no change to the driver volume.

Parts Express sells L-pads.  But, you'll need to inspect what's in your 40s, to see what type you need.  L-pads come in different impedance's, as well as different wattage ratings.  Mono and stereo too.  Plus, the L-pad shaft has different lengths, depending on cabinet thickness.

https://www.parts-express.com/Search.aspx?keyword=l-pad&sitesearch=true

So, inspect the L-pads.  You'll probably have to pull a woofer to access it and the crossover.  Also, test the drivers with a multimeter.  You'll want to read their resistance, to see if they match between the 2 speakers.  And while the woofer is out, inspect the crossovers.  Look for burned components.  Caps can fail, and inductors can melt, from high power.  Let us know what you find, and we can proceed from there.

Good luck.

[Stimpy]

Oh, one more thing.  You aren't going to find off-the-shelf crossovers for VMPS speakers.  Brian basically hand built the crossovers into each speaker.  No premade circuit boards.  Only point to point wiring.  So, if damaged, you'll have to repair it in the speaker.  VMPS crossovers were typically first order, series designs, which makes them fairly simple in layout.  Not many parts.  But, you'll need a good multimeter and a good capacitance meter to test them. 

A component lead needs to be unsoldered, in order to test a part.  Otherwise, you'll be testing the whole crossover and not an individual component.

Also, Brian used very good capacitors.  You'll need to use good caps too.  The same brands, if they can be identified.  And if me, if I change a part in one speaker, I'd change that same part, with the same brand and value, in the other speaker.  It's best to keep them matched.  Use some one like Sonic Craft or Parts Connexion, for replacement capacitors.  Both vendors offer tight tolerance parts matching, and will provide matched pairs too.

[John Casler]

Thanks, John.  I have 4 mid-range drivers so it sounds like I'll need to check each of the 4.

1.  When you say take a screwdrive and "turn it", I'm not sure what it is having never taken the VMPS apart.  Tomorrow night I plan to visually inspect the 4 mid-range drivers there but thus far I've no idea what to expect.  I'm fairly mechanically inclined but electronics and speaker challenged.  And soldering iron challenged.

2.  If it turns out to be L-pads, are replacement L-pads available out there and might this be something I can replace?

3.  Is it close to impossible to locate Neopanels these days? 

4.  Do you happen to know if the mid-range drivers are daisy-chained such that if one blows all cease to function?

5.  If a crossover, are there any similar crossovers available if this one can't be rebuilt?

The RM-40's have been fabulous and trouble-free until tonight and I'd hate to consider alternatives.

Very much appreciated, thanks.

1) You need not take anything "apart", and until you check the condition of the L-Pads, I wouldn't.  As Stimpy described, the L-Pads are the little shafts on the back of the speaker, where you adjust tweeter and Neo levels.  BE VERY CAREFUL AND GENTLE WHEN TURNING THEM.

Your description and cause sound like you overheated them and they burned.  If so, you are lucky and it is cheap and not too difficult to replace them.  If the L=Pad burns it would take out all the panels in that speaker.

[stehno]

Thank you both very much.  I was able to turn the mid-range L-pad with some ease.  Gently turning the 3 other L-pads all seemed to have a very evident increase in friction.  When turning all 4 L-pads, I could feel the little indentations / notches during the turn.  But the L-pad in question did have a fairly significant less amount of friction than the others.

My mid-range L-pads are set at 12 o'clock high (neutral) while the tweeter L-pad is set at about 9:30 o'clock.  Just curious if my mid-range L-pads are always set to 12 o'clock high, would by-passing that L-pad change the impedence any and hence potentially generate other problems?

I looked at some L-pads per Stimpy's link but also elsewhere.  There doesn't seem to be a lot of L-pad resources.   I realize there's more requirements that need to be met but it seems nearly all L-pads are 8ohm.  As I recall the RM-40 speakers are 4 ohm.  Does that imply all speaker drivers are also 4 ohm including the x-over network?  Would an 8 ohm L-pad lead to failure?

FWIW, my Class D amps are 575 wpc@8 ohm and I think 1100 wpc@4 ohm loads.  But I'm also using a passive volume attentuator (no active gain state).  I mention this because it seems the highest rated L-pads I saw on Parts Express were 100 watts.  I'm curious what ratings I need to look for?

Anyway, if the L-pad in question is noticeably easier to turn might that be an indiction of potential failure?

