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why do preamps often have XLR line inputs?
Old 23rd February 2012
  #1
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why do preamps often have XLR line inputs?

Many preamps, e.g. the Vintech X73i have a line input on the back that is XLR.
Why aren't the inputs 1/4", since that is the type of output many line level instruments like synths have?

Thanks
Old 23rd February 2012
  #2
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I agree, TRS-TRS cables are much cheaper than TRS-XLRM. I've had to get that kind of cable going from my patch bay into the line ins on my Daking. I'd like a combo Neutrik at the very least so that we're given the option. It's probably a noise or balancing thing, but for me it's annoying to have to deal with.
Old 23rd February 2012
  #3
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Quote:
Originally Posted by Slikjmuzik View Post
I agree, TRS-TRS cables are much cheaper than TRS-XLRM. I've had to get that kind of cable going from my patch bay into the line ins on my Daking. I'd like a combo Neutrik at the very least so that we're given the option. It's probably a noise or balancing thing, but for me it's annoying to have to deal with.
Why would it be a noise or balancing thing? both TRS and XLR are balanced.
Old 23rd February 2012
  #4
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Quote:
Originally Posted by Slikjmuzik View Post
I agree, TRS-TRS cables are much cheaper than TRS-XLRM. I've had to get that kind of cable going from my patch bay into the line ins on my Daking. I'd like a combo Neutrik at the very least so that we're given the option. It's probably a noise or balancing thing, but for me it's annoying to have to deal with.
That is kind of what has me confused. Isn't the 1/4" out on most synths unbalanced?
So, would the correct cable to use be unbalanced TS to Male XLR when plugging directly into the line level XLR input of a preamp?
Old 23rd February 2012
  #5
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Quote:
Originally Posted by iCompress View Post
Why would it be a noise or balancing thing? both TRS and XLR are balanced.
Exactly my point, since they are both balanced and shouldn't be a difference in quality, why aren't we given the option?
Old 23rd February 2012
  #6
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Fletcher's Avatar
Quote:
Originally Posted by hell View Post
Many preamps, e.g. the Vintech X73i have a line input on the back that is XLR.
Why aren't the inputs 1/4", since that is the type of output many line level instruments like synths have?
Because they're meant to accept a professional +4dbu "line level" input... and the standard / convention for that kind of signal has been the XLR connector for about the last 45 or so years.

"Line level" from instruments / synths are rarely at a +4dbu level... they're generally high impedance outputs that are down around -40 or so.

Peace
Old 23rd February 2012
  #7
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Quote:
Originally Posted by Fletcher View Post
Because they're meant to accept a professional +4dbu "line level" input... and the standard / convention for that kind of signal has been the XLR connector for about the last 45 or so years.

"Line level" from instruments / synths are rarely at a +4dbu level... they're generally high impedance outputs that are down around -40 or so.

Peace
Thanks Fletcher,

That makes sense, but aren't preamps generally going to be accepting line level instruments like synths for most applications? That's why I am confused by the standard seeming to be balanced XLR inputs.

What type of cable would you use to connect directly from the 1/4" out of a synth into the balanced XLR line-input of a preamp?

I know this is probably basic stuff, but I searched and couldn't find a good definitive answer on the topic of synths and line level preamp xlr inputs. Thanks again.
Old 23rd February 2012
  #8
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Quote:
Originally Posted by Fletcher View Post
"Line level" from instruments / synths are rarely at a +4dbu level... they're generally high impedance outputs that are down around -40 or so.
Synths are low output impedance and very much close to +4dBu line level, some of them are HOTTER than +4dBu
Old 23rd February 2012
  #9
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Quote:
Originally Posted by hell View Post
That is kind of what has me confused. Isn't the 1/4" out on most synths unbalanced?
So, would the correct cable to use be unbalanced TS to Male XLR when plugging directly into the line level XLR input of a preamp?
I would still use a TRS cable. On the unbalanced side, the 'ring' would just be dormant.
Old 23rd February 2012
  #10
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Quote:
Originally Posted by hell View Post
Why aren't the inputs 1/4", since that is the type of output many line level instruments like synths have?
Because the LINE input on the back of your x73i is intended for studio line level (+4 dBm) sources, such as the output of your D/A, multitrack, console, or compressor, which you're now going to process using said preamp. In the vast majority of traditional (professional) studio environments, XLR is the dominant connector type present in these balanced line level sources.

