scientist36

i've built stereo active speaker use TDA 2005 bridge amp,with 18 vdc psu from 5 ampere step down transformator,when system on without input there's no huming sound,but when i conect the input from television audio output i heard some huming sound but when i touch the ground input the sound is decrease a little,whats wrong in my design,help me to resolve the problem,i see some home theater that sold in store dont produce huming sound.help me THX

crutschow

Is the amplifer working otherwise? Does it amplify the signal from the TV as you expect?

If so, it sounds like you have a ground loop. You could remove the safety earth ground connection from your amp power supply (which I assume you have) but that can lead to a dangerous shock condition. Since the amplifier you are using has a differential type input when used in the bridge configuration, a better option is to operate the amp in a differential mode as follows:

Remove the audio input common connection on the input connector from your circuit ground.

Remove the capacitor (C2) ground connection on the second input and connect to the input connector common.

Connect an approximately 1k ohm resistor (value not critical) from this input common to your circuit ground (to avoid a floating input).

That should break up any ground loop.

scientist36

my power amp is working to amplify input signal from an tv audio output but i heard some huming sound when my power amp get an input from tv,would you show me the schematic for general ground loop elimination,i use pasive tone control,and how about transformer replacement for my circuit.thanks

crutschow

If you can post a schematic for your amplifer and supply I can show you how to do the changes to eliminate the ground loop.

audioguru

Maybe the TV doesn't have a big enough filter on its power supply for its audio section so it produces the hum. Its speakers are tiny and don't reproduce the hum.

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Uncle $crooge

Menticol

Sorry by the draw quality, this was my solution when I had the same problem

(again, is just a pictoric draw not schematic)

Its not necessary to redesign anything on your TV or amp