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Can I plug a GA PRE 73, Blue Robbie or even a Aphex Channel into a Scarlett 18i20?
Old 7th August 2014
  #1
Can I plug a GA PRE 73, Blue Robbie or even a Aphex Channel into a Scarlett 18i20?

Hey guys, I want to upgrade at some point from my Focusrite itrack solo to be able to use different pre's (Love the itrack BTW) and strips but I don't think they would connect to it. So I've been thinking of purchasing the 18i20. Would I be able to plug in a Blue Robbie, Aphex, or a GA Pre 73 into it? And if so thru what inputs/outputs? And in case I missed something before i go blow alot of money, would the plug into the back of my itrack solo from Focusrite?
Old 8th August 2014
  #2
Quote:
Originally Posted by genesisgk View Post
Hey guys, I want to upgrade at some point from my Focusrite itrack solo to be able to use different pre's (Love the itrack BTW) and strips but I don't think they would connect to it. So I've been thinking of purchasing the 18i20. Would I be able to plug in a Blue Robbie, Aphex, or a GA Pre 73 into it? And if so thru what inputs/outputs? And in case I missed something before i go blow alot of money, would the plug into the back of my itrack solo from Focusrite?
Both interfaces are outfitted with preamps on all line inputs. It's not ideal to plug your preamp into another preamp, but for all intensive purposes it's probably fine. Just keep the gains on the interface pre all the way down. And yes, it would work the same for either interface.
Old 8th August 2014
  #3
Quote:
Originally Posted by chinesewhiteman View Post
Both interfaces are outfitted with preamps on all line inputs. It's not ideal to plug your preamp into another preamp, but for all intensive purposes it's probably fine. Just keep the gains on the interface pre all the way down. And yes, it would work the same for either interface.

So are you saying, for example, I could plug a Avalon 737 into the xlr input of my Focusrite iTrack solo where I would usually plug my mic into?
Old 8th August 2014
  #4
Yes. You'd ideally have line inputs without any preamp circuitry, but it should work.
Old 8th August 2014
  #5
Quote:
Originally Posted by genesisgk View Post
So are you saying, for example, I could plug a Avalon 737 into the xlr input of my Focusrite iTrack solo where I would usually plug my mic into?
Quote:
Originally Posted by chinesewhiteman View Post
Yes. You'd ideally have line inputs without any preamp circuitry, but it should work.
NO. you'd plug it into the line input. Which on a budget interface is usually a TRS jack input - might be part of the combi jack input.

DON'T connect it via the XLR - not only could you fry the output if you leave phantom power on accidentally, but the gain will be mic level and thus far too hot.
Old 8th August 2014
  #6
Quote:
Originally Posted by chinesewhiteman View Post
Both interfaces are outfitted with preamps on all line inputs. It's not ideal to plug your preamp into another preamp, but for all intensive purposes it's probably fine. Just keep the gains on the interface pre all the way down. And yes, it would work the same for either interface.
PS it's "all INTENTS AND purposes'

But as I said, it's preamp out -> line in, not mic in. Then just leave line gain at unity.
Old 8th August 2014
  #7
Old 8th August 2014
  #8
Thanks.

So the trs and xlr have don't route to the same circuitry? Didn't know that. Mic must run to an opamp or something first? Because the same gain pot is used for either...
Old 8th August 2014
  #9
Quote:
Originally Posted by chinesewhiteman View Post
Thanks.

So the trs and xlr have don't route to the same circuitry? Didn't know that. Mic must run to an opamp or something first? Because the same gain pot is used for either...

The long version:

The XLR and the TRS inputs on a Focusrite interface do in fact use the same circuitry. The XLR input is connected to the mic pre op amp through coupling caps to block the DC phantom power from the op amp. The TRS is coupled through a resistive attenuator after the coupling caps. The attenuator serves two purposes, first to reduce the line-level signal to a voltage level that won't overload the op amp, and second to raise the input impedance to a value that's higher than the direct mic input. There is no "...Mic must run to an opamp or something first? Because the same gain pot is used for either..." situation. The same op amp is used for the necessary mic gain, and the line level signal is reduced to match the required signal level for the mic pre gain staging.

When using the TRS input, the mic pre is operated at a relatively low gain, so effectively becomes a balanced buffer stage. Since Phantom power is applied before the coupling caps, and the attenuator is after, PP is always blocked from the TRS inputs, protecting any line-level output that may be connected.

On lower-cost and moderately priced mic pres, and interfaces containing internal mic pres, the signal path after the input amplifier is unbalanced. That's why mic pres, channel strips, and the occasional interface which have "Insert" Input/output jacks which provide only unbalanced send and unbalanced return lines.

