[DrewWinters]

I've done some searching and tried to track down the source of my problem, but to be honest, I just don't have the time right now to teach myself everything I need to know, so I was hoping someone could help me with a problem without screaming "go search noob!"

I'm hearing a radio station very softly in the right channel of my 650's. The sound exists with the source turned off and it does not get louder or softer with changes in volume - so I figure it must be coming in after amplification takes place, but I don't really know enough how an amp works electrically to make sense of it. Also, the sound disapeers with volume below ~5% and above 95%, but otherwise does not change volume.

My setup should appear in my signature, but besides that, I should note that it is plugged into a wall socket that is directly grounded. That is, when I moved in the house wiring was not properly grounded at all, so I "installed" a grounding rod and ran a grounding wire directly to the socket that my system runs off of. The only other item plugged into it is a HEPA filter, but its being turned on or off made no difference either.

Any help you can provide would be much appreciated. I will double-check the grounding tommorrow just to make sure, but otherwise I'm not really sure what to do next. TIA!

 

[gordolindsay]

I have the same problem but I have a SS amp and not a tube amp. When I was reading on how to try and fix my problem, someone with a tube amp answered. He told me that he wrapped tinfoil around the tubes in his amp and it fixed it. Try it and see what happens.

 

[DrewWinters]

Would that not get the tubes really,really hot?

 

[Jazper]

easiest solution is a faraday's cage kind of arrangement (earthed)

Chicken wire or metal plates with lots of holes in them, arranged in a box type arangement over the tubes, or even the entire amp.

 

[rickcr42]

Move the amp to a 45 degree angle to what it is now and see if the sound goes away.If yes then you need to reposition your amp because it just happens to be in the path of a strong radio signal.Tilting the amp will "detune" the station hopefully.
That is the easy fix.

If not (or moving is not possible) you most likely have a very high input impedance which is making your amp a radio and the fix is to put RFI protection devices at the input.If possible inside the amp but if not right at the jacks externally and by "right at the jacks" I mean exactly that or you wil accomplish nothing but pretty decorative ferrites on the cables

 

[Glod]

Has it always been like this? Or did it suddenly just present it self? Do you hear the same phenomenon if you disconnect completely from the source or change source? Is it the same if you plug in the amp in another room?

I have heard of similar issues with equipment located very close to high effect broadcast masts. Is there a local radio station in the vicinity? Perhaps a pirate station...?

I don’t know what causes this phenomenon. I am just collecting troubleshooting data

The question is obviously; what does pick up the radio signal, the mains, amp or a wire somewhere?

 

[rickcr42]

Quote:

what does pick up the radio signal, the mains, amp or a wire somewhere?

if it was on the mains would not be a clearly heard signal but noise.since this IS recognizable radio signal it can only be coming in on the input .Mosy don't ralise a gain stage and a radio reciver are very close to the same thing with the most difference being you can tune a radio without moving it

With audio gear you have a gain stage somewhere that if it receives a radio signal at the input will "amplify" that signal making it audible.The only way to get rid of it is either get rid of the source of the RFI (not practicle),move the gear out of the path of the RFI (sometimes practical) or filter it out at the beginning before it enters the gear (best method,should already be in ALL gear)

 

[EdipisReks]

i had the same issue, and putting ferrites around the interconnects as close as possible to the amp cleared it up.

 

[Mikey01]

Quote:

Originally Posted by EdipisReks i had the same issue, and putting ferrites around the interconnects as close as possible to the amp cleared it up.

That does the trick in most cases. If you still need more than that then recable the 650's. Use a cable that has a good well knitted copper braided shield around it. Ground the copper shielding to the 1/4" plug end or if it is an interconnect, ground to the end being plugged into the source, not the other end. Be sure to ground one end only with the shielding and that must be the source end. This will carry away the RFI to the source for grounding. Do the positive and negative headphone terminal post as you normally would and in your 1/4" plug as well. While making the cables you can heatshrink a snap together cable magnet to each source end just after the plug as well. If that don't do it then sell out and move.

 

[DrewWinters]

But since the volume control does nothing to the signal, doesn't that mean it is entering the system after the gain?

I just got home and turned the amp on, so the tubes aren't warm yet (does that matter) but I can only hear the tiniest whisper (~1db) so this may not be something I can easily reproduce, or it may only be a problem late at night when the ionosphere is not so charged (and thus the signal is stronger; I remember this much from back when I operated HAM gear in approx. the same frenquency band as FM radio). I have only noticed it late at night - but then, most of my headphone listening is late at night.

I have only begun to notice it recently and I have also just recently rearranged my room, placing the audio gear on the opposite side of the room... but I sure hope that isn't the problem because it was quite a hassle moving everything around and there really isn't another place to put it now...

Thanks for your replies so far, I will do a little more experimenting tonight but I have very limited time to devote to it... grad school is a bear ya know...

 

[DrewWinters]

Well, the sounds definitely get strongly later at night, also, they go away when I unplug the interconnects. I tried wrapping the interconnects in Al foil, but that didn't really seem to do anything, nor did moving the amp around.

 

[rickcr42]

Did you try ferrites on the input cable ? The sinple test would beto yank a couple of your computer susyem (monitor,printer maybe.etc) and try them out and if that cures the problem shoot down to a computer store or a radio shack and pick up two.
The other option though ones less common is the signal is rinding n on the output cable and feeding back through the feedback loop.A simple 47-100 ohm resistor between the amp and cable should fix this

 

[DrewWinters]

I don't have any ferrites around to try, but I'll try to make it over to the Radio Shack to pick some up. I can't say I've ever bought any before... is there something in particular I should be looking for?

So I be dissapointed with the Zu cables? I'm not a big believer in cables (not a nihilistic either though) but I thought I had picked good enough cables that this would not be a problem. ??

 

[rickcr42]

radio shack $5.50

http://www.radioshack.com/product.as...t%5Fid=273-105

but they really are available all over.Freebies can be had on the AC cords to moniyors if you have a couple kicking around