Vs65r Strange Noise Especially When Reverb Turned Up

bigfilsing

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Hi all
I have an issue with my combo and I'm hoping somebody can help identify the cause
On the clean channel (1) I have a slight hum that isn't really a problem but in the background, you can hear a faint repetitive clicking sound.
On the overdrive channel (2) the hum is almost gone but the clicking is slightly louder
On either channel when i turn up reverb the clicking gets really loud.
It makes no difference if a guitar is plugged in or not.

I'm not very experienced with amps but have a basic understanding of electronics
I have downloaded and printed the schematics
what I've done so far
Replaced the power switch ( unrelated)
Replaced the preamp tube ( i have 2 spares ......neither effects the issue)
Replaced the wire crimps at the transformer that attach the 0 (black) neg and pos (red) leads
Inspected both boards for the infamous bad solder joints / loose components
Replaced all the caps on the power amp board ( some looked old )
Tried disconnecting the reverb tank
Inspected the reverb tank internally

I haven't been able to identify the cause so far. The amp plays fine without reverb but id like to resolve this issue as well if possible. I'm hoping somebody recognises the sound.
I've made a YT video so you can listen to it. ( Headphone wearers beware Its bad)


All help and suggestions appreciated Thanks in advance
Cheers
Phil
 

m1989jmp

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Have you tried bypassing the eff. loop send and return with a cable? Have you cleaned the pots and jacks with a good contact cleaner? That's usually the place to start.

After that, try prodding various components with something non-conductive while the amp's on and take care not to short something out and also beware of high voltages, even after the amp's been of for 20-30 minutes.

Could also be a noisy IC.
 

bigfilsing

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Heh m1989jmp Thanks for the quick response. I've just tried the eff send return with a cable and no difference. All the pots are clean and working well No scratchiness or odd noises.

My next move will be to isolate reverb IC section. If I'm reading the schematic correctly removing capacitor C4 and resistor R61 should isolate the reverb send and return section
good idea-bad idea ??
picture attached
 

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chee16

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So when you turn down VR11 you are essentially disconnecting R61 anyways, so I think you have already isolating things to the reverb section. I would test the supply voltage for that IC and make sure it's correct and if you have a scope try to isolate things further, though I would guess that part of that IC is faulty. Is the IC expensive? I couldn't make out the numbers on that schematic.

It looks like VR10 is the master? With the reverb all the way down how does the master effect the noise?
 

bigfilsing

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Thanks for joining in chee16
with the reverb all the way down the clicking noise is barely noticeable
I will check the power to IC1 soon as well as identify what it is
Unfortunately, I don't own a scope (yet) ( this might be a good excuse to buy one)
There's also an electrolytic cap in the reverb circuit (C2) so ill be swapping that out as well.
 

chee16

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Not a bad idea to swap out cheap electrolytic caps, but if it still clicks with the reverb tank disconnected, then that cap is probably fine.
 

bigfilsing

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Not a bad idea to swap out cheap electrolytic caps, but if it still clicks with the reverb tank disconnected, then that cap is probably fine.
Ok, so I've identified the reverb chip as a quad op-amp LM348N and just so happened my local electronics shops had them in stock so i changed it . No change in clicking
Changed the C2 cap (47u 10V) in the reverb send and receive circuit No change
Measured the supply voltage to the chip ( P4+ & P11-) and it's 30.65 VDC which seems high !!???
 

m1989jmp

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Do you have something near the bench that could produce interference?

Upon listening it again, the noise seems periodic. Cell phone, WiFi router, neon lights? Does it happen everywhere in the house?

Edit: that voltage is fine if you're measuring between those two points. Measure each in reference to the ground, it should be half.
 
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bigfilsing

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Do you have something near the bench that could produce interference?

Upon listening to it again, the noise seems periodic. Cell phone, WiFi router, neon lights? Does it happen everywhere in the house?

Edit: that voltage is fine if you're measuring between those two points. Measure each in reference to the ground, it should be half.