Most (all?) synths and similar devices do not operate at studio line level, but rather an intermediate instrument level somewhere between a passive instrument pickup (no standard, perhaps -30 dBu) and consumer line level (-10dbV). Instrument level sources are usually unbalanced, using 1/4" TS jacks. Critically, synths want to see a fairly high impedance instrument input, such as are employed on a plethora of instrument amplifiers, effects devices, and DI boxes, which is why 1/4" jacks are used. The LINE input of your Vintech is neither high impedance, nor instrument level (in addition to being balanced), and so it uses an XLR connector.
Old 23rd February 2012
  #11
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iangomes's Avatar
Quote:
Originally Posted by hell View Post
Thanks Fletcher,

That makes sense, but aren't preamps generally going to be accepting line level instruments like synths for most applications? That's why I am confused by the standard seeming to be balanced XLR inputs.

What type of cable would you use to connect directly from the 1/4" out of a synth into the balanced XLR line-input of a preamp?

I know this is probably basic stuff, but I searched and couldn't find a good definitive answer on the topic of synths and line level preamp xlr inputs. Thanks again.
I think what may be confusing you is that the output of synths isn't technically line level, nor is it called that. You want to plug your synth into the instrument in on a pre or into a di and then the mic input of a pre.
Old 23rd February 2012
  #12
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Yes, what Fletcher said. He posted while I was typing.
Old 23rd February 2012
  #13
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Quote:
Originally Posted by hell View Post
What type of cable would you use to connect directly from the 1/4" out of a synth into the balanced XLR line-input of a preamp?
You probably wouldn't. If the preamp has a high impedance "instrument" input, or DI, that would be the best bet for most (especially older) synths.

If you really want to connect the unbalanced output of the synth to the XLR line input of the preamp, then just wire a TS-XLR cable, with pin 3 tied to pin 1 inside the XLR connector.
Old 23rd February 2012
  #14
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Sorry, everyone said what I said while I was typing!
Old 23rd February 2012
  #15
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Quote:
Originally Posted by Fletcher View Post
Because they're meant to accept a professional +4dbu "line level" input... and the standard / convention for that kind of signal has been the XLR connector for about the last 45 or so years.

"Line level" from instruments / synths are rarely at a +4dbu level... they're generally high impedance outputs that are down around -40 or so.

Peace
Very good point, if I were connecting a synth or an instrument, I'd use a preamp with a dedicated instrument in or use a good DI and going in mic level. Line level would be coming from a compressor, EQ, preamp, or output of a board.
Old 23rd February 2012
  #16
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Fletcher's Avatar
Quote:
Originally Posted by hell View Post
That makes sense, but aren't preamps generally going to be accepting line level instruments like synths for most applications?
If you're coming out of a synth or instrument... most of these things have a "DI" ["Direct Injection"] 1/4" input on the front... either use that, or use the DI of your choice into the mic input and you'll be fine.

Peace
Old 23rd February 2012
  #17
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Quote:
Originally Posted by EisenAudio View Post
Because the LINE input on the back of your x73i is intended for studio line level (+4 dBm) sources, such as the output of your D/A, multitrack, console, or compressor, which you're now going to process using said preamp. In the vast majority of traditional (professional) studio environments, XLR is the dominant connector type present in these balanced line level sources.

Most (all?) synths and similar devices do not operate at studio line level, but rather an intermediate instrument level somewhere between a passive instrument pickup (no standard, perhaps -30 dBu) and consumer line level (-10dbV). Instrument level sources are usually unbalanced, using 1/4" TS jacks. Critically, synths want to see a fairly high impedance instrument input, such as are employed on a plethora of instrument amplifiers, effects devices, and DI boxes, which is why 1/4" jacks are used. The LINE input of your Vintech is neither high impedance, nor instrument level (in addition to being balanced), and so it uses an XLR connector.
The light bulb just went off. Thank you. That was a great answer.
Old 23rd February 2012
  #18
XLR - professional connection - more robust, you can't short it, and so on.

TRS - space saving, cheaper, sem-pro connection.

