Can someone explain what determines the quality of a DI-box?
I can see that there is a whole bunch of active and passive DI's, and
the price range is going from 30$ - 400$. I know that some of these are
actually DI/preamp in one, but what are the main features that differ
quality from each other. Connectors? Active/passive? Attenuation?
Impedance on the output?....

Lets say that I need a DI to connect to mixer (with a preamp), and then
mixer to some recording gear (HDD recorder, tape, computer...). So, I
just need the impedance conversion (since I have a preamp on the mixer),

not all that gain, EQ... controls, just the simplest one. What should I
look for when deciding which one to buy? Impedance mach for mixer (or
maybe for the recording device after the mixer???)? Do they all put out
signal with the same impedance? Is there some sort of standard?

thanks.

Stevan Svilokos wrote:
Can someone explain what determines the quality of a DI-box?
I can see that there is a whole bunch of active and passive DI's, and
the price range is going from 30$ - 400$. I know that some of these are
actually DI/preamp in one, but what are the main features that differ
quality from each other. Connectors? Active/passive? Attenuation?
Impedance on the output?....

Impedance on the input

Distortion level

Isolation quality

That's really about it.

Lets say that I need a DI to connect to mixer (with a preamp), and then
mixer to some recording gear (HDD recorder, tape, computer...). So, I
just need the impedance conversion (since I have a preamp on the mixer),

Right. What impedance conversion do you need, though? If you are coming
out of a keyboard, a 1kohm input is fine. If you are coming out of a passive
bass pickup 1Mohm may not be enough.

The small passive ones are fine for synths and other things that don't need
the highest input Z. The active ones will give you a higher input Z.

not all that gain, EQ... controls, just the simplest one. What should I
look for when deciding which one to buy? Impedance mach for mixer (or
maybe for the recording device after the mixer???)? Do they all put out
signal with the same impedance? Is there some sort of standard?

They all have more or less the same output Z. What you care about is the
input Z, and the distortion, and how good the ground isolation is. If you
have a ground loop, can you break it effectively? If you have a lot of
RF trash, does it leak into the DI box or not? You pay for that isolation.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article writes:

Can someone explain what determines the quality of a DI-box?

The same sort of things that determine the quality of any other audio
device (or car, or coffee grinder, or office chair) - the basic design
philosophy, the circuitry, the components that go into it, and the
construction.

I can see that there is a whole bunch of active and passive DI's, and
the price range is going from 30$ - 400$. I know that some of these are
actually DI/preamp in one, but what are the main features that differ
quality from each other. Connectors? Active/passive? Attenuation?
Impedance on the output?....

All of the above, though output impedance is least significant of the
lot unless you're planning to send the output back to an instrument
amplifier. But there's a wide range of designs for an active DI -
tubes, discrete solid state, op-amps, and a range of component
quality. If there are five capacitors in a DI, building basically the
same circuit using 35 cent capacitors rather than one dollar
capacitors doesn't sound like much, but do that and you'll (hopefully)
want to use better resistors, better connectors, a robust and well
shielded power supply (if not battery or phantom powered) and a more
solid box. Even though there's only a small difference in the price of
individual componetns, once it's on the shelf at your dealer's, it can
increase the price by $50-75.

Passive DIs consist of a transformer and possibly some additional
resistors and capacitors to control the phase response of the
transformer. There are $2 transformers and $60 transformers, both of
which will provide a suitably great number of ohms so as not to load
the pickup, but one will have lower distortion, or a more pleasant
kind of distortion, than the other.

There are other things that can affect the price and performance of a
DI, but that should give you an idea.

Lets say that I need a DI to connect to mixer (with a preamp), and then
mixer to some recording gear (HDD recorder, tape, computer...). So, I
just need the impedance conversion (since I have a preamp on the mixer),

It depends on what you're connecting to the mixer. If it's a line
level device such as a synthesizer or a drum machine, unless you're
running the cable for a great distance like between the stage and
house mixing console, you might get better sound without a DI at all,
just connecting the line level output to the mixer's line level input.
If you're connecting an electric guitar or bass to the mixer, that's
where you need the DI. That provides a high input impedance for the
pickup (which the line input of a mixer would come pretty close to
doing) but as well, it would reduce the signal level to roughly that
of a microphone so you can take advantage of the gain of the mic input
of the mixer and boost the signal back to the standard mix level. If
you just connected a pickup directly to the line input of a normal
mixer, you wouldn't have enough gain in that channel to bring the
signal up to the level of the rest of the mix (assuming you're mixing
to the nominal "0 VU" output level of the mixer.

