need advice on DI/new interface

[TheDriller]

hey lads,

i've been frustrated by the tone im getting with amp-sims for a while. today i looked at the spec sheet for my interface (M-Audio Firewire Solo) and found that the instrument in has an impedance of only 270k

so now i have 2 options, get a nice DI box and run it into one of the unbalanced line-ins, or get a new interface.

does anyone have any recommendations for an affordable DI box? or would i just be wasting my time?

here is the specs for the Firewire Solo:
http://www.m-audio.com/products/en_us/FireWireSolo.html


if i were to go for a new interface, it would need to be affordable, with a good instrument input and decent conversion. not bothered about having loads of inputs, as i never track more than one mic or one instrument direct in at one time.

dirtyedit: my guitar has an EMG 81 , the spec sheets says that has an output impedance of 10Kohm,
i assume i will be needing a DI box close to this impedance, rather than the 1Mohm that is usually recommended?

thanks!

 

[TheDriller]

wait,
hold the phone,

shouldn't i just plug the guitar straight into the line-in?
10Kohm into a 14Kohm input?

 

[deLuther]

EMG sounds good in high impedance, 14 kOhm is too low, but EMG can sound good even with this impedance, but, I think, plugging into Hi-Z will give better result.

 

[TheDriller]

but the EMG output impedance is 10Kohm , which is lower than even the 14Kohm impedance of the line-in socket?

im gonna try this out later and see what happens

 

[deLuther]

You should plug lower impedance into higher one.

 

[TheDriller]

You should plug lower impedance into higher one.

Nah man, you've got it totally wrong

http://en.wikipedia.org/wiki/Impedance_matching

impedance must always be matched for proper power transfer.

 

[Toni S.]

The Lexicon usb interfaces have a 1Mohm instrument input, which should pretty much cover the range of a guitar signal. I'm gonna get one for the same reason as you, tracking my DI for amp-sims.

 

[deLuther]

Formulas to calculate losses due to impedance: http://www.moollon.com/techntip/impedance_e.asp
I liked tone of EMG 85 pluged to my mic/instrument pre (1 MOhm) more than straight to line input of my card (10KOhm - i.e. same impedance as pickup).

 

[Metaltastic]

Nah man, you've got it totally wrong

http://en.wikipedia.org/wiki/Impedance_matching

impedance must always be matched for proper power transfer.

Nope, not in this case - I'm not sure about the theory or math behind it, but the accepted logic is for maximum preservation of tone (especially highs and detail) from really any transducer, you want to plug it into something with substantially higher input impedance than what it's outputting. As I said, don't ask me why, but I know I preferred the tone of a passive pickup through a Countryman over my Redeye when I did my DI shootout, but the differences between the Countryman and Redeye when using an EMG85 (with a lower impedance being output because of the internal preamp buffering the signal) were far less obvious

And furthermore (this isn't entirely directed at you), all of this is covered in great detail in the "Preparing your tracks for re-amping" thread, I don't really know why these threads keep coming up

 

[TheDriller]

Nope, not in this case - I'm not sure about the theory or math behind it, but the accepted logic is for maximum preservation of tone (especially highs and detail) from really any transducer, you want to plug it into something with substantially higher input impedance than what it's outputting. As I said, don't ask me why, but I know I preferred the tone of a passive pickup through a Countryman over my Redeye when I did my DI shootout, but the differences between the Countryman and Redeye when using an EMG85 (with a lower impedance being output because of the internal preamp buffering the signal) were far less obvious

And furthermore (this isn't entirely directed at you), all of this is covered in great detail in the "Preparing your tracks for re-amping" thread, I don't really know why these threads keep coming up

Thanks man,
will look into that.

its strange, from a quick test last night i've found that i prefer the tone from going straight into the line-in with the EMG 81.
perhaps the instrument-in on my interface is just dogshit.

Im not sure why guiitar pickups should be the exception to the rules of impedance matching though

 

[deLuther]

Quote from http://en.wikipedia.org/wiki/Impedance_matching
( http://en.wikipedia.org/wiki/Impedance_matching#Power_transfer )
"Impedance matching is not always desirable. For example, if a source with a low impedance is connected to a load with a high impedance, then the power that can pass through the connection is limited by the higher impedance, but the electrical voltage transfer is higher and less prone to corruption than if the impedances had been matched. This maximum voltage connection is a common configuration called impedance bridging or voltage bridging and is widely used in signal processing. In such applications, delivering a high voltage (to minimize signal degradation during transmission and/or to consume less power by reducing currents) is often more important than maximum power transfer."

So, in case of guitar into interface, higher voltage is preferable. Like in formula on moollon site.

 

[TheDriller]

thanks for that