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| how to isloate audio ground from the amplifier |
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| Audioguru:
On a bridged amplifier no speaker wire is grounded, each speaker wire is powered from its own amplifier, then the speaker voltage is doubled and the speaker power is almost 4 times higher. If you ground a speaker wire then you cause distortion and probably will blow up the amplifier. The amplifier has a ground which is the 0V or negative of its DC power supply. Therefore one or more terminals on its DC power jack is a ground connection but you must measure it to see which terminal. |
| Buriedcode:
You should read up on the terms "bridged" and "differential". I used the latter term, but in the context of speaker amps its the same thing as bridged (albeit probably less specific). What has been said a few times here is - each connection to the speaker is driven by an amplifier, neither of these connections are at ground. You are still thinking in terms of "single ended" amplifiers, where one side of the speaker is connected to ground, whilst the other side is driven by an amplifier. In that case, your VU meter would have no problems, but your amplifier board - and many modern amplifiers - drive speakers differentially. So, if you use a scope and measure each speaker terminal with reference to ground (the DC jack) you will see a signal. One will be the opposite of the other - as one side of the speaker is driven high (with respect to ground) the other side will be driven low. So if an amplifier is powered by 12V, it can create ~12V across the speaker in one direction, but also in the other direction. Like a H-Bridge! Check out the datasheet on page 6: http://www.st.com/resource/en/datasheet/cd00205863.pdf So what this means is... you have two signals for each speaker, neither of which are ground. You can either just look at one of these signals, which means your VU meter will see a signal sitting at half the power supply voltage, and only give half the indicated voltage (you can use a series capacitor to block DC so it only shows the signal and not the DC offset) ... OR... combine the two differential signals into one, which is why I mentioned a differential amplifier. This creates a single signal, referenced to ground, that will work with your VU meter. It doesn't have to be accurate, so even an LM358 would do. I'll post an edited picture of your boar din a minute to confirm the ground connection. |
| Buriedcode:
SO yes, the area you indicated is "ground" (0V reference). I have also attempted (badly) to show the signals on the speaker outputs. Neither of them goes negative, but the signals are centered on half the supply voltage, and are opposites - the speakers on care about the difference between these signals. Connecting your VU meter to one of these terminals, and our actual ground (as indicated on the diagram) would mean your VU meter would show half voltage at all times. Using a DC blocking capacitor would mean it only see's AC, but as each output is only half the signal it would show half the voltage. Try it yourself - connect your VU meters ground to the amplifier boards ground, and the "signal" to one of the speaker outputs - any of the 4 outputs will do. And see what it shows. |
| Adhith:
--- Quote from: Audioguru on March 23, 2018, 04:54:00 pm ---On a bridged amplifier no speaker wire is grounded, each speaker wire is powered from its own amplifier, then the speaker voltage is doubled and the speaker power is almost 4 times higher. If you ground a speaker wire then you cause distortion and probably will blow up the amplifier. The amplifier has a ground which is the 0V or negative of its DC power supply. Therefore one or more terminals on its DC power jack is a ground connection but you must measure it to see which terminal. --- End quote --- Thank you again for your reply. Ok sir now things are getting cleared about the ground connections. |
| Adhith:
--- Quote from: Buriedcode on March 23, 2018, 05:43:05 pm ---You should read up on the terms "bridged" and "differential". I used the latter term, but in the context of speaker amps its the same thing as bridged (albeit probably less specific). What has been said a few times here is - each connection to the speaker is driven by an amplifier, neither of these connections are at ground. You are still thinking in terms of "single ended" amplifiers, where one side of the speaker is connected to ground, whilst the other side is driven by an amplifier. In that case, your VU meter would have no problems, but your amplifier board - and many modern amplifiers - drive speakers differentially. So, if you use a scope and measure each speaker terminal with reference to ground (the DC jack) you will see a signal. One will be the opposite of the other - as one side of the speaker is driven high (with respect to ground) the other side will be driven low. So if an amplifier is powered by 12V, it can create ~12V across the speaker in one direction, but also in the other direction. Like a H-Bridge! Check out the datasheet on page 6: http://www.st.com/resource/en/datasheet/cd00205863.pdf So what this means is... you have two signals for each speaker, neither of which are ground. You can either just look at one of these signals, which means your VU meter will see a signal sitting at half the power supply voltage, and only give half the indicated voltage (you can use a series capacitor to block DC so it only shows the signal and not the DC offset) ... OR... combine the two differential signals into one, which is why I mentioned a differential amplifier. This creates a single signal, referenced to ground, that will work with your VU meter. It doesn't have to be accurate, so even an LM358 would do. I'll post an edited picture of your boar din a minute to confirm the ground connection. --- End quote --- Thank you again for your kind reply. could you help me with the type and value of the capacitor that can be used for the dc blocking. I'm planing to first use this amplifier ground and if its not that good then i'll move on to the differential amplifier option. |
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