JVC RX-315 amp high pitched whine - diyAudio
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Old 17th May 2007, 03:43 AM   #1
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Default JVC RX-315 amp high pitched whine

I recently got a cheapie 2nd hand JVC amp. There was a fairly quiet but totally annoying treble hum coming through the speakers at all times. It didn't matter which input the amp was set to or whether there was anything besides an output connected toit. The hum was especially apparent when using headphones and would make my head ache after a while.

I searched online to see if anyone had the same problem, and only saw one post on another forum with no replies. I decided to fool around with the amp a bit and see if I could make the hum go away.

Open the case and there is a secondary circuit board mounted above the main one in the back right corner. That's the AM/FM tuner. I found that by disconnecting the two black ribbon-like cables from the board, the intereference disappeared.

So! It would seem you either have to live with the hum or give up the radio tuner. I do not listen to the radio with this, so it was a perfect solution for me.

Now the signal to noise ratio seems very reasonable. There is only a faint hiss when the amp is turned up all the way, beyond where it would ever be during use.

This is just here as a reference, for anyone else with this otherwise decent amp. (I would have replied to the one post I found on the other forum, but I couldn't register with any of my email addresses )
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Old 14th July 2010, 05:17 AM   #2
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Default RX-315 Whine

I have that amp and took it out of service when it developed a whine. On the o-scope it appears as a square wave with small duty cycle ... low level and around 1.2 KHZ as I recall ...

I will check and see if it is coming from the FM receiver as you found... strangely however, it seemed to go away after cycling the speaker outputs on and off while running a test square wave into the unit....

I thought it might be due to leaking electrolytic capacitors that bypass the DC supply ... the old 6800 uF caps look like they leaked out onto the circuit board. will measure and replace them when I get a chance....
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Old 14th July 2010, 12:00 PM   #3
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often in machines like that can have leacky electrolytics in the tuner area that might drive the tuner in oscilation and for a couple of times this oscilation was effecting either pre or main resulting a tone or a hiss in the output no matter what input selected ...
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Last edited by east electronics; 14th July 2010 at 12:18 PM.
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