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Balanced out to unbalanced in

Discussion in 'Pro Audio Equipment' started by Shannon Adkins, Feb 24, 2012.

  1. Shannon Adkins

    Shannon Adkins Active Member

    I'm looking at getting a new pre to go along with my Steinberg MR816.
    I want something clean to go along with my sm7 since it is already a colored mic.
    So the two I'm really interested in are the Focusrite ISA One and Grace m101. Really, the ISA is calling my name because of it's extra features. But the problem is that the only way to bypass the preamps on my MR816 is through the inserts on channels 1 and 2....and they're both unbalanced.
    So, the ISA does not have an unbalanced out, but the Grace does.
    Will there be any negative effects if I insert the ISA into an unbalanced input? ....Is this a deal-breaker that puts the Grace heads above for me in this competition?
    Thanks,
    -Shannon
     
  2. Boswell

    Boswell Moderator Distinguished Member

    No, it's not a deal-breaker. I don't know the exact details of the balanced output of the ISA One, but since Focusrite do not sing anything special about it, my guess is that it is a standard drive circuit using separate output amplifiers for the + and - pins of the output connector. If this is the case, it would be quite safe to use pin 2 of the XLR as an unbalanced output with pin 1 as ground, leaving pin 3 unconnected. You will get 6dB less output signal with this connection, but as I think you will be in danger of overloading the +14dBuFS insert returns on the MR816 anyway, this scheme gives you a bit of extra margin.

    You will need to make up an XLR(F) to TRS plug cable using single-conductor coax cable. Use the coax inner conductor to take the signal from pin 2 of the XLR to the ring connection on the TRS plug and then wire the cable screen from pin 1 of the XLR to the sleeve of the TRS plug. Don't wire anything to XLR pin 3 or the TRS tip connection.

    That will give you a workable analog connection. However, my advice really would be to go for an ISA One with the digital output option, and then you can run S/PDIF digitally into the MR816 with a much higher conversion quality and no worry about overload (of the MR816).
     
  3. Shannon Adkins

    Shannon Adkins Active Member

    Thanks a bunch, Boswell. I would very much like to get the digital out card to go with it, and probably will end up getting it later on (if I see that the ISA is a significant upgrade over the MR's pres....and it should be).
    One of the MR's strong points is supposed to be it's conversion, which I've been told is exactly the same hardware as the RME fireface models have. Would the conversion on the ISA really be that much better?.....if so that would be great too!
    About an hour ago I read about someone using a Daking Mic Pre One with the inserts of the MR and there was no mention of overload. I don't know anything about the Daking unit, but hopefully I have similar luck with the ISA.
    Well, this makes me feel a lot better about the ISA in general. And with the option to expand on it's in/out capabilities later on, I feel like it almost has to be the first dedicated pre I try out.
     
  4. Boswell

    Boswell Moderator Distinguished Member

    I'm sure it will be fine. Since none of the pre-amps you have been talking about feature transformers on their outputs, you are not going to get much in the way of a tonal change as you vary the gain to give you different output levels.

    To tell you that you are not overloading the insert returns of the MR816 you can inspect the waveform displays in your DAW software, but that is no guarantee that you are running in the "sweet spot" of the MR816's converters. You may have to back off 12 dB or so for that and compensate by increasing the digital level in the DAW. This may sound as if it's going against the teachings of correct gain staging, but finding a sweet spot is a much more subtle pursuit that can only happen after you have got the basics right.
     
  5. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    I find this to be a handy reference when interfacing balanced and unbalanced signal:

    Sound System Interconnection
     
  6. Shannon Adkins

    Shannon Adkins Active Member

    Is there a pre close to that price range that does have a tranny on the output?
     
  7. audiokid

    audiokid Staff

    I had a similar issue but the other way round / balanced summing amp ( mixdream) using unbalanced hardware ( transient designer 2) as an insert with other balanced gear in the chain. I contacted the manufacturer and they simply told me to connect pins 1 and 3 together either by switching the trs to a 1/4 inch or run a jumper across 1 & 3 on the trs for unbalanced gear, and it works like a charm. No noise and the levels are equal to other gear now. This of course may or may not work for you but I though it was worth sharing.
     
  8. Boswell

    Boswell Moderator Distinguished Member

    Using insert returns is a special case that is not usually covered in the literature, even the very good Rane paper linked to by Bouldersound.

    Transformer-output pre-amps are rather rare and expensive beasts these days. I have both API 3124+ and Neumann V476Bs that have transformers on inputs and outputs, and putting drum tracks through them that push the output transformers into mild saturation is a very pleasurable experience.
     
