This question is aimed to TRUE Elec Engineers, not fuse or wire directionality believers.

Can’t say as I had. Then again, I’d expect whatever voltage was getting into the system, to follow the path of least resistance. Even with an inductor(as opposed to a cap), the woofer would be the first victim and(if playing music at the moment) the caps in the crossover, would already be charged/blocking. My home systems(even the 8", 2 way) were all warranted to handle 356 Watts(peak program). Far as clipping, I twisted the cathodes of a couple Zeners(voltage chosen according to the particular tweeter) together, stuck them in a TO-39 heatsink, and hot-melt-glued them on the crossover board, across the tweeter leads. The only condition in the warranty: If the glue was melted out of the sink, they only got the first tweeter free, along with a verbal treatise on amplifier clipping(sold a few Haflers that way). Only ever had to warranty one pair. Replaced LOTS of other brands’ tweeters for the many college students, in that area and installed/sold lots of those little protection devices. As a result, I regained my love/passion for college parties. What sucked was having just put down $30K, on a $130K building(land contract), one month b4 the sinkhole. You’d have to remember the economy, and how hard it was to get a commercial loan, back in 1980. NO banks were doing it(in Florida, anyway) and $30K was a lot more money, back then. I was always in the Black, b4 that. Again: Sorry to the OP, for the hijacking! https://www.electronicsurplus.com/thermalloy-aavid-2228b-hardware-heatsink-for-to-39-or-to-5-compone...

@ramtubes, I am aware that MOStTSSRs use thyristors and are not suitable for audio applications.  They are designed for motor controls.  That is why I am getting ones made with back to back Mosfets.  Pls see my post above regarding the audio SSRs specifically made for this purpose that are being sold by Holton electronics in down under.

Yikes!! Sorry to hear about that!
Did you ever see a case where the tweeter was damaged by a shorted output transistor? I only saw it happen if the amplifier was overloaded (in which case the woofer often survived).

"That’s because there is no need. I’ve got plenty of scopes but its academic." Sorry to say, that’s what I expected. Regarding, "Ask any speaker designer." I made my living, in Orlando/Winter Park, FL, repairing/reconing speakers, designing/building and selling pro and home audio speaker systems, back in the 70s and early 80s. The ’Great Winter Park Sinkhole’, pretty much put me out of business. It ate part of my property(along with all utilities) and three neighboring businesses, almost bought it as well(two did, not that any of that matters). Happy listening! https://www.orlandosentinel.com/news/nationworld/os-fla360-pictures-winter-park-sinkhole-20121113-ph...

For anyone who risk blowing their thousands of dollars costing speakers because they rely on tweeter caps, be my guest and good luck.

I still will be building my protection circuit :-)

That's because there is no need. I've got plenty of scopes but its academic.
Just don't put a cap on the tweeter that is larger than it what is needed to cross it over properly, and you won't be able to damage the tweeter when DC is applied to the speaker. Ask any speaker designer.

1) "Finally, although it’s more of an academic point than one having practical significance, if a large DC voltage is suddenly applied to a capacitor, and a large current briefly flows corresponding to C(dv/dt), the nearly instantaneous change in voltage means that spectral components are present at non-zero frequencies, at and near that instant. Which by definition means that the voltage is not DC, at and near that instant." 2) "The tweeter was damaged because there was significant inrush current to charge that particular cap. Once charged no more current flows. That is how an exponential charging curve works." That explains why transients both blew the tweeter and caused the pops from the woofer, when the discharged capacitor and battery were reconnected. Whatever was passed through the nonpolarized capacitor ("spectral components"/DCV/Dark Energy?), it blew the tweeter and created sound(however briefly) through the woofer. Again, I wish I had a scope, with which to better record the duration and amplitude of the spike.   Apparently, no one out there with a scope, cares enough to perform such a simple experiment, to either confirm or disprove my results.

Ok, I bought a pair of these from down under:

https://holtonprecisionaudio.com/collections/diy-audio-products/products/audio-solid-state-relay-hpa...

I will post on this thread later when I have time to add them to my circuits.

Thanks

@cakyol Has any of you ACTUALLY worked with and recommend a SSR which does not introduce any audible distortion on the speaker line and which can operate with a large range of trigger voltages (12 - 48 VDC, may need to have on board voltage regulator for this range). I am building a speaker DC protector and do not want to use electro mechanical relays becoz of DC arcing and contact erosion issues. It needs to be capable of switching up to 15 amps at about 100 volts.Only TRUE engineers reply please.Thanks

Please begin a question without an abbreviation of the most important item.

