[ZAKski288]

Which devices are you speaking about from this photo below?



 
The two caps you circled. The yellow capacitor is an Auricap by Audience and the Brown (reddish)capacitor next to it.  Zak

[PMAT]

Those are great speakers. I think you need a specialist. Whoever soldered that crossover together had zero pride. I own VMPS as well.

[LosGatosSTI]

I agree and it must have been put together by Brian or one of his people because I bought them from one of Brian's dealers and Brian came to my house to tune them.   I was shocked to see how poorly made the crossovers appear.  I guess looks don't matter when they are hidden inside the speakers.

By the looks of it it appears that there are only two capacitors connected to the green and blue wires then it looks like those wires attach to the Lpad then another pair of green and blue run up to the tweeters. Is this tweeter wire routing correct?   

[jules]

Can you get hold of a schematic for the Xover?

Given the state of the soldering, there's nothing to lose by removing the Audience cap and the smaller one in parallel with it to check if they're working. You'd certainly need to use new, clean wire to replace the caps.

Where is the Lpad set on it's range ... low, medium or high resistance?

The large red caps look as though they have slight scorching around the terminals. Is that an illusion?

[LosGatosSTI]

Hi Jules,

It would be great to have a schematic of the RM40 crossovers but do not know if anyone has that or has created that?  If so please share if possible.

I will try and test the caps like Hal and Zakski said. 

I'll probably buy upgraded caps by Dueland or Mundorf as long as I can find them somewhere and I can match the 1.2 uF of the Auricap and the other cap if it is indeed bad. 

Does anyone have opinions on Mundorf or Deuland?

As far as the scorching on the TRT caps...I'm not sure what these looked like at the beginning so I have no reference. 

Lpads are near the middle of the span set about 12:30 oclock. 

[Tyson]

Duelands are better than Mundorf.  But I'd actually recommend getting the Jupiter Paper/Wax/Copper cap instead - it gives you Dueland level performance for a lot less $$.

[HAL]

I am still thinking as a previous poster, that the Bryston 6BSST 3 channel amp should be checked.

The DC or AC voltage to burn out the series capacitors in the crossover before the L-Pads would have had to be very large to kill them.  Ultrasonic oscillation from an amp would be more likely.

At this point, I would get the amp tested and check the speaker crossover parts.  Depending on amp age, might be time for a power supply replacement of capacitors.   Other problems might be spotted on the bench.

Just a thought.

[Tyson]

Oh yes, I agree with HAL- it's probably the amp.  If memory serves, Bryston has a crazy good warranty so use it!

[jules]

Sorry I can't help with a schematic Scott, but given you know the full history of your speakers, the wiring should be correct, though you'd have to wonder about that particularly horrible bit of soldering.

I guess it all hangs on the state of the Audience cap and its partner at the moment, though if they're dead it's looking like you need to have the amp checked. It might be helpful to get a second opinion on the state of the TNT caps, or perhaps you could post a close-up here.

[LosGatosSTI]

Left Speaker cap test results with Fluke 87 meter:
- Auricap - 1.2 uF with 0L reading (Open Circuit)
- Brown cap 0.067 uF with 0L reading (Open Circuit)
Sum of caps approximately 1.35 uF

Right speaker (Brian used 4 caps from 3 different manufacturers for some reason):
- Auricap 1.26 uF with 0 ohms
- Large brown cap - 0.07 uF with 0L reading (Open Circuit)
- Small brown cap - 0.016 uF with 0L reading (Open Circuit)
- small orange cap - 0.01 uF with 0L reading (Open Circuit)
Sum of caps approximately 1.35 uF

I still want to upgrade the caps even though they don't appear to be the real problem here.

1) Do I need to match 1.35 uF with new caps?

2) Does the voltage rating of the caps I choose matter?  Any voltages to specifically avoid like minimum rating or whatever? 

Tyson suggested Jupiter Paper/Wax/Copper cap.  Looks like on partsconnexion web site I can get 600VDC versions and get to 1.33uF with a 1 uf and a .33 uF.  I will get matched pairs if possible.

What is the need or benefit of getting to exactly 1.35 uF? 

Would you buy them from anywhere else?

Thanks,

Scott

[HAL]

Scott,
If the caps are reading 0 ohms when probes are across the leads with the Fluke 87 meter, something is shorted out and might be the reason the tweeters are dying.  The reading should be nearly infinite.  If the 0 is flashing that means out of range and probably they are not shorted and fine. 

 

[jules]

It would seem impossible that all the caps could be shot and of course the only drivers that died were the ribbons, so presumably most, if not all of the xover is/was working.

Going back to your first post Scott, both G2 ribbons went at exactly the same time. I'm not sure from what you said if the FST ribbons had the same sort of failure or if you replaced them based on the flaking etc? As you said yourself, it's unlikely that both xovers spontaneously suffered from the same fault so maybe the amp is still suspect. I'd suggest that if this is happening at exactly the same moment on both channels you're looking at a problem that occurs in the amp before the separation of the channels. I'm not familiar with the design of your Bryston but some part in the transformer[s?], rectifier[s?] caps in the amp's power supply could be the culprit.

You do need to get to the bottom of the problem before spending a truck load of cash on new caps.

