+48V Phantom Power Mic Preamp Loopback Input Question

G29

New Member
Thread Starter
Joined
Jun 20, 2019
Messages
31
I have a Focusrite 8i6 that has 2 variable gain balanced XLR mic preamp inputs with +48V Phantom Power and 4 fixed gain balanced TRS inputs.

The Focusrite 8i6 USB soundcard is clock synced to a USB DAC's clock.

I can't use the 2nd mic input for the loopback due to the +48V phantom power.

How can I select one of the 4 fixed gain inputs in REW ? The REW measurement window appears to only offer the left or right mic input, not any of the 4 fixed gain inputs.

Thanks much.
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
3,907
Which OS? If you are on Windows the Java drivers are limited to stereo channels by the Java runtime, but a soundcard will often have multiple entries for the various pairs of stereo channels it offers. If not, using the ASIO driver option should allow access to all the device channels. If your input and output are on separate devices you will need to use an ASIO wrapper to make them appear as one device for ASIO, such as FlexASIO or ASIO4All.
 

EarlK

Member
Joined
May 22, 2017
Messages
168
How can I select one of the 4 fixed gain inputs in REW ? The REW measurement window appears to only offer the left or right mic input, not any of the 4 fixed gain inputs.
There's no 48V phantom present on either of the channels 1 or 2, TRS input jacks.

Simply plug a TRS-TRS cable from output #2 into input #2 ( which is the neutrik combi jack found on the front ) .

2103-i-combo.png


:)
 

G29

New Member
Thread Starter
Joined
Jun 20, 2019
Messages
31
Which OS? If you are on Windows the Java drivers are limited to stereo channels by the Java runtime, but a soundcard will often have multiple entries for the various pairs of stereo channels it offers. If not, using the ASIO driver option should allow access to all the device channels. If your input and output are on separate devices you will need to use an ASIO wrapper to make them appear as one device for ASIO, such as FlexASIO or ASIO4All.
Thanks John, I am using Win7 Ultra 64-bit. I was using JAVA and it only showed mic channels 1 & 2.

If I switch to ASIO, I can not use JRMC's WMD directly, but it appears I can do so configuring the ASIO4ALL wrapper to utilize JRMC's convolver inputs and Focusrite 8i6's inputs [3-6].

If I select Focusrite's ASIO input directly (without ASIO4ALL), it won't all me to select JRMC's WMD, just Focusrite's inputs and outputs.

There's no 48V phantom present on either of the channels 1 or 2, TRS input jacks.

Simply plug a TRS-TRS cable from output #2 into input #2 ( which is the neutrik combi jack found on the front ) .

View attachment 38465

:)
That would burn out my DAC's output, thus the OP.

You can plainly see the +48V Phantom Power switch at the top of the front panel unit just to right of the input #2 gain pot. It applies to both combi-inputs and is also controlled by Forcusrite's Control Panel Software. It can not be configured to just apply to one of the inputs.

My microphone requires +48V phantom power, else it does not work.

Also, the DAC has XLR I/O, and the 8i6 inputs [3-6] are TRS, thus I need a XLR-2-TRS patch cable.

"... 48V – press to enable 48 V phantom power at the XLR contacts (mic inputs) of the Combo connectors. The 48V indicator illuminates red when phantom power is selected. ..."

g8804I43G-F.jpg
 
Last edited:

DanDan

Moderator
Staff member
Joined
Mar 10, 2018
Messages
412
Yes those Combi sockets are simply 1:1 TRS : 321. You can proceed with REW without Loopback.
If you ever get to the specific measurements or techniques which require such precise timing, you will know.
 

G29

New Member
Thread Starter
Joined
Jun 20, 2019
Messages
31
Yes those Combi sockets are simply 1:1 TRS : 321. You can proceed with REW without Loopback.
If you ever get to the specific measurements or techniques which require such precise timing, you will know.
FWIW, I purchased the Focusrite 8i6 specifically because it could be slave clock synced from the DAC's AES3 output and it appears loopback is also doable. It was also cheaper than a Lynx E22 or E44 and does not require an open PCIe slot.
 

DanDan

Moderator
Staff member
Joined
Mar 10, 2018
Messages
412
Many people use USB Mics. There is no Loopback channel. REW works without Loopback.
 

G29

New Member
Thread Starter
Joined
Jun 20, 2019
Messages
31
Many people use USB Mics. There is no Loopback channel. REW works without Loopback.
I have a Cross Spectrum Labs calibrated UMIK-1 that I am moving away from due to separate unsync'd mic and DAC clocks.
 

EarlK

Member
Joined
May 22, 2017
Messages
168
@G29

If you get yourself a multimeter ( and after plugging in a TRS-2-TRS cable into the 1/4" input of the neutrik combi jack for channel 2 ) you'll find the there's no dc ( phantom voltage ) to be measured at the other end of the cable ( measure Tip to Sleeve + then Ring to Sleeve ).

>>> FYI, I've measured my own Scarlett 2i2 ( as described ) .<<<

The units OM should clarify for you what the Neutrik combi-jack is .



:)
 

DanDan

Moderator
Staff member
Joined
Mar 10, 2018
Messages
412
My apologies EarlK, I have wired Combis here but it was some time ago. I guess there is choice to bridge or not in the design. Room anomalies are up to 30dB in magnitude. For measurement purposes perhaps you could omit some of your gear. e.g. the DAC or the Focusrite.
 

G29

New Member
Thread Starter
Joined
Jun 20, 2019
Messages
31
@G29

If you get yourself a multimeter ( and after plugging in a TRS-2-TRS cable into the 1/4" input of the neutrik combi jack for channel 2 ) you'll find the there's no dc ( phantom voltage ) to be measured at the other end of the cable ( measure Tip to Sleeve + then Ring to Sleeve ).

>>> FYI, I've measured my own Scarlett 2i2 ( as described ) .<<<

The units OM should clarify for you what the Neutrik combi-jack is .



:)
Thanks for the clarification. If the TRS is wired differently than the XLR on the same physical port, I find that design choice an expensive accident waiting to happen. Maybe too clever of a design for the uninitiated.

Again, the DAC does not use TRS so a XLR-2-TRS would still be required.
 
Top Bottom