DI Box the solution?

[TripleJ]

Hey,

I have my electric guitar running into the line in on my mixer (acting as a preamp) (Yamaha MG10/2) then out of my rec.outs into my PC.

Now I am using an amp simulator on my pc to get some effects going.

My problem is however that to get a hot enough signal I have to turn the gain on the mixer/preamp up alot resulting in noise.

Would using a DI box between the guitar and the line in on the mixer solve my noise problems, or not?

Thanks
-Dan

 

[scrubs]

The DI won't add any gain, but, if you use a DI, it will balance your signal to an XLR, meaning you can go into the XLR input of your mixer, rather than the 1/4" instrument input. Many XLR inputs on preamps/mixers are "hotter" than the comparable 1/4" input, meaning, you shouldn't have to use as much preamp gain. I don't know the specifics for that particular mixer, however, so I would look that up before buying anything.

 

[RAK]

Hey,

I have my electric guitar running into the line in on my mixer (acting as a preamp) (Yamaha MG10/2) then out of my rec.outs into my PC.

Now I am using an amp simulator on my pc to get some effects going.

My problem is however that to get a hot enough signal I have to turn the gain on the mixer/preamp up alot resulting in noise.

Would using a DI box between the guitar and the line in on the mixer solve my noise problems, or not?

Thanks
-Dan

The reason you have to push the gain so much is because your guitar level is lower than the level the line input on hte Yamaha is looking for. If you use a DI, that will convert the guitar level to Mic level, and then you hook the XLR output into one the XLR Mic Ins on the Yamaha, and should be straight.

Microphone, Instrument, and Line are all different levels, so it's best to match them up.

 

[boingoman]

The reason you have to push the gain so much is because your guitar level is lower than the level the line input on hte Yamaha is looking for. If you use a DI, that will convert the guitar level to Mic level, and then you hook the XLR output into one the XLR Mic Ins on the Yamaha, and should be straight.

Microphone, Instrument, and Line are all different levels, so it's best to match them up.

No offense, but that is pretty much all incorrect.

To the original poster- an active DI would probably take care of the problem. A passive may work, or could result in as much noise as just plugging into the line input. The problem is impedance, not level. Your guitar pickups won't interface with line-level inputs very well. Line-level inputs are around 10,000ohms, your guitar wants to see at least 100,000ohms, preferably much higher. The result of plugging a guitar into a line input is often a weak signal, with lots of noise and distortion.

An active DI can have very high impedance. A passive may or may not have enough, depending on what it's plugged into.

 

[RAK]

No offense, but that is pretty much all incorrect.

To the original poster- an active DI would probably take care of the problem. A passive may work, or could result in as much noise as just plugging into the line input. The problem is impedance, not level. Your guitar pickups won't interface with line-level inputs very well. Line-level inputs are around 10,000ohms, your guitar wants to see at least 100,000ohms, preferably much higher. The result of plugging into a line input is often a weak signal, with lots of noise and distortion.

An active DI can have very high impedance. A passive may or may not have enough, depending on what it's plugged into.

Dude seriously, I was trying not to get too technical speaking about impedance. Relax.
As I said, and as you say, plugging his guitar into the line levels would yield a low level, (low impedance I didn't say). He can use either an Active or a Passive DI, that doesn't matter. In fact, Passive DIs having a transformer as they do, are better at noise cancellation.
And by the way I have experienced plugging an acoustic guitar into the line in on a board and been able to get enough signal out of it (when the guitarist doesn't plug his cable into the insert jack that is )

Either way DIs convert instrument level to Mic level, and then he plugs the DI output into the mixer Mic Input. Mic Level is low impedance/low level compared to Line Level which is high impedance/high level.

I don't usually say this, but nothing in my earlier post was incorrect.

And if you do go with an active DI, remember it needs phantom power.

 

[boingoman]

Dude seriously, I was trying not to get too technical speaking about impedance. Relax.

Not getting too technical is one thing, but all that stuff you posted was wrong anyway. Sorry.

Impedance is his problem. He is running an electric guitar into a line input and getting noise. He should use an active DI or something like a Sansamp, a passive DI likely won't have enough impedance to give good results.

DIs do not convert signals to mic level.

