Help - killed both Cerwin Vega tweeters (or worse) with APM-200?

[Grenadeslio]

They've been cranking away (loud) for the last year with no fuses. Now, I will say the PO said he re-foamed them, and re-capped them. The foam is nice, but I've never cracked them open to see what he did to the caps and speaker wiring. Ugh....

There are those that believe the "right" fuse sounds better, and others that all fuses degrade the sound? Maybe they were removed as an upgrade lol? Either way it's possible other things were changed, incorrectly?

Take some pictures of the crossover, wiring and post them here if not able to make heads or tails of the wiring diagram, maybe we can see something amiss.

 

[lokerola]

You don't need no stinkin' fuses; the speaker drivers will protect the other, more delicate components...

There are those that believe the "right" fuse sounds better, and others that all fuses degrade the sound? Maybe they were removed as an upgrade lol? Either way it's possible other things were changed, incorrectly?

Take some pictures of the crossover, wiring and post them here if not able to make heads or tails of the wiring diagram, maybe we can see something amiss.

OK, will do. Thanks much.

 

[45rpmspinner]

I believe there's a separate relay/switch for the tweeters which is supposed to re-set on it's own.

PTC on the wiring diagram?

 

[lokerola]

Use the lowest, 200 ohm or the next one up 2000 ohm.
The tweeter (two wires) must be disconnected from the speaker crossover to get an accurate reading. Hopefully yours use push on terminals and aren't soldered on.
Oh boy, no protection, hope they aren't blown.
Fuses are dirt cheap and worth every cent once you've blown something up.
I Googled them, it appears there may be some sort of fuse or breaker on the back next to the connection terminals.

EDIT---I see you have checked them and got 3.3 ohms, they should be good based on that.
IS IT POSSIBLE they weren't working before?
If the fuse is inline with the tweeters I don't see how they would have worked before if there were no fuses installed.

I just wanted to reply back that now I feel like I'm losing my mind (or perhaps my hearing). MAYBE they never worked????! Jeezus......

I'm going to spend some time just listening tonight and see if I can tell a difference.

 

[lokerola]

I believe there's a separate relay/switch for the tweeters which is supposed to re-set on it's own.

Interesting. Not sure how I would find that relay. On the crossover I assume? Can you tell if it's been reset?

Anyone have any ideas on which fuses actually fit these beasts? I was never able to google the correct fuse. Thanks AK - you're the best!

 

[lokerola]

Interesting. Not sure how I would find that relay. On the crossover I assume? Can you tell if it's been reset?

Anyone have any ideas on which fuses actually fit these beasts? I was never able to google the correct fuse. Thanks AK - you're the best!

Never mind, I see it on the schematic: 3AG 2.5Amp slow blow glass

 

[lokerola]

Im suspecting the tweeter relay thingy. Now I just need to figure out how to find and test and/or reset it.

Fuse from parts-express is someone else needs them for their VS-120's

https://www.parts-express.com/littelfuse-25a-3ag-slow-blow-fuse-5-pcs--071-700

 

[45rpmspinner]

Never mind, I see it on the schematic: 3AG 2.5Amp slow blow glass

Nope, that's not it. Look for "Raychem Polyswitch RDE050A".
I think it's a thermal switch. In line with the tweeter.

 

[lokerola]

Nope, that's not it. Look for "Raychem Polyswitch RDE050A".
I think it's a thermal switch. In line with the tweeter.

I think we may be talking about two separate things.

1. The link I listed was the glass fuse that installs on the outside of the speaker, next to the binding posts. Those have always been missing on my speakers.
2. You listed the tweeter relay, which is installed inside the speaker, on the circuit board - awesome, thanks!

- Sorry for my electrically stupid question, but how do I test this relay?

Thanks!

 

[lokerola]

This thread has a link to the wiring diagram, if I'm reading it right the entire speaker is fuse protected, not just the tweeters, maybe someone else can verify that.

http://audiokarma.org/forums/index....rossover-schema-and-drivers-impedance.561340/

So, schematic-experts, question for you...on the schematic I see "fuse" spelled out on the upper left, inside the green box. Then I see "FU" in the upper left, connected to the positive binding post, but outside of the green box. The key says the FU = fuse. Does that mean that there's an external and internal fuse? Two fuses total?

 

[goodolpg]

I just wanted to reply back that now I feel like I'm losing my mind (or perhaps my hearing). MAYBE they never worked????! Jeezus......

I'm going to spend some time just listening tonight and see if I can tell a difference.

Like I mentioned, it's got me scratching my head!
Hoping someone smarter than me can help you out.
I agree, crossover pics might help as it appears the fuses were bypassed when the speakers were recapped previously, could be other changes as well.

 

[lokerola]

Like I mentioned, it's got me scratching my head!
Hoping someone smarter than me can help you out.
I agree, crossover pics might help as it appears the fuses were bypassed when the speakers were recapped previously, could be other changes as well.

Yea, good point. I will sleep on this and pull the woofers tomorrow so I can get a look at the wiring and crossovers.

Thanks all - more info to come.

 

[goodolpg]

So, schematic-experts, question for you...on the schematic I see "fuse" spelled out on the upper left, inside the green box. Then I see "FU" in the upper left, connected to the positive binding post, but outside of the green box. The key says the FU = fuse. Does that mean that there's an external and internal fuse? Two fuses total?

Google images shows on the back of the speakers there are red/black wire terminals and some sort of gray/black plastic covering right next to them that I assume is where the fuse should be?

