Is it possible to send 2 separate signals into guitar amp w/ 1 input?, [TOS #6: was "Amplifier input query"] Options

[replicait]

Hi all,

Is it possible to send two separate audio signals (one from a guitar, the other fx from a MOTU output) into a basic guitar amplifier, using a Y-split cable or similar?

In an ideal world:

Guitar > DI > SPLIT [One signal to the audio desk for FOH speaker send, the other into the amplifier] & an output from the MOTU into that same amplifier.

It only needs to play back a few effects cues, not music, so I'm not too worried about the audio quality.

Any advice would be great.

Many thanks

[pdq]

It is never a good idea to connect two outputs together, but there are inexpensive devices called mixers that will do the job. Even less expensive would be to place a resistor in series with each of the sources to safely combine them. Choice of resistor values would control the relative signal strength of the two signals.

[mixminus1]

Also keep in mind the extreme differences in signal levels you're looking at: output from a guitar is in the microvolt range (especially single-coil pickups), the output from your MOTU interface's line out will be in the millivolt-to-volt range, i.e. orders of magnitude higher.

You will need to greatly reduce the output from the MOTU using a resistive pad, as pdq suggested, before mixing the two signals together.

[DVDdoug]

Also keep in mind the extreme differences in signal levels you're looking at: output from a guitar is in the microvolt range (especially single-coil pickups),

And, there are impedance differences... Guitar inputs are unique. They are neither line or microphone compatible. (I thought the voltage is higher than microvolts... I thought it was nearly line-level with a high impedance load of 1M ohm or more.).

I don't know if there's an existing mixer with both line & instrument inputs, and an instrument output. It would be an easy thing to build... for someone who knows how to build op-amp circuits.

Someone might make a pedal with an guitar-in plus a line-in, but I don't know. Almost everything with a guitar-input and a guitar-output is some kind of pedal...

Or, if you have a guitar amp with two inputs (which means it has a little built-in mixer), you can probably plug-in the MOTU, turn down the MOTU output a bit, and turn-down the gain for the channel the MOTU is plugged-into and get a reasonable mix. Someone might make an amp-head with a line input?

This post has been edited by DVDdoug: Apr 23 2012, 18:50

[RobWansbeck]

What sort of DI box are you using?

A DI box usually has a balanced output to feed into a low impedance mic input. Connecting the output to an unbalanced guitar input could cause hum in your FOH speakers. DI boxes also typically reduce the amplitude of signals by a factor of 10.

PS. DVDdoug is correct. The open circuit output from a guitar can be several volts.

This post has been edited by RobWansbeck: Apr 23 2012, 21:48

[Arnold B. Kruege...]

Hi all,

Is it possible to send two separate audio signals (one from a guitar, the other fx from a MOTU output) into a basic guitar amplifier, using a Y-split cable or similar?

In an ideal world:

Guitar > DI > SPLIT [One signal to the audio desk for FOH speaker send, the other into the amplifier] & an output from the MOTU into that same amplifier.

It only needs to play back a few effects cues, not music, so I'm not too worried about the audio quality.

Could you be more specific (make, model) about the "basic guitar amplifier"?

Usually, one uses a mixer to feed one amplifier from multiple sources.

Here's an example:

Mixer for feedbug more than one source through an amplifier