connecting the output of one Class D amplifier to the output of another and short circuit protection?

[olds1959special]

So I was playing around with my passive bi-amped speakers and accidentally ran the amps while the metal plates connecting the highs and lows were attached! Eek! I’m actually not sure if all four amps were on or only two, but I believe the short circuit protection was tripped because one pair of amps was kinda hotter than normal. So I turned them all off to cool down. I’m assuming I’ll be O.K. thanks to the short circuit protection in my Aiyima A70 mono amps.

 

[Everett T]

So I was playing around with my passive bi-amped speakers and accidentally ran the amps while the metal plates connecting the highs and lows were attached! Eek! I’m actually not sure if all four amps were on or only two, but I believe the short circuit protection was tripped because one pair of amps was kinda hotter than normal. So I turned them all off to cool down. I’m assuming I’ll be O.K. thanks to the short circuit protection in my Aiyima A70 mono amps.

Be careful, are you sure that's what the protection is for?

 

[olds1959special]

Be careful, are you sure that's what the protection is for?

I believe it is?

 

[NTK]

I believe it is?

Not really. You are driving the output of one amp into the output terminals of another amp, and short circuit protection is usually not to protect against that.

 

[olds1959special]

Not really. You are driving the output of one amp into the output terminals of another amp, and short circuit protection is usually not to protect against that.

So what exactly would be the consequence of doing it for a short time and then shutting everything down? I was getting sound as normal from the speakers, but it appeared only two amps were on. Maybe I never had them all running together, although they were all plugged in. Was this just a close call?

I googled to see about what would happen if the second amps were off and it said:

"Directly connecting the output of one Class D amplifier to the output of another is highly likely to cause severe hardware damage, even if one of the amplifiers is powered off. In this configuration, the active amplifier's power output is forced into the output circuitry of the second unit. Without functional short-circuit protection, there is no safety mechanism to disable the output stage when massive fault currents occur."

So is that why the amps got hot? Did the short circuit protection prevent immediate failure? Is the okay to still use the amps if they work?

I'm anxious about this. I was distracted by something when I did this.

 

[NTK]

So what exactly would be the consequence of doing it for a short time and then shutting everything down? I was getting sound as normal from the speakers, but it appeared only two amps were on. Maybe I never had them all running together, although they were all plugged in. Was this just a close call?

Hard to say. It is a complicated situation, and I am guessing several things happening ...

1. An amp's output impedance is very low, and will appear as a short for the other amp. If the amp A doesn't shutdown, it will drive a current through amp B, and the output transistors of both amps will have to dissipate that power. Not good.
2. Amp B will also be doing the same thing to amp A.
3. Unclear how each amp's protection circuit will react.
4. Unclear how the feedback circuit will react.
5. ...

 

[olds1959special]

I'm using my system now and it sounds fine. The amps are running cool like normal. Did I damage anything?

 

[levimax]

I'm using my system now and it sounds fine. The amps are running cool like normal. Did I damage anything?

Probably no damage if they are working normally.

 

[MaxwellsEq]

I'm using my system now and it sounds fine. The amps are running cool like normal. Did I damage anything?

Impossible to know without measurements of especially distortion. You may have caused some early aging which could result in shorter lifetime.

 

[popej]

Aiyima uses TPA3255 chips, which has multiple protections. Against shortcircuit, overcurrent, overheating. If it works now, then I guess amp is ok.

 

[olds1959special]

Aiyima uses TPA3255 chips, which has multiple protections. Against shortcircuit, overcurrent, overheating. If it works now, then I guess amp is ok.

When I think back to what happened, it seems the pair of amps for the lows was turned off. Then I plugged in the speaker cables, and realized my mistake. But I don't think I turned on the amps for the lows at all. The music kept playing as normal. I think the amps that were on were working normally and not affected by plugging in the second set of cables because the amps they came out of stayed off. When I said the amps seemed warm I realized later it was a normal level of heat (once the amps have been left on for a while.)

So I don't think anything happened at all.