For such a mic pre, interface or channel strip to provide a true balanced "Line-level" input connected "post mic pre" would require a separate input balanced (differential) input stage (another op amp) and a means of switching to the separate input path. That does not lend itself to remote DAW/computer control unless relays are used, and complicates the Mic/Line selection circuitry and also generally requires separate gain controls for each signal path, further complicating the controls. The extra parts add a significant cost, so are left out of all but the best (or at least the more costly) interfaces and channel strips.

In the much more typical method of using an attenuator and the existing mic pre balanced input, the same function is achieved at a much lower cost. Modern audio op amps operating at moderate gain (usually 19 to 24 dB) in this application are very transparent, and the noise floor will be below the output noise floor of any typical "line-level" device connected in front of the TRS input. It's really not an issue, and the people who get their panties in a knot complaining about the signal going through the mic pre, conveniently forget about the extra op amp stage or stages that must be added to the signal path to provide a dedicated, balanced input anyway.

As was stated clearly by psycho_monkey, don't ever connect a line-level output from a mic pre, or any other line-level device (EQ's , compressors, etc.) to a mic input. It will almost certainly overload the mic input and will put the line-level device at risk of damage from accidental PP being applied. There are a few small interfaces, (such as the RME Babyface ) that do use the XLR as a line input as well as a mic input (they have no TRS inputs). The Mic/Line switching is done under software driver control, and there are plenty of "higher-end" interfaces with XLR "Line-level" input jacks, so you must remember that all XLR inputs are not always mic inputs, just as all TRS jacks are not always "line" inputs.

The function of an audio I/O jack is what is important, not the kind of connector that happens to be used.
Old 8th August 2014
  #10
So rather than the mic being boosted, the line in is attenuated before it hits the pre.

Still, if using an external pre it would be preferable to have line inputs without built in preamps in the path.
Old 8th August 2014
  #11
Okay great thanks everybody for the responses. One final questions that's been bugging me, would a RME babyface give me better sound quality than the small Focusrite iTrack solo? I mean converter wise and pre. I like the focusrite pre, it's super clean and clear. But would getting the babyface make any difference that the human ear can actually hear? IDK...If not I'll just buy a GA Pre 73 & a Blue Robbie and use them with my iTrack. If that sounds right...
Old 9th August 2014
  #12
Quote:
Originally Posted by chinesewhiteman View Post
So rather than the mic being boosted, the line in is attenuated before it hits the pre.

Still, if using an external pre it would be preferable to have line inputs without built in preamps in the path.
Yes to both, hence the reason you have people obsessing about interfaces with true bypass line inputs.

But with a half decent interface pre, leaving the gain at unity should make minimal audible difference, if any.
Old 9th August 2014
  #13
And guys, just to clarify. Look on the back here. So 100% sure I can plug a pre into this? Focusrite iTrack Solo | Sweetwater.com I see 2 Line outputs on the back of my interface.
Old 9th August 2014
  #14
Actually no. There's no line in - that's a real "bare bones" beginner interface, designed to be used standalone. Line out is OUTPUT. You need a Line INPUT. A guitar input is not the same thing.

If you were upgrading a preamp, you'd need to upgrade the interface as well.
Old 9th August 2014
  #15
Quote:
Originally Posted by psycho_monkey View Post
Actually no. There's no line in - that's a real "bare bones" beginner interface, designed to be used standalone. Line out is OUTPUT. You need a Line INPUT. A guitar input is not the same thing.

If you were upgrading a preamp, you'd need to upgrade the interface as well.
Yeah I just did some research & figured it out. I'm gonna just purchase a used Focusrite 6i6, I will have -4 Line outputs & -2 Line inputs which should be enough.
Old 9th August 2014
  #16
This might sound crazy, but if you just need 2 line ins I highly recommend the Lexicon Alpha. It's a lot cheaper and equal quality wise. I had one and a ff Saffire pro 24 DSP. I haven't used the 6i6, but all the Saffire and Scarlet interfaces are the same quality. You get different features per model, but they'll sound the same. Used my Lexicon and ff side by side for years, trust me you won't miss anything in the Lexicon compared to ff.

IMO, a better option would be to save up and step up to the RME/Audient/Apogee level where you'll real notice a significant difference in quality. But if you just want to get going the Lexicon Alpha is dirt cheap. I also really like that it has a DAW/direct crossfade pot for monitoring and no software, it's very nice.

BTW, I wrote reviews of the ff and the Audient interfaces.
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