Solid State relays typically employ SCRs which will have a dead zone at the zero crossing. Try to measure it Its large and will cause a lot of distortion. Crossover distortion is the worst. Rail fuses are your best bet. They are in the feedback loop, and do no harm and no zero crossing.

Other than that a good relay is useful though rail fuses, not speaker fuses, are far better.

BGW used a parallel clamp when DC was detected. The front panel circuit breaker/power switch then opened and all was well. Great solution if your devices can pull the breaker.

@rodman99999
I'm not saying the tweeter was not damaged. I am saying it was damaged for a different reason than the capacitor not doing what caps do (which is block DC).

The premise that I’ve been testing, is that NO DC voltage would get past a non-polarized capacitor. At least, that’s what’s been proffered in this thread.

 You don't need to put a tweeter on the cap. Just put a resistor. Let it sit there for a while (the bigger the value, the longer it has to sit) and then measure the DC voltage across the resistor. There will not be any- because the cap is charged. This assumes a working capacitor of course.


Capacitors, especially electrolytics, have a little bit in common with a battery. They can be charged up and hold a charge but unlike a battery, the time it takes is very dependent on the resistance in series.


The tweeter was damaged because there was significant inrush current to charge that particular cap. Once charged no more current flows. That is how an exponential charging curve works. 

Back to back MOSFETs suggested here will work but they need a 10V floating voltage source or some photovoltaic coupler to a DC detection circuit. These have time delays. The tweeter should be able to handle a short single spike. Average power will be low.
Power requirements for a tweeter is very low so driving from a 100V source kinda don't make sense. Bi amping using low power amp for tweeters does.
Tube amps have transformers isolating from DC and typically sound good.
A normal mechanical relay has a delay time as well, like 8 - 20 ms  so some energy will reach the tweeter. I would think there is a cap in series with the tweeter, that will block DC. A small relay could be placed after the cap maybe even a reed relay.
As some have posted here, a fast crowbar circuit is used to blow a fuse where extreme protection is needed.
If a power amp has glitches that puts DC on the output it should be fixed or else replaced. 
Additionally, HF energy can pass the speaker high-pass filter and some protection for the tweeter is needed here.  I have burned up tweeters with amp stability problems. Perhaps limit the max frequency the tweeter is exposed to. 
DC on the output of audio amps is a problem that was solved 40 years ago, as I can recall. This really should not be an issue.

"OK- you didn’t damage the tweeter with a 0.1uf cap, but you did with a 33uf cap. The 33 uf cap allows for much lower bandwidth of information through the tweeter, which in most cases only handle a few watts. My surmise is the 33uf cap made for too much excursion." There is no, "much lower bandwidth of information", that could possibly proceed from a battery. Also- that tweeter blew when the multimeter was taken out of series. I never tried it, using the .01uF, without the multimeter. I may just dig a tweeter out of my old inventory, to(perhaps) sacrifice. I had a box of EV Interface A & B, paper coned tweeters, for doing EV’s warranty work(REAL cheap), back in the early Eighties).  That'll have to wait until the temps in my garage, get above 0 Degrees(F).  The premise that I’ve been testing, is that NO DC voltage would get past a non-polarized capacitor. At least, that’s what’s been proffered in this thread.

Regarding the woofer’s excursion; That’s what happened, with 1.5 VDC. Infer what you like. I suppose, were I to dig through my shoppe’s old inventory, found a 4 or 5uF cap, and an 8 Ohm resistor, then bought another O-Scope, I could provide more details, regarding exactly what’s occurring, regarding the DC voltage spike, through the cap(s). The facts are: the tweeter blew and there’s a distinct pop, from the woofer, when connected to a C cell, through a non-polarized capacitor. That indicates there’s a transient, being passed to the driver. As I mentioned at the outset, these are experiments that can easily be done, by anyone really interested. Anyone that does conduct such: I’d like to hear their results/conclusions(particularly, if you own/use an O-Scope).

Same results, for a moment. BUT, now the tweeter’s blown(it literally/audibly, "popped"). Trying to read, across the tweeter’s terminals, wasn’t any more, "meaningful"(since I already knew DC voltage would pass), BUT- decidedly more EXPENSIVE! Explaining the results is easy(ie: non-polarized film capacitors, WILL pass DC).

@rodman99999
OK- you didn’t damage the tweeter with a 0.1uf cap, but you did with a 33uf cap. The 33 uf cap allows for much lower bandwidth of information through the tweeter, which in most cases only handle a few watts. My surmise is the 33uf cap made for too much excursion.

