AdamGrossmanLG
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What Cable To Use From Mic Tube PreAmp To Audio Interface
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!
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fret_man
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 14:40:09
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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.
post edited by fret_man - 2016/02/28 21:36:25
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mettelus
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 14:47:13
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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).
post edited by mettelus - 2016/02/28 15:06:56
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 15:07:01
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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?"
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 15:09:53
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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 :(
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mettelus
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 15:29:10
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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?
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 15:37:03
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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?
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mettelus
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 15:43:03
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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.
post edited by mettelus - 2016/02/28 16:00:45
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 15:45:09
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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/
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mettelus
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 16:06:50
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☄ Helpfulby SilverBlueMedallion 2016/02/28 20:56:49
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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Paul P
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 18:52:20
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SilverBlueMedallion
The back of the preamp has a BALANCED XLR output and a unbalanced TRS output.
If it's TRS (tip-ring-sleeve) it should be balanced (it's three wires just like xlr) or stereo. So it's probably just TS (tip-sleeve) . This thread might be a bit confusing to some since a jack in Britain = a plug in North America (where a jack is the socket). Phone connector.
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fret_man
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/28 21:25:17
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I stand corrected in my original post above. I edited it to be correct. Thanks.
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 07:47:22
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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?
I could do unbalanced, I just always read I shouldn't for some reason. So never use an XLR to TLS cable? This is the one I ordered: http://www.amazon.com/gp/product/B00OWG4MV6?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00 Im not sure if it is an "impedance matcher" as you stated earlier, not sure what that is either. :(
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Paul P
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 12:09:23
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You want to connect the xlr output (balanced) of your tubepre to one of the the xlr inputs (balanced) on your UR22.
The 1/4" ts output on your tubepre is unbalanced and you should avoid using it.
The adapter you bought is simply a connector change (xlr balanced to trs balanced) and doesn't do anything on its own. There's no use for it in this case, but adapters are always useful to have lying around so never a waste.
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 12:27:28
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Paul P
You want to connect the xlr output (balanced) of your tubepre to one of the the xlr inputs (balanced) on your UR22.
The 1/4" ts output on your tubepre is unbalanced and you should avoid using it.
The adapter you bought is simply a connector change (xlr balanced to trs balanced) and doesn't do anything on its own. There's no use for it in this case, but adapters are always useful to have lying around so never a waste.
Well for my Steinberg UR22 I need that cable as when you plug in an XLR mic, it is adding another layer of amplification, but if you use a TRS input, then it sees it as Line Input and doesn't add additional amplification, which can distort the signal. I am forced to use this adapter, I just wonder what this statement means, as I also thought the cable does nothing but convert the signal: mettelus
By "XLR->TRS" you are referring to an "impedance matcher" I am assuming
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tlw
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 15:28:06
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An impedance matching adaptor contains a transformer and other bits so that e.g. a low impedance mic with and XLR connector can be connected to a guitar amp that only takes TS jack plugs and expects a much higher signal at its input. Blues harmonica players using a low impedance SM57 into a guitar amp often use them. Without the impedance matching the mic signal is too low to get a high enough output from the amp.
A TRS-XLR or TS-XLR adaptor that isn't impedance matching just connects the relevant plug connections to each other. Electrically its no different to just soldering a TS or TRS plug onto a balanced/stereo cable.
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Paul P
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 15:45:44
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First of all, I just noticed that your inputs on the UR22 are combination XLR/TRS, but that doesn't change anything. SilverBlueMedallion
Well for my Steinberg UR22 I need that cable as when you plug in an XLR mic, it is adding another layer of amplification, but if you use a TRS input, then it sees it as Line Input and doesn't add additional amplification, which can distort the signal.
Why do you think there'll be an extra level of amplification if you use the TRS hole ? I'm pretty sure the respective XLR and TRS contacts are just wired together. 
I am forced to use this adapter,
I don't think so.
I just wonder what this statement means, as I also thought the cable does nothing but convert the signal:
mettelus
By "XLR->TRS" you are referring to an "impedance matcher" I am assuming
I imagine mettelus is referring to a balanced XLR to unbalanced TS adapter like this one. You don't need that either. I've found them useful in electromagnetically noisy environments to permit running long balanced (xlr) cables instead of unbalanced 1/4" instrument cables.
post edited by Paul P - 2016/02/29 16:09:04
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Jeff Evans
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 16:09:57
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☄ Helpfulby SilverBlueMedallion 2016/02/29 22:51:16
I have downloaded the manual for the Steinberg UR22 and can give you the correct information after studying the blcok diagram and that is what you shoud to do to get the real picture. The XLR input and the line inputs (combo) on the UR22 are basically the same. You are NOT avoiding the Mic Pre when feeding signals into the so called line inputs on the UR22.