His guitar may put out less than line-level, but that by itself usually won't be much of a factor in the noise level as the impedance. Incorrect impedance drastically affects tone, output level, and noise in passive pickups. Also, many electrics actually put out pretty strong signals. Humbuckers can easily put out signals that come close to line level. My Strat can put out almost 1 volt, with single coils.

I'm relaxed, but even if I wasn't that wouldn't change the fact that you wrote out a bunch of wrong stuff in your first post, and followed it up with more in your second.

It certainly can matter if he uses an active or passive. Passive DIs use transformers, and thus do perform well in a balanced circuit. But generally won't have enough impedance to work well with electric guitars. It may work fine, though.

Plugging an acoustic into a line input? With active pickups? Totally different situation than an electric guitar with passive pickups. Active pickups usually run at relatively low impedances, which bridge into a line input very well They can also tolerate a wider range of input impedance without suffering tonal issues, unlike passive pickups.

DIs do not convert to mic level. Passives drop the signal an average of 20db. Whether that puts the signal at mic level or not depends on the strength of the signal in the first place. Active DIs can have any amount of attenuation, including none.

Plugging an electric guitar into a passive DI, besides giving it a low impedance to work with, will drop the signal level further, raising the noise floor even further.

Active DIs need phantom power- unless they can run on batteries, of course.

 

[RAK]

Not getting too technical is one thing, but all that stuff you posted was wrong anyway. Sorry.

Impedance is his problem. He is running an electric guitar into a line input and getting noise. He should use an active DI or something like a Sansamp, a passive DI likely won't have enough impedance to give good results.

DIs do not convert signals to mic level.

His guitar may put out less than line-level, but that by itself usually won't be much of a factor in the noise level as the impedance. Incorrect impedance drastically affects tone, output level, and noise in passive pickups. Also, many electrics actually put out pretty strong signals. Humbuckers can easily put out signals that come close to line level. My Strat can put out almost 1 volt, with single coils.

I'm relaxed, but even if I wasn't that wouldn't change the fact that you wrote out a bunch of wrong stuff in your first post, and followed it up with more in your second.

It certainly can matter if he uses an active or passive. Passive DIs use transformers, and thus do perform well in a balanced circuit. But generally won't have enough impedance to work well with electric guitars. It may work fine, though.

Plugging an acoustic into a line input? With active pickups? Totally different situation than an electric guitar with passive pickups. Active pickups usually run at relatively low impedances, which bridge into a line input very well They can also tolerate a wider range of input impedance without suffering tonal issues, unlike passive pickups.

DIs do not convert to mic level. Passives drop the signal an average of 20db. Whether that puts the signal at mic level or not depends on the strength of the signal in the first place. Active DIs can have any amount of attenuation, including none.

Plugging an electric guitar into a passive DI, besides giving it a low impedance to work with, will drop the signal level further, raising the noise floor even further.

Active DIs need phantom power- unless they can run on batteries, of course.

Wow dude, He's only having problem with noise because he has to turn the gain up really loud to get a decent level, so he's also turning up all the noise. The reason he has to turn the gain up all the way is because he's plugging in an instrument level device (with instrument impedance) into a line-level input (with line level impedance).

Of course an Acoustic is different than an electric, maybe I shouldn't have used that example, I was just showing that you can plug a guitar into a line input if you have to. Sheesh.

Direct Injection Box's don't convert to mic level you say? Now that's the most blatently wrong thing I've read on here in a while. The point of a DI is to get your guitar or bass or keyboard or whatever to a level/impedance that your board can read, meaning, being able to go into the mic pre-amp inputs.

DI are not made to be plugged into Line Level sources, they're made to be plugged into Mic Level sources, which are low impedance. That's just the way it is.
The most basic setup in the world with DI that most anybody knows goes like this: guitar 1/4" to DI 1/4" IN, (1/4" Thru to Guitar amp.) XLR Out to XLR Mic In on your console. It's that simple. Is this bizarro world or something? And I've never had a problem using an electric guitar or bass with a passive DI.

"I'm not sure this word means what you think it does" - Inigo Montoya

 

[bubbagump]

Hold on a sec.... a passive DI is simply a step down transformer. So with a typical DI being a 500:1 transformer let's look at Ohm's law. Current is constant.

