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Advice on RFI with a new integrated amp

I need some assistance on my Exposure 2010S. The only input I am using is the cd player, but with volume turned all the way down, I am picking up radio signals. If I turn the dial to the moving coil phono setting, even though nothing is attached to it, I can hear radio pretty loudly.

The corner of the house where our stereo is in under the outside wires, and it sits right next to the terminal for our Verizon Fios -- not the most ideal location, but it
is the only option.

Using the CD pots on the amplifier, you can only hear the radio pretty faintly, when the volume pot is turned all the way down. If I am playing cds, you can't hear anything, but since when I switch to the phono/aux1 setting, as I mentioned, I am picking up radio signals, and
the volume is louder. From what I read (and hear), it appears that the phono pot (perhaps in cahoots with the moving coil phono stage) is acting as a antenna, and picking up signals, which are cross-talking
across the other inputs on the amp.

How would you recommend addressing this? I am currently considering
shorting terminators on the phono, and other output pots and found some terminators online (audiophilia article).

At first I thought it might be my changing the speaker cables, from very thick cables to the slimmer DMNs, but that would not explain why the RFI is louder at the phono input than any of the others.

Whatcha think? Does this make sense?

The other option would be RCA caps.

Thanks,

Marty
martyw
jea48
2,944 posts
 
Marty,

You might try some clamp-on ferrite beads on the power cord of the amp and on the speaker cables.
You never answered how long the speaker cables are....

RFI Tips And Tricks
Quote from Link:
AUDIO AMPLIFIERS
It's quite likely that the audio amplifier is performing RF detection. You need to place ferrites on the speaker cables as close to the audio output (right at the PC board if possible) with as many windings as possible. If it is audio detection, it won't matter at all how many ferrites you install on the power cord or cable TV or antenna cable although this will cut down on the amount of
RF getting into the TV via those conductors. Direct pick-up onto speaker wires causes most problems. Don't go into the television if it is not your own.

Jim
martyw OP
68 posts
 
Sorry -- they are 6 feet DMN cables
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almarg
8,673 posts
 
Jim, I really doubt that the writeup you referenced is applicable in this case. It is dealing with the situation where a ham radio transmitter, which typically may be outputting several hundred or even 1000 watts of rf energy, is interfering with a neighbor's tv set perhaps 100 feet away.

In that situation, yes, it seems conceivable that speaker cables in or connected to the tv set could pick up some of that energy, from where it would blast its way into the audio or video circuits of the tv and be rectified, and perhaps amplified as well.

With Marty's integrated amp, on the other hand, the speaker cables are likely to be picking up rf measured in microvolts, or millivolts at most, corresponding to nanowatts. That pickup will be loaded down to much less than even that low level, by the amplifier's output impedance (likely a tiny fraction of an ohm), and also by the speaker, which is not capable of reproducing low level rf signals unless they are both rectified and amplified.

The power cord and wiring would seem to me to be an unlikely entry point as well, due to the capacitive filtering, etc., that is in the amplifier between the ac input and the signal path.

Best regards,
-- Al
jea48
2,944 posts
 
Hi Al,

You are probably right but if Marty has some ferrite beads it won't cost him anything to try them on the speaker cables and or the power cord. Maybe the radio tower transmitting antenna is close to where Marty lives..... Or maybe it is a hi-power radio station.

The amp received a good review from Stereophile and I can't imagine the proper shielding was not incorporated into the design and build of the unit.

Is it possible the amp could sound good and still have a cold solder joint somewhere along a signal ground path?
Jim
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almarg
8,673 posts
 
Is it possible the amp could sound good and still have a cold solder joint somewhere along a signal ground path?
Yes, that certainly is conceivable, Jim, although of course it would be very difficult to troubleshoot.

Marty, I realize that this is all probably moot, because you are proceeding to look for a replacement amplifier, but I see in the thread that you started today that you actually did mention nearby radio transmitters. It would be interesting to know how far away they are, whether they are am or fm, how many watts they are (perhaps that is indicated on their website), and if when you hear them through your system you hear actual music and/or voices, or just static-like interference.

Regards,
-- Al
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