You want to plug your iPOD or MP3 player into your guitar amplifier, but there are so many conflicting opinion on the internet — many of them wrong. Hopefully I can clear a few things up.

Let’s get two things straight first up:

1. I am no expert. There are so many conflicting views on the internet that I set out to try find the facts. This post is the result of my research; let’s hope I have done my research well. If you are an expert in this area and find something incorrect on this page, please post a comment at the end of this article and I will fix it.
2. Electric guitar amps generally do not have high fidelity speakers — they are only designed to reproduce the guitar’s sound range, so you will not get the highs and lows of a high fidelity speaker. Electric guitar amplifiers are also generally mono, whereas most music sources are stereo. In other words, your home audio or even a set of powered computer speakers will reproduce music better than a guitar amp. If you are just after pure volume though, a guitar amp should do the trick.

The internet contains a lot of wrong information as to what source you can plug into what output device. Sure, you can buy adaptors to plug just about anything into anything else, but you risk damaging your equipment. Just because you can buy an adaptor to do it, does not mean that you should!

Guitar players seem to be a pretty gung-ho lot. As long as they can find an adaptor to make a plug fit a socket, they will give it a go and hope that they do not release the ‘magic smoke’. If you want better information, you need to start searching the audiophile web sites and discussion boards.

Some terms

To better understand what you can plug in and apply it to your own situation, first you need to understand a few terms.

Mono vs stereo vs surround sound

Mono means that there is only one sound signal, often produced through only one speaker. If mono is played through two speakers, the same sound comes out of both speakers.

Stereo audio means that there is a different sound signal for left and right speakers. Stick your head between two stereo speakers and listen carefully — you should notice different sounds coming from each speaker.

Surround sound takes it to a whole new level, with left/right and front/back speaker signals, plus a sub-woofer speaker for bass. Surround sound systems generally have five or seven speakers and are usually found in home entertainment systems to play movies or computer games.

Balance vs unbalanced signals

Audio cables are designed to carry signals that are either balanced or unbalanced.

A balanced cable uses two conductors surrounded by a shield to carry the signal. By inverting one signal, any noise/hum that is picked up by the cable can be removed from the signal. Balanced cables are usually used for microphones. Because of the extremely low signal produced by microphones, any minor interference can be amplified into audible noise. A balanced microphone/cable/amp should eliminate the noise.

Unbalanced cables have a single conductor surrounded by a shield to carry the audio signal. Where cable length is relatively short, an unbalanced cable will usually provide adequate hum rejection and will cost less. Examples of unbalanced cables are those used for electric guitars, iPOD/MP3 headphones and RCA leads.

Signal levels

Different devices use different signal levels. Unfortunately, there is no way to accurately tell what signal level you are dealing with, without looking in your device’s handbook. Even then, many devices do not specify the signal levels used. The following is therefore only a general guide.

Note: this table is in development — values may be incorrect.

Level	Strength	Nominal signal level (approx)	Input impedance (approx)
Microphone level	weak	-50 dbV	Low <600 ohm Medium 600 – 10 k ohm High >10 k ohm
Instrument level	fairly weak	-20 dBV	1 M ohm
Line level (consumer)	moderately strong	-10 dBV	10 k ohm
Headphone level	strong	+10 dBV	8 to 600 ohm
Speaker level	very strong	+10 to 40 dBV	<16 ohm

Note that the impedance bridging principle is often used in audio circuits, where a low impedance output drives a high impedance input. For example, a typical line out connection has an impedance from 100 to 600 ohms. Line inputs though, have a much higher impedance, typically 10 k ohms or more. The impedance bridging principle will be relevant when we discuss plugging an iPOD or MP3 player into a guitar amp below.

Connections

Unfortunately, it is not possible to simply look at the connection being used and determine the nominal signal level and impedance.

The RCA or phono plug is also used to connect unbalanced line-level signals and is commonly seen in stereo equipment.

The 3-pin professional audio connector (XLR) is used with cables for balanced microphones and other balanced equipment.

The ¼-inch phone plug is generally used to connect unbalanced line-level or instrument-level signals. Examples includes plugs on cables used with guitar amps, mixers, electric keyboards, electric guitars, and some power amplifiers.

The stereo phone plug is used with stereo headphones and with balanced line-level cables.

The only way to know whether a 1/4″ phone jack is balanced or unbalanced, mono or stereo is by looking at the specifications in your equipment manual.

How to plug your iPOD (or MP3 player) into a guitar amp

Some general rules of thumb:

• If you try to plug a device with a low signal level into a device designed to take a high signal level, you will need to turn the up the amplifier volume, introducing noise.
• If you try to plug a device with a high signal level into a device designed to take a low signal level you will get clipping at high volumes. Turn the volume down low and you will probably be okay.
• Because of the impedance bridging principle, it is okay to plug a low impedance device into a high impedance device. It is not okay to plug a high impedance device into a low impedance device. Examples of this principle can be found in guitar equipment: 1) Plug instrument into effects pedal socket, but from then the signal is at line level through several pedals, but the line level finally going into the high impedance instrument level amp socket. 2) Plug line out level or headphone output into AUX in socket in guitar amp. Similarly, because of the impedance bridging principle, a headphone output can generally drive a line input; but a line input generally can not drive a set of headphones.
• It is NOT okay to simply join the left and right stereo channels and use them as a mono signal. This is how many ‘Y’ adaptors work. They are essentially shorting the two channels together and may damage the source device. Use a small mixer to combine stereo left and right channels before plugging into mono equipment.

 

Using AUX in socket

If you are planning to plug your iPOD, MP3 player, home stereo or other device into a guitar amplifier, you are best to use the stereo line level output (RCA leads or headphone output) from the device and plug it into the stereo AUX in jack of the guitar amplifier. This will bypass the amp’s guitar special effects, as well as safely combine the stereo signal from the electronic device into the mono output of the amplifier.

Guitar amps such as the Roland Cube 15 XL or Marshall MG15 have AUX in sockets that should be suitable. AUX in sockets are pretty common on small guitar amps, so check you product manual.

Plugging into the amp’s guitar socket

Not all guitar amplifiers have an AUX in, so what can you do? Do NOT use a Y-adaptor to combine the stereo line level output of a device into the guitar amp’s instrument input.

If you want to plug a stereo line level device into the guitar amp’s ¼” inch socket normally used to plug a guitar in, you need to use a mixer, such as the Behringer Micromix MX400. The MX400 and other similar mixers can be purchased for about $30 online.

Use two adaptors to convert the left and right RCA cables into two separate ¼” mono phone plugs on the mixer. These will then be outputted to a single ¼” mono line level that can be plugged directly into your guitar socket on your amplifier. Of course, you need to switch off all effects on the amp, otherwise your music is going to sound pretty weird!

The usual disclaimer applies.