Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #31 of 35 Old 03-01-17, 11:47 AM
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Re: Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture

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Lumen wrote: View Post
Just wanted to stress that the TRS-TRS connection for loopback timing is crucial for the Focusrite 2i2, which routes phantom power to both XLR inputs simultaneously. AFAIK, The 2i2 will suffer damage if an XLR-TRS connection is used for that purpose, because phantom power will be applied to the output. I learned this the hard way, but it's no longer an issue now that I'm aware.
The phantom power feed circuit looks like this:

Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture-phantom.jpg

or this

Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture-phamtom2.gif

The circuit is balanced, DC-coupled with a 6800 ohm source resistance. Any audio interface output circuit is going to have series coupling capacitors so I suppose it becomes a matter of the breakdown voltage of those caps vs the actual voltage applied across them with those series resistors. Seems like risk of damage is minimal. There will be a thump when Phantom Power is turned on/off, but that alone is not damaging to circuit components.

Edit:

The second diagram above shows the mic preamp input with phantom power feeding the mic itself. Replace the mic in the diagram with the output stage of an audio interface, AC-coupled (probably) and designed to drive high output levels (always). If each of the two balanced output drive devices can handle the 7 mA current (if not AC-coupled), then there should be no problem.

I am not saying it is impossible to fry an audio interface that way. IF you say you did, then you probably did. I would say it sounds like the output stage was under-engineered if you did.
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post #32 of 35 Old 03-01-17, 12:38 PM
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Re: Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture

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Phillips wrote: View Post
Hi please can someone tell me which is the better choice?
Thanks in advance
If you're still watching it's probably in amusement. I'm sorry for the sidebar that's not really contributing to your decision except to steer you toward the Roland.

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post #33 of 35 Old 03-01-17, 12:48 PM
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Re: Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture

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AudiocRaver wrote: View Post
I am not saying it is impossible to fry an audio interface that way. IF you say you did, then you probably did. I would say it sounds like the output stage was under-engineered if you did.
Your engineering analysis is a relief in the face of what few circuit skills I have.

I honestly cannot remember the exact conditions of the mishap, but I am certain it happened while trying to take a loopback measurement. Give a newbie a few instructions and look what happens! A couple years later, I'm ready for some more punishment in time-domain land; so I'll report back if I manage to destroy another one... this time paying closer attention.

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post #34 of 35 Old 03-01-17, 04:34 PM
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Re: Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture

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jtalden wrote: View Post
I didn't realize that the calibration process I suggested could damage the audio interface if the phantom power was not disabled. I think that thread should be deleted as it is very easy to make that mistake. I am surprised I have not made that mistake already.

Will the Staff please remove it? Link
I removed it.
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post #35 of 35 Old 03-01-17, 05:01 PM
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Re: Focusrite Scarlett 2i2 vs Roland UA-55 Quad-Capture

Thanks!
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