Caps charge along something called an exponential curve. At the beginning of the curve a lot of current flows and not so much at the top of the curve.

The **amount** of current that can flow has a lot to do with the value of the cap! 33uf is a lot more than 0.1uf and so the additional current was enough to do the tweeter in.

IOW that fact that you were able to damage the tweeter does not say anything about how a tweeter would pan out in a properly designed crossover. If we do the math:


F = 1/C x R x 2Pi

Where F is frequency
C is capacitance and
R is resistance

To make this formula easier to use, because Farads are a lot of capacitance, we will use Microfarads (uf); so we can replace the 1 with 1,000,000 and that will give us the Frequency in cycles per second. So:
804Hz = 1,000,000/33 x 6 x 6.28


With a 0.1uf cap, we get 265KHz. IOW, a **lot** more energy was allowed to pass through the tweeter with the larger cap. Most tweeters need to be crossed over pretty high- 5KHz is common and for that a 5uf cap would suit. See if you can damage the tweeter with your battery and a 5uf cap. You can’t, because the cap allows only about 1/6 as much energy before current stops flowing.


This is the tip of the iceberg here. But the bottom line is that tweeters survive output transistors shorting in the power amp quite easily- unless the crossover cap isn’t rated to handle the resulting DC voltage and is thus damaged by it (speaker manufactures don’t like to ship boxes around any more than they have to so they make sure to put in crossover caps with a high enough voltage rating).


To put myself through engineering school I worked in several consumer electronics service shops and repaired many speakers damaged by shorted output transistors. IOW, I replaced **woofers**. When the amplifier clips but is otherwise damaged, that’s when tweeters fail, as the clipping generates harmonics that the crossover can’t block. The tweeter is damaged by the great power of the distortion harmonics. The solution in most cases where this is seen is to get either a more powerful solid state amp or get a tube amp (which makes less higher ordered harmonics).

Thanks for the additional datapoints, Rodman. I don’t think the pronounced pop at the moment the battery was connected (or when the cap was discharged into the driver) is surprising. For a theoretically ideal capacitor i = C(dv/dt), of course, ("i" = current; "C" = capacitance; "dv/dt" = change in voltage per unit time), so completing the circuit by touching wires or leads together would result in a nearly instantaneous change in the voltage applied to the cap, resulting in a large (dv/dt). And discharging the cap into the driver would have similar consequences, as the voltage across the charged cap would abruptly be forced toward zero by the low resistance of the paralleled driver.

But in the event of an amp failure resulting in a large DC output, how likely is it that the DC voltage will be ramped up in a comparably abrupt manner? I don’t know the answer to that.

And what I don’t understand in your latest results is how the C cell could hold a 200 watt woofer at full excursion. Even if the DC resistance of the driver is as low as 2 ohms, the battery would be putting not much more than 1 watt into it. And 200 watts into any reasonable woofer resistance corresponds to vastly more than 1.5 volts, of course.

Also, it seems relevant that the capacitors used in many tube-based preamps and other tube-based components to couple the signal at the plates of various interstage and output tubes to the grids of a subsequent stage or to the input of another component, such as a power amp, are in many cases used to block DC on those plates of well over 100 volts (at least if a cathode follower is not used, in the case of output stages). Yet that never seems to be a problem. And in many cases those caps have values that are not much different than the 0.1 uF cap Rodman experimented with. And I seem to recall that some McIntosh designs, at least, have used fairly large electrolytics for their output coupling capacitors, having values not all that much lower than the 33 uF he also experimented with.

Finally, although it’s more of an academic point than one having practical significance, if a large DC voltage is suddenly applied to a capacitor, and a large current briefly flows corresponding to C(dv/dt), the nearly instantaneous change in voltage means that spectral components are present at non-zero frequencies, at and near that instant. Which by definition means that the voltage is not DC, at and near that instant.

Regards,
-- Al

My apologies to the OP, for the departure from their basic query.

Conducting an experiment(yesterday) with a Speakerlab W1048P, 10" woofer(two layer, 2", 10mm overhang voice coil, 200W power handling), with only the C cell and 33uF Clarity ESA, produced a pronounced pop, at the moment the battery was connected(iow: a DC voltage spike). The first time I tried that with the tweeter(cap/C cell/tweeter/in series), the spike was sufficient to take out the tweeter. Removing the battery and discharging the cap into the driver, produced the same transient(rhetorical). As far as the amount of juice, provided by a C cell: without the capacitor, it was sufficient to hold the woofer at it’s full, linear(10mm, measured) excursion, as long as I kept it connected(also- rhetorical, but- the tweeter couldn’t take it, even through the cap). Wish I hadn’t sold my O-Scope. I could measure the transient’s actual time/voltage(if frogs had wings....). I have little doubt, variations in capacitor values(uF/VDC), would alter the results(at least regarding duration).