What should I
look for when deciding which one to buy?

Actually, price isn't a bad measure of quality, unless you
particularly like the sound of a particularly trashy sounding DI. This
is one of those things that you pretty much get what you pay for.

Impedance mach for mixer (or
maybe for the recording device after the mixer???)? Do they all put out
signal with the same impedance?

Roughly the same. However, they vary quite a lot in input impedance,
that is, what the instrument going in the DI sees. A typical
transformer DI will have an input impedance in the range of 25k to
50k Ohms. A typical active DI will have an input impedance in the
range of 250k Ohms to several megohms. What's best here is a function
of the pickup, if you're plugging in a guitar or bass, and it's less
of a concern if you're plugging in an active device such as a
keyboard. Some guitars really sound good when going into a good
transformer, some sound a whole lot better when going into a very high
impedance active input.

Use your ears, or if you can't do that, just buy as much as you can
afford. It can never be "too good" and some day a cheaper one might be
"too bad."




--
I'm really Mike Rivers - )

First of all thanks for the responce!


Scott Dorsey wrote:

Right. What impedance conversion do you need, though? If you are coming
out of a keyboard, a 1kohm input is fine. If you are coming out of a passive
bass pickup 1Mohm may not be enough.

No, I don't have keybords. Only bass and guitar with passive pickups... SO, I
need a DI that can accept impedance of what, like more than 1Mohms??? Not that
I'm expert or something, but isn't that like huge resistance...?

The small passive ones are fine for synths and other things that don't need
the highest input Z. The active ones will give you a higher input Z.

oooohhh... great. I saw that active one (with battery not phantom powerd) is not
to dificult to make...

They all have more or less the same output Z. What you care about is the
input Z, and the distortion, and how good the ground isolation is. If you
have a ground loop, can you break it effectively? If you have a lot of
RF trash, does it leak into the DI box or not? You pay for that isolation.

hmmm... so the isolation on transofrmator (in case of passive DI's) is what I'm
paying for.
I don't have much problems right now... so far everything is OK when I plug
guitar into a mixers line in, but when I record it, i have only responce in
bottom frequencies... I need more "action" in midrange for guitar. As far as I
know it's only because of impedance, since I record into the Midiman Audiophile
2494 wich has flat frequency responce, and I have behringer mixer, wich also has
almost flat freqvuency responce. So it has to be DI.

Thanks.

In article , says...
Can someone explain what determines the quality of a DI-box?
I can see that there is a whole bunch of active and passive DI's, and
the price range is going from 30$ - 400$. I know that some of these are
actually DI/preamp in one, but what are the main features that differ
quality from each other. Connectors? Active/passive? Attenuation?
Impedance on the output?....

A good audio transformer costs an arm and a leg. The kind of transformer
in a $50 passive [transformer] DI is unlikely to be high quality.

Transformer DIs have one big advantage: they can be used for earth loop
isolation in unbalanced circuits.

In article znr1057929519k@trad, says...

In article writes:

Can someone explain what determines the quality of a DI-box?

The same sort of things that determine the quality of any other audio
device (or car, or coffee grinder, or office chair) - the basic design
philosophy, the circuitry, the components that go into it, and the
construction.

I can see that there is a whole bunch of active and passive DI's, and
the price range is going from 30$ - 400$. I know that some of these are
actually DI/preamp in one, but what are the main features that differ
quality from each other. Connectors? Active/passive? Attenuation?
Impedance on the output?....

All of the above, though output impedance is least significant of the
lot unless you're planning to send the output back to an instrument
amplifier. But there's a wide range of designs for an active DI -
tubes, discrete solid state, op-amps, and a range of component
quality. If there are five capacitors in a DI, building basically the
same circuit using 35 cent capacitors rather than one dollar
capacitors doesn't sound like much, but do that and you'll (hopefully)
want to use better resistors, better connectors, a robust and well
shielded power supply (if not battery or phantom powered) and a more
solid box. Even though there's only a small difference in the price of
individual componetns, once it's on the shelf at your dealer's, it can
increase the price by $50-75.

Passive DIs consist of a transformer and possibly some additional
resistors and capacitors to control the phase response of the
transformer. There are $2 transformers and $60 transformers, both of
which will provide a suitably great number of ohms so as not to load
the pickup, but one will have lower distortion, or a more pleasant
kind of distortion, than the other.

There are other things that can affect the price and performance of a
DI, but that should give you an idea.

