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
)
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
)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....
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....
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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Yes! Thank you. This fixed the annoying whine going on with my unit.
How did you pull the black cables out though? I just removed the white tabs holding them in, but couldn't get the cables out.
Thanks again!🙂
How did you pull the black cables out though? I just removed the white tabs holding them in, but couldn't get the cables out.
Thanks again!🙂
in lieu of having your baby.....
I picked up a used RX-315 a couple of years back for $20 to replace an old head unit in my office. I tried every thing I could think of to get rid of that whine aside from taking the unit apart(That was probably why they got rid of it) and then finally decided to live with it. Today I had enough and finally decided to google it AGAIN and whadyano?
BIG THANKS MIEKEDMR!!!!!!! I was about to wear out the speaker selector from turning it off so much.
BTW, same leaky 6800uF caps here too. And,(axiozen) the white plastic tabs act to decompress the spring contacts on the receptacle. When you push them down, they should disengage the metal contacts that hold the tinned ends of the wire. You could also remove them and use a small flat screw driver to disengage the contacts manually and wiggle the wire from side to side and they will work loose.
I picked up a used RX-315 a couple of years back for $20 to replace an old head unit in my office. I tried every thing I could think of to get rid of that whine aside from taking the unit apart(That was probably why they got rid of it) and then finally decided to live with it. Today I had enough and finally decided to google it AGAIN and whadyano?
BIG THANKS MIEKEDMR!!!!!!! I was about to wear out the speaker selector from turning it off so much.
BTW, same leaky 6800uF caps here too. And,(axiozen) the white plastic tabs act to decompress the spring contacts on the receptacle. When you push them down, they should disengage the metal contacts that hold the tinned ends of the wire. You could also remove them and use a small flat screw driver to disengage the contacts manually and wiggle the wire from side to side and they will work loose.
Yes! Thanks, miekedmr. Finally got rid of that annoying hum. Removing the ribbon cables is how, though I applied more of a brutal tearing rending technique to get them loose. Probably should have read more carefully. The internet, she is a beautiful thing.
fixed the issue with the noisy JVC rx-309 amp
I picked up this amp off Craig's list. It also had the annoying whine from the speakers which level stayed constant regardless of volume setting. I disconnected the am/fm receiver cca as suggested above and it went away. I wanted the radio though. I discovered there was a small resistance between the chassis and signal ground. With a scope, I saw noise (1420 and 280 hz) from the + output to - output, but quiet from + output to chassis. I noticed a good deal of corrosion on the cca grounding points where the copper clad screws go through. I removed these screws all around the unit and cleaned up the pads and retightened the screws. The resistance and noise went away!
BTW, if anyone needs a service manual package for this amp, I have it.
I picked up this amp off Craig's list. It also had the annoying whine from the speakers which level stayed constant regardless of volume setting. I disconnected the am/fm receiver cca as suggested above and it went away. I wanted the radio though. I discovered there was a small resistance between the chassis and signal ground. With a scope, I saw noise (1420 and 280 hz) from the + output to - output, but quiet from + output to chassis. I noticed a good deal of corrosion on the cca grounding points where the copper clad screws go through. I removed these screws all around the unit and cleaned up the pads and retightened the screws. The resistance and noise went away!
BTW, if anyone needs a service manual package for this amp, I have it.
Hi all, new here and first post. I know this is an old thread but...
Hummin Hum Nailed it.
I had this issue also. Checked the two screws on the AM/FM CCA and they were quite tarnished... well the screws were ok but the pad that they screw into were hardly recognizable as metal. I did an ohms check between the head of the screw and chassis, 0.2 ohms.. not bad. I then did an ohms check between the pad that the screw tightens down on and the chassis and I had 320 ohms. Very bad. I removed the screws and used a kratex stick on the pads to remove the polish, reinstalled the screws, and now have 0.2 ohms pad to chassis.
Buzz 90% gone. Almost couldn't hear it.
I then decided to see if there were any other similar grounding schema on the other boards and I found two, one on the main board and one on the power in/relay board on the back left. I cleaned both with kratex stick and reinstalled and WOW zero buzz.
I wonder how many electrolytic caps have been changed out and the problem was accidentally fixed by removing and reinstalling the screws.
Thank you Hummin Hum, well done.
My neighbor has a similar hum in his Sony, I'll check it for the same/similar issue and report back.
Two other instances of grounding screw issues coming to mind immediately:
* several old Grundig amplifiers (I think SV2000 being one of them?)
* old Kenwood transceivers (manifesting as excessive drift)
Still not a super common problem absolutely speaking.
* several old Grundig amplifiers (I think SV2000 being one of them?)
* old Kenwood transceivers (manifesting as excessive drift)
Still not a super common problem absolutely speaking.
I have a JVC AX-R551 that, out of the blue, started humming, really load. Maybe at 7kHz... Tried different power outlets, plugging in RCA cables in/out, all sorts of "easy" fixes. Then found this thread - and lo and behold - after I turned the grounding screws of the main board 1/8 of a turn the buzz disappeared! So happy now... Grounding screws - I never even gave 'em a second look before...