JVC A-X9

[Ed400]

Hi,

I am working on a nice JVC A-X9.. The right channel very randomly produces a popping noise.. It could go hours without it, and suddenly, a few minutes with popping noises.
I narrowed it down to the pre-amp. Before I start replacing some transistors, I was wondering if anybody out there has experienced a similar problem. I suspect the culprit could be the FET pair of transistors encapsulated in a chip format. 2SK150A.
Any suggestions are welcome.

Regards
Ed

 

[JoseHH]

Hello,
there are some 2SC458 in this circuit. The old version of this transistor did exactly that. Zeners also can do this. The JFET is less likely to be the cause in my opinion.

 

[Ed400]

Hi JoseHH,
Thank you for your comment.
I replaced the 4 x 2SC1775 transistors with 2SC1845, as they were in the audio path and were the primary suspects. Interestingly, after replacing the 4 transistors, the popping noise came down significantly, almost completely. It used to do it once every 10 or 20 minutes. And now, after having the amp switched on for 4 hours while I was doing other stuff, I heard the popping noise again, only a couple of times.. I am glad I changed these anyway, and I may do the same with the other channel to keep things consistent. I'll keep testing, and my next target will be to replace the 2SC458.

 

[Ed400]

Hi,
Just wanted to report that the culprit for the popping noise was the transistor X320, 2SA899.
I replaced it (and I did the same on the other channel) with MJE350G. I also replaced the trim pots for the DC offset, which were too sensitive and replaced them with a 25-turn pot to allow better control.