Moved to other room No difference.
I have temp removed C4 & R61 which isolates the reverb send and receive section and still had the faint problem. So it would seem the reverb section just amplifies the issue and isn't the cause of it. Whats weird is the normal volume and gain and the overdrive channel don't amplify it. I can hear it faintly but it doesnt react to the increased volume or gain.
Thanks for confirming the voltage. I do indeed have -15 & + 15 volts at IC1 ( reverb op amps)
Just measuring from pin4 to ground with a multimeter i noticed the clicking noise got fainter !! Power rail issue i guess
Im now going to reinstate the reverb circuit to original.
Could the D5 or D6 zenners cause this kind of noise ??
 

bigfilsing

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Now with C4 & R61 back in and with reverb turned up to 20% if i measure the IC1 pin 4 and pin 11 to ground, the noise gets louder
 
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m1989jmp

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Now with C4 & R61 back in and with reverb turned up to 20% if i measure the IC1 pin 4 and pin 11 to ground, the noise gets louder

Try grounding the signal paths one by one from the input all the way to the speakers to ground. Be very careful not to short voltage supply in the process. When the clicking stops, your problem is around that area.

Only that way you'll be able to pinpoint the noisy section/component.
 

bigfilsing

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Try grounding the signal paths one by one from the input all the way to the speakers to ground. Be very careful not to short voltage supply in the process. When the clicking stops, your problem is around that area.

Only that way you'll be able to pinpoint the noisy section/component.

Ok Im pretty new to amplifiers but i think i get the idea
Unfortunately I've been called overseas for work for a couple of weeks so it will have to wait till i get back
Thanks for your help and ideas so far
 

bigfilsing

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It probably is the electrolytic caps. Just because of age I would change them.
I think that would be a good idea either way as while most look OK i don't trust them.
There's a couple positioned right next to a couple of 5 watt 330ohm ceramic resistors that have undoubtedly suffered from heat.
ill order replacements and swap them all out when i get back from a work trip
Thanks
 

ampmadscientist

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Hi all
I have an issue with my combo and I'm hoping somebody can help identify the cause
On the clean channel (1) I have a slight hum that isn't really a problem but in the background, you can hear a faint repetitive clicking sound.
On the overdrive channel (2) the hum is almost gone but the clicking is slightly louder
On either channel when i turn up reverb the clicking gets really loud.
It makes no difference if a guitar is plugged in or not.

I'm not very experienced with amps but have a basic understanding of electronics
I have downloaded and printed the schematics
what I've done so far
Replaced the power switch ( unrelated)
Replaced the preamp tube ( i have 2 spares ......neither effects the issue)
Replaced the wire crimps at the transformer that attach the 0 (black) neg and pos (red) leads
Inspected both boards for the infamous bad solder joints / loose components
Replaced all the caps on the power amp board ( some looked old )
Tried disconnecting the reverb tank
Inspected the reverb tank internally

I haven't been able to identify the cause so far. The amp plays fine without reverb but id like to resolve this issue as well if possible. I'm hoping somebody recognises the sound.
I've made a YT video so you can listen to it. ( Headphone wearers beware Its bad)


All help and suggestions appreciated Thanks in advance
Cheers
Phil


One other thing is:
Take the reverb tank out and check for broken wire / broken spring inside the tank.
When the spring breaks, it can cause a hum if the spring touches ground.

Measure the 2 coils that connect to the springs w/ an ohm meter.
(transponder coils)
Sometimes these coils open up, the coils can go bad occasionally.
Look at the RCA jack inside the tank and check for a broken wire.
I don't know why, (because it shakes around)
but the wire that connects to RCA jack seems to break a lot.

The tank has a number on it, which specifies replacement tanks.
 
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bigfilsing

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Hi guys. I'm back from overseas and have now changed all the caps in the amp. Some were leaky so it was definitely time for the re-cap. Unfortunately, the "clicking" noise is still audible.
Next step will be to trace the signal path and ground it out to try and localize the source. I'm still confused why it is only amplified by the reverb circuit. Its audible with the reverb pot turned down.

I seem to recall seeing that somebody had made a "test pen" to ground out the signal but cant seem to find that info anymore. Can I literally just make a ground lead to thee chassis then try various points in the signal path ??
All input appreciated
 

bigfilsing

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Just reporting in that this issue has finally been solved !!! Took the amp to a friends house. Guess what no more strange noise!! To say i was baffled is an understatement.
Turns out it was interference from my ethernet over power adapters ( TPlink) Doh !!! It occurs all over my 3 bedroom apartment Just so happens is my practice room is also where my computer is and as such the ethernet over power adapter hooks up to the internet in that room.
Think i may investigate a line power filter to see if that helps.

Thanks for all the support and input guys At least now i have recapped the whole amp and should be able to enjoy this amp for a few more years ( i tested some of the removed caps and they had drifted quite a bit)
Im still a bit baffled by it only really being audiable when the reverb is turned up but happy its working again
 


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