Thanks again for your help,

[Stimpy]

Hi Stehno,

Did turning the midrange L-pad restore sound?  You didn't say.

Also, not to sound blunt, but we can't guess and tell you what's in your speakers.  Speakers have impedance ratings.  But, that's a static figure, as resistance varies with frequency.  So, having a 4 ohm speaker, doesn't mean you'll have a 4 ohm L-pad.  In this instance, you'll have to pull a woofer, and investigate.  You need to match what's already there.  No choice.

Since L-pads come in different impedances, you need to know if you have a four, eight, or sixteen ohm L-pads in your 40s.  Using the incorrect L-pad can shift crossover points.  Bypassing the L-pad, can shift crossover points, since that would change resistance.

As to power handling, everything wired to you amp absorbs and dissipates wattage.  The speaker wire, all the individual speaker drivers, and all the crossover components, including the L-pads, absorb power.  So, no one component sees your 1100 watts.  Which is a good thing, because you could have burned out the whole speaker, as a result of the party mode playback session.

One other thing to think about when replacing the failed components, you might be able to bump up to a part with greater power handling, but should you?  If the midrange L-pad is what failed, swapping in a higher wattage pot may prevent failure in the future?  But, in your case, the L-pad acted as a fuse, and hopefully saved your speakers.  A higher wattage L-pad may save the L-pad, but allow the speakers to fry!  What would you rather do, spend a few bucks on a new L-pad, or try and source expensive, rare drivers?  Your choice?  Oh, I'd also fuse the speakers, or buy Cerwin Vegas!  Again, your choice.   

Good luck.

[ZAKski288]

I pretty sure this is the L-pad (#260-265 , 100watt, 1” shaft,  8 ohm ) for RM 40, both L-pads in my 40’s are the same (100watts). But you still want to check what Brian used in your speakers. Good luck Zak

https://www.parts-express.com/speaker-l-pad-attenuator-100w-mono-1-shaft-8-ohm--260-265

The best way to access the L-pads and crossovers is to lay the speaker on it side and remove the base and the passive

[stehno]

Hi Stehno,

Did turning the midrange L-pad restore sound?  You didn't say.

Also, not to sound blunt, but we can't guess and tell you what's in your speakers.  Speakers have impedance ratings.  But, that's a static figure, as resistance varies with frequency.  So, having a 4 ohm speaker, doesn't mean you'll have a 4 ohm L-pad.  In this instance, you'll have to pull a woofer, and investigate.  You need to match what's already there.  No choice.

Since L-pads come in different impedances, you need to know if you have a four, eight, or sixteen ohm L-pads in your 40s.  Using the incorrect L-pad can shift crossover points.  Bypassing the L-pad, can shift crossover points, since that would change resistance.

As to power handling, everything wired to you amp absorbs and dissipates wattage.  The speaker wire, all the individual speaker drivers, and all the crossover components, including the L-pads, absorb power.  So, no one component sees your 1100 watts.  Which is a good thing, because you could have burned out the whole speaker, as a result of the party mode playback session.

One other thing to think about when replacing the failed components, you might be able to bump up to a part with greater power handling, but should you?  If the midrange L-pad is what failed, swapping in a higher wattage pot may prevent failure in the future?  But, in your case, the L-pad acted as a fuse, and hopefully saved your speakers.  A higher wattage L-pad may save the L-pad, but allow the speakers to fry!  What would you rather do, spend a few bucks on a new L-pad, or try and source expensive, rare drivers?  Your choice?  Oh, I'd also fuse the speakers, or buy Cerwin Vegas!  Again, your choice.   

Good luck.

Hey, Skimpy.  No. Turning the mid-range L-pad did not change anything.  But I will try once more whil by gently turning the L-pad out from the 12 o'clock position to maybe 10:00 o'clock or even 2 o'clock to see if that changes anything.

I did presume that you and others here had VMPS speaker specific knowledge, sorry my bad. 

Party mode session?  Um, yeah, I suppose I have my guilty pleasure moments playing at 103-105db.  It's as important to me as a nice classical or instrumental piece at 87-95db.

Good points on not changing things out and hence potentially changing the weakest component in the link blowing.

Good suggestion on installing a fuse.  Bad suggestion on installing a pair of Cerwin Vegas.  If I'm able to get things working again, where would be the best place to install, before or after the x-over?  And do you know the criteria for installing the appropriate fuse?

