• Techniques
  • What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 14:15:08
AdamGrossmanLG
Hello,
forgive me if this is a "noob" question, but I have an AKG C214 mic plugged into a Presonus TubePreamp with an XLR cable (phantom power on at the tube preamp phase).   
 
Then I am connecting the preamp to my audio interface.   I notice it works when I connect the preamp to the audio interface via XLR and also via TRS cable (using an XLR>TRS cable converter).   

I notice when I use the XLR cable, the signal is much louder than when I use the XLR>TRS converter to go from the preamp to the audio interface.
 
I am unsure the difference besides the volume, but is one preferred over the other?

I also see I have an UNBALANCED output, not sure what that is either.
 
Thank You!
2016/02/28 14:40:09
fret_man
It is often assumed the signal on a 1/4" TRS cable is much bigger (i.e., line level) than the signal on the XLR jack (i.e., mic level). So you're interface probably has more again for its XLR connection to make up for the assumed smaller signal. Apparently your Mic Pre has the same level of signals for both connections, so it'll sound louder due to the extra gain your interface has for its XLR connector.
 
Regarding balanced and unbalanced signals, balanced signals will ALWAYS be better than balanced signals, although it may only be noticeable for small signal levels or long cable lengths. The disadvantage of balanced signals is they require balanced cables, jacks, and electronics which are more expensive than the single-ended (AKA unbalanced) counterparts.
 
By "better" I mean balanced signals pick up less hum and interference since the shield carries no signals - only interference. The two never have a chance to share conductors (whereas for unbalanced signals the shield carries both the interference and the signal ground). Also, balanced signals inherently have less 2nd order distortion when the signal gets very big (i.e., both half-cycles of the waveform will clip ~equally, while for unbalanced signals usually one side clips before the other). Finally, balanced signals do not suffer from common-mode effects. This is one reason why phantom power works so well. But again, usually the differences are not great unless the signal is very low (10's of mV) or cables are long, arguably 20' or so.
2016/02/28 14:47:13
mettelus
I am glad I reread this before I responded. By "XLR->TRS" you are referring to an "impedance matcher" I am assuming, which is terrible to use except under extreme instances. I actually have one of those lying around here somewhere and forget the specs on it, but it's something to throw into a drawer and forget you own TBH.
 
Quick answer - Run XLR->XLR (or TRS->TRS). Same cable (balanced/shielded) with different tips basically.
 
Balanced means that a mono signal is running down what is essentially a stereo cable (same signal both paths), which makes them less susceptible to noise and you can run longer runs of them without issues. This is why microphones use them, and also why you never see a recommendation to use a 3' XLR cable.
 
XLR has an advantage over TRS in that you can SEE the connector, and know it is balanced inside the box. A TRS jack looks identical to a TS (tip-sleeve) which is unbalanced, so unless you know (read the manual) that the jack is a TRS, you may in fact have an unbalanced run going on (a TRS connects fine to a TS jack, but only one path is connected losing its noise reduction purpose, i.e. no longer balanced).
 
Bottom line, for signal routing you always want to run balanced cabling and XLR is the most common (especially for your case).
2016/02/28 15:07:01
AdamGrossmanLG
fret_man
It is often assumed the signal on a 1/4" TRS cable is much bigger (i.e., line level) than the signal on the XLR jack (i.e., mic level). So you're interface probably has more again for its XLR connection to make up for the assumed smaller signal. Apparently your Mic Pre has the same level of signals for both connections, so it'll sound louder due to the extra gain your interface has for its XLR connector.
 
Regarding balanced and unbalanced signals, unbalanced signals will ALWAYS be better than balanced signals, although it may only be noticeable for small signal levels or long cable lengths. The disadvantage of balanced signals is they require balanced cables, jacks, and electronics which are more expensive than the single-ended (AKA unbalanced) counterparts.
 
By "better" I mean balanced signals pick up less hum and interference since the shield carries no signals - only interference. The two never have a chance to share conductors (whereas for unbalanced signals the shield carries both the interference and the signal ground). Also, balanced signals inherently have less 2nd order distortion when the signal gets very big (i.e., both half-cycles of the waveform will clip ~equally, while for unbalanced signals usually one side clips before the other). Finally, balanced signals do not suffer from common-mode effects. This is one reason why phantom power works so well. But again, usually the differences are not great unless the signal is very low (10's of mV) or cables are long, arguably 20' or so.




 
thank you for your response.  
 
