Help With Balanced versus Unbalanced Connections on the Axe II

Q

quark

Experienced
I'm trying to get clear on how to safely connect up the various ins and outs on the Axe-II and the balanced vs unbalanced options have me a bit confused:

What I think is true so far is:

1) Balanced are low impedance and are carried by XLR or 1/4" TRS cables.
2) Unbalanced are high impedance and are carried by 1/4" TS cables
3) You should never mix balanced and unbalanced
4) You can convert from unbalanced to balanced using a DI box
5) You can't convert from balanced to unbalanced.
6) You can improve AXE unbalanced outputs by using a TRS-TS humbusting cable but they are still unbalanced.

If that's right, then does it mean that,

1) In1 and In2 can only be be fed a 1/4" TRS cable from a balanced output. If I want to plug a guitar into In1 or In2, I have to use a DI box and convert the XLR output connector to 1/4" TRS.

2) I can only plug the 1/4" Out1 and Out2 into unbalanced inputs using a TS cable unless I use a DI box.

3) XLR Out1 can only fed an balanced input taking an XLR plug and can never fed an unbalanced input.

Seems like I've read about some connections that don't always follow these rules, .. e.g. plugging a guitar directly into In1 or In2 .. so maybe I don't understand all of this too well. Can anybody help clear this up for me?

Thanks ....
 
  1. Both the balanced and unbalanced outputs on the Axe-Fx are low-impedence.
  2. All the inputs are high-impedence.
  3. You can mix balanced and unbalanced. (If you feed an unbalanced output into a balanced input, you'll get a 6 dB reduction in level; there will be no other audible difference unless there's a ton of interference in the air.)
  4. Yes, a DI box can convert unbalanced to balanced. Which means it's also converting balanced to unbalanced at the same time.
  5. Humbuster cables will only improve the sound if there is a ground loop going on. They won't help with hum from other sources. And yes, they are unbalanced.
 
i gave my answer in the other thread you posted:

quark said:
1) Unbalanced signals are hi-impedance and are usually carried by 2 terminal conductors (e.g 1/4" - TS)
2) Balanced signals are low-impedance and are usually carried by 3 terminal conductors (e.g XLR or 1/4"- TRS)
3) You never want to send an unbalanced signal into a balanced input
4) You never want to send a balanced signal into an unbalanced input
5) You can convert an unbalanced signals to a balanced signals using a DI box
6) You can't convert balanced signals into unbalanced signals
Click to expand...

i've never heard anyone really say "never" in #3 and #4, but by design you are correct.

What has me confused are applications (e.g your 2 guitar into one Axe video ) that seem to put an unbalanced signal into a balanced input - like when a TS guitar cable is plugged into the rear Input 1 which requires a TRS cable and balanced signal.

If you want to put an unbalanced signal into Inputs 1 or 2 shouldn't you use a DI box to convert the signal to balanced or perhaps risk damaging the electronics?

and

If you want to run the unbalanced out 1 and 2 into a balanced input (e.g mixer ) don't you need a DI box to convert?

Any insights are appreciated before I blow my Axe up with wrong connections ....
Click to expand...

you won't blow anything up with guitar level signals and line level outputs. there's no high current/voltage going on. you do have to be careful when dealing with Phantom power and/or Amp outputs and Speaker cables as these carry a high voltage and current to power things (mics, speakers, etc).

i'm not and engineer or electrician, so i don't know what's really going on when i use a TRS cable out of the unbalanced outputs then to an XLR, but it works well. [Rex has since answered this above]

a DI box is mostly used before a PA mixer to change the impedance of a signal from hi to low to allow for longer cable runs with less interference. a side-effect is that the signal usually goes from unbalanced to balanced. you generally never use a DI box to go into the axe fx or any other effects device.

if you use the unbalanced outputs and hear noise or you are doing cable runs longer than 18 feet, then it may be better to use a DI box. but it's mostly to avoid noise and interference rather than avoiding damage.

as for the Unbalanced guitar cables going into Balanced inputs, it works - i was gonna explain some stuff like TRS and TS etc, but it works. you won't damage anything.
 
General rule of thumb is to keep the input impedance of the receiving device at least 10 times higher than the output impedance of the sending device for good signal transfer (10:1 ratio or higher). That means roughly 90% of your original source signal should make it into the receiving device. The higher that ratio, the less signal you lose to ground from the voltage divider effect between the two devices.

Axe FX's input impedance is 1M ohm (1 million ohms), so anything with an output impedance of less that 100K ohms (100,000 ohms) should have no big issues with signal transfer.

With that 1M input impedance and a typical say 10K ohm output impedance from a passive guitar circuit, you'd have a 100:1 ratio and roughly 99% of your guitar signal makes it into the Axe FX.

Granted this is a very simplified take on impedance matching, and it gets much more complicated when you take into account that impedance can and usually does change with frequency, but it's a decent quick and dirty rule of thumb.
 
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