RFI STEREO

[flintstone mop]

Hello my friends
This is an OLD subject, I know, BUT I have a sound system that's getting RFI from my station.
I narrowed it down to the input. If I disconnect the input cable from the stereo it goes away. I started breathing easier, because of speaker leads, AC power cord, etc. I tried wrapping the input cable in ferrite beads and cores and all I can do is reduce the RFI. I need to get inside the unit to bypass the RF to ground. I'm thinking that it would be a disc capacitor from the hot side of the audio connector to ground.
The question is what value??
Any other thoughts are appreciated too.
Summer is here!!!!!!

Fred

[WA1GFZ]

How about an overbraid shield and float the shield at the stereo input.
Adding caps might mess up frequency response if you go too high in value.

[ve6pg]

..FRED..RF FILTERING "POWER BARS",AND 3 CONDUCTOR WIRE (2 WIRES AND SHIELD) HAVE WERKED FER ME...
...SUMMER IS HERE TOO IN TORONTO....94*F THIS AFTERNOON,AND VERY HUMID...TIM...SK..

[k4kyv]

I once had the same problem with a transmitter speech amp.  I found it better to place a 2.5 millihenry rf choke in series with the hot audio lead, than bypassing the input with a capacitor.  If it is a high-Z line, it doesn't take much capacitance to affect the high frequency response, especially with a stereo amp which presumably carries more than just speech.

[flintstone mop]

I'll have to do a little more research. I might be able to cure the problem with a different core material. I wrappped several turns of the offending cable around a Radio Shack type of ferrite core. And this only reduces the RFI. I have a similar setup in the same room for a Satellite XM Receiver and wrapping the input cable around a core of material laying around completely removed the RFI.....go figure

Fred

[W1RKW]

Fred,
How about some small ferrite beads on the input of the first transistor stage (right on the leg of the transistor) or at the jacks themselves.

[flintstone mop]

Thanks Bob
This will require surgery inside the woofer cabinet, it's one of those computer speaker systems.
I found another one of those ferrite blocks that splits open and it's bigger than the Radio Shack unit. Maybe this will be the magic one. I wrapped about 8 turns around it. I'll have to do some 'dead band testing'.

Fred

[K6JEK]

Fred,
How about some small ferrite beads on the input of the first transistor stage (right on the leg of the transistor) or at the jacks themselves.

Many transistors don't have legs anymore.  There are surface mount devices with no room for beads on legs.  I've had some nasty RFI problems and have solved them all without cracking open any cases.  If you want nice looking but not cheap filters ICE has some  http://www.iceradioproducts.com/filtersrf2.html#1   I ended up homebrewing cables with mix 77 ferrites which I got from Amidon http://www.amidoncorp.com/aai_specifications.htm

Good luck,

Jon

[flintstone mop]

Thank you all,
I'll check out the RFI website, right now I think my problem is reduced enough that my wife is happy.
The outlook inside the box looks like IC's and no chance for ferrite beads. Where did the good ole days go?
Fred

[flintstone mop]

Hate to bring this to the Forum again BUT 
I don't know what kind of service ICERADIOPARTS gives you guys, but they are VERY slow. I ordered a filter from them June 8 and have not recieved it. They do say that there are backlogs 1-3 weeks..........geesh. They do not answer any email, I guess it's time to call. They did not charge my card yet.

Thanks
Fred

[k7yoo]

A ground rod driven through the center of the offending device--silver plated works best, especially during a full moon

[AB2EZ]

Since the input of the stereo is a high impedance (typically 10k ohms or more)... you can fix the problem by doing the following:

In a small plastic project box... install four (4) RCA jacks (not grounded together)

One pair of two (2) RCA jacks will be used to make a filter for the Left channel, and the other pair of jacks will be used to make a filter for the Right channel.

Connect the center conductors of the Right channel pair of jacks with two (2) 2200 ohm resistors in series. Likewise, connect the grounds of the Right channel pair of jacks with two (2) 2200 ohm resistors in series. Connect a 1000 pF capacitor between the point point where the two 2200 ohm resistors of the center conductor connection come together, and the point where the two 2200 ohm resistors of the ground connection come together.

Do the same for the Left channel connectors.

The above will attenuate RF by more than 40 dB, but will not affect the audio.

Stu

[flintstone mop]

Thanks Stu,
I printed your info and I'll build up the filter you described.
Fred

[flintstone mop]

Hello Gang
Sorry to report that the I.C.E. filter on the input did not help. The RFI was coming in on the AC side. I installed an isolation transformer I had in the shack and hooked the LCD TV, video stuff and the little sound system to it and the RFI is gone.
Must have been a hot spot for RF 'cause there is no RFI to any other electronics in the house.
Fred

[W5AMI]

I'll have to do a little more research. I might be able to cure the problem with a different core material. I wrappped several turns of the offending cable around a Radio Shack type of ferrite core. And this only reduces the RFI. I have a similar setup in the same room for a Satellite XM Receiver and wrapping the input cable around a core of material laying around completely removed the RFI.....go figure

Fred

Fred,

I got 23 clamp on ferrite beads from www.radiodan.com.  These are the proper mix and work a lot better than the RS types do.  I have a surround sound system, satellite, etc.  The ones I got are the RCT-4 23 for $50.  Not cheap stuff, but they work wonders.  I wrapped as many turns of all the input leads into the amp as I could.  I didn't need to wrap the speaker leads at all.  I can key my 8877 to 2KW now and get no RFI, only some faint lines on the TV screen.  No, I didn't use all 23, but you can never have too many of these RCT-4's laying around for new RFI problems.

Brian

[flintstone mop]

Brian
thanks. Very good site for other goodies. Good deals on some amps. I'll check out the ferrite cores.

Fred

[wb1aij]

I have a neighbor about 5 0r 6 houses away that said they heard my voice coming out of their computer speakers very clearly. They could identify my voice and hear every word clear as a bell. The solution? I switched to SSB. Now they can't identify my voice or understand a word I say. Works for me.

[Ed - N3LHB]

Fred,

Don K4KYV had it right... at the input put a 2.5 mh choke on the inpoot with a 200 pf cap at each end to ground. That should kill any rf trying to get in to your system. I've used the same before and it works perfectly... Try it, you'll like it...