F1X DI out Radio Noise

[Picure]

I just did a soundcheck in Bejing China this morning and I was getting radio interference from the DI out. The ISO/GND switch had no effect. I ended up using the full range out into a Radial DI with the ground lifed which is now dead quiet. I had this same problem at another music festival in China last week too. Is there something wrong with my DI out? Because I read somewhere on this froum that Mica said that the full range output and DI share the same signal.

[edwin]

Did you have it set pre or post?

[Picure]

Did you have it set pre or post?

Post

[edwin]

Next time see if it does it in the pre setting.

[Picure]

Ok, Ill try it this weekend. Im playing in China... again. Haha

[mario_farufyno]

Did you have it set pre or post?

Does this matters?

[mario_farufyno]

I am less than a hobist and know just a little about electronics but I'm puzzled. DI and unbalanced output shares the same signal, we can see this in photos and schematics, the main difference is that the direct out has a transformer to balance the signal (doubling it, inverting copy's phase and matching their impedance before sending it through mic lines). Using it Pre or Post EQ shouldn't change much, specially if it is sounding ok using the unbal out through the Radial. The signal seems clean before the transformer. So may be there are some a differences in the way Radial shields its transformer to the way Alembic does.

Again, I'm not electronic wise, but may be there is a way to improve F1X RF shielding. The enclosure is metal made, but it is grounded?

I rehearse in a studio very close to radio station antenas and electromagnetic interference is a real concern (imagine me there with these Alembic's sensible PUs!). They use ferrite beads on every instrument cables asking you to not use yours and even instaling beads in AC cables.

This makes sense to our club's electronic gurus? Using inductors at AC cable would work for Picure? Is there a way to shield the F1X DI transformer better?

[mario_farufyno]

Just read about DI box transformers and they are smaller than the ones used on Amps (like F1X is) and totaly shielded. The metal enclosures itself should be shield enough, but some top DI boxes use transformers with some extra protection. Is Alembic's transformer like that? Looks like they are (I assume it is the shiny metal box right in the middle of the F1X pic).

[Picure]

Oh, and one more thing, up till now, the ISO/GND switch has not made a difference to the noise (when present) on stage or at rehearsals. Does the F1X ground switch work in a different way from regular DI ground switches?

[Picure]

Using inductors at AC cable would work for Picure? Is there a way to shield the F1X DI transformer better?

I have added a clip on ferrite bead on my AC plug for yhe F1X. The only thing I havent tried is using a AC cord without the 3rd ground prong and flipping the plug upside down when plugging into the outlet. This sometimes works for amps and stuff to cancel out electronic noise.

[edwin]

Given the nature of the noise, I'm suspecting that it isn't a grounding issue, which is why the ground switch isn't making a difference and that bypassing the third pin on the power cable probably won't, as well. The reason I suggested trying pre versus post is that post has a bunch more circuitry in the signal path and that might help narrow down where the noise is getting into the circuit. Another thing to try, if pre/post doesn't make a difference, is to try plugging the bass into the return and see if the noise goes away. If that's the case, the first thing I would do is to try changing out the tube.

Also, it might be worth checking that all the wires from the circuit board to the XLR are all properly connected and don't have any shorts/breaks.

[rv_bass]

I posted this on the one Twocan started.  Don’t know if it will help, but it has a few suggestions:

https://www.thegearpage.net/board/index.php?threads/does-your-amp-pick-up-radio-signals.281178/

[mario_farufyno]

Thanks, Edwin and Rob

[keith_h]

Is the tube shield in place? If this tube has been replaced but didn't fit the shield it might not have been reinstalled.

[Picure]

I just did 4 rehearsals in Taiwan with the F-1X and it was clean with the DI out, although the pre was a bit cleaner but I think that is because the post is much hotter than the pre, therefore raising the noise floor.