I know this is an old post but I have a pair of JC1 monos that are about 2 years old and the exact same thing happened! Listening to music at low volume and turned it up a little bit and POP!! Like a firecracker and smoke! It was the exact same thing on mine! Everything on the left rail was burnt. At parasound now getting looked at. I bought them from the original owner so no warranty for me! Lol! Anyone else had this happen? What was the repair bill? Funny thing is I bought them to try while my Krell FPB-350m monos are getting recapped! Now I’m SOL for a while. |
Excessive DC can be caused by a DAC that is direct-coupled or even a preamp that is out of whack. |
Angela - the bias pots can actually drift, or a component can fail to cause high bias currents.
DC on the inputs can cause the amps to shut down as well. You should measure the DC on the outputs of the preamp. If it is more than 15 mV, this is too much for many amps.
Steve N.
Empirical Audio
Manufacturer/modder |
they all are enjoying music Audio Girl! |
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Audioengr,
What would cause excessive DC offset on the input to the amp?
How can that be resolved?
My friend also said that sometimes when he would cut his house lights on or off, the amp would shut off for 3 or 4 seconds, the halo light would turn red, then it would come back on and resume normal operation.
His house lights and appliances are on different circuits than his JC-1's.
What would cause this?
Thanks again for your excellent responses.
Angela |
Seadogs1, I suggest you contact your dealer and/or Parasound as mentioned above to discuss problems you may be experiencing. John Curl does not visit this website and rarely gets involved in service matters. Tony or Bob can help you. |
I've repaired some of these type problems. If the amp is shutting down intermittently, there is at least two reasons:
1) there is excessive DC offset on the input to the amp
2) there is excessive bias current to the output transistors - this can be caused by a failing output transistor or an out of adjustment bias pot |
Perhaps it's time for Mr. Curl to enter this. I too have the shut down problem for seconds at a time then everything is normal. I think it may be connected to the protection circuit of the amp except there is no reason it should be kicking in. Any thoughts by John would be much appreciated. |
The Parasound amps do have a protection circuit for extreme low impedances (as in a damaged speaker). This will turn off the unit before blowing up (usually). If your buddy blew it up once then there are probably parts that sustained damage but tested ok at Parasound. THese parts were likely starting to give out before the thing finally blew up (again). It has been my experiance that once an amp has been blown up it will never be the same unless you replace everything inside the chasis (in which case you might as well buy a brand new unit).
I guess that the 10-15% discount from retail that the average retailer is willing to give looks good after buying used, repairing used, then having to decide if repairing used is worth it the second time. Not trying to add insult to injury but sometimes it is better to drink fresh beer than second hand champaign.
Sincerly, good luck to your buddy. Having big $$$ go up in smoke is tough. |
Guys,
Thanks for all your replies!
My friend has his JC-1's plugged directly into dedicated outlets.
Unfortunately, he bought the units used about 15 months ago, so there is no warranty on them.
He did have this amp repaired by Parasound in July 2005.
He accidently dropped an interconnect on the speaker cables where they exit the amp, and it caused a short circuit and they had to replace all the output transistors, mosfet drivers, fuse, some resistors, emiter diodes, etc.
This time, however, he did nothing wrong...the amp just self destructed.
He also said that the amp hadn't acted completely normal since it was repaired. He said it would shut itself off occasionally for a few seconds, then resume normal operation. He said when it would do this the blue halo light around the power on button would turn red.
He said this would happen up to 4 times per hour on certain days, and was totally unpredictable.
Thanks again for all of your responses!
Angela |
Thanks for posting, Richard.
Regards, |
First thing I came up with was one transistor not up to par, before reading all of the posts. can almost guarantee thats really the only thing capable of that unles a ground or power wire came lose and shorted, but common whats the chances of that? It had to be a shorted transistor from overheat or something, maybe not in perfect contact with the heatsink, they use a grease kinda stuff to make contact, something happend. |
Sometimes you just get a bad part no matter how hard a manufacturer screens components. The failure shows up down the road. It would be hard to say if the output transistors failed or something up the line failed (as in the power supply.) It has been my experience that when one output transistor blows, it takes a few with it.
With that said, I don't think the JC1's are less reliable than any other high quality amp would be. Just chalk it up to s--- happens. Parasound should have no qualms about repairing the amp under warranty.
I owned a pair for a short while and one of mine like to shut down regularly for no reason. It would shut down even in stand-by. Never did figure it out. One day, it stopped doing it. It was only one of the pair. It also seemed strange that the transformer in this particular amp hummed right loud vs the other one being dead silent.
Lot of high quality parts in these things but nothings perfect. |
Possibly some internal component failure or a potent power spike through the AC line could be responsible. Does your friend use a surge supressor or does he plug the amps directly into the wall? |
That sounds bad but assuming no damage was done outside of the amplifier the 10 year warranty from Parasound should take care of any problems. I haven't heard of the JC-1's doing that. I don't think that this is a problem that is happening in the JC-1's on a regular basis. The company should replace the amplifier without any hassel I would imagine. |
Ask John Curl, he is a regular here. http://www.audioasylum.com/audio/general/bbs.html |
Why don't you contact the tech dept at Parasound?
The techs with the most JC 1 experience are Tony Pointes at 415 675-7273 7am to 2pm or Bob MacDonald at 415 675-7274 10am-5:30pm.
Tell them the serial no. of the unit.
Richard |
Same thing happen to me with a Carver Lightstar reference amp. Blow out sixteen transistors all with a wonderful haze of smoke and burning wire. At least that is what a tech told me after openning the amp.He also said it happens when manufactures place cheap transitors in their gear to cut cost. |
Angela, this is rare as far as I know, but when a JC-1 gets into a runaway condition a domino effect of output device failure is possible. Your friend should contact Parasound service, toll free 866-770-8324, and it probably wouldn't hurt for him to let his dealer know of the occurrence. A nice thing to know is the warranty is ten years parts, five years labor. Best of luck!
Brian |
