Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Ivan Feder]

Hi PSW,
I am looking for a quick way to make an adapter that would not pass 48 v when I plug in a mixer output into to my sound card.
I have a Focusrite Scarlett which when the 48 v button is on, sends to both inputs. I don't want to send 48v to the mixer output as this could fry it! I am using Smaart with a mic on input one and a ref signal from the console on input two.
Thanks for your advice,

[Scott Holtzman]

Hi PSW,
I am looking for a quick way to make an adapter that would not pass 48 v when I plug in a mixer output into to my sound card.
I have a Focusrite Scarlett which when the 48 v button is on, sends to both inputs. I don't want to send 48v to the mixer output as this could fry it! I am using Smaart with a mic on input one and a ref signal from the console on input two.
Thanks for your advice,

You need to build a filter using a simple RC time constant.  Total resistance is twice the impedance so 1200 ohms.  You may get a bit of HF rolloff so see how it sounds.

One of theses in series with each of the audio leads.  https://www.parts-express.com/22uf-100v-electrolytic-non-polarized-crossover-capacitor--027-324

You could also put 100kohm resistor to ground upstream of the capacitors to bleed off any excess current without loading the circuit.

[Mike Caldwell]

Hi PSW,
I am looking for a quick way to make an adapter that would not pass 48 v when I plug in a mixer output into to my sound card.
I have a Focusrite Scarlett which when the 48 v button is on, sends to both inputs. I don't want to send 48v to the mixer output as this could fry it! I am using Smaart with a mic on input one and a ref signal from the console on input two.
Thanks for your advice,

Transformer isolation would do it. Since your using it for measurement you want to get a good transformer.

[Todd Friemuth]

Is going XLR to TRS an option for you? I use an Eridol UA-25 interface, not a Focusrite, but that is all I do to get around the 48V issue. The TRS inputs don't get phantom on my UA25.

[Ivan Feder]

Transformer isolation would do it. Since your using it for measurement you want to get a good transformer.

thanks for your answer, a simple 600/600 Ohms transformer would work?

[Ivan Feder]

Is going XLR to TRS an option for you? I use an Eridol UA-25 interface, not a Focusrite, but that is all I do to get around the 48V issue. The TRS inputs don't get phantom on my UA25.

Hi, I think going to TRS is not an option as the inputs on the Scarlett are combo XLR/TRS

[Scott Holtzman]

thanks for your answer, a simple 600/600 Ohms transformer would work?

Freq=0 Inductive Reactance=0 so yes current transfer will be 0 however I would still use the DC blocks to keep from loading the interface considering the low DC resistance of the windings on the transformer.

[Pete Erskine]

Hi PSW,
I am looking for a quick way to make an adapter that would not pass 48 v when I plug in a mixer output into to my sound card.
I have a Focusrite Scarlett which when the 48 v button is on, sends to both inputs. I don't want to send 48v to the mixer output as this could fry it! I am using Smaart with a mic on input one and a ref signal from the console on input two.
Thanks for your advice,

No transformer needed, just non polarized caps in each side - pin 2&3

[John Roberts {JR}]

No transformer needed, just non polarized caps in each side - pin 2&3

Yes capacitors are cheaper than a transformer. For that size (22uF or larger) you will probably use polar caps so orient the + leads toward the higher voltage source. Note: caps are in series with pins 2 and pin3, leave pin 1 hard connected.

JR

[Mike Caldwell]

Yes capacitors are cheaper than a transformer. For that size (22uF or larger) you will probably use polar caps so orient the + leads toward the higher voltage source. Note: caps are in series with pins 2 and pin3, leave pin 1 hard connected.

JR

If you go DIY with a little finesse your could probably fit the caps into an XLR connector, if there's not room to fit two caps in one connector put one on the appropriate connections at each end of a short DC blocking cable or build it into an XLR barrel connector.
You can by DC blocking XLR barrels as well.

I was assuming you may have a iso transformer laying around to save building or buying something.

[Keith Finch]

As Todd Stated use a F-XLR to TRS no 48v power is supplied to the 1/4" socket on the interface. It will also get you in LINE level mode

[Tim McCulloch]

Uh.... how about lifting Pin 1?

Phantom power *ground* is on Pin 1, +48v is on pins 2 & 3.  Lifting pin 1 means no ground and no phantom power.

[Pete Erskine]

Uh.... how about lifting Pin 1?

Phantom power *ground* is on Pin 1, +48v is on pins 2 & 3.  Lifting pin 1 means no ground and no phantom power.

Somewhere your system will find a common ground....

[John Roberts {JR}]

Uh.... how about lifting Pin 1?

Phantom power *ground* is on Pin 1, +48v is on pins 2 & 3.  Lifting pin 1 means no ground and no phantom power.

Do you feel lucky?

Mixer is most likely grounded. Sound card ?? don't know.

Caps are cheap and will block DC current from flowing. If sound card is not grounded it might still float up to 48V from cap leakage. Small (high value) drain resistors from sound card side of lines 2 and 3 to pin one will drain leakage from the caps.


JR

[David Sturzenbecher]

As Todd Stated use a F-XLR to TRS no 48v power is supplied to the 1/4" socket on the interface. It will also get you in LINE level mode

^^ This

[Ivan Feder]

^^ This

Thanks to the board ,
I will measure the TRS to see if there is in fact no 48 v across the connector. If there is , I will probably try a transformer since I have an in-line one lying around. Plan C will be the caps across pin 2&3.
Thanks to all,
Best regards from Paris!

[Dave Garoutte]

Or you could get a remote phantom power supply for the mic and leave the Phantom off on the Scarlett.

[David Sturzenbecher]

Thanks to the board ,
I will measure the TRS to see if there is in fact no 48 v across the connector. If there is , I will probably try a transformer since I have an in-line one lying around. Plan C will be the caps across pin 2&3.
Thanks to all,
Best regards from Paris!

I just measured my Scarlett 2i2 and there was no phantom on the 1/4" when there was on the XLR.

[Ivan Feder]

I just measured my Scarlett 2i2 and there was no phantom on the 1/4" when there was on the XLR.

Thanks David for measuring for me :-) Problem solved

[Justice C. Bigler]

I guess I'm late to the party, but the Scarlett 2i2 (assuming you have a 2i2 or 2i4) manual says that phantom power is supplied only to the XLR connections and not the 1/4" sockets. Which, being that the 1/4" sockets are also TS and TRS, could royally fuck up the guitar electronics if they passed 48v to the instrument input also.

[Ivan Feder]

I guess I'm late to the party, but the Scarlett 2i2 (assuming you have a 2i2 or 2i4) manual says that phantom power is supplied only to the XLR connections and not the 1/4" sockets. Which, being that the 1/4" sockets are also TS and TRS, could royally fuck up the guitar electronics if they passed 48v to the instrument input also.

Yes I have a 2i4 and thanks for looking up the info, Justice 

[ProSoundWeb Community]