Protective Circuit in Receiver (1 Viewer)

[Thomas Willard]

When playing a DVD with a sound track with special effects at moderate levels, the protective circuit of my Kenwood will trip and turn off the receiver. If I lower the volume and return to that point in the DVD, the receiver is OK.

The front speakers are inefficient suspension (AR-4x's). Am I just reaching a point where the receiver is trying to deliver too much power and the protective circuits are just doing their job, or is something else going on?

 

[ChrisWiggles]

It could be that you're driving the receiver too hard with inefficient, or low impedance speakers.

I would check all your wire connections. You may have a stray strand somewhere crossing terminals causing a short. I would disconnect, and carefully reconnect all the speakers to make sure this is not the culprit.

Also, make sure you have nothing underneath, or above the receiver. Give it plenty of airflow. Make sure it is not on carpet, for instance, as this will obstruct the airflow from the bottom, and of course dont cover it.

Lastly, something like a crossover, or a voice coil got fried in one of your speakers might have failed/caused a short. You could try to single out the culprit. If this is a newly occurring problem, then there has to be something wrong with connections, heat, or bad speakers somewhere.

 

[Thomas Willard]

Thanks for the input Chris. Since the problem only occurs when sound effects and not music is being played I lean toward your first thought that the receiver is tripping the protective circuit when asked to provide too many amps. During those sound effects the speakers, especially the front left and right might be at a low impedance.

There are two other possibilities. Perhaps as you say the cross over circuit might be shorting out under certain conditions. The other possibility might be the receiver protective circuit becoming too sensitive.

I will see if the problem reoccurs with greater frequency. if not then I suspect I might be driving the receiver just a little too hard. I know transistor finals can be easily blown, so it might be that the protective circuit is set accordingly.

I will try to recreate the tripping when the receiver is cold to see if heat build up could also be the cause.

 

[MikeTz]

An inexpensive workaround might be to raise the crossover frequency between your sub and speakers. Most of your amplifier's power goes to reproducing the lower octaves in the frequency spectrum. If you raise the crossover frequency from 70Hz to 100/120Hz you will ease the burden on your receiver amplifier enough so that the protection circuitry may not initiate. Give it a try.

MT

 

[ChrisLazarko]

I would agree with MikeTz's idea.

 

[Thomas Willard]

Mike:

Thanks for the input. Last night I did some troubleshooting. I found that the protective circuit trips even if the receiver is cold, so heat is not an issue. I found that if I put the receiver in stereo mode rather than pro logic II (or the case of my DVD Star Wars Episode I, Dolby 5.1) I can run high volume and the circuit does not trip at the same part of the CD. I think that rules out the front speakers and leads me to think that the receiver just can't handle a heavy volume level calling for sound effects. It could also be that the protective circuit is becoming more sensitive. I will watch and see if the receiver trips more often. If it does then that would lead me to think the protective circuit itself is the problem.

 

[MikeTz]

Thomas:

One reason the receiver may be trouble free in stereo mode and not in DPL modes is because in stereo the amplifier can use all of its energy for two speakers. However in DPL (or any of the Dolby Digital) mode the amplifier shares its energy with 5 or more speakers. On loud transient effects the amp may not have enough energy to supply all these speakers and it shuts itself down.

Raising the crossover frequency would result in the amplifier having more energy for the 5/7 speakers and put more of the burden on your powered sub (I'm assuming you have one). Most powered subs are equipped to handle these transient power demands.

MT

 

[Thomas Willard]

Mike:

I agree, in the 5.1 mode there probably is just not enough juice available to drive all of the speakers. In fact once I forgot and had both the A and B speakers on. The unit promptly shut itself down.

I do have a powered sub. I have a switch that either directs all frequencies to all speakers or directs the low frequencies to the powered subwoofer. Unfortunately the receiver trips regardless of the switch position.

The other possibility is that the protective circuit itself is the problem. If the receiver shuts down more frequently then that will prove that the circuit itself is the culprit.