BTW, would you still guess that it could be the midrange L-pad?

Much appreciated,

[stehno]

I pretty sure this is the L-pad (#260-265 , 100watt, 1” shaft,  8 ohm ) for RM 40, both L-pads in my 40’s are the same (100watts). But you still want to check what Brian used in your speakers. Good luck Zak

https://www.parts-express.com/speaker-l-pad-attenuator-100w-mono-1-shaft-8-ohm--260-265

The best way to access the L-pads and crossovers is to lay the speaker on it side and remove the base and the passive radiator.


Pictures of RM 40 L-pads and crossover
Left L pad for tweeter ( green and blue wires )
Right L pad  for midrange panels (red and red/green stripe wires)

Thanks for the pic and info, Zak.  So the base plate (looks like MDF) comes off?  I just assumed it was glued.  In fact, it all looks like MDF around the bottom so I assumed it was all glued together permanently.  Especially since the fully loaded cabinet weighs in at 240 lbs.  So it's screwed / bolted together?

Thanks,

[Stimpy]

Hey, Skimpy.  No. Turning the mid-range L-pad did not change anything.  But I will try once more whil by gently turning the L-pad out from the 12 o'clock position to maybe 10:00 o'clock or even 2 o'clock to see if that changes anything.

I was hoping for sound.

I did presume that you and others here had VMPS speaker specific knowledge, sorry my bad. 

Unfortunately, Brian didn't publish VMPS documentation.  So, it's difficult to know what's inside a particular model without actually owning it.  One thing I want to work on.  Start a thread, trying to catalog documentation and schematics.

Party mode session?  Um, yeah, I suppose I have my guilty pleasure moments playing at 103-105db.  It's as important to me as a nice classical or instrumental piece at 87-95db.

I was being intentionally rude.  Sorry about that, but I didn't want you to (further) damage your speakers.

Good points on not changing things out and hence potentially changing the weakest component in the link blowing.

As above.  Caution with the volume control.

Good suggestion on installing a fuse.  Bad suggestion on installing a pair of Cerwin Vegas.  If I'm able to get things working again, where would be the best place to install, before or after the x-over?  And do you know the criteria for installing the appropriate fuse?

Fuse wiring diagram, from my Acoustic Research manual.  No reason this won't work for your 40s.

http://www.classicspeakerpages.net/library/acoustic_research/ar-9_series_1978-1981/ar-9_series_manuals/ar-9_manual/ar-9_manual_pg25.html

BTW, would you still guess that it could be the midrange L-pad?

That's just a guess.  But, I'd think it's most likely, due to all 4 panels failing at once.  I'd look at the L-pad first, and the midrange crossover capacitor second.

Much appreciated,

You are most welcome!

[ZAKski288]

Hello Stehno,  This is want I would do. I taken a large bedroom pillow placed on the floor, two feet from the bottom of the speaker , I then grab the top of speaker  and tilt it down. Now the speaker is on a tilt we’re the base is off the ground. There are a bunch of holes in the base, but the 4 large holes hold the base , 4 long wood screws, unscrew them.  That removes the base. Now unscrew the 8 screws on the passive radiator. You may have to pry the passive from the cabinet gently. Good luck ZaK

[stehno]

IT WORKS!!!!!   So it seems the L-pad is fried at the usual 12 o'clock high mark but not eslewhere.  Had to move it back to about 10:30 before the midrange works again.

Thank you all.  Your advice and time is much appreciated.  Tweeters have already been dialed down to about 9:30 for some time and by adding a another few decibels at the volume attentuator, I'm back in business. 

Obviously the L-pads should be replaced.  Then again, I can easliy live with them in their current 10:30 positions because if I do replace them, if they are not identical to the originals I just might be opening up another can of worms or expose the next weak link as Stimpy was saying.

Zak, you on the other kinda' teed me off.       I'm big on vibration mgmt, even though Brian Cheney of VMPS wasn't, and I'm confident that with properly anchoring the speakers into the subflooring I should be able to extract some very evident performance gains.  In fact, I recently purchased 4 steel plates that I could awkwardly fasten to what I thought was a glued on base plate and then I could mount my specially designed cones/points to the the steel base plate.  Because of their shapes, none of the steel plates purchased will replace the standard base plates to fasten to the bottom of the RM-40's

But with your pics and description, I can now see that just purchasing some 1/2" or 3/4" steel base plates to perhaps identical in size to the current MDF base plates I can do exactly what I hoped to accomplish and keep them looking nice and tidy too.