[HAL]

Agreed.  Amp check first.

[brj]

I'm not sure I appreciate the logic backing the concept that the amp is the prime suspect beacuse both tweeters failed at once.  Presumably the system was seeing roughly the same signal on both the left and right channels (unless you were playing something with a significantly asymmetrical soundstage).  If so, a fully functional amp would have amplified the signal in the same manner on both channels.

What, specifically, was being played at the time of the failure?  A drum thwack?  Something less challenging?  How loud was the system playing?  Was it clipping?

I'm not saying you shouldn't have the amp checked, but it may also be performing fine and just amplifying a signal that is simply beyond what the crossover/tweeter can handle.

Also, don't most VMPS speakers have a variable L-pad on the tweeter, often using a potentiometer?  If so, what kind of shape are they in?

[jules]

 , actually I agree with that too and I'd add the comments I just made to those I made earlier!

The ribbons are the canary in the coal mine, so if the L-pads are failing [though it would be surprising if they were both in exactly the same state of disrepair] or their adjustment doesn't suit the G2s it could certainly be the issue. If it's possible to find the specs somewhere I'd also be checking out the relative sensitivity of the G2 against the original ribbons the xover was designed for.

[*Scotty*]

Oscillation can be unrelated to the input signal level as well as the power levels that are producing the audible program SPLs at the time. When large scale oscillation occurs the amp may put out enormous amounts power at ultrasonic frequencies. Sometimes the output devices will fail due to the heat generated during the event.
 There are better than even odds that the amp has a fault. Depending on the impedance the series capacitor has at ultrasonic frequencies, it may be able to pass more than enough power to fry the tweeter and remain undamaged. The Aurum Cantus G2 is rated for 40 watts, the amp could easily dump up to 300 watts at ultrasonic frequencies in a worst case scenario, even if it put out only 60 or 70 watts this would be more than enough to create the observed fireballs.
Scotty

[jules]

On the caps value question: If you're looking at filter caps they should be of the same value, otherwise you'll change the frequency of the crossover point. For DC blocking caps the value isn't as important.

Don't go below the voltage value of the caps installed at the moment but caps with very high voltage ratings aren't going to be of any advantage, except they'll cost more.

Remember that to sum the value of capacitors they need to be in parallel.

If you want to give your head a workout with different cap options, check out this site:

http://www.humblehomemadehifi.com/Cap.html

[LosGatosSTI]

Sorry...I corrected my posting.  All the capacitors seem fine as they all read .0L which must mean overload or infinity on the Fluke.

I have been reading the humblehomemadehifi cap reviews and do believe that an upgrade to the 14 year old tweeter caps is probably warranted now that they are unsoldered anyway. 

Background on Failures: 
- Source in each failure was a new Oppo UDP-205 playing a Beck SACD through a Sunfire Theatre Grand III processor or a Marantz AV-7703 processor. 
- Bryston used in all failures. 
- First ribbon failure was with original 14 year old FST tweeters. 
- Second ribbon failure was after replacing the burnt up ribbons on original FST tweeters with new Aurum Cantus G2 ribbons from parts express.
- I suspected tweeter transformer failure and noticed degrading (flaking off) coating on the 14 year old FST magnets so decided to replace them.
- Selected the G2 because parts express said they were the closest to the original tweeters at 8 ohms.  Don't know if that is true or not?
- Third ribbon failure was with NEW Aurum Cantus G2 tweeters and Marantz as the pre pro. 
- All ribbon failures occur approximately 1 hour or so into a high volume listening session.  Volume at 75% to 80% or so of max.  No clipping was shown on Bryston.

What gets me is the simultaneous ribbon failure at about 1 hour into listening session. 

Regarding cap choices: I should try and stay above 250 VDC rating on caps.  Try to get close to 1.35 uF with matched combination of caps wired in parallel.  I can go higher in voltage rating on the but it costs more.

Regarding Lpads:  I'm not sure on the status of the Lpads as when I cycled them through the entire range of rotation on each Lpad I didn't hear any hisses, pops, crackles or anything that would indicate any issues with them.  I did not notice any arcing shown on the metal back covers.

Bryston 6BSST has separate power supply for each channel. 

[JerryM]

What speaker cables are you using?

[jules]

Scott, I think the G2s are 6 ohm, though I could be wrong.

The simplest thing you can do before going any further is to check the specs of both the FST and the G2. The FST is quite probably a "stronger" ribbon while the pure Al G2 has the advantage of being super light and hence doing high, highs better. I know they're rated to run from 1700Hz up but at these lower frequencies they're under a fairly high load.

So, if you can find out the crossover frequency between the ribbon and the mids, the power ratings of the G2 and the FST, the relative sensitivity of the FST and the G2 it will cost nothing but might be helpful.

If, for example, the G2 is rated 6 ohm and the FST 8 ohm, it's possible to change the xover appropriately. From memory Tyson had the ribbons on his RM40s swapped so maybe he might be able to help on this side of things.

The problem with my thinking is, that both FST and G2 ribbons have burned out so that cancels out a lot of what I've said 

Do other RM40 owners have ribbon problems?

What gets me is the simultaneous ribbon failure at about 1 hour into listening session

Yes, that's what gets me too!!!