Dummy Loads with the PLWO Tripping the DCP

mlucitt

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#1
Good time to bring this up, I hope Joe will chime in because this is in the theoretical realm. With a PL 400 on the bench, I use my 8 Ohm 300 Watt resistors as dummy loads to measure the loaded output voltage of the amplifier. But if the amp has one of the DC protect boards installed, it will kick the amp off when I connect one of the dummy loads. As soon as I unplug the big power resistor, the amp comes back online. So naturally, the DC Protect board does not like the dummy load, but an 8 Ohm speaker is fine?

Thoughts?
 

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#2
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

The DC protect "should" allow the use of a dummy load unless something is not right with it.
 

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#3
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

I have tested this one of Don's and when you get below a hundred hertz it doesn't like the continous low freq sine wave. I haven't got it to accept a signal over 200 watts continous with both driven, whether that is a sign of something wrong I don't know, continuous low frequencies are pretty rare. In that amp[litutude and duration. We seem to be able to trip these at will on the bench, but in system tests I don't think we even get close.
 

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#4
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

The lower in frteq we go the more it looks like DC to it, so maybe as a percentage of the signal, or harmonic factors come into play. Maybe a load resistor has a little different look at low freq??
 

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#5
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

Is that what you are seeing too Mark? As long as it is AC with no large DC offset, I don't see why it would be tripping.
 

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#6
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

Ok with one channel loaded and driven I can get this Ser II to 288 watts befor the DC protect trips, I am not seeing a distortion component of any magnitude yet. This is at 20HZ. With both channels loaded and driven I get to 70 watts output before tripping. Also no distortion seems present, and the DC protects source voltage is the AC side of the BR. It starts at 59.78 volts and only drops to 57.80 there is another sense voltage it uses also, have not monitored that yet.
 

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#7
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

I will monitor DC at the outputs and see if we have any significant amounts there.
 

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#8
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

I don't know how well my Fluke 179 can reject AC while looking For Dc as the DC reading jumps around quite a bit, but did see 1.734 volts Dc a few times. And it tripped just after that .
 

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#10
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

With one channel driven I saw some over 2 volt DC spikes, but once again was that what was really there.

Joe, I recently acquired an HP 400F Voltmeter, would that be more suitable to what I'm trying to do here??
 

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#11
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

You would be better served putting an RC filter on the output and seeing what the average voltage does on the scope. I am assuming you are running a sine wave into the amp Lee. Correct?
 

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#13
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

Gepetto said:
I am assuming you are running a sine wave into the amp Lee. Correct?
Yeah.. that has me scratchin too... How and were did you see a 2v DC spike on the scope? Was it a flatline on the waveform around the zero volt crossover points?
 

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#14
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

On the 179 i was in DC mode and had it hooked to the outputs while driving and monitoring with the AP and Leader scope.
 

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#16
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

Ok, what do i do to whip up a RC filter?? .1uf?? 200 volt with a 10 ohm resistor??
 

mlucitt

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#17
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

I was using 2kHz and the only thing that comes to my mind is that the wire wound resistor is ringing and the feedback is causing the DC Protect board to trip. I'm not sure how the uPC1237 IC deals with inductive resonance. Maybe a capacitor in parallel with the resistor would reduce the resonance.
 

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#18
Re: Jerry's "Gonna Rebuild me PLWO 1000" thread

Na, I'm thinking that would ring like a bell then.
 

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#20
My Fluke 179 was seeing DC on the outputs while the Leader scope was checking the wave and the AP was generating signals and doing the output level test. The 179 was flashing DC numbers, but only briefly, hence the spike moniker.
 
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