1.5V across 6 Ohms = 0.25A or 0.325 Watt

Correction:
1.5V across 6 ohms = 0.25A or 0.375 Watt

I think the current is pass through the tweeter voice coil and charge up the cap, if there's 80VDC the voice coil will blow in seconds.

the driver was working, prior to being connected to a 33uF, non-polarized film cap and a C cell. It was reading 6 Ohms(correct nominal, according to the tweeter’s label), before it opened up.

1.5V across 6 Ohms = 0.25A or 0.325 Watt

Back EMF?
or
Is the capacitor fully discharged before connect to the tweeter?

Battery anatomy/specs aside, the driver was working, prior to being connected to a 33uF, non-polarized film cap and a C cell. It was reading 6 Ohms(correct nominal, according to the tweeter’s label), before it opened up. Imagine what(perhaps) 80VDC, would do. The tweeter had been sitting on a shelf, for the past 20+ years. My son blew the other, clipping his amp into a pair of Quart One bookshelf speakers, back when he was a kid. Not a big loss(at all), but- thanks for your condolences .

Ouch!  Sorry to hear that, Rodman. 

I'm very surprised, though.  Here is a datasheet for an Energizer alkaline "C" battery, indicating a **minimum** nominal internal resistance of 0.15 ohms.  Even if we make the extremely unrealistic assumption that it could maintain an output of 1.5 volts into a direct short, and even if we make the extremely unrealistic assumption that the DC resistance of the tweeter is zero, and even if the capacitor offered zero resistance to the resulting current, the battery could only provide (1.5^2)/0.15 = 15 watts, which in that situation would all be dissipated in its internal resistance.  While datasheets I've seen over the years for various tweeters all show power handling capabilities of at least several tens of watts.

Regards,
-- Al

ssg308,

Crydom relays are typically for motor control apps.  They will not have a low enuf switching resistance and linear frequency response for an audio signal.

Same results, for a moment. BUT, now the tweeter’s blown(it literally/audibly, "popped"). Trying to read, across the tweeter’s terminals, wasn’t any more, "meaningful"(since I already knew DC voltage would pass), BUT- decidedly more EXPENSIVE! Explaining the results is easy(ie: non-polarized film capacitors, WILL pass DC).

@Rodman99999, I'm not sure how to explain those results, but if I understand correctly the meter was indicating the voltage across a series combination of the battery, the cap, and the tweeter.  Wouldn't it be more meaningful to put the meter across just the tweeter, and put the battery across the series combination of the cap and the tweeter?

Regards,
-- Al 

Interesting followup- I just tried the same experiment, but substituted a ClarityCap ESA, 33uF, 250V cap and got a constant 1.45VDC reading, with either polarity. 

Less than one minute ago, I concluded an experiment. In series, I connected a .1uF Jupiter, copper foil/paper/wax capacitor, a Quart, 8 Ohm tweeter and the negative, of my Fluke multimeter(set to 2 VDC). Touching the multimeter’s positive lead to the + end of a 1.5V, C cell battery and the capacitor’s open lead, to the battery’s - end, results in a momentary(1-2 sec), 1.5VDC reading on my multimeter. Reversing the polarity, results in the same, every time. If there is full DC getting through, long enough for my multimeter’s digital display to recognize and register it, It’s difficult for me to believe, that(perhaps) 80VDC, from a toasted SS amp’s outputs, wouldn’t fry a tweeter. Color me skeptical.

@rodman99999
Without a load it will appear that the cap is passing a voltage in your example. The voltmeter, which is typically 10 megohms, is high enough impedance that it will appear as if the cap is passing voltage, but if there were any significant load you would not see anything like this.

In fact a non-polar will block DC quite effectively- and protect a tweeter from DC coming from an amplifier. The problem with non-polar caps is that they are actually two electrolytics in series. As a result, they make distortion in both directions since electrolytics can draw considerable current if reverse biased.
Now if you took two electrolytics and put them in series ('back to back', so to speak, which is how a non-polar is built) but then **also** biased their junction with a DC voltage, as long as the AC waveform going through them has less amplitude then the DC voltage (thus keeping them forward biased) they can be as low distortion as a good film cap.

