I am in the process of of repairing my Parasound JC1 amplifier. I have built a light bulb current limiter cable and tried it on my good amp (at least it is used to be). When I turn on the amp the inrush current is making the bulb light up but the protection board relay is triggering off/on cycle that repeats over and over. The caps do not get a chance to charge up. I am using 100W incandecent bulb (highest wattage I have available). I suspected it would not work for this amp but I haven't powered on the good amp in a while (not sure if it is still functional).
What would be my other alternative? I do not have variac. I believe we have Chroma in the office that can generate various AC mains voltages and shapes. Should I try using it and set the voltage lower than 120V? Any suggestions?
What would be my other alternative? I do not have variac. I believe we have Chroma in the office that can generate various AC mains voltages and shapes. Should I try using it and set the voltage lower than 120V? Any suggestions?
You might want more than one bulb in parallel if you can. This may be normal behavior for the amplifier when it cannot fully power up.
It seems to me that the light bulb & protection relay board are doing exactly what they should given the situation of
an amplifier that has a fault.
an amplifier that has a fault.
I do not have another 100W bulb to run in parallel (just 75W). There is no voltage on the bulk caps, the AC protection triggers before they start charging I guess.
I will have to dig up the model # of chroma I have at work. I believe it should have delayed current limiter (0.5s resolution) and can set it to trigger 1s after the initial power on (unless someone can recommend another delay), but not sure if it is powerful enough to work with this amp. It should in low bias mode. In high bias mode it was pulling around 250W or 300W from the AC mains (depending on the bias setting) if I remember correctly.
I see ...
after googling, your AMAZING amplifier (a bit like mine = 1400W @ 2ohms) with its class A region probably runs at quite high quiescent current.
My thinking is that you should disconnect the input to 'protection circuit board' and then see what the light bulb does before increasing its wattage.
PS.
How bright is the bulb?
after googling, your AMAZING amplifier (a bit like mine = 1400W @ 2ohms) with its class A region probably runs at quite high quiescent current.
My thinking is that you should disconnect the input to 'protection circuit board' and then see what the light bulb does before increasing its wattage.
PS.
How bright is the bulb?
It is hard to say how bright the bulb gets due to very short duty cycle. Though it doesn't appear to get to full brightness based on my biased opinion. Here is the short video showing what's going on. I did see that protection kicked in once and when stopped attempting to power on the amp. It took 5 attempt cycles, but I believe typically it will go indefinitely. On the DMM I am showing positive voltage rail.
tested the bulb current limiter on couple of subwoofers. It is working as expected. On more powerful subs (i.e. SVS PB13ULTRA) it lights up quite a bit during the initial inrush but it doesn't stay on for more than 1 second. Though the bulk capacitance inside that amp is nothing to write home about in comparison to JC1 power amp.
Please ignore the DMM readings I have posted earlier. I wasn't measuring the rail voltage. Bulk caps have 30 some V when I measure them after trying to power on and stay at that level nearly indefinitely. I guess there is no discharge resistor. I didn't see it on the schematic.
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The "good" amp powered on without issues when I connected power cord straight into AC outlet. The bulk caps get discharged to 11 some volts right away when the power is turned off so switching to bulb afterwards didn't work. Perhaps the only option I have is to run multiple bulbs in parallel. Did anyone tried installing the switch in parallel with the bulb and turn it on during power on sequence? It is probably too risky. I wonder if caps have enough energy stored (33000 uF times 4 , plus some little ones) to destroy output transistors in with AC disabled...
That's a good question ... you are dealing with some pretty high voltage & HEAPS of stored energy.
I'm pretty sure if you post schematic information there would be some members able to offer you more valuable advise.
PS.
Given the sheer power of the amp, 100W + 75W bulbs together would probably be a reasonable situation.
I'm pretty sure if you post schematic information there would be some members able to offer you more valuable advise.
PS.
Given the sheer power of the amp, 100W + 75W bulbs together would probably be a reasonable situation.
I was able to power up the unit with 4 bulbs. 100/75/75/75W. I also tried once with 100/75/75 and it worked after a few cycles of protection board triggering. Even with 4 bulbs protection may trigger, but will start. The bulbs are glowing even in low bias setting. Thank you to Mister Audio and daqvin_carter. I assembled the repaired amp back but when was connecting driver board found a cold solder joint on the GND connector. Perhaps it contributed to the failure. This is new board I bought from Parasound!