BTW, Zak.  Nice choice of woodgrain on your cabinets.  Can you tell me approximately how long the 4 long base plate screws are?  Philips, flathead, or socket head?   Because the RM-40's weigh 240 lbs. each they simply are a bit much for me to easily handle moving, tipping, etc.  My prior speakers all weighed 180 lbs. or less and at least those were manageable whereas the RM-40 are not.  Hence, I never tilt them just out of curiosity cuz I might die.

Anyway, thank you guys, especially for taking the time to spell things out a bit since I'm very electronics challenged.  It's really very much appreciated. 

DRINKS ON ME !!!!!

[stehno]

I was hoping for sound.

Unfortunately, Brian didn't publish VMPS documentation.  So, it's difficult to know what's inside a particular model without actually owning it.  One thing I want to work on.  Start a thread, trying to catalog documentation and schematics.

I was being intentionally rude.  Sorry about that, but I didn't want you to (further) damage your speakers.

As above.  Caution with the volume control.

Fuse wiring diagram, from my Acoustic Research manual.  No reason this won't work for your 40s.

http://www.classicspeakerpages.net/library/acoustic_research/ar-9_series_1978-1981/ar-9_series_manuals/ar-9_manual/ar-9_manual_pg25.html

That's just a guess.  But, I'd think it's most likely, due to all 4 panels failing at once.  I'd look at the L-pad first, and the midrange crossover capacitor second.

You are most welcome!

BTW, Stimpy, thanks for the fuse diagram, just a simple in-line fuse.  Considering the potential complexities of each and every reasonable speaker, this seems like it should be mandatory for every thoughtfully designed speaker.

Thanks again.

[ZAKski288]

Stehno, Really glad there working.

There really not that difficult to tilt down on there side, and they out weight  me by 65lbs.  I think bases are actually two pieces, but you have to remove the 4 large Phillip screws (approx. 4”) first. That removes the base from speaker. Then you can remove 8 screws (1.5 -2 “) that hold the bottom to the side of the base.  Good luck Zak

[stehno]

Stehno, Really glad there working.

There really not that difficult to tilt down on there side, and they out weight  me by 65lbs.  I think bases are actually two pieces, but you have to remove the 4 large Phillip screws (approx. 4”) first. That removes the base from speaker. Then you can remove 8 screws (1.5 -2 “) that hold the bottom to the side of the base.  Good luck Zak

They only outweigh me by 15 lbs. but still it's a risk mgmt thing.  I remember the seller and I carrying them up the stairs into my listening room.  That extra 60 lbs. or so from my older speakers makes a big difference for some reason.

The base plate is MDF, isn't it?  It would be so nice and easy to now replace with a simple steel base plate so I fasten in my points.

Thx,

[John Casler]

Stenho,

Glad to hear it was the L-Pad as I thought.  I have seen this quite often, and learned the lesson 1st hand myself with my first pair of RM-40.

"1812 Overture Cannons" at high volume was the issue with mine.

The L-Pad being a resistance device heats up, and if sustained High Power is applied they will burn.

Sometimes they can even burn the cabinet.

In any event, I would change them out on BOTH speakers, as the burned windings will reduce sound quality.

Brian bought them from Parts Express often, and they are very inexpensive.  Best plan is to see if you can get the part number from yours, and take a picture on your phone to sent to Parts Express. 

Remember, they have been "hot glued" into position, so be VERY CAREFUL to slowly pry them lose.  Take your time, or you may damage the cabinet.  When you Glue the new L-PAD in place, take GREAT CARE to position it so that 12:00 is at the top.

Also be very careful to mark the wires and what each was soldered to.  Again, a phone photo can be helpful.

Also as a resistance device, the more "wide open" you run them, the lower the resistance and heat created.  I always ran mine hot (like 1:00 or 2:00)  Brian generally ran lower than that, but seldom blasted.

[Bob Stark]

Hey John S.,

We had a couple long talks 4-5 years ago.   I still have my pair of RM40 BCSE with the MLS cabinets.  My bottom plate of the speakers had the 3" side MDF supports glued into it.  There was no removing the bottom plate on mine.  Just thought you should know as it could also be true of yours.

Good luck,
Bob