I do believe you meant to say "balanced signals will ALWAYS be better than unbalanced signals, right?"
2016/02/28 15:09:53
AdamGrossmanLG
mettelus
I am glad I reread this before I responded. By "XLR->TRS" you are referring to an "impedance matcher" I am assuming, which is terrible to use except under extreme instances. I actually have one of those lying around here somewhere and forget the specs on it, but it's something to throw into a drawer and forget you own TBH.
 
Quick answer - Run XLR->XLR (or TRS->TRS). Same cable (balanced/shielded) with different tips basically.
 
Balanced means that a mono signal is running down what is essentially a stereo cable (same signal both paths), which makes them less susceptible to noise and you can run longer runs of them without issues. This is why microphones use them, and also why you never see a recommendation to use a 3' XLR cable.
 
XLR has an advantage over TRS in that you can SEE the connector, and know it is balanced inside the box. A TRS jack looks identical to a TS (tip-sleeve) which is unbalanced, so unless you know (read the manual) that the jack is a TRS, you may in fact have an unbalanced run going on (a TRS connects fine to a TS jack, but only one path is connected losing its noise reduction purpose, i.e. no longer balanced).
 
Bottom line, for signal routing you always want to run balanced cabling and XLR is the most common (especially for your case).




 
Well my Presonus Tube Pre V2 only has an XLR output for it's BALANCED output, so I am forced to use an XLR->TRSE cable if I feeding LINE-INPUT which I am to my audio interface.   The back of the preamp has a BALANCED XLR output and a unbalanced TRS output.
 
I was told to use Balanced, so now I am super confused as to what I should be doing :(
2016/02/28 15:29:10
mettelus
Some amps have a selector switch near the XLR for XLR signal level, but without a switch it is probably line level. Does your interface accept line levels on the XLR input? From the OP I assume this was one test you did (and maybe preferred).

If the TRS says unbalanced, that is actually a TS jack (1/4" instrument jack for an external effects loop most likely).

Which amp and interface are you using?
2016/02/28 15:37:03
AdamGrossmanLG
mettelus
Some amps have a selector switch near the XLR for XLR signal level, but without a switch it is probably line level. Does your interface accept line levels on the XLR input? From the OP I assume this was one test you did (and maybe preferred).

If the TRS says unbalanced, that is actually a TS jack (1/4" instrument jack for an external effects loop most likely).

Which amp and interface are you using?



Hi thanks for the reply.
 
My interface accepts line levels on the XLR input (its a combo input).  My interface is the Steinberg UR22.  There is no LINE/MIC switch... it switches to LINE automatically when you use a TRS cable.   
 
My tube preamp is a Presonus TubePre v2.   As far as balanced output, it is only XLR, so I have no other way then to go in XLR -> TRS cable, correct?
2016/02/28 15:43:03
mettelus
There should be no need to go from XLR to TRS, just low gains on the interface and amp when connecting and bring them up slowly.

If the input shifts automatically to line and that is a combo jack (takes XLR or TRS inputs), inside that box the connection is immaterial (i.e., both connector types go to the same wiring). The interface doesn't know XLR from TRS.

It is possible the wiring is separate to the same connector, but seems highly unlikely.
2016/02/28 15:45:09
AdamGrossmanLG
mettelus
There should be no need to go from XLR to TRS, just low gains on the interface and amp when connecting and bring them up slowly.

If the input shifts automatically to line and that is a combo jack (takes XLR or TRS inputs), inside that box the connection is immaterial (i.e., both connector types go to the same wiring). The interface doesn't know XLR from TRS.



right but if I use an XLR into the mic pre, then I am essentially having 2 Mic-ins instead of 1 mic-in and 1 line-in which would be amplifying the signal twice - according to this which I just found:

http://therecordingrevolu...reamp-reader-question/
2016/02/28 16:06:50
mettelus
Okay, had to look both of those up, looks like the UR22 does have a switch in the combo connector to know which type is being used. You are correct that you will be double-amping that signal using the XLR input. Depending on how it sounds, this may not be an issue as you can offset the amp by lowering input gain - may or may not be effective depending on how that pre-amp is coloring the signal.
 
Other option - Unbalanced cables are not heinous (is what guitar cables are), you just want to be careful to not run them for long distances in most cases. Do you have a 1/4" to 1/4" to connect the "unbalanced" on the TubePre to the Input on the UR22?
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