Standalone DI Boxes

thegummy

When a good quality preamp like a Neve clone or an API etc. has an "instrument in" does it render a separate DI box as obsolete as that circuitry will be included inside the box in a high quality version? And so the standalone DI boxes are strictly for consoles and preamps that only have a microphone input?

Or is there an argument to say a dedicated DI box would still be preferred to the "instrument input" on even a high end preamp?

Stuckfast

No and yes. Like a good instrument input, a good DI box will present a suitably high input impedance for things like electric guitars and basses. But a good DI box does other stuff too. For instance all the ones I own have a Thru socket so you can simultaneously record a DI and pass the instrument signal on to an amp. Also of course you can put a DI box in the live room close to the instrument to which it's connected.

Instrument inputs on preamps are a bit variable in quality. I seem to remember the Neve ones actually have quite a low input impedance and sound noticeably darker than a good DI box.

Danny1969

The purpose of a DI box is basically to convert a hi impedance signal into a low impedance balanced signal which can then travel a long down a mic cable \ snake etc before reaching the pre amp. Balanced signals carry a mirror image of the wanted signal and the difference between them is amplified so any noise common to both conductors is cancelled out. With an unbalanced signal any noise picked up on the cable is amplified. This is the main reason we use DI boxes live ... balanced signals can survive a 100 metre run and more so with no noise. Unbalanced less than 10 metres. The impedance issue is also corrected with a DI box .... basically they have a high input impedance and a low output impedance. Plugging something like a guitar straight into a 600Ohm mic pre amp would result in a shit tone as well as a lot of noise ... the DI box corrects this

Cheap DI boxes generally contain an opamp wired as a differential amplifier .... this does the job in terms of producing a balanced output of low impedance but the quality isn't anything special. Other cheap DI boxs will use a cheap transformer and they will work but will introduce their own distortions and non linearity 

Any buffered pedal will correct the impedance issue and for very short distances unbalanced lines are fine so I don't tend to use DI boxs for recording myself.