Routing options for external preamps

Chris F

Chris F

New member
I am mostly a performer who enjoys recording, so I have far more musical chops than recording chops...so forgive me if this is a basic question. For several years I have been happily recording acoustic music into Logic through a Presonus Firestudio Project. I have considered upgrading the interface, but since it has performed so flawlessly to date I am hesitant to do that. I would like to experiment with different preamps, though, and was wondering what my options for connecting them to the interface might be in order to minimize gain staging issues. My question is, what are my connection options for using an external preamp through the Firestudio using it as the converter/interface? Let's assume the preamps I try at first have only balanced and unbalanced analog ins and outs. Any and all input appreciated!
 
You're looking at the thing aren't you? What holes has it got? Which ones match what you're trying to plug into it? It doesn't make a lot of sense to plug a preamp into another preamp, but...

...What do you hope to achieve here? That preamp is most likely as flat, clean, and quiet a preamp as most anybody could ever hope for. If you hear a difference with your outboard preamp it's because that one is filtering and/or distorting the signal. The Focusrite pre will do a fine job of getting that distorted and filtered signal into the computer and wouldn't be expected to distort or filter it any more than a line input would.

This is not really rocket science here. Plug it in and turn the knobs til it sounds good. If you can't get it to sound good, plug it into something else. I can sit here and explain the subtleties of the electronic interactions between the various circuits and you'll be all like "...so which one is best???" or you can dive in, use your hands and your ears and then you'll actually know which is which and why in the empirical sense. You can't blow anything up unless something's already broken.
 
Sorry the question seem to have annoyed you. I was simply wondering whether I could use the Firestudio as an interface and play with the preamp colors of other preamps without getting into strange gain staging issues; or if there was away to do this, how to minimize gain staging issues. Sounds like from your reply that there isn't a way to do this. Thanks for taking the time.
 
That's not at all what I said. Sorry if it sounded snippy, but really it should work just fine. If there are just plain line inputs on the interface, use them. If not, use the mic inputs and adjust the gain knob as close to unity as possible based on what comes out of the preamp.
 
If its a decent pre you should be able to use the digital paths, no point reconverting? use S/PDIF or ADAT that way you get all the flavour of your additional pre and you don't lose a channel.
 
Chris F said:
Sorry the question seem to have annoyed you. I was simply wondering whether I could use the Firestudio as an interface and play with the preamp colors of other preamps without getting into strange gain staging issues; or if there was away to do this, how to minimize gain staging issues. Sounds like from your reply that there isn't a way to do this. Thanks for taking the time.
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It's just it could be taken as if you hadn't looked into the question yet, or read the manual what have you, as (well I looked 'caus I don't own one.. :>).. six of the eight in's are clearly 'line level'.
Down in the specs' page, they show a nice wide range right up to +20 something.

Now what's not in the manual that could be helpful :>) 'Nominal' line level. That's the 'center average working level is +4dBU. Most gear -preamp outs etc, A/D converter line ins and outs, run in and around that area, leaving the '+20' or more number for operating head room -safety room for peaks.
The game is set your preamps (as directed by the manufacture) to get your level in where it wants to be first and earliest in the chain (+/- a little doesn't matter). Then continue with a minimum amount of mucking' with your now 'line level signal as practical. In this case now you tweak as needed your line in to the A/D.. for their recommended record level ( -18 to 24 average/RMS somewhere in that range likely.
We use variable input controls (if you have them- my RME ADI-8's don't have them..) or sometimes variable line out controls on some pre's etc, mostly for tweaking the smaller difference between gear.
 
Thanks! Sorry if I was unclear. I have read the manual and it seems like I have two possible options: the obvious one is to plug the out of the external pre into the input of the interface. If I do this, what is the best way to set the levels of the two devices to get the color of the external preamp? Run a reasonably hot signal on the external pre and use as little of the pre on the interface as possible? That makes the most sense in that it would be like using the input gain and master of an amplifier.

The other option that I wondered about would be running the external pre as an insert. That kind of makes sense, but I'm not sure enough about insert and return routing to understand what would really be going on there. Plus, it would negate the possibility of the variable impedance on certain preamps that I might try.

What brought this up is I have the possibility of borrowing several nice preamps to experiment with, but as far as I know several of them don't have digital options for output signal. I don't hate the onboard Presonus preamps, but wanted to experiment with other colors; and since i would be borrowing the preamps to try the colors they impart, I wanted to check and see if there were any basic guidelines to follow.
 
Understood.
If I do this, what is the best way to set the levels of the two devices to get the color of the external preamp? Run a reasonably hot signal on the external pre and use as little of the pre on the interface as possible?
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I don't have much opinion here. From what I've seen -which is a pretty narrow experiences is with mostly pretty clan pres. Precision 8, RNP's a Mike-e and some Chameleon 7602's that might respond to being pushed just a bit.
Mostly the differences are very subtle. -Also way down the line in things that matter.
Guess it also depends on which pres? There's some that likely have more variation though. I'd say do some searches on the one you're looking at, and if it's one that tone' is even gain dependent.

Oops..
I guess 'inserted..? Means in-line after your pre raises the mic signal up to line level, then you have to pad that back down to the next pre..? Sounds like the hard way ..and I guess more noise?
 
I think mixsit and I both gave the same answer to that question in slightly different ways.