In addition to the above...
Old 23rd February 2012
  #19
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Quote:
Originally Posted by iangomes View Post
I think what may be confusing you is that the output of synths isn't technically line level, nor is it called that. You want to plug your synth into the instrument in on a pre or into a di and then the mic input of a pre.
You're right. I think that is what was confusing me. I have read so many articles that say synthesizers are line level. A quick google of the phrase gets me lots of hits that say things like this:

"Most synthesizers have Line-Level audio outputs that can overload a typical effects box"
Guitar Pedals for Keyboard Players | Sweetwater.com

So, I guess from what you guys are saying: synths generally have a hotter output than a guitar, but NOT as hot as a pro +4 line level signal? Does that make any sense or am I still thinking of it wrong?

Thanks again for all of the great answers, guys.
Old 23rd February 2012
  #20
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Quote:
Originally Posted by EisenAudio View Post
Most (all?) synths and similar devices do not operate at studio line level, but rather an intermediate instrument level somewhere between a passive instrument pickup (no standard, perhaps -30 dBu) and consumer line level (-10dbV).
Most of my analog synths have really hot outputs esp the Minimoog, Taurus, and OB-X. I'm running them into a Rane SM-82 which can accept +4dBu with the input at nominal, and I had to bring the input DOWN to tame the hot outputs of those analogs. No way are they -30dBu or -10dBV.

Quote:
Critically, synths want to see a fairly high impedance instrument input, such as are employed on a plethora of instrument amplifiers, effects devices, and DI boxes, which is why 1/4" jacks are used. The LINE input of your Vintech is neither high impedance, nor instrument level (in addition to being balanced), and so it uses an XLR connector.
A quick peek at the spec of the output impedance of a minimoog is 1K (low output jack). The active output stages of most synths is not much worse than that. While the 600ohm balanced mic input would be inappropriate, high impedance instrument inputs are appropriate for instruments with passive outputs (such as guitar pickups) but not necessarily for synths with active outputs. Any competent EE knows this via the law of maximum power transfer.
Old 24th February 2012
  #21
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Quote:
Originally Posted by The Real MC View Post
Most of my analog synths have really hot outputs esp the Minimoog, Taurus, and OB-X. I'm running them into a Rane SM-82 which can accept +4dBu with the input at nominal, and I had to bring the input DOWN to tame the hot outputs of those analogs. No way are they -30dBu or -10dBV.
Good to know, thanks! The Rane SM-82 demonstrates an important consideration in that it has a 100k (that's 100,000 ohms) input impedance, which is great for active instrument outputs and their not-so-low output impedance (i.e. 1k? as you've pointed out). The Moog output stage barely does any work at all when driving 100k, allowing it to swing full output voltage (and cleanly!). Meanwhile, its 1k output would yield a -8.5dBu loss if trying to drive a 600 ohm input, thanks to the voltage divider effect. I imagine this would cause distortion as well, assuming said output stage isn't designed to source/sink so much current. Inappropriate, as you say.

Quote:
Originally Posted by The Real MC View Post
A quick peek at the spec of the output impedance of a minimoog is 1K (low output jack). The active output stages of most synths is not much worse than that. While the 600ohm balanced mic input would be inappropriate, high impedance instrument inputs are appropriate for instruments with passive outputs (such as guitar pickups) but not necessarily for synths with active outputs. Any competent EE knows this via the law of maximum power transfer.
Recording studios haven't operated via power transfer in a long, long time. We are concerned with voltage transfer, which is why line level inputs are typically 10,000 rather than 600 ohms, and most line level outputs are less than 100 ohms (and can only deliver 1W at best). This is called a bridging connection, and it has been a constant in consoles, recorders, and outboard since tubes gave way to transistors. Here's the way I was taught it as an EE undergrad: a low (relative to 600) impedance output (aka source) feeding an input (aka load) of at least 10 times greater impedance will result in at least %90 of the voltage drop across the load rather than the source, hence optimal voltage transfer. (Of course this simplification assumes DC or low frequency [e.g audio band]. There are different considerations for RF, digital, and transmission lines, but I digress...) In other words, what we're looking at is an equivalent voltage divider formed by the source as series resistor and the load as shunt resistor, as I touched upon above. Indeed, ten times 1k is 10k, which is one reason why your Moog and indeed many active instruments can do alright plugged straight into a (active) bridging line input. However, the 10k LINE input of a Neve style preamp, such as Vintech, is accomplished by a transformer containing a DC winding resistance much lower than 10k (500ohms, for example), which an active instrument output may have difficulty driving.

Moreover, the majority of musical instruments (i.e. synths) are not designed according to recording studio standards and can be quite different from make to make, which accounts for the disparity of synth output levels we've discussed.

