Noise and Hum in Audio Circuits


“I currently have a car stereo set that i use as an amplifier in my living room. but my main problem is that i a lot of noise hum when ever it is on especially when there happens to be a drop in the supply Voltage. i decided to use a voltage regulator and capacitor across (1600uF)…but it only reduced the hum a little. how can i completely eliminate the noise”. – Question ¬†by FP

Answer by delabs 

Ensure that the power supply has a full wave or bridge rectifier. If power supply transformer is say 12-0-12 two diodes must be there and a center tap ground OR If a square or round bridge is used with four leads or four diodes, then it is fine. Half wave rectification or a blown or leaky diode can cause this problem. Put all the filter caps you want and add a series choke as well the better the power supply the audio will be good.

The power supply transformer rating – voltage and current both may need to be boosted. Some very low budget transformers do not use CR-GO plates for lamination (i think it is Cold Rolled Grain Oriented ). They use plain thick metal plates without coating and hence hysteresis and eddy current both cause problems. Then you have ground loop hum and noise of semiconductors, the speaker ground and amplifier ground carry current and they should be directly connected to power supply ground, These you can understand by looking at these pages……

I am only aware of Phillips transistor based designs used 20 years back, but these have more…

Noise in Audio Amplifiers

“Noise has enormous nuisance value with sensitive (i.e. high gain) circuits, but the information provided by most IC and transistor makers..”Avoiding Ground Loop Hum

“To solve the problem, the goal is to reduce the magnitude of the loop current. This is done simply by inserting isolation resistor(s) in series with the audio cable ground(s)…”

Audio, Power, and Control Lines

“The correct place for an audio ground is at the microphone connector entrance to the shield enclosure of the radio…”




Product Design - Industrial Automation and Instrumentation.

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