[JakeJ]

If this is in the wrong circle just send it where it should go.

So the other day I'm listening to FM on 102.3 local Jazz station when I reach down to the next lower shelf and turn on my Musical Paradise MP-D2 DAC and the radio goes silent except for some faint crackling.  Turn the DAC off and the signal returns.  I can tune up or down the dial ~50 to 100MHz and pick up stations but not in the dial zone from about 101.7 to 103.1.  Below is a diagram of the physical location of the gear.



The tuner is a Naim NAT-05 feeding the preamp, a Grace Design m920, and the DAC is my MP-D2.  I can't think it is anything other that physical proximity of the DAC and tuner to each other.  The obvious fix is to rearrange the two so they are not close to one another and not vertically stacked.

Any thoughts?

[TomS]

There are clocks in the DAC which could radiate and interfere with the tuner. What is your antenna setup - coax, dipole, outside?

[JakeJ]

Didn't think it was the antenna, it's a dipole sitting on the preamp.  I did move it around and that had no effect.

[aldcoll]

Is there a external power supply for the DAC mod or is that all internal?

I would try some coax and move the antenna a ways away , just thinking?

I have to have mine about 8 ft away from the audio area.  And I thing the issue is my cable box.


Alan

[JakeJ]

Hi Alan,

No external boxes with the Modwright mod.  I plan to try moving things around tonight and see what the results are.  It's an old Radio Shack with a captured 300 ohm antenna wire.

[TomS]

Didn't think it was the antenna, it's a dipole sitting on the preamp.  I did move it around and that had no effect.

Having the dipole antenna in close proximity to the DAC vs a shielded coax connection to an outside antenna would likely make a big difference. As you said, the best experiment is to move the DAC away from the antenna connection into the tuner and especially the dipole itself. By design the antenna picks up whatever RF it can sniff and a dipole would pick that up nicely. Easy enough to try 

[Phil A]

Perhaps something in the DAC (transformer?) causing RFI?

[gregfisk]

It seems quite obvious to me Jake, the Dac is jealous

[JerryM]

I'd swap the DAC and tuner positions, i.e. preamp remains where it is but now sits atop the DAC. Does the phenomena remain the same?

[Steve]

If this is in the wrong circle just send it where it should go.

So the other day I'm listening to FM on 102.3 local Jazz station when I reach down to the next lower shelf and turn on my Musical Paradise MP-D2 DAC and the radio goes silent except for some faint crackling.  Turn the DAC off and the signal returns.  I can tune up or down the dial ~50 to 100MHz and pick up stations but not in the dial zone from about 101.7 to 103.1.  Below is a diagram of the physical location of the gear.

..........The obvious fix is to rearrange the two so they are not close to one another and not vertically stacked.

Any thoughts?

Yep, you understand Jake.

For public, RF oscillation harmonic signal leaking from the DAC is much stronger than any station signal at the frequencies Jake cited, even over loading a little, as evidenced over a couple of mhz, and is in essence jamming, as military did jamming communications in WW2 etc.

At those frequencies, a shield is not a perfect shield, more importantly, any opening will allow RF to escape. Moving the offending components apart will fix problem, but what distance is necessary, trial and error. I get a feeling it may be some distance though, due to strong leakage signal.

I am sure Jake will let us know the distance necessary.

cheers

steve

[WGH]

Maybe your DAC needs a hat

[Doublej]

I'd rotate the DAC 90 degrees and see if the issue is gone.

[guest61169]

Substitute another dac and if the problem goes away send the Musical Paradise packing?

[JakeJ]

It seems quite obvious to me Jake, the Dac is jealous

How dare I listen to that bitch tuner!  All that incredible junk spewing out around the clock.  Harumph!  Listen to me, your music server.  I have all your favorite music, you know you want to.

I'd swap the DAC and tuner positions, i.e. preamp remains where it is but now sits atop the DAC. Does the phenomena remain the same?

Can't do that because the DAC has tubes sticking out the top of the chassis.

Yep, you understand Jake.

For public, RF oscillation harmonic signal leaking from the DAC is much stronger than any station signal at the frequencies Jake cited, even over loading a little, as evidenced over a couple of mhz, and is in essence jamming, as military did jamming communications in WW2 etc.

At those frequencies, a shield is not a perfect shield, more importantly, any opening will allow RF to escape. Moving the offending components apart will fix problem, but what distance is necessary, trial and error. I get a feeling it may be some distance though, due to strong leakage signal.

I am sure Jake will let us know the distance necessary.

cheers

steve

Hopefully this evening.

Maybe your DAC needs a hat

 

Mighty funny!

[JakeJ]

First, apologies for misinforming you.  The diagram above is wrong.  The empty bottom shelf actually has my Audio Magic Stealth XXX power filter, the DAC is sitting directly on that and second shelf has my CEC TL-51X disc spinner on it.  I was going on my bad memory and forgot I had tried the DAC on the middle shelf and swapped it with the spinner because the rectifier tube was maybe a half an inch from the bottom of the top shelf and I really didn't like that.  I was still going on the thought the Stealth XXX and the TL-51X were on the bottom so no need to put them in the diagram  Then comes the tuner and preamp as shown.

So the tuner is playing right now.  I turned on the DAC and listened to the sound die from the speakers.  I picked up the tuner and preamp and lifted them straight up about ten inches.  Still nothing.  Then I moved them to the right about six inches while still at the height I lifted to and lo and behold the sound returned.  Simple positioning, who'd a thunk it.

I was in too big a hurry to hear it after it returned from Modwright Instruments I didn't really pay attention to component placement.  Plans are to get the system settled for some serious listening to the MP-D2 with Modwright mods.

Life's always in flux .

[2wo]

I think the clock frequency is jamming your tuner, ether that frequency band or one of the tuner oscillators.

In any case do you need to have the DAC on when listening to the radio?     

[poseidonsvoice]

Jake,

Thanks for sharing. I’m in agreement with TomS as to the theoretical reasoning.

Many of us may not own tuners as such we may not experience what you did but we do learn from it and it is fun to understand why.

Best,
Anand.

[*Scotty*]

Here is a hypothesis, the tuner has a gated input which prevents overload of the front end of the tuner if a broadcasting station transmitter is too close and the signal strength is too high. The DAC may have a clock or other oscillator that is causing RFI at those frequencies on your FM dial at a very high amplitude and the gating is being triggered.
 As you have found, proximity to the offending DAC is the problem and it appears that you have it solved
I have encountered similar problems with switching power amps interfering with radios as well as TVs.
Scotty

[Steve]

So the tuner is playing right now.  I turned on the DAC and listened to the sound die from the speakers.  I picked up the tuner and preamp and lifted them straight up about ten inches.  Still nothing.  Then I moved them to the right about six inches while still at the height I lifted to and lo and behold the sound returned.  Simple positioning, who'd a thunk it.

Ah, yes, very high frequencies are very directional. The jamming signal has a typical radiation pattern from the leakage point. Move out of the pattern and the signal is reduced significantly.

Glad it all worked out ok Jake.

steve

[Tone Depth]

If repositioning didn't work, it may have been the radio station broadcast interrupting. I experience that occasionally listening to analog radio broadcasts.