Idea to reduce RFI

>> 06-21-08: Kirkus
>> If you want to eliminate an RF interference problem,
>> then you must take the system completely, totally
>> apart, then add each component to the system one at a
>> time to see the point at which the RFI appears.
good advice, in general.

>> That is, start with just power amp and speakers.
Now, how does Milen007 get music to play thru the speakers? Run the CDP directly into the power amp? If yes, the 2V CDP will most likely saturate the power amp input stage & cause high SPL (distorted) sound. He could buy some in-line attenuators but then that's costing Milen007, which he might not be willing to do (?)

>> Second, if you can hear the audio signal (modulation),
>> it's an AM transmitter, not TV, or FM,
Theoretically you are correct - FM is constant envelope modulation. However, in really life due to interference from buildings, foliage, terrain, etc the FM signals are somewhat AM. So, the possibility of catching a FM station thru Milen007's system is quite real.

>> And third, the 'balanced' nature of balanced
>> interconnects have no effect on RFI
this statement could NOT be further from the truth!! It seems to be a statement you have made out of total ignorance in the matter.
Go look at any RF layout whether it is I.C. layout or PC board layout & you will see differential circuits used exclusively! Differential circuits ARE balanced circuits. It is one very important way to curb RFI.

>> very few balanced input stages have much common-mode
>> rejection above 3KHz or so.
Another terribly ignorant statement!! If your statement is true then the designer of that circuit has failed miserably!
If the designer has designed the circuit correctly the CMR frequency range would be atleast upto the -3dB corner & even upto the unity gain frequency of the circuit.

One cheap, easy way to see if interconnects are your problem is to temporarily try the typical cheap ones that come w/VCRs, you know the type(i.e red/blue/yellow, 3 all together). Sonically they suck, but they are very well grounded! If RFI disappears with them, you'll know to upgrade to good grounded interconnects.

Search the archives for advice on grounding your system as a whole. Best solution is one ground from the rig to a copper rod buried outside. You can read for hours on best way to do this.

Power conditioners suck the life out of most amps. Avoid if possible.

The suggestion to rearrange gear 90 degrees, didn't mean to move it to a different wall. Just turn each component 90 degrees on its shelf and see if it makes a difference.

Another crazy thing to try is take aluminum foil and wrap it around where interconnects attach, particularly on preamp. Jud Barber of Joule Electra suggested this to me a long time ago when diagnosing an RFI issue. If it helps, try adding Cardas caps on your unused inputs and outputs. Cheers,

Spencer

You can't hear RFI. The RF signal must be demodulated. Corrosion at a connection can create a diode which provides the demodulation. So, clean all your connections.

I have never experienced the RFI problem except long ago with a turntable/phono (high gain) connection. I have experimented with trying to induce the problem using cordless phones and cell phones activated just inches away from the audio equipment, but I hear no effect.

>> That is, start with just power amp and speakers.
Now, how does Milen007 get music to play thru the speakers? Run the CDP directly into the power amp?

Uh, er, you don't LEAVE the system this way for listening to music. You stick your ear by the speaker to see if, in the original poster's case, the offending "radio channel" can be heard. If it can, then the interference MUST be solved in this configuration BEFORE it can be reliably solved in a more complex one.

the FM signals are somewhat AM. So, the possibility of catching a FM station thru Milen007's system is quite real.

Nope. FM interefence on baseband audio electronics is manifested mainly has hum and buzz, that changes in intensity and timbre as cables are moved around.

>> very few balanced input stages have much common-mode
>> rejection above 3KHz or so.
Another terribly ignorant statement!!

Whatever, dude. Actually, 3KHz is even quite optimistic, especially for active balanced inputs -- most I've measured deteriorate up from 60Hz by at least a single-order slope.

For more information on the subject, I recommend Bill Whitlock's excellent papers (available at jensentransformers.com), which I agree with the vast majority of. I also highly respect the work of Douglas Self and recommend reading all of his stuff . . . even though on this particular subject I differ with his conclusions.

>> For more information on the subject, I recommend Bill
>> Whitlock's excellent papers (available at
>> jensentransformers.com), which I agree with the vast
>> majority of. I also highly respect the work of Douglas
>> Self and recommend reading all of his stuff . . . even
>> though on this particular subject I differ with his
>> conclusions.
Kirkus, thanx for the reading recommendations. I'll check them out.