Amplifier Board

Amplifier Board

How do guitar amplifiers work?

I have to write a technical description for class on a guitar amplifier but I'm not familiar with them. Im specifically writing on the Roland Cube-15x because it looks the simplest (I'll take recommendations). As of now I have no idea where the power source is, is it an ac adapter, on board battery, does it even use electricity? And my last question is does anyone know where i can see pictures of how its constructed so i can draw an exploded view of this amplifier.

If a device is going to add gain to a signal, then it has to have some type of power source. Be it AC or battery powered, you have to get the extra energy from somewhere.

I'm not familiar with the Roland amp, but they all work in a similar fashion. We will stick with how a solid state amp works (tube amps will be similar, but have additional power supplies).

The sole purpose of a guitar amp (or any amp for that matter) is to increase the level of the signal put into it so that it can be reproduced by a speaker. Think about it this way...if you plugged an electric guitar straight into a speaker would you hear anything? No, because the speaker requires several volts to operate (while the guitar is probably only putting about about 1/10th of a volt.

The basic blocks of a guitar amp are:

1. PREAMP - this is where the signal from the guitar is connected, and the first stage of amplification occurs. Usually, this gain is anywhere from 10 times to 100 times, depending on the design of the amp.

2. PREAMP 2 (optional) - some amps have a second gain stage which allows you to implement a controlled overload of the second stage in order to generate distortion

3. TONE STACK - this is where the Bass, Mid, and Treble controls would fall. These are normally passive controls (in other words, they can only take away frequencies, and not put more in to the signal). The tone stack is usually a low pass, a band pass, and a high pass filter in series.

4. PHASE SPLITTER - the phase splitter does just what the name says, it splits the signal into two paths. The signals are 180 degrees out of phase with each other (complimentary). This is necessary to drive a push-pull power amp, which is the most common type.

5. POWER AMPLIFIER - up until now, our signal has been somewhere in the 1 to 2 volt range, and only a few milliamps of current. The power amplifier provides that last boost to the signal in order to drive the signal. If our amp is rated at 100w of output, then it's probably putting out somewhere around 20 volts at around 5 amps max.

6. SPEAKER - the last stop for our signal is the speaker, which takes the electrical energy from the power amplifier and converts it to acoustic energy.

The amp would also have a power supply which will normally have a number of output voltages. The preamp section usually takes betwee +/- 5Volts DC to +/-15Volts DC. The power amp will usually take between +/-40 to +/-80Volts DC.

That's a very high overview of how an analog solid state guitar amp works. Tube amps, again, are similar. Digital modeling amps are very different animals all together.

Good luck.

Greetings from Austin, TX

Ken