DI box without phantom protection

[ricci]

Hello everybody,

i would like to buy the Mooer micro DI box and since it is not powered by the phantom but only with 9V, i would like to know if it is possible to protect the XLR output ( diode or other thing...) in case the sound engineer casually sends the phantom. I ask this because i have already asked to Mooer who confirmed that the XLR output is not protected against phantom.

Thanks in advance

[The Dude]

I'd have to see a schematic to be sure, but I'd think adding coupling/blocking caps to the XLR hot and neutral would work. That would keep DC from entering the unit but still allow signal to pass.

[Enzo]

That is what they do inside a mixer.

[ricci]

I'd have to see a schematic to be sure, but I'd think adding coupling/blocking caps to the XLR hot and neutral would work. That would keep DC from entering the unit but still allow signal to pass.

I don't know how the scheme is done but last night I bought a Mooer clone and after a couple of hours I have come to know that splitting the guitar signal, one towards the amp (LINK input) and the other (XLR) towards the mixer , the latter is weaker, so I guess there is not even a buffer, i.e. LINK and XLR are in parallel.

[The Dude]

Mic level is supposed to be lower than instrument level, so maybe the box is doing what it is supposed to be doing by adding some compensation to get the correct levels at each output.

[ricci]

I hope it is just a question of volume and not of sound deterioration

[Enzo]

Imagine plugging your hot guitar into a mic input. Link is likely direct and XLR is likely through a transformer. Unless the box uses active circuits and a power supply.

[ricci]

I don't know the schematic but I'm sure there is no transformer but op amp like the TL072.

[ricci]

The input called "LINK" is a copy of the hot guitar input signal so the sense is that the signal splits into "Y" and loses consistency

[g1]

The signal coming out of the XLR should be lower level than the link out. The XLR out is not parallel, it is buffered and usually attenuated.

[ricci]

The XLR out is not parallel

Sorry i was wrong to write, i meant that the LINK signal is a copy of the input.

it is buffered and usually attenuated.

But if the XLR out is buffered, shouldn't this compensate for the weakening of the signal ? Why attenuate Intentionally ?

[The Dude]

It's attenuated because it's meant to feed a microphone input on a mixer. If it were not attenuated, it might clip the mixer input. All direct boxes work this way.

[g1]

What he said above. Microphone puts out a much weaker signal than guitar, so the DI xlr out mimics the low level signal of a mic.
Some of the Mooer DI clones have switchable attenuation level, I guess yours does not?

[ricci]

Exactly, this Micro DI also has a switch to vary the gain by +/- 20dB but they seem like a lot to me... i'll see when Ii receive the product and even if the signal is a bit weak i think it can always be increased by the sound engineer. Ok, i'll let you know, thank you.

[ricci]

Pedal arrived and no transformer inside but electronic circuit with op amp 2262C, as seen from the attached image.
I tried it splitting the signal into both the amp input and the XLR inside the sound card and I didn't notice anything bad, on the contrary the Ground Lift switch pleasantly surprised me, in fact when activated it instantly eliminated that bit of hum that was there in the background.

Anyway, back to my phantom curiosity, I would be tempted to activate that on my sound card but I think it's not a good idea.