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| how to isloate audio ground from the amplifier |
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| Adhith:
--- Quote from: Buriedcode on March 23, 2018, 07:38:22 pm --- --- Quote from: Adhith on March 23, 2018, 07:17:59 pm ---I just used a multi meter ohm function and found that the dc jack ground and the left channel ground is having a resistance of 350 ohm. --- End quote --- The left channel has no ground. Nor does the right channel. No speaker is connected to ground. Both terminals of the speaker are driven by push-pull outputs. In this way the reason they label them "+" and "-" is for phasing. If you connect speakers backwards you will still hear music it will just be out of phase with the other channel, it has nothing to do with ground reference. --- End quote --- sorry sir my mistake. i meant the wire other than the +Ve output of the amplifier. SO what should I call that terminal. the lower side terminal will do?? |
| Adhith:
--- Quote from: Hero999 on March 24, 2018, 04:44:48 pm --- --- Quote from: Adhith on March 23, 2018, 07:20:10 pm ---Ill connect the ground to the vu meter let you guys know about it. --- End quote --- Yes, that will work. As this is a class D amplifier, you might find the existing filter is inadequate at removing all the high frequency content, so the VU meter might indicate there's a signal, even though there isn't one. Another RC low pass filter might be required, before the VU meter. --- End quote --- thank you again. could you suggest me a RC low pass filter for it, the values of R, C??. If i'm using it then there is no need of an additional DC blocking capacitor right?? I have attached the schematics of my VU meter circuit and the circuit do have a 2.2mf electrolytic capacitor at the input and I was under the assumption that its a filter for the input. Is this the case or I'm wrong?? |
| Adhith:
I just fed the ground near the DC jack and the +ve audio output of the left channel to the VU meter input (without any RC filter), but the led was not even lighting up. There is no problem with the VU meter circuit since I have tested it with the previously mentioned LA4440 amplifier board and it works fine. So what would be the reason that the board is not working with my class D amp board?? While measuring the voltage between this +ve left channel output and the ground near the DC jack it is found that it is around a constant of 6.4V. its not changing a little according to sound or increasing or decreasing with the volume or even when there is no audio playing. The voltage appears at these terminals as soon as the amp is powered, afterwards its moreover a constant. So why is it so??. does this shows the ground of the amp is some other terminal?? |
| Zero999:
--- Quote from: Adhith on March 25, 2018, 04:55:08 pm ---I just fed the ground near the DC jack and the +ve audio output of the left channel to the VU meter input (without any RC filter), but the led was not even lighting up. There is no problem with the VU meter circuit since I have tested it with the previously mentioned LA4440 amplifier board and it works fine. So what would be the reason that the board is not working with my class D amp board?? While measuring the voltage between this +ve left channel output and the ground near the DC jack it is found that it is around a constant of 6.4V. its not changing a little according to sound or increasing or decreasing with the volume or even when there is no audio playing. The voltage appears at these terminals as soon as the amp is powered, afterwards its moreover a constant. So why is it so??. does this shows the ground of the amp is some other terminal?? --- End quote --- That's to be expected. The output of the amplifier will be biased at half the supply voltage, hence the 6.4V. I don't know why the VU meter isn't responding at all. It could be the RF parts of the signal. The VU meter needs to be AC coupled to the amplifier. Try adding this circuit between the amplifier and VU meter. It both blocks DC and greatly attenuates the ultrasonic class D switching frequency. If it doesn't work, then you might need to build another op-amp based amplifier, connected to the input of the class D amplifier and drive the VU meter from that. |
| Audioguru:
Your VU meter circuit is completely wrong: 1) The LEDs are backwards with the anodes at ground and the cathodes driven to +12V. 2) The input diode passes DC to the input of the LM3915 and ruins the accuracy of the lower LED turn on voltages. The diode and the 2.2uF capacitor it charges form a very poor peak detector that shorts the amplifier output badly each time the input goes 0.7V or more positive that could blow up the amplifier and/or the diode. The datasheet shows a simple opamp peak detector circuit that I have used and it works perfectly. It is accurate and has an input capacitor to block the 6.4VDC from the amplifier output. The opamp needs a dual polarity supply or an opamp that has inputs that work all the way down to ground like one of the two opamps in an LM358. You cannot add a series capacitor to your horrible diode circuit. Since the amplifier output is +6.4V then it must have a +12.8V supply. Then if the horrible unregulated pot in your circuit is set so that the 10th LED lights when the input peak is 10V, the series diode's voltage drop prevents the 1st and 2nd LEDs from lighting when they should. A peak detector with an opamp will allow all LEDs to light when they should. In your circuit, the +6.4VDC will cause the 8th LED to light in the DOT mode or cause LEDs 1 to 8 to light in the BAR mode with no signal. The horrible pot in your circuit is its unregulated reference voltage but the LM3915 alredy has a regulated reference voltage at pin 7 that is set with two resistors on pin8. You show 2N3906 transistors with a maximum allowed current of only 200mA driving LED strips that might draw 500mA each? You have each output of the LM3915 driving 1k resistors in series with the base of the transistors. Then when all LM3915 output are driving these resistor the LM3915 will be too hot and will fail. The datasheet recommends reducing the output currents so the heating is not too high. How much current does each LED strip need? Here is my peak detector circuit: |
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