Both the Mic and Line inputs still run through the Mic Pre on the UR22. On the UR22 the Mic Pre is not disconnected as it is on some other interfaces. It is better to bypass the Mic Pre with a line input and feed any line level input signals further down the line but this does not happen with the UR22. They simply attenuate the signal and alter the input impedance.
The is not so bad as the Mic Pre will be using much less gain (and hence less noise as well) with the line level input signal and it should not alter the sound too much in the process.
So you need a balanced XLR to TRS cable to get the signal in. This cable represents no form of impedance matching or conversion. It is simply a cable that connects XLR to TRS signals. The output impedance of the Valve Pre is low (50 ohms) and the input impedance of the UR22 is high (well 20 K anyway) so there will be no impedance mismatch in this case and no signal loss anyway. The Valve Pre may introduce a little more noise if anything in the process.
Do not use any form of adaptors as you are introducing a transformer into the equation and it wont be a great one at that price anyway. (Unless you like what the sound of the adaptor does but it is not necessary) At line levels some transformers saturate early and can distort the signal in an unpleasant way. They work better at Mic levels which is what they are meant to do.
You are probably better off running your Mic signals direct to the UR22 unless of course the sound of the Presonus Valve Pre V2 is really offering something that you want of course. There are plugins out there that can emulate the sound a valve Pre as well you know.
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mettelus
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 16:12:18
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Not at a computer here, but the manual for the UR22 says it switches modes depending on the connector used, so there is a switch internal to the UR22 (I assumed was identical wiring at first as well).
What I did not verify is the 1/4" plug in the center of that UR22 combo jack. I am not sure if it accepts a balanced TRS or is simply a TS connection inside?
*If* (massive if) that jack is a TS, there is nothing to be gained from an XLR->TRS adapter over using a instrument cable from the pre-amp unbalanced to the UR22. If someone could verify that it would be most appreciated.
The clarification on the impedance matcher above are spot on (and not applicable).
Edit: Just saw Jeff's post above, thank you!
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Jeff Evans
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 16:19:16
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☄ Helpfulby SilverBlueMedallion 2016/02/29 22:52:29
You could use an unbalanced lead from the unbalanced out on the Valve Pre to the combo input as well. But you will loose 6 dB of level in the process meaning that you will have to add a little bit of extra gain on the UR22 to make it up. I would be inclined to use the balanced lead from the valve Pre to the UR22 because it will give the extra signal level hence making you turn the UR22 gain down a little further.
Mic Pres apply less of their sound and less noise when you are using less gain with higher level signals going in.
All the happens when you use the centre combo inputs on the UR22 is that the signal is forced through an attentuator (passive) which offers the 20K impedance and drops the level down so the Mic Pre won't overload. It does not really change its mode as such but rather forces the signal through a different path before going into the Mic Pre.
The Mic Pre is never bypassed. This is common on cheaper interfaces. What should happen is line inputs should bypass the Mic Pre completely and they do on the better units.
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Paul P
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 17:39:39
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Jeff Evans
So you need a balanced XLR to TRS cable to get the signal in.
Why not just use an XLR to XLR cable ? That's what I'd do. Why the conversion ? The Presonus Tubepre has an XLR output (balanced). Its 1/4" output is not balanced (only TS). Here's a schematic for another Steinberg product that shows a similar input circuit where XLR and TRS are just wired together (you can ignore the Hi-Z switch).
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 22:41:53
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Paul P
Jeff Evans
So you need a balanced XLR to TRS cable to get the signal in.
Why not just use an XLR to XLR cable ? That's what I'd do. Why the conversion ?
The Presonus Tubepre has an XLR output (balanced). Its 1/4" output is not balanced (only TS).
Here's a schematic for another Steinberg product that shows a similar input circuit where XLR and TRS are just wired together (you can ignore the Hi-Z switch).
Well, I just ran some tests. I kept the gain on the audio interface completely down and had the gain on the preamp up at around 50%. First I tested XLR -> XLR, then I tested using the XLR -> TRS cable to the audio interface. The XLR connection was about 15db louder than the XLR -> TRS connection (no changes on the gains made). This proves the XLR connection is adding amplification. I bought this cable for my XLR -> TRS connection: http://www.amazon.com/gp/product/B00OWG4MV6?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00 Am I ok with this? Thanks everyone for helping me out, I really appreciate it. I'm sorry I don't understand all of it.
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Paul P
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/02/29 23:24:38
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SilverBlueMedallion
The XLR connection was about 15db louder than the XLR -> TRS connection (no changes on the gains made).
Glad you've worked things out. I just read the manual and as mettelus pointed out, and you've been affirming, there is a difference between the two. This is not always the case. "When connected to an XLR-type plug, this jack automatically switches to microphone input sensitivity, and when connected to a phone-type plug, it switches to line input sensitivity." You should be fine with your cable.