The ideal in gain staging is to get all the gain you're going to need as soon as possible and the try not to turn it back down and definitely don't turn it down just to turn it back up again. In most cases that's going to mean setting the external pre so that it's sending a signal right around 0VU (+4dbu) and then leave the interface right at unity.

But if you're trying to actually push these pres into distortion (which may have been an assumption on my part, but is at least half the fun), then you will at some point have to turn it up quite a ways past what we'd consider a reasonable line level. Then you will have to turn it down some to get that line level at the converter.

On most pres, that's going to mean turning the pre/input/whatever knob (usually the one furthest left ;) ) until you get the distortion you want and then turning the post/output/thing (usually over toward the right) down until the interface is cool at unity. Some don't quite work that way and then you do what you can.

If you're going through the insert, I'd try to get most of the necessary gain from the interface, but if it starts to distort before the pre, then you'll maybe turn it back a bit and then get the rest of the gain at the pre. Then adjust the output of the pre to bring it back down to nominal.

But like I said, all of this is generalized theory, and you can't know exactly how one piece of gear is going to interact with another until you do it and hear it. Plug it in, follow the above instructions, if it doesn't sound the way you want, turn the knobs until it does. Nobody's going to come in and tell you you're wrong. If you don't have unwanted distortion or intolerable noise, you're good.
 
All I have here at home is a couple of vintage M-Audio pres that probably aren't any better than the ones built into the Presonus unit. But I have a friend who has a bunch of nice stuff who has offered to let me borrow some pres to see if I like them before shelling out any $$$ on them. Everything from an ART Pro Channel on the low end to nicer stuff including the UA LA610- MKII and dbx 676. I have no idea if I will hear the true color of these units running them into Logic through another pre like this, but what could it hurt?
 
There you go!
Got'ta say I've had some intermittent lust for that UA tube one. 'Reads' like one of them out there with ligit (obvious) color.
 
Hmm. Check this out
 Return 1 and 2 (Line Inputs).
These are the line-level inputs for channels 1 and 2. Their gain structure
is identical to the ¼” inputs for channels 3-8 and are typically used for signals not requiring preamplification (CD/MP3 players, effects processors, etc.).
These inputs are normalled to the channel 1 and 2 preamp outputs, so they take precedence over the corresponding Mic/Instrument input on the front of the FireStudio Project.
(This means that if a cable is plugged into the channel 1 return input on the rear of the FireStudio Project, the channel 1 Mic/Instrument input will be inactive, and it will become active again when the cable is removed from return input 1.)

Would it be better' -or any audible dif vs 3--8's line ins-- Woo' knows!
 
mixsit said:
Hmm. Check this out
 Return 1 and 2 (Line Inputs).
These are the line-level inputs for channels 1 and 2. Their gain structure
is identical to the ¼” inputs for channels 3-8 and are typically used for signals not requiring preamplification (CD/MP3 players, effects processors, etc.).
These inputs are normalled to the channel 1 and 2 preamp outputs, so they take precedence over the corresponding Mic/Instrument input on the front of the FireStudio Project.
(This means that if a cable is plugged into the channel 1 return input on the rear of the FireStudio Project, the channel 1 Mic/Instrument input will be inactive, and it will become active again when the cable is removed from return input 1.)

Would it be better' -or any audible dif vs 3--8's line ins-- Woo' knows!
Click to expand...

This is exactly the kind of thing I was wondering about, but am too ignorant about technical specs to understand properly. As a professional bassist, there are many instances where I take a preamp with me when traveling so I can bypass the preamp circuit of whatever backline is provided and just use the power section of the amp with my own preamp color. Is this send and return structure on the Firestudio similar to an effects loop on an amp? If so, then this might be a good option.
 
Chris F said:
This is exactly the kind of thing I was wondering about, but am too ignorant about technical specs to understand properly. As a professional bassist, there are many instances where I take a preamp with me when traveling so I can bypass the preamp circuit of whatever backline is provided and just use the power section of the amp with my own preamp color. Is this send and return structure on the Firestudio similar to an effects loop on an amp? If so, then this might be a good option.
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Gads, other than a possible 'given everything is usually 'pre first, but who knows.
Where would/do you typically go in -other than the sometimes dedicated 'power amp in' point?

Maybe do what some of us gittar' players do-- pack a Quilter (or other) '2 pound' 200 (400 now for thier bass is it?) watt all in one '6" box'.
(I tuck an Aviator head under the seat as a spare now :>)
 
Most bass amps have a preamp gain on the front end and a power amp master on the back end. If you don't like the sound of the preamp, you can use a preamp you like into the effects return and bypass the built-in preamp. Normally, of course you'd just plug into the input jack, but then you are stuck with the voiced color of the built in preamp.

So if the Firestudio is set up the same way, then maybe using an external pre i could use the insert circuit like an effects loop on an amp and bypass the built in preamp. That was what I was getting at (and phrased very badly) when I started this thread.
 
So if the Firestudio is set up the same way, then maybe using an external pre i could use the insert circuit like an effects loop on an amp and bypass the built in preamp.
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Sorry, seems I missed your sort of restating the original question (? ..and still not sure
From that bit I posted copied out of your interface manual.. It would seem they are very much the same concepts.
But.. as Ashcat said, will bypassing' an amp/chip' or so make any audible difference..?
ashcat_lt said:
... but really it should work just fine. If there are just plain line inputs on the interface, use them. If not, use the mic inputs and adjust the gain knob as close to unity as possible based on what comes out of the preamp.
Click to expand...
 
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