So Voltage = Current x Resistance

So if my input is 100v

100v = 1 x ? which is 100ohm

put it through a 100:1 transformer for simplicity.

10v =1 x 10ohm

So As the voltage drops, so does the impedance. So a line level signal going into a DI not only lowers its resistance but also its voltage (which we describe as decibels in audio). Am I nuts here?

 

[RAK]

Hold on a sec.... a passive DI is simply a step down transformer. So with a typical DI being a 500:1 transformer let's look at Ohm's law. Current is constant.

So Voltage = Current x Resistance

So if my input is 100v

100v = 1 x ? which is 100ohm

put it through a 100:1 transformer for simplicity.

10v =1 x 10ohm

So As the voltage drops, so does the impedance. So a line level signal going into a DI not only lowers its resistance but also its voltage (which we describe as decibels in audio). Am I nuts here?

Makes sense to me. Can't argue with Ohm's Law V=IR, which is why I was saying a mic is low level AND low impedance, I just didn't bring up impedance in my initial post. The difference between resistance and impedance as I understand it is impedance is frequency dependant.

 

[TripleJ]

Wow I didn't realise I stepped upon such a contentious question!

So I *am* looking for a DI, but whether it's 'passive or active' is the argument?

 

[boingoman]

Hold on a sec.... a passive DI is simply a step down transformer. So with a typical DI being a 500:1 transformer let's look at Ohm's law. Current is constant.

So As the voltage drops, so does the impedance. So a line level signal going into a DI not only lowers its resistance but also its voltage (which we describe as decibels in audio). Am I nuts here?

You are only as nuts as you feel. I feel pretty nuts.

I'm not sure how you are using Ohm's law for this, I just multiply or divide by the turns ratio. You can use Ohm's law to figure out the current flow on both sides of the transformer, though.

You are missing a source impedance...

DIs typically use around 10:1 transformers, not 500:1.

So a 1.7V 1000ohm source (typical line-level gear) hooked into a passive DI comes out as 170mV@100ohms, which goes into a 2500ohm mic pre nicely. The line-level gear see the mic pre's impedance X10, or 25,000ohms, which gives it a good bridged input to go into.

A passive DI's input impedance is actually the input impedance of the mic pre input, seen through the tranformer winding, so it is multiplied by 10. Hence the usual advertised input impedance of 20-25,000ohms for your average passive DI plugging into your average mic pre with 2000-2500ohms input impedance.

So the DI lets the mic pre "see" a source as having a lower impedance than it does, and lets the source "see" a higher impedance at the input than the mic pre actually has. Both end up happy, impedance-wise, and the lower-impedance circuit is less susceptible to noise in general, as well as being balanced.

 

[boingoman]

So I *am* looking for a DI, but whether it's 'passive or active' is the argument?

A DI will do what you want, whether an active or passive will work better for you......you will find out.

 

[boingoman]

Wow dude, He's only having problem with noise because he has to turn the gain up really loud to get a decent level, so he's also turning up all the noise.

The reason his signal is so weak and noisy in the first place is most likely due to the impedance mismatch between the pickups and the input. The pickup's output will drop drastically, the tone will be affected, and the high impedance makes the circuit really vulnerable to noise. Yes, lots of gain at the input will add some noise, but his problem starts with impedance, not low levels. If he just boosted his signal, he would probably have the same problems with noise.

A passive DI could have the same impedance problem, which could be made even worse as the signal is dropped by about 20db, requiring more gain to bring it back up, which will add more noise.

If you look, I said a passive might work, it might not, but I'd bet an active will be a better solution in any case.

Direct Injection Box's don't convert to mic level you say?.

Yes, I do say. A passive DI drops the level by about 20db. A signal going into a passive DI will come out about 20db down from the level it was. That may or may not end up being in the range considered to be mic level. The signal is attenuated, not "converted". A signal at +10 into the DI will come out at -10, for instance. It is not automatically dropped to mic level, and still may need to be padded so it doesn't overload the mic input.

Pay attention: Active DIs don't necessarily drop the signal level at all. Many pass the signal through at unity, and have on-board pad switches to drop the level if it needs attenuating.

