Diode on output?

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What would happen if i were to put a Diode on the output of my amp (hybrid)Faceing out(ie the current can flow out but not in)? Would it mess it up? my idea is i want to make some circuitry that measures the resistance the the positive to negitive connections of each speaker terminal when you first hook them up so if the load ever drops below 8Ohms it lets the groud of my power in relay float so it turns off and turns the amp off beofre damage can be done.

"Would it mess it up?"

For the time the diode was in circuit, the sound would be very distorted - you'd only be reproducing one half of the audio waveform. Not only would this sound bad, but it wouldn't do your speakers any good either. I say stick to more conventional protection circuits.

See ya,
Well i really kinda liked my idea about cutting the power off if the risistance was too low and could damage the amp (i had an AiwA that did this once it was the shiznit you could do anything to that radio and not hurt it) any circuit suguestions? i really want to protect my amp from overdraw
Output stage protection

Output stage protection is often done with two current monitors, typically measuring the voltage dropped across the emitter (or source) ballast resistances of the source and sink devices. Overcurrent in either device, as indicated by excessive voltage across the resistor, causes the overcurrent circuitry to steal drive from that device.

Once you developed the "overcurrent" signal, you could then use it to inhibit the entire amplifier if you wanted to, but the above approach works well.

A few years back Elector published an amplifier with an interesting protection circuit. It had an output relay and before it was switched on, the protection circuit measured the DC resistance of the speaker. If the resistance was above a certain value, then the relay was closed.

I'm not sure but I think it monitored the output emitter currents aswell and, of course, DC voltage on the output.

Perhaps that is what you are looking for?

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Diode on output

trwh said:
CryingDragon, here is an article that should answer your questions:


I do not agree to the core of this article. The V/I limiter doesnot switch off the current, but softly limits it to a preset value. There is no voltage spike as a result. The spike could only occur if the current is abrubtly cut off, but that is not the case.

LaughingDragon, you can *measure * the speaker impedance by putting a defined DC current into it and then check the DC voltage with a comparator to a preset voltage. Only switch on the relay if the comparator says it's OK.

Jan Didden
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