Seriously guys, the McIntosh fan bois appear to be ganging up and not clarifying anything here.
E-Stat may be a little difficult at times, but nobody has clarified the way the MC501 power guard and thermal protection works.
The Powerguard in the MC501 is just a simple circuit that attenuates the input signal to the voltage stage. It is not magical. It simply compares the signal input voltage to the padded down feedback from the output stage and turns on an LED that causes a ubiquitous LDR to go low in resistance and shunt some of the input audio to ground.
Bottom line: PowerGuard turns the volume down for you.
The thermal protection shuts the amp down. Each channel has its own NTC thermistor and sensing transistor switch. Nothing special here either.
The current limiting is separate, conventional in nature and not monitored or displayed.
The fact that it shut down after 5 mins at 1/3 power suggests to me that there may have been a dodgy NTC in one channel or it was a very hot day in JA's labs. Or it is simply, a poor design.
You cannot dismiss the very preconditioning tests that lead to the quality gear we now treasure, just because one mighty Mc failed in this regard.
We know the current limiting is separate, I have already explained this umpteen times, but it appeared to be upsetting Mr E-Stat.
I also pointed out the Sentry circuit function.
The wording was not correct in the article, nothing more nothing less, it was misleading as to how the thermal protection functions
The thermal protection works like this according to the schematic I have here, the thermistor senses the temp which is in turn using a driver transistor can utilize the Sentry Circuit to reduce the current load of the output section and ultimately reduce the temperature of the said output section.
My point was, which was ignored by only one person, is that the thermal state is measured by the Thermistor (Thermal sensor), not the Sentry Monitoring Circuit (as McIntosh call it), I'd describe what they call the "Sentry Monitoring Circuit" as a simple current limiter circuit.
The thermal sensor can also shut down the amplifier completely, I haven't looked at that part, but in most cases it will shut down the main DC rails and disconnect the output from the speaker, I admit I haven't studied this part so cannot go into detail at this point.
Nobody said there was anything unique or special about it at all, lots of amps have protection built in, which in my opinion is a good thing.
I would like to think it was a faulty Thermistor or or other faulty component, but perhaps, the thermal management was not up to the task, but seriously, at 30W it shut down, to me this suggests fault.
We certainly do not see people complaining of their 501's shutting down every other day.
Maybe we'll never know what the issue was.