Both, however, have a low-impedance output. For passives, the impedances depend on what is plugged into it, and the turns ratio of the transformer. A passive with a 1000ohm keyboard plugged into it will have about 100ohms output impedance, which interfaces with a 2000ohm mic pre nicely. An 8000ohm electric pickup through the same DI will show about 800ohms to the mic pre, which could cause problems.

DI are not made to be plugged into Line Level sources, they're made to be plugged into Mic Level sources, which are low impedance. That's just the way it is.

I'm pretty sure you mean "destinations" not "sources". And no shit, they are mean to plug into low impedance inputs. That's what they are for, and what I have been trying to tell you.

 

[boingoman]

Makes sense to me. Can't argue with Ohm's Law V=IR, which is why I was saying a mic is low level AND low impedance, I just didn't bring up impedance in my initial post. The difference between resistance and impedance as I understand it is impedance is frequency dependant.

I'd really love to hear how you relate Ohm's law to all this, but my stupid barrel is all full today. Any more RAK-talk and I might have retarded children.

I'm gonna archive this, and ask the people at Shure all these questions and more next week, you obnoxious moron. It's one thing to be wrong, it's another to be RAK. You give good advice when you talk about your own experience, stay there, it's for the best. And read up on DIs.

Have a nice weekend.

 

[bubbagump]

Hrm... it seems Google is pretty worthless for finding more info on this. To the original poster, we're into semantics here, so don't worry about the rest of this. I am just curious to understand the mechanics better myself. I'll have to pick the brain of a few of my electrical enginerring buddy's to see if they can distill it better. The impedance part is what gets me as I understannd step down coming into your house (10,000v to 120 v for instance) but in audio, the whole output/input imdenace of a device puts a wrench in the works. Ah well, to the library I go.

 

[bubbagump]

Well, I learned something about baluns today as I had never heard the term before. RAK, you are indeed incorrect. It is simply an impedance matching device. Here's what I learned.... when making a balun, you can use a transformer with a 1:1 ratio and that only converts between balanced and unbalanced. If you construct a balun with a ratio (such as 10:1 or whatever) then it impedance matches. No voltage difference is introduced. Th edifference being, if we were to go from a simple unbalanced signal to an unbalanced signal, from what I gather, you would have a voltage difference. However, by changing to a balanced signal, you have an impedance change and not a voltage change. Based on this link the balun differs from a standard step down in that the signal goes to ground to allow for balancing where as you don't have that in a voltage step down transformer. (I am working on finding an article to confirm my suspicion.) You learn something new all the time.

 

[Farview]

The impedance part is what gets me as I understannd step down coming into your house (10,000v to 120 v for instance) but in audio, the whole output/input imdenace of a device puts a wrench in the works.

The stepdown coming to your house is voltage, not impedance.

To the original poster: I would get an active DI. I have had problems with passive DIs screwing up the tone of passive pickups. Active pickups, like EMG's, basses with batteries in them, acoustic guitars with built in pickups that take batteries, etc... as well as line level devices like keyboards will work with passive DI's AND active DI's. Passive instruments tend to have tone problems with passives.

 

[Farview]

BTW: Passive DI's attenuate by a certain amount. The output may be mic level or not depending on the signal level on the input.

 

[bubbagump]

Alright, a friend of mine set me straight. Here is the guts of it:

If you haven't done the math above, you probably haven't figured out that regardless of balanced or unbalanced configuration at the output, the very first thing that can be said about this DI box transformer is that it must be a step down transformer. Lots of turns on the input and not so many on the output (high impedence primary/low impedence secondary).

The Impedence and Voltage swing are inexorably locked in step with each other, you cannot change one without changing the other. But whatever the output of that transformer is hooked to can change the impedence at the transformer's input. Hook the output to a 10 ohm input and you likely will have much the same kind of problem you had when attempting to hook the pickup directly to the low impedence input even though the DI transformer is in the circuit. You have loaded it down too far and that loading will be reflected back through the magnetic field transfer to the transformer's input with the same resulting signal amplitude degradation and the EQ shift.

So essentially it is the pipe "backing" hitting a low impedance input up that causes the transformer to change impedance.

 

[rayc]

Ohms Law - isn't that the rule about chanting that Buddhists adhere to?
Now, in the lotus position veryone. 1st finger & thumbs making a nice circle in each hand, eyes closed, & repeat after me...
Ohm is where the ART is.