Lets say that I need a DI to connect to mixer (with a preamp), and then
mixer to some recording gear (HDD recorder, tape, computer...). So, I
just need the impedance conversion (since I have a preamp on the mixer),

It depends on what you're connecting to the mixer. If it's a line
level device such as a synthesizer or a drum machine, unless you're
running the cable for a great distance like between the stage and
house mixing console, you might get better sound without a DI at all,
just connecting the line level output to the mixer's line level input.
If you're connecting an electric guitar or bass to the mixer, that's
where you need the DI. That provides a high input impedance for the
pickup (which the line input of a mixer would come pretty close to
doing) but as well, it would reduce the signal level to roughly that
of a microphone so you can take advantage of the gain of the mic input
of the mixer and boost the signal back to the standard mix level. If
you just connected a pickup directly to the line input of a normal
mixer, you wouldn't have enough gain in that channel to bring the
signal up to the level of the rest of the mix (assuming you're mixing
to the nominal "0 VU" output level of the mixer.

What should I
look for when deciding which one to buy?

Actually, price isn't a bad measure of quality, unless you
particularly like the sound of a particularly trashy sounding DI. This
is one of those things that you pretty much get what you pay for.

Impedance mach for mixer (or
maybe for the recording device after the mixer???)? Do they all put out
signal with the same impedance?

Roughly the same. However, they vary quite a lot in input impedance,
that is, what the instrument going in the DI sees. A typical
transformer DI will have an input impedance in the range of 25k to
50k Ohms. A typical active DI will have an input impedance in the
range of 250k Ohms to several megohms. What's best here is a function
of the pickup, if you're plugging in a guitar or bass, and it's less
of a concern if you're plugging in an active device such as a
keyboard. Some guitars really sound good when going into a good
transformer, some sound a whole lot better when going into a very high
impedance active input.

I know someone using a Proco CB1 on a bass guitar. According to Proco
this transformer DI has the following specs:

"INPUT IMPEDANCE:
Greater than 185 kohm @ 1.0 kHz.
Greater than 140 kohm @ 10 kHz.
Nominal source impedance is 20 kohm."

Which is the actual impedance of the transformer (for comparison
purposes). Would the bass guitar work better on an active DI?

In article znr1057929519k@trad, Mike Rivers wrote:

Lets say that I need a DI to connect to mixer (with a preamp), and then
mixer to some recording gear (HDD recorder, tape, computer...). So, I
just need the impedance conversion (since I have a preamp on the mixer),

It depends on what you're connecting to the mixer. If it's a line
level device such as a synthesizer or a drum machine, unless you're
running the cable for a great distance like between the stage and
house mixing console, you might get better sound without a DI at all,
just connecting the line level output to the mixer's line level input.
If you're connecting an electric guitar or bass to the mixer, that's
where you need the DI. That provides a high input impedance for the
pickup (which the line input of a mixer would come pretty close to
doing) but as well, it would reduce the signal level to roughly that
of a microphone so you can take advantage of the gain of the mic input
of the mixer and boost the signal back to the standard mix level.

Mmm... do *active* DIs reduce the level too ?

--
André Majorel URL:http://www.teaser.fr/~amajorel/
No actual neurons were harmed in the making of this Usenet post.

Mainlander *@*.* wrote:
Can active DIs break ground loops? It's easy to figure out that a passive
DI can, because the secondary circuit is physically not connected to the
primary one.

Yes, BUT it's true that they can't use phantom power when doing this,
because the ground is needed for the phantom reference.

The exception to this is is the Radial J48, which does some really neat
trickery to isolate the power seperately (it uses a little switching supply)
so you can break ground and still use phantom.

UY Most passive DIs I've seen, however, use non centre tapped
windings with the earth connection left open on the balanced side rather
than using a centre tap. That should be easy enough to do with a active
DI using electronics?

Sure. Some of the active DIs, though, use output transformers for better
isolation. In an active DI, the output transformer just provides isolation,
not impedance conversion, and it can be inefficient. This means you can
get an inexpensive transformer that will perform very well because the hard
stuff isn't being done by the transformer any more.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article *@*.* writes:

I know someone using a Proco CB1 on a bass guitar. According to Proco
this transformer DI has the following specs:

"INPUT IMPEDANCE:
Greater than 185 kohm @ 1.0 kHz.
Greater than 140 kohm @ 10 kHz.
Nominal source impedance is 20 kohm."

Which is the actual impedance of the transformer (for comparison
purposes). Would the bass guitar work better on an active DI?

With specs like that, heck if I know. 185K is mighty high for a
transformer. Since it goes down significantly between 1 kHz and
10 kHz, it looks like the capacitance of the windings is substantial.
This sounds suspicious to me.

