• Hardware
  • Do I need a DI box for recording my guitar? (p.2)
2015/12/29 16:35:49
Jeff Evans
I prefer active DI's because usually they offer a much higher input impedance. I think just choose a quality unit.
 
What I have done with guitar tracks sometimes is pan the pure sound left but with some decent amp sims etc on that sound and the miked guitar cab right. You can the get into some nice stereo imaging that way from just a single mono source.
 
Or mix or blend the miked sound with the amp sim sound. There are some decent amp sims out the like SGear and also AcmeBargig Headcase. (Danny put me onto that one and it is killer)
2015/12/29 17:47:41
tlw
The main thing to check is that the DI box actually does habe an input impedance of 1MOhm or above. Also, connecting the guitar to the DI and the DI's 'direct output' to effects/amp often results in the guitar seeing the impedance of the DI box and the fx/amp as parallel resistances. This happens when the direct out on the DI is simply another jack socket wired directly to the input.

The result would be the guitar seeing e.g. 1MOhm at the DI plus a parallel 1MOhm from the amp. Which Ohm's Law tells us means the guitar is now seeing a 500Ohm load, which is a bit lower than ideal.

One way round this is to put a buffer with a 1MOhm+ input impedance between guitar and DI so the buffer is the first thing the guitar sees. Every Boss pedal (and quite a number of others) contains such a buffer, which is permanently active whether the pedal is on or off so long as it is receiving power. Most guitarists have at least one Boss pedal kicking around the place...

The whole DI before effects thing does falls flat on its face if you use certain pedals, such as Fuzz Faces and similar transistor fuzzes or some wahs because the guitar and pedal form a single circuit and if the pedal doesn't see the right range of impedances 'upstream' at the guitar then the pedal circuit doesn't operate as designed. Putting such pedals after a buffer, or even another effect that isn't true bypass or is switched on, also means they don't work properly. Typically fuzzes become much brighter, more distorted and refuse to clean up properly as the guitar volume and tone controls are adjusted.

The whole thing is a trial and error process. If you don't use the kind of pedals that are affected, don't worrry about it. Just run a buffer between guitar and DI.
2015/12/30 06:19:05
Jeff Evans
It also depends a bit on how that link output is organised on the DI box. On many DI's that link output is in direct parallel to the input so in that case any pedals that come from the link out will in fact still see the guitar and its equivalent circuit and should be no different to running the guitar direct to the first pedal etc.. The buffer is actually built into the active DI and is the first thing the signal passes through before going onto the balanced XLR output circuit and provides total isolation to that which is what you want.  And if the input impedance of that internal buffer is very high eg 1M ohms etc it will have no effect on the guitar.  They are also best run on phantom power too.
 
But if the link out though is coming from a separate internal buffer that is in fact distancing the guitar circuit from the link output and as tlw correctly points out it will effect how the pedals that may follow will react.
 
One way to find out is to check the block diagram of the proposed DI you may be interested in. Some manufacturers actually provide the circuit diagram so it is easy to see.  I think in many cases the link output is just wired direct to the input socket eg in parallel.
 
Watch out for passive DI's though with guitars. The transformers can only offer an input impedance in the area of 100K ohms or so and the primary of that transformer ends up in parallel with the guitar circuit and could easily alter things quite seriously as tlw suggests. The input impedance of a transformer is also dependent on the load to the secondary as well which makes things a bit more murky.
2015/12/30 07:58:27
maximumpower
I will look for an active DI but if I went passive, I could put it after my compressor. It has an input impedance of 1Meg Ohm and output of 2.2K Ohm. Or after my EQ; input 1M, output 510 Ohms.
 
Thanks again for the great advice!
2015/12/30 13:21:23
jpetersen
The OP wants to connect the DI out from the amp to the mixer/interface.
 
> On the amp, the line out description says:
> The LINE OUT 1/4” jack is for connecting to power amps or mixers
 
The DI out of the amp will have a low output impedance and will be fully compatible with the jack input of the m-audio Profire 610 interface. There will not be any losses in the high end.
 
I further mentioned the advantages of using a DI box between the guitar and the amp.
If the OP chooses to use a DI box, then the connection to the interface must be with an XLR-to-XLR cable, not a 1/4" jack.
 
2015/12/30 13:47:46
Rimshot
I called Live Wire about their passive direct box today and asked if the input signal and output signal on the front of their box is exactly the same and they said yes. 
It seems someone was saying that the signal is degraded in some way but according to Live Wire, on their passive boxes, the signal coming out of the front is exactly what is going in. This output is not the XLR output on the box but the parallel out on the front.
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