How much DC is tolerable on a tweeter?

[solderdude]

Infinity did it.

Spoiler: Kappa tweeter

View attachment 418076

It requires at least a series resistor before the zeners and a fuse. When there is no series resistor (and no fuse) the diode(s) will short and load the amp with the coupling capacitor which most amps won't particularly like.
Older Beyerdynamic headphones also had 12V zeners across the drivers but were intended to be driven from 120ohm sources.

 

[JohnnyAudio]

Zero DC

 

[SSS]

It requires at least a series resistor before the zeners and a fuse. When there is no series resistor (and no fuse) the diode(s) will short and load the amp with the coupling capacitor which most amps won't particularly like.
Older Beyerdynamic headphones also had 12V zeners across the drivers but were intended to be driven from 120ohm sources.

You are right, textbook recommends this. My thought is that the diodes are only for catstrophic failures of the amp itself. At regular mode if output voltage will reach the zener voltage then a extended current flow will occur at the zener voltage. Most amps are protected for overcurrent due to shorted output. If defect of the amp itself then there should be a fuse in the rails.

 

[SSS]

No special considerations, just the max voltage wanted across the tweeter. I think someone over at diyaudio measured increased distortion as the voltage across the zeners approached breakdown voltage.

EV used a different diode protection scheme. They used a full wave bridge across the tweeter. The output of the bridge would open a relay between the bridge input and the tweeter. Once the signal dropped below the relay hold voltage the circuit would reset.

Sure you get a somekind rectangle signal at when passing the zener voltage which causes much distortion. Under normal listening conditions there is no extra distortion due to the zener diodes.

 

[LionIT]

I resume this thread to ask something about speaker protection.
I have remedied an Hypex NC122MP to drive the mid driver of my R3s.
Unfortunately it emits a noticeable pop off, which from a raw measurement exceeds 100mV DC.
Maybe it won't do anything but I would like to be safe. Making a protection circuit or buying one it is too expensive honestly.
So I thought of using a relay to short the pos and neg of the amp as soon as I disconnect the power from the system, in order to avoid the current to the voice coil.
These Hypex amps seem to have single-ended output stage, not BTL, so I assume this kind of short-circuit is not a problem.
Am I thinking badly?

 

[DVDdoug]

Unfortunately it emits a noticeable pop off, which from a raw measurement exceeds 100mV DC.

Power = V squared / R so 100mV is 0.0025W into 4 Ohms or half that into 8 Ohms.

So I thought of using a relay to short the pos and neg of the amp

Shorting the output of an amplifier is a VERY BAD IDEA. But you could put a relay in series. ...I tried that on a car system that was making big turn-off thump from the subwoofer but I guess the relay wasn't fast enough and it didn't help. Awhile later the subwoofer amp died and the new one doesn't do that.

 

[egellings]

Ok, the title I think is clear.

In your opinion, how much DC is tolerable on a tweeter, both in continuous (DC offset) and in peak (turn on / off spike)?

I currently use a Neurochrome Modulus 86 Rev 2.4 with SMPS. The Modulus has a DC servo circuit with a dedicated opamp, which reaches less than 1mV of DC offset and a few tens of mV during shutdown with 8 ohm load (with the multimeter I can't see exactly the peak but this should be the order of magnitude).

The tweeters that I drive directly with this amp are those of the Kef R3 Meta Uni-Q (crossover bypassed), that I don't know exactly how much power they tolerate.

There are no DC protection circuits on the amp, but I think I'll put them in the future.
Apart from that, what do you think of the aforementioned DC values?

Tweeters don't get exposed to DC from an amplifier because the high pass filter between the amp and the tweeter blocks DC by way of using a series capacitor to carry the signal. You wouldn't want DC or bass frequencies to hit the delicate tweeter. It's possible that a tweeter could be damaged if the amplifier failed by hitting the voltage rail at a very high speed, and the leading edge is steep enough to carry damaging amounts of energy to the tweeter. I see that as unlikely, though.