In my own experience, I haven't used a transformer DI that sounds as
good as a decent active DI on a bass, but then I've never used a
really good transformer DI, nor have i tried a DI on every bass.
They're all different.

You get what you got when you only got one.



--
I'm really Mike Rivers - )

In article writes:

Mmm... do *active* DIs reduce the level too ?

Sure, if they're intended to go into a mic level input. But these
days, we tend to expect an outboard mic preamp (which has a line level
output to have a high impedance, low gain unbalanced input suitable
for connecting an instrument pickup. If you're talking about that kind
of "active DI", then, no, you'd expect a little gain, enough to get
the instrument up to line level, same as a microphone.



--
I'm really Mike Rivers - )

In article znr1057969454k@trad, Mike Rivers wrote:
In article *@*.* writes:

I know someone using a Proco CB1 on a bass guitar. According to Proco
this transformer DI has the following specs:

"INPUT IMPEDANCE:
Greater than 185 kohm @ 1.0 kHz.
Greater than 140 kohm @ 10 kHz.
Nominal source impedance is 20 kohm."

Which is the actual impedance of the transformer (for comparison
purposes). Would the bass guitar work better on an active DI?

With specs like that, heck if I know. 185K is mighty high for a
transformer. Since it goes down significantly between 1 kHz and
10 kHz, it looks like the capacitance of the windings is substantial.
This sounds suspicious to me.

I'd expect way more capacitance than that if the transformer really
had that high an input Z. So I bet there is a series resistor in
front of it to increase the effective input impedance. That doesn't
seem like a really good idea.

And even so, that is a whole lot of input capacitance. I bet the top
end isn't so flat.

In my own experience, I haven't used a transformer DI that sounds as
good as a decent active DI on a bass, but then I've never used a
really good transformer DI, nor have i tried a DI on every bass.
They're all different.

I thoroughly agree, although with a bass that has active pickups,
all DIs will more or less sound the same. (And none will sound good
if you ask me, but that's another issue for another time).

You get what you got when you only got one.

I do really like the March 1998 Recording Magazine project. It won't
let you lift the ground so it's no good for stage use, but it's lots of
fun in the studio, very high-Z, and cheap to make.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In Article znr1057929519k@trad, (Mike Rivers) wrote:

In article writes:

Can someone explain what determines the quality of a DI-box?

The same sort of things that determine the quality of any other audio
device (or car, or coffee grinder, or office chair) - the basic design
philosophy, the circuitry, the components that go into it, and the
construction.

I can see that there is a whole bunch of active and passive DI's, and
the price range is going from 30$ - 400$. I know that some of these are
actually DI/preamp in one, but what are the main features that differ
quality from each other. Connectors? Active/passive? Attenuation?
Impedance on the output?....

Many have added a lot of very good info here. I can only say there's a BIG
differecne between my IMP passive direct and Groove Tubes DITTO. The DITTO
still doesn't take all of the sting out of a piezo under-saddle acoutic
guitar pickup, but it does a VERY nice job on electric guitar and keys.

The DITTO is a two tube stage "front end", with a transformer balanced
output and a variable gain stage control between the two tube stages. Very
nice sound.

It has the usual ground lift switch and a handy 1/4" pass through jack so
you can feed your stage amp as well as the DITTO itself.

Regards,

Ty Ford

For Ty Ford V/O demos, audio services and equipment reviews,
click on http://www.jagunet.com/~tford

In article znr1057969454k@trad, says...

In article *@*.* writes:

I know someone using a Proco CB1 on a bass guitar. According to Proco
this transformer DI has the following specs:

"INPUT IMPEDANCE:
Greater than 185 kohm @ 1.0 kHz.
Greater than 140 kohm @ 10 kHz.
Nominal source impedance is 20 kohm."

Which is the actual impedance of the transformer (for comparison
purposes). Would the bass guitar work better on an active DI?

With specs like that, heck if I know. 185K is mighty high for a
transformer. Since it goes down significantly between 1 kHz and
10 kHz, it looks like the capacitance of the windings is substantial.
This sounds suspicious to me.

In my own experience, I haven't used a transformer DI that sounds as
good as a decent active DI on a bass, but then I've never used a
really good transformer DI, nor have i tried a DI on every bass.
They're all different.

You get what you got when you only got one.

Another Q. The transformer steps down the voltage going to the lower
impedance, is that correct? So if the pickup only puts out a pretty small
voltage, the secondary voltage into 600 ohms must be miniscule...

