I need an Audio Detective

@jr96aolcom

This is one of those situations that will drive many audio-enthusiasts crazy. It really depends on how much work you want to put into this. You could simply keep the DAC off (along with all LED lighting) while listening to your tuners. That would be the easiest solution here.

Or, you could unplug all audio interconnect cables from the DAC (with the unit powered ON), and see if that makes a difference, and report back your findings. It’s very possible you *might* be able to reduce this RFI using ferrite on some of the DAC cables (which ones will need to be determined). One tuner (the Magnum) might be more sensitive to this RFI vs your other tuners.

Hmmm, an audio-enthusiast that still values OTA (over the air) FM listening. I'm impressed. 

@jr96aolcom

Is this the first time this has ever happened when both units were powered up, and you were listening to the tuner? Or have you never had a reason to power up the DAC before, when listening to your tuner?

It sounds like the DAC is emitting some RFI which is getting into the tuner circuitry. The question is, how is the DAC emitting this RFI; via audio interconnects, or AC cable? Is the RFI energy entering the tuner circuitry by each chassis being so close together? 

If I really want low noise FM reception, I have to turn off all LED lighting in my house. Most LED lighting and dimmers emit RFI which reaches into the FM and AM bands.

@jr96aolcom

For over 25 years I was Chief Engineer of a number of both FM and AM radio stations. I was always on the hunt for a tuner that provided to me at home (to monitor the audio quality of the FM station’s I engineered) the same performance of our station’s modulation monitors (which sample RF directly from the station’s transmitter output - no multipath of any sort is introduced). I found that one day in the Yamaha T-85 (I also owned a MR 78 at one point in time). If you’ve never tried one...

I was actually able to confirm the audio performance of the T-85 by installing a few (at different transmitter sites), and hooking them up to an A-B audio switch (A being the station’s modulation monitors, and B being the T-85). With audio levels matched, I could easily switch back and forth between the two, and the T-85 always sounded almost exactly like the modulation monitors. Just in case you were interested.

One last thing; for outdoor FM antenna reception, many times I used lower loss Belden 9292 (RG-11) over various RG-6 cables. It’s harder to terminate (as RG-11 connectors require a special crimping tool), but can help with fringe reception.

Belden 9292

So it's confirmed the DAC is emitting RFI garbage. I wonder if that RFI is permeating any other audio gear (besides the tuners) when it's ON, to the point it's having an effect on noise floors.