Electrolytics have a bad reputation as coupling caps but they can work quite well if one understands how they work.

Anyone, living under the delusion that the NON-POLARIZED FILTER CAPS, used to block low frequencies from tweeters, WON’T PASS DC, needs to try measuring the voltage of a battery in series with one. That’s assuming you own a multimeter(or voltmeter).

Hope I don't get into hot water here for the link.

https://www.ebay.com/itm/New-VHC-1-SPDT-Vacuum-Relay-26-VDC-for-RF-Switching/390332847631?hash=item5...

These could be triggered by a conventional circuit. I've used them to handle a couple kilowatts of RF. Trigger time is in the low milliseconds.
There may even be quicker ones. Contacts are vacuum sealed and very tough. There are RF types and high current DC types. Either should handle anything you can throw at them.

crydom D2450 it has 50A at 240V and yes when control voltage drops below 3V it will disconnect.
Control voltage between 3-32V

I would recommend getting any older full sized soundcraftsman amp And take it apart.   if your goal is to kill the dc at the rails before it reaches the speakers they did this back in the 80s 

Accuphase

http://www.accuphase.com/pdf/p-4500_e.pdf
https://www.widescreenaudio.be/wp-content/uploads/2017/11/e-650_protection_circuit_3.jpg

3:18am

Hi Gibbs
I was referring to the main drivers that will burn, I am well aware of the audio bypass cap on tweeters...which wont pass dc.ANDthere are speakers out there with a resistor to limit the tops, so they could be smoked.Many retro speaker systems used a resistor on the tops.

A simple in line fuse will protect your main drivers that have no blocking capacitor.    I have much experience with this as well.

@cakyol

Please look at the link I posted. It should answer your questions regarding the use of solid state relays in audio amps. 

 

Hi Gibbs
I was referring to the main drivers that will burn, I am well aware of the audio bypass cap on tweeters...which wont pass dc.ANDthere are speakers out there with a resistor to limit the tops, so they could be smoked.Many retro speaker systems used a resistor on the tops.

Take a look at this link: http://sound.whsites.net/articles/mosfet-relay.htm

@gibsonian. Thanx for sharing your experiences with phase linear.  I guess i am trying to err on the side of being excessively cautious and not take the risk of leaving the tweeter protection to its filter capacitor. 

I did not mean to say I wont use a fuse. This is an ADDİTİONAL protection. Fuses will of course be there. 

And yes I will need a mosfet for at least 150 Vdc since 100 v is too close for comfort. 

As for fuse directionality changing the quality of sound I am sorry to say that I have done tests on this and have not observed ANY sound changes whatsoever. My ears are normal human ears not superhuman :).  So as far as PERSONALLY I am concerned fuses and how they are inserted, do NOT AFFECT sound. 

It’s an expression used by someone who still thinks there’s room for argument regarding aftermarket fuses and fuse directionality. A renegade. A refusenik.

What is a fuse believer?

Most speakers have a capacitor in circuit before the tweeter which blocks all DC.   The tweeter won't be harmed in this case.

I used a Phase Linear 700 without output relay for years, (original design had no relay) and it had multiple issues and would go full DC (105V) on  occasion.   Fuses protected the speakers each time this happened.  

Mechanical relays work as well to protect speakers.   Two solutions out there already, that are time tested, and my empirical experience confirms it quite well.   

failure with no fuse could burn your speakers and the amp pcb ...you flip the coin if it really makes a difference in what your ears tell you.

I have +/- 90 Volt rails.

This is more like it:

https://www.mouser.com/ProductDetail/Infineon-Technologies/IPB017N10N5LFATMA1?qs=sGAEpiMZZMshyDBzk1%...

100V, 180 amps, 1.5mohms (almost lower than the speaker wire itself), about 80 nanosecond turn off time (increase that becoz of inductive speaker load) and only about 8 bucks a piece.

I think you need higher voltage rating than 100V

http://www.geofex.com/Article_Folders/ampprot/dcprot.htm

As long as the MOSFETS stay hard on between 20 - 20khz it will be fine :-)

Yup- if they are On, then the frequency is almost irrelevant.

But there is no dark side of the moon; as a matter of fact it's all dark.

Even NASA uses fuses

That's how they got Apollo 8 to circle and come back, they just reversed the fuse as they went behind the dark side of the moon, the rest is history.

Unfortunately, these are about $220 -> $320 on average:

https://omronfs.omron.com/en_US/ecb/products/pdf/J144-E1-05.pdf

Hopefully an SSR will replace this.