BrunoARG
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Hum with single-to-split power supply for equalizer.
Hello people.
About a year ago I built an audio amplifier which sounds very very well, but it has been continuously making a pretty annoying 100Hz hum that I couldn't ever fix.
It consists of two parts: A 4 channel mono equalizer, and a 4 channel (actually using only 3 but equalizer channels are summed up to get a flat response) output stage made with TDA7294 and a passive filter for each one, and sounds very very loud and its bass response is excellent (with a 10" woofer).
The power supply comes from a single 12V transformer I got from a desk lamp (60W). The output voltage is about 16 or 15V (depends of the AC line) and for signal proccessing (equalizer and preamplification) I splitted it in lower symmethrical voltages (to scape from that annoying ripple, which can make it down to 13 or 12V at maximum volume.).
The problem I have is, when I connect my phone directly to the power stage, the amplifier sounds great, no hum and so loud. But when I connect it to the equalizer and then it to the power stage, there comes the hum, even with no music playing. The circuit is the following and the simulations show it should work fine.
Circuit diagram
Split power supply voltages
Amplifier 1KHz signal from preamplifier and entering power amp input stage (seems well).
Do you know if there is a trick or something I didn't take into account? I will make some measurements in the actual circuit to show, when I can.
Thank you in advance.
Hello people.
About a year ago I built an audio amplifier which sounds very very well, but it has been continuously making a pretty annoying 100Hz hum that I couldn't ever fix.
It consists of two parts: A 4 channel mono equalizer, and a 4 channel (actually using only 3 but equalizer channels are summed up to get a flat response) output stage made with TDA7294 and a passive filter for each one, and sounds very very loud and its bass response is excellent (with a 10" woofer).
The power supply comes from a single 12V transformer I got from a desk lamp (60W). The output voltage is about 16 or 15V (depends of the AC line) and for signal proccessing (equalizer and preamplification) I splitted it in lower symmethrical voltages (to scape from that annoying ripple, which can make it down to 13 or 12V at maximum volume.).
The problem I have is, when I connect my phone directly to the power stage, the amplifier sounds great, no hum and so loud. But when I connect it to the equalizer and then it to the power stage, there comes the hum, even with no music playing. The circuit is the following and the simulations show it should work fine.
Circuit diagram
Split power supply voltages
Amplifier 1KHz signal from preamplifier and entering power amp input stage (seems well).
Do you know if there is a trick or something I didn't take into account? I will make some measurements in the actual circuit to show, when I can.
Thank you in advance.