  9. audiokid

    audiokid Staff

    nicely said Bos. That sounds so appealing. I have instant G.A.S. thumb
     
  10. Shannon Adkins

    Shannon Adkins Active Member

    Thanks everyone for the very helpful replies!
    Boswell, I just want to make sure I understand correctly what you were saying about the fact that these pres I'm looking at have transformerless outputs. Are you stating that I won't hear much tonal change over the MR's pres? Or that I won't be able to vary the signiture sound of each repective pre to any noticable degree?
     
  11. Boswell

    Boswell Moderator Distinguished Member

    I probably did not phrase it very well: when using a pre-amp that has a transformerless output, you get very little change of tone (or the "signature sound" that you refer to) over the range of output amplitudes. This is not the same thing as saying over the range of the gain control, as gain variation is usually done by changing the amount of negative feedback in the circuit, and that in itself can alter the character of the sound.

    The pre-amps you have mentioned all have their own sonic character, and this will be different from that of the pre-amps built-in to the Steinberg unit. Injecting the signal from the external pre-amp into the insert return is a good way of making sure that the desirable qualities of the external unit are not masked by whatever qualities the Steinberg pre-amps exhibit. With this routing, you are still going through the Steinberg drive amps and ADC, which will themselves have a signature, and it is for that reason that I suggested that the ISA unit with its internal ADC would be a marked improvement. It's fine to leave that as a future upgrade.
     
  12. Shannon Adkins

    Shannon Adkins Active Member

    Thanks so much for your time, Boswell. It's been so helpful and educational!
    I'm looking very farward to finding out what a new pre will do with my mics. Also, it just came to my attention that the Daking One is available for $650 right now. That may be stretching it for me at the moment, though. The ISA would be $500, which is exactly what I have to work with. So it will probably be the ISA.
    On a side note, some of what you said about finding the converters sweet spot is new to me, but it will be fun exploring this.
    Thanks again and have a good weekend.
    -Shannon
     
  13. RemyRAD

    RemyRAD Well-Known Member

    Shannon you can find used API 312/512 series preamps used for around $500. And those have a quality Dean Jensen input transformer and API's own fabulous, multiple tab output transformers. They are wondrous sounding and you can kick the crap out of them with level. And with its multiple output tap transformer, you can send up to 3 transformer isolated individual outputs per each preamp. In a sense, it can also be used as an active splitter and distribution amplifier at the same time. You can find 312 cards or the 512 lunchbox series both are identical. The Daking are quite nice, don't get me wrong. But you can generally find a 312 card which only requires an external power supply of ± 15 V DC, a volume control, a switch, connectors. Phantom power optional which requires a small +48 V highly filtered power supply through 3.9 K, .5% mil spec resistors, metal film or carbon. I've got a couple of external outboard 2 channel phantom power supplies that I use with some older API 312 cards. They aren't expensive and they do come in handy from time to time.

    The prenup makes more difference than the converters
    Mx. Remy Ann David
     
  14. Shannon Adkins

    Shannon Adkins Active Member

    Thanks Remy! I'll do some homework on that. Not going to be making a decision for a few more days, so if anyone else has suggestions feel free:)
    I actually found a shootout with the Daking and MR preamps, and a Great River vs MR preamps also. High res MP3 files of course, so that kinda stinks. But all and all the MR held up really well against both units. It was close with the Daking.....closer than I would've thought for a $700 difference per channel. The Daking had ever so slightly more on the high and low end; very minimal. The Great River sounded more focused...not by a mile, but you could tell. But now were talking about an $1150 unit.
    So being that the MR held up well against those, and that it's supposedly on the neutral to bright/sparkly side. I'm starting to feel like a character pre might be more useful to me. Maybe something with punch and warmth that would be great for DI bass and electric guitar. So those API's that Remy mentioned might be one of the more useful options. Or maybe something tube based like a solo 610.
    haha. I didn't catch that the first time.
     
  15. RemyRAD

    RemyRAD Well-Known Member

    I really wasn't trying to be funny I was serious about that comment. The entire recorded character of the sound emanates more from the preamp. So a API or NEVE will still sound a lot better going into a average converter than having a lesser preamp into a premium quality converter. And even if you think other preamps might sound better than those classics, think about how many hits were recorded with those classics and how many hits have been recorded with all those others? So better isn't better it's only different. If you want something different from established hit making devices, that's perfectly fine. You have to be happy with the that's the bottom line.

    Old-school broad
    MX Remy Ann David
     
  16. Shannon Adkins

    Shannon Adkins Active Member

    ISA One on the way. Will be here tomorrow:)
     

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