An oscilloscope is used to test any source of poor sounds in an amplifier. Such sources of poor sounds could be a possible blown fuse, signal alteration or even inappropriate biasing. An oscilloscope displays the shape of signal waves, enabling one to test given electrical currents and observe waves. Depending on the type of the oscilloscope, it can display waves on a cathode ray.
There are two main types of oscilloscopes; digital and analog oscilloscopes. The digital style oscilloscope shows waves on cathode rays, while the older style oscilloscope structures a digital screen. This article outlines how to test an amplifier by use of an oscilloscope.
Types of oscilloscopes
1. A digital oscilloscope
This type of oscilloscope uses an LCD screen. The main difference between this type and the analog type is that, when using this digital oscilloscope, an extra step to convert a signal into a digital stream is needed, and thus there is no need for CRT screens. It allows space for more and newer features and also makes the design less complex.
2. An analog oscilloscope
These oscilloscopes display their wave on a cathode ray, and thus they need high gain amplifiers. This oscilloscope is equipped with several channels, namely, vertical channels, a trigger system, a time base, a CRT module and a horizontal channel.
- Vertical channels are composed of an analog delay line, a preamplifier, a vertical amplifier and finally, an attenuator. The vertical amplifier amplifies a given signal to the required level for the cathode ray model.
- A horizontal channel will always come in a two work mode. The work modes are internal and external.
- A trigger system contains certain level adjustments which always switch between the increasing and the decreasing levels.
When using an oscilloscope, you need to get some terminologies to help you connect with ease. Examples of the vocabularies include;
- Bandwidth – determines the ability of an oscilloscope to measure a given signal.
- A Rise time – this usually tells the frequency range. If an oscilloscope has a fast rise time, this means it will capture details faster and accurately.
- A Sample rate – signifies how frequently the oscilloscope takes snapshots of signals.
- Memory depth- is usually a determinant of the amount of data captured with each given channel.
- The waveform capture rate – this is just how fast an oscilloscope can capture and acquire waveforms.
Steps on how to test an amplifier using an oscilloscope
You should ensure that you have a screwdriver to help you open the amplifier
Using your screwdriver, remove the top panel of the amplifier and safely put the screws aside. Then remove the back panel of the amplifier and also put the screws in a safe place. When placing your screws, make sure to put them according to the order you removed them. It is always advisable to place them on a strip to avoid confusion.
Once you are done removing both the top and the back panel, the circuit board and the chassis ground are visible.
It would help if you now connected a working generator to the input of the amplifier. A generator is needed depending on the test to be conducted. For example, a generator is not required when testing for the voltage of the circuit board.
It is better to have a generator connected to the amplifier than always connecting and disconnecting a given one.
Locate the output socket of the amplifier, and you should have a red cable. Connect the red cable to the output socket. The electronic load will receive power and stimulate an operation without the amplifier processing any signal. During the test, the amplifier is supposed to function normally.
When speakers are connected, it is advisable first to disconnect them as they can get damaged and damage your ability to hear. Here, the current is not stagnant, so the electric load has to absorb it and protect the output stage of the amplifier when testing.
Connect the cable at the ground of the oscilloscope to the chassis ground of the amplifier. The chassis ground is mostly a bolt on the back or the side of the chassis’ inside. It would help if you turned on the generator and set all oscilloscope controls to zero. Then set the oscilloscope to a direct current.
Now turn the audio amplifier on and be keen not to disconnect the ground cable in the process of testing. If the ground cable accidentally detaches, then you are at a high risk of electrocution.
Onto the part of your amplifier to be tested, press the probe and tightly hold it to avoid it slipping off the amplifier. Carefully adjust both the oscilloscope’s time and volts dials. It will help adjust the view on the grid. There are two different axis that represent other things. Time is displayed by the horizontal axis, while the vertical axis represents voltage.
A curve is displayed. The curve explains how power dispels when flowing through the amplifier.
Move the probe from side to side on the amplifier as you keenly observe the grid. If there happen to be uneven wave formations, then there must be a problem with the amplifier that needs to be corrected. If the wave formations are even, then your amplifier is fine.
Now turn off the generator and connect the oscilloscope to the AC for you to test the transformer’s power supply. If there are no ripples on the waveform, then there is a possibility of shortened winding.
You should always note that the texture of the wave determines the quality of sound. A smooth wave will lead to the production of a better sound compared to a rough wave. Always understand the oscilloscope’s terminologies, as they will help you know your work with ease. An oscilloscope helps one get to know how voltage can change over time by showing the waveforms.
When testing your amplifier, always maintain utmost care, mostly when handling the ground cables. Do not connect the wires in a wet area or even when your hands are wet. Always remember to turn off the power where needed to avoid electrocution. If the above steps do not help you test your amplifier, you need to consult a professional.