These are some reasons why many responders have suggested the original poster use a Hi-Z instrument input for his synth, and why the Rane SM-82 you're using offers another safe solution. Barring an esoteric discussion of thermal noise, parasitics, minimum load/termination, and s/n ratio, a greater (i.e. 100k to 1M, as typical) impedance instrument input stage can't hurt at the signal voltage levels we're describing. (...assuming you still get the tone you want! Maybe the harmonics generated by your synth output working too hard are a part of the great-sounding patch you've got going? )
Old 24th February 2012
  #22
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Besides the above reasons
1. using same connector for mic and line means keeping less part # instock for a manufavture and better pricing from suppliers.
2 Ease of support/ harder to confuse i and o
3 I know of at least one consultant who will not spec a piece of gear (exception being mixers) with out XLRs.
Old 24th February 2012
  #23
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Quote:
Originally Posted by EisenAudio View Post
These are some reasons why many responders have suggested the original poster use a Hi-Z instrument input for his synth, and why the Rane SM-82 you're using offers another safe solution. Barring an esoteric discussion of thermal noise, parasitics, minimum load/termination, and s/n ratio, a greater (i.e. 100k to 1M, as typical) impedance instrument input stage can't hurt at the signal voltage levels we're describing. (...assuming you still get the tone you want! Maybe the harmonics generated by your synth output working too hard are a part of the great-sounding patch you've got going? )
In the specs of the Rane unit (posted below) that you guys are talking about...what does "20% limit" mean? Thanks again for all of the helpful information that has been provided!

Inputs:
Channels 1-8: 100k ohms 20% limit
Receive: 100k ohms 20% limit
Expand: 20k ohms 1%
Outputs:
Main: 100k ohms 1%
Loop Send: 100k ohms 1%
Expand: 100k ohms 1%
Old 24th February 2012
  #24
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Quote:
Originally Posted by iCompress View Post
Why would it be a noise or balancing thing? both TRS and XLR are balanced.
Because as Neil Muncy pointed out a long time age. As far as noise and interference are concerned, the XLR is a much more symmetrical circuit.
Old 24th February 2012
  #25
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Quote:
Originally Posted by hell View Post
In the specs of the Rane unit (posted below) that you guys are talking about...what does "20% limit" mean? Thanks again for all of the helpful information that has been provided!

Inputs:
Channels 1-8: 100k ohms 20% limit
Receive: 100k ohms 20% limit
Expand: 20k ohms 1%
20% limit is +/-20% IE min 80K max 120K

Quote:
Outputs:
Main: 100k ohms 1%
Loop Send: 100k ohms 1%
Expand: 100k ohms 1%
Typo should be 100 ohms not 100Kohms
Old 24th February 2012
  #26
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Quote:
Originally Posted by Speedskater View Post
Because as Neil Muncy pointed out a long time age. As far as noise and interference are concerned, the XLR is a much more symmetrical circuit.
I believe he was referring to the symmetry of balanced lines vs. unbalanced. Symmetry can be achieved with a balanced TRS.
Old 24th February 2012
  #27
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Quote:
Originally Posted by kennybro View Post
I believe he was referring to the symmetry of balanced lines vs. unbalanced. Symmetry can be achieved with a balanced TRS.
No he and others were talking about symmetry in two conductor cables and connectors. Cables with foil shields and drain wires are less symmetrical and more subject to noise pick-up. A XLR connector and the attached wires are much more (but not perfect) than a TRS connector.
Old 24th February 2012
  #28
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Fletcher's Avatar
Quote:
Originally Posted by Speedskater View Post
Cables with foil shields and drain wires are less symmetrical and more subject to noise pick-up.
depends on the gauge of the drain wire... if its in keeping with the "hot" and "neutral" then its generally not a problem. You can often get a more complete shield with foil than with a braid... though it can be more easily susceptible to damage if its moved around quite a bit.

Quote:
A XLR connector and the attached wires are much more (but not perfect) than a TRS connector.
There is greater contact area on an XLR than on a TRS... but TRS connectors are perfectly fine as the contact area of the connector is sufficient for the task at hand.

Peace
Old 24th February 2012
  #29
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Often, it can be an issue of structural reliability also. You can trip over an XLR and give the cable a pretty good tug before disturbing the connection. A 1/4" TRS will break and pull free much easier. Probably more important in live concert situations.
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