I'm thinking the F-U-S-E is the same as the FU and there is only one fuse.
And the PC board is the crossover board itself.
Could be wrong though...

Just wondering, are the original spring loaded terminals still on the back of the speakers or have they been replaced with 5 way (round head most likely) binding posts?

 

[45rpmspinner]

I'm thinking the F-U-S-E is the same as the FU and there is only one fuse.
And the PC board is the crossover board itself.

I agree.

Someone has jumped the fuses as they're clearly in-line.
Nothing else makes sense.

 

[Grenadeslio]

I believe there's a separate relay/switch for the tweeters which is supposed to re-set on it's own.

PTC on the wiring diagram?

So right, and going back to the original post, the whole system shut down.

"I turned it on and didn't see a lot of movement on the meters, so I turned it up. The amp clicked off."

Now it seems the tweeter protection relays are either damaged, or continuing to do their job protecting the tweetes, maybe from fried coils L3?

"They've been cranking away (loud) for the last year with no fuses"

Or possibly something wrong with the APM 200 that caused the damage.

 

[restorer-john]

are you 100% sure there are not resettable circuit breakers on the crossover? They would require a push-to-reset.

 

[Grenadeslio]

are you 100% sure there are not resettable circuit breakers on the crossover? They would require a push-to-reset.

According to a wiring diagram posted in another thread the polyswitch that's on the circuit board is the same as below. The good news is, if defective Parts Express carries them.



But I still find it odd if defective this would cause the amp to shut down, I still think there's something else.

 

[lokerola]

According to a wiring diagram posted in another thread the polyswitch that's on the circuit board is the same as below. The good news is, if defective Parts Express carries them.

View attachment 1087494


But I still find it odd if defective this would cause the amp to shut down, I still think there's something else.

Thanks. I'll probably order a couple of these, along with the glass fuses, and two of the L3 voice coils. Not sure if the voice coils are available, but I assume they will be. I'll call PE on Monday (or Tuesday if they're closed for MLK).

So right, and going back to the original post, the whole system shut down.

"I turned it on and didn't see a lot of movement on the meters, so I turned it up. The amp clicked off."

Now it seems the tweeter protection relays are either damaged, or continuing to do their job protecting the tweetes, maybe from fried coils L3?

"They've been cranking away (loud) for the last year with no fuses"

Or possibly something wrong with the APM 200 that caused the damage.

Could be. I did have the APM set to 8ohm, when the speakers are 4ohm (duh). So it could have been my fault...ugh.....Or the APM could be bad. It did power on and light up. If course that doesn't mean something isn't wrong with it, but it's all I got. I'll be in no rush to hook it back up once I get the speakers working.

I agree.

Someone has jumped the fuses as they're clearly in-line.
Nothing else makes sense.

Yea, I'll take a look at the wiring later today or tomorrow.

Google images shows on the back of the speakers there are red/black wire terminals and some sort of gray/black plastic covering right next to them that I assume is where the fuse should be?

I'm thinking the F-U-S-E is the same as the FU and there is only one fuse.
And the PC board is the crossover board itself.
Could be wrong though...

Just wondering, are the original spring loaded terminals still on the back of the speakers or have they been replaced with 5 way (round head most likely) binding posts?

The original spring loaded terminals are still on the back of the speakers - there's just no glass fuse in the holders. Also, the fuse covers are long gone.

 

[mhardy6647]

So -- I'm skimming this thread, but I am also wondering -- has the OP tested the loudspeakers' tweeters directly for functionality?
It is easy to do with a small, low voltage "battery" (e.g., an AA or a C cell) and a couple of wires (clip leads are extra handy).

Hook one terminal (of the tweeter) to one end of the battery with one wire/clip lead (i.e., hold it in place on the battery). Hook the other wire/clip lead to the other terminal of the tweeter. Touch the other end of second wire/clip lead to the other terminal of the battery. If the tweeter is working, one will hear a click or some scratchy static as the circuit is closed.

This test won't hurt the tweeter as long as the duration is short (momentary contact) -- the DC voltage will generate heat in the voice coil, but the voltage and current are low with a small cell, so momentary contact won't hurt the voice coil.

If one gets no click/static at the moment of contact, the tweeter's voice coil (or the internal wiring to it) is probably "open".


PS "Polyswitches" are of the Devil in terms of their sonic impact.
A regular fuse is a better solution, I'd opine (if slightly less convenient than an auto-resetting gizmo).

No fuses in the signal path is OK -- as long as the amplifier is capable and the user is prudent.

 

[mhardy6647]

PS I doubt that the APM setting had any impact. Probably all that switch does is scale the output meter reading so that it's "accurate" (not that it is probably really accurate). These meters measure voltage not power, and are simply calibrated to show Watts of power based on Ohm's Law. 1 watt into 8 ohms is 2.83 AC volts -- but 2.83 volts into 4 ohms is 2 watts.

More likely, this was the coup de grace.

I turned it on and didn't see a lot of movement on the meters, so I turned it up.

These are high-sensitivity loudspeakers that will play quite loud with very low power input. The range of the APM-200 meters* really isn't well suited to show meaningful output 'data' for power into high-sensitivity loudspeakers: thus the "didn't see a lot of movement" observation. "Turning it up" probably took the OP into dangerous territory.

Fortunately, Anything that doesn't kill one makes one stronger.

* EDIT: The APM-200 might show reasonable excursion at the "2 watt" sensitivity setting --- if that's what the OP was using... then my comments on the death of the loudspeaker (and/or amplifier) are probably wrong