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Jeff Evans
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/03/01 07:09:42
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☄ Helpfulby SilverBlueMedallion 2016/03/01 08:45:58
On the block diagram it says Mic Input Nominal level -54 dBu to -10 dBu Line Input Nominal level -34 dBu to +14 dBu Specs say Max input level for Mic is 0 dBu Max input level for Line is +24 dBu That tells us the attenuator is reducing the gain by 24 dB from Mic to Line level. Hence reason why XLR to XLR is not a great choice. It would work but you may overload Mic Pre XLR to TRS is great choice so now you have 24 dB of headroom. Presonus Pre will never overload it then. Also Input impedance is only 4K ohm on the XLR which is OK but lower than 20K on line input. The fact the Presonus output impedance is very low eg 50 ohms means it will still drive into a 4K ohm load fine. (so will a microphone because Mic output impedance is usuall pretty low) If the output impedance of the Presonus was say 2K ohms then things would be different. 2K feeding into 4K means signal loss. 2K feeding 20K however would not be significant if at all. Rarely are XLR and TRS wired directly in parallel if feeding the same Mic Pre although I have seen it. Usually there is some form of attenuation going on from XLR to the TRS jacks. Capacitors usually block any phantom power as well from getting back into the line inputs. (from the XLR's) Although that is worth checking. The diagram does not show any but they should be there. If you feed a Kurzweil synth (latest models) into XLR/line inputs that have phantom power present you will blow the output stages of the Kurzweil in an instant. (they told me so!) I nearly fed mine into a pair of XLR's that had phantom power on them but decided to ask them first. Just as well I did! Phantom power would not harm the Presonus Pre because usually valve pres's have an output transformer that would prevent that DC from doing any harm. Sorry, just some useless information. 
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AdamGrossmanLG
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/03/01 08:32:54
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no no, not useless... good stuff in there - i don't understand electronics really, but you made me feel more confident in my XLR > TRS cable :)
Thank you!
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mixmkr
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/03/01 09:16:12
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Jeff Evans
You are probably better off running your Mic signals direct to the UR22 unless of course the sound of the Presonus Valve Pre V2 is really offering something that you want of course. There are plugins out there that can emulate the sound a valve Pre as well you know.
I use the UR44 (guessing the same pres as the UR22) and the mic pres on it do not offer enough gain for many mics. Hence I use an outboard preamp as well, before going into it, so the gain on the Steinberg unit isn't cranked to max. With little gain on the initial preamp and the same on the Steinberg, things are kept pretty quiet. But for typical ribbons and even my dynamic RE-20, the Steinberg doesn't cut it by itself. Besides the low headphone volume the unit also produces, I'm liking it...but two major downfalls imo.
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AT
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/03/01 10:53:54
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I've never had a problem using XLR- balanced 1/4 inch. I've had to buy a few for using outboard. Some times they do make it hard to tell, esp. on the internet, but balanced to balanced (I've never seen an unbalanced XLR but that doesn't mean it doesn't exist, esp. after running a dolly over it a few times).
XLR from preamp output to 1/4 inch line input on a combo input should work fine. As detailed above, most automatic switch sensing basically pads the line input as it goes to the mic input. Plugging an XLR line output into an XLR mic input will drop your beautiful line level signal way down into the noise.
FYI, I've used many Monoprice cables available on Amazon with few problems and no returns (yet!).
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Jeff Evans
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Re: What Cable To Use From Mic Tube PreAmp To Audio Interface
2016/03/01 13:18:07
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The UR44 is slightly more interesting interface. The Mic Pres do look similar but the UR44 in fact has a dedicated pair of proper line inputs. eg channels 5/6. These inputs have no actual Mic Pre as such. They are balanced inputs and accept a much higher level and have a higher maximum input level as to be expected.
So if you a running a full Mic Pre prior to the UR44 you should be patching the output of your Mic Pre into inputs 5/6 instead and avoid the Mic Pre inputs all together.
Unless as mixmkr points out you may want to run a mic into a Mic Pre and use a little less gain there and then out of that into a Mic Input on the UR44 and use a little more gain there which you could do for sure. You will get more gain that way overall. Maybe a little more noise at the same time but it may not be too noticeable.
Specs i5-2500K 3.5 Ghz - 8 Gb RAM - Win 7 64 bit - ATI Radeon HD6900 Series - RME PCI HDSP9632 - Steinberg Midex 8 Midi interface - Faderport 8- Studio One V4 - iMac 2.5Ghz Core i5 - Sierra 10.12.6 - Focusrite Clarett thunderbolt interface Poor minds talk about people, average minds talk about events, great minds talk about ideas -Eleanor Roosevelt
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