Mainlander *@*.* wrote:

Another Q. The transformer steps down the voltage going to the lower
impedance, is that correct? So if the pickup only puts out a pretty small
voltage, the secondary voltage into 600 ohms must be miniscule...

The pickup puts out a pretty high voltage. Take one apart and look at how
many winds are on that thing. It'll put out a good volt or so, but it
has no ability to put out any current at all.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article *@*.* writes:

Another Q. The transformer steps down the voltage going to the lower
impedance, is that correct?

Yes.

So if the pickup only puts out a pretty small
voltage, the secondary voltage into 600 ohms must be miniscule...

Have you measured the output voltage of a guitar pickup lately? A
slamming rhythm player can get a couple of volts out of the pickup
into an open circuit. But pickups have a high internal resistance, so
when you load them with a relatively low impedance such as a
conventioal mic input (or even a line level input, which almost has
enough gain if it's a "-10" input) most of the voltage gets dropped
across the internal impedance of the pickup and doesn't get out to
where you're amplifying it. See my article on amps, volts and ohms in
the August issue of Recording Magazine if you don't understand this.

The idea of a DI box is to get the level of the instrument pickup down
to the (admittedly miniscule) level of a microphone so the micrphone
pickup can do its job and amplify it as cleanly as it does a
microphone.

Your assumption is that the output level of a guitar is very low. It
isn't, at least when essentially unloaded. An instrument amplifier or
DI presents a very high impedance so that almost all the voltage
coming from the pickup gets to the next device along the chain. A
guitar amplifier has substantially less voltage gain than a mic preamp
(however it DOES have power gain since it has to drive a speaker).




--
I'm really Mike Rivers - )

In article znr1058103918k@trad, says...

In article *@*.* writes:

Another Q. The transformer steps down the voltage going to the lower
impedance, is that correct?

Yes.

So if the pickup only puts out a pretty small
voltage, the secondary voltage into 600 ohms must be miniscule...

Have you measured the output voltage of a guitar pickup lately? A
slamming rhythm player can get a couple of volts out of the pickup
into an open circuit. But pickups have a high internal resistance, so
when you load them with a relatively low impedance such as a
conventioal mic input (or even a line level input, which almost has
enough gain if it's a "-10" input) most of the voltage gets dropped
across the internal impedance of the pickup and doesn't get out to
where you're amplifying it. See my article on amps, volts and ohms in
the August issue of Recording Magazine if you don't understand this.

The idea of a DI box is to get the level of the instrument pickup down
to the (admittedly miniscule) level of a microphone so the micrphone
pickup can do its job and amplify it as cleanly as it does a
microphone.

Your assumption is that the output level of a guitar is very low. It
isn't, at least when essentially unloaded. An instrument amplifier or
DI presents a very high impedance so that almost all the voltage
coming from the pickup gets to the next device along the chain. A
guitar amplifier has substantially less voltage gain than a mic preamp
(however it DOES have power gain since it has to drive a speaker).

OK, I must be thinking like a dynamic mic, which has a pretty small
output voltage.

In article znr1058103918k@trad, says...

In article *@*.* writes:

Another Q. The transformer steps down the voltage going to the lower
impedance, is that correct?

Yes.

So if the pickup only puts out a pretty small
voltage, the secondary voltage into 600 ohms must be miniscule...

Have you measured the output voltage of a guitar pickup lately? A
slamming rhythm player can get a couple of volts out of the pickup
into an open circuit. But pickups have a high internal resistance, so
when you load them with a relatively low impedance such as a
conventioal mic input (or even a line level input, which almost has
enough gain if it's a "-10" input) most of the voltage gets dropped
across the internal impedance of the pickup and doesn't get out to
where you're amplifying it. See my article on amps, volts and ohms in
the August issue of Recording Magazine if you don't understand this.

I don't know whether that magazine is available in this country, but I
understood it pretty well from DC voltage theory, like when you talk
about the "internal resistance" of a power source, such as a battery, to
start a car or whatever the internal resistance needs to be very low
otherwise a lot of power gets dissipated across the battery and doesn't
get used for anything useful at all.

I just assumed that since dynamic mics put out millivolts, pickups must
be the same.

One thing I don't know about is why high impedance circuits are more
susceptible to noise pickup.

Mainlander *@*.* wrote:

OK, I must be thinking like a dynamic mic, which has a pretty small
output voltage.

Right, because it's got a low-Z output. That's basically what impedance
means... a low-Z out will supply a lot of current and not much voltage,
a high-Z output will supply a lot of voltage and not much current. You
can trade one for the other with a transformer.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."