Hi
I am looking for some advice for my first amp. project.
I want to build a micro controlled audio circuit that contains an amplifier and am looking at something like the TDA7266 (TDA7266 7 W + 7 W dual bridge amplifier - STMicroelectronics).
I want to use a digital volume control on the system so I am looking at putting something like this http://www.ti.com/lit/ds/symlink/pga2311.pdf on the amplifier input.
The question I have is that the datasheet for the TDA7266 states that the open loop gain for the chip is 26dB. The output of the circuit feeding the amp is giving 2V RMS centered around ground. If my math is correct that would result in an output of 56V P-P (10^26/20*2/sqrt(2))???? So I would need some sort of additional attenuation on the input.
What is the best way to achieve this? Could I use an additional PGA2311 or is there a better way. Do I also need to provide a bias to the input signal to center it around something other than ground?
Any comments would be much appreciated as although I am fine in the 'digital domain' analog is out of my comfort zone. I will post my finished project with all schematics and code when the project is complete.
Thanks in advance for your help and support.
I am looking for some advice for my first amp. project.
I want to build a micro controlled audio circuit that contains an amplifier and am looking at something like the TDA7266 (TDA7266 7 W + 7 W dual bridge amplifier - STMicroelectronics).
I want to use a digital volume control on the system so I am looking at putting something like this http://www.ti.com/lit/ds/symlink/pga2311.pdf on the amplifier input.
The question I have is that the datasheet for the TDA7266 states that the open loop gain for the chip is 26dB. The output of the circuit feeding the amp is giving 2V RMS centered around ground. If my math is correct that would result in an output of 56V P-P (10^26/20*2/sqrt(2))???? So I would need some sort of additional attenuation on the input.
What is the best way to achieve this? Could I use an additional PGA2311 or is there a better way. Do I also need to provide a bias to the input signal to center it around something other than ground?
Any comments would be much appreciated as although I am fine in the 'digital domain' analog is out of my comfort zone. I will post my finished project with all schematics and code when the project is complete.
Thanks in advance for your help and support.
I am sorry but does nobody have any ideas on how best to do this.
A small amount of guidance would have been much appreciated.
A small amount of guidance would have been much appreciated.
28 db gain is a fairly typical figure for an audio amp and would give a decent sensitivity from most sources. Remember that 2 volts rms (CD max level) is something that real music won't ever approach.
As an example, a 100 watt amp would typically have a 1 volt sensitivity. 100 watts into 8 ohms is 28 volts rms. Gain = 29db. Its a typical value.
You do not need any bias network because that is included in the chip. You must keep with the AC coupling at the input though.
If you did find the sensitivity a little high then a simple resistive attenuator (divider) is all that is needed on the input of the IC (before the input cap) .
As an example, a 100 watt amp would typically have a 1 volt sensitivity. 100 watts into 8 ohms is 28 volts rms. Gain = 29db. Its a typical value.
You do not need any bias network because that is included in the chip. You must keep with the AC coupling at the input though.
If you did find the sensitivity a little high then a simple resistive attenuator (divider) is all that is needed on the input of the IC (before the input cap) .
'
<< I would need some sort of additional attenuation on the input >>
I'm not certain it answers your question, but take a look at the Typical Application on page 2: http://www.ti.com/lit/gpn/lm3875
This is the divider that Mooly speaks of, and it's pretty much "the way you do it." Simply use a potentiometer (in this case Rin) as a voltage divider. It doesn't matter that this circuit is for a full-on amplifier chip, it works the same across the board.
By the way, audio line level is nominally (i.e. very approximately) 1 volt, but 2 volts is no biggee.
.
<< I would need some sort of additional attenuation on the input >>
I'm not certain it answers your question, but take a look at the Typical Application on page 2: http://www.ti.com/lit/gpn/lm3875
This is the divider that Mooly speaks of, and it's pretty much "the way you do it." Simply use a potentiometer (in this case Rin) as a voltage divider. It doesn't matter that this circuit is for a full-on amplifier chip, it works the same across the board.
By the way, audio line level is nominally (i.e. very approximately) 1 volt, but 2 volts is no biggee.
.
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