Ok as some of you may know I've been tossing around with the idea of a noise cancelling, portable headphone amp for a while now. Together with things i've slowly been learning, and the release of TI's new headphone amp chip, and my ambitions to start an SMD project i've decided to comit something to paper.
Here is the first attempt at the amp, taking into account everything I know (which admittantly isn't much) and what I read in the datasheets. (oh i know the GND on input jack is drawn incorrectly)
The amp needed to be the following:
Portable (thinking small hammond case)
Modular (the noise cancelling should be optional and separate.)
Sound good.
Be able to drive a large variety of headphones.
Discussion:
PSU:
The amp will be powered by 8 AAA batteries, and center tapped for GND.
The OPA614 was chosen to buffer the PSU ground because of it's 350mA current output, and it looks pretty reasonable for the job. The opamp is implimented accroding to what I read on tangent's website however it uses the GND references from the batteries and not from resistors. I hope this works, but then again if it doesn't It should be very easy to add pulldown resistors.
AMP:
The amp itself doesn't have any noise cancelling provisions, however it does have a mic jack on the input. THe idea is for it to be modular and not bulky. The noise cancelling amp can then be a simple inverted opamp and can be whatever it wants to be.
I didn't add an input capacitor in the signal since my sources are generally pretty good with DC offset regards (prob because of output caps of their own), and the signals are summed through 50ohm resistors.
The TPA6210 needs 4 capacitors which are drawn in, and is configured for a gain of 11. As per the datasheet I decided against using a feedback resistor of 10k, but used a 2k instead of the recomended 1k because I intend to power high impedance loads with it. Other then that it's fairly standard as far as the datasheet implimentation goes.
GND:
This is what is pretty new to me, and i tried to copy the PPA's implimentation of the GND opamp. I'm not sure if this will work but from the looks of things i think it may just be correct. The opa627 was chosen because it's unitygain stable, and because i have them comming out of my ears here.
So what are your thoughts and comments if any? Am I in over my head and have no idea what I'm doing?
Here is the first attempt at the amp, taking into account everything I know (which admittantly isn't much) and what I read in the datasheets. (oh i know the GND on input jack is drawn incorrectly)
The amp needed to be the following:
Portable (thinking small hammond case)
Modular (the noise cancelling should be optional and separate.)
Sound good.
Be able to drive a large variety of headphones.
Discussion:
PSU:
The amp will be powered by 8 AAA batteries, and center tapped for GND.
The OPA614 was chosen to buffer the PSU ground because of it's 350mA current output, and it looks pretty reasonable for the job. The opamp is implimented accroding to what I read on tangent's website however it uses the GND references from the batteries and not from resistors. I hope this works, but then again if it doesn't It should be very easy to add pulldown resistors.
AMP:
The amp itself doesn't have any noise cancelling provisions, however it does have a mic jack on the input. THe idea is for it to be modular and not bulky. The noise cancelling amp can then be a simple inverted opamp and can be whatever it wants to be.
I didn't add an input capacitor in the signal since my sources are generally pretty good with DC offset regards (prob because of output caps of their own), and the signals are summed through 50ohm resistors.
The TPA6210 needs 4 capacitors which are drawn in, and is configured for a gain of 11. As per the datasheet I decided against using a feedback resistor of 10k, but used a 2k instead of the recomended 1k because I intend to power high impedance loads with it. Other then that it's fairly standard as far as the datasheet implimentation goes.
GND:
This is what is pretty new to me, and i tried to copy the PPA's implimentation of the GND opamp. I'm not sure if this will work but from the looks of things i think it may just be correct. The opa627 was chosen because it's unitygain stable, and because i have them comming out of my ears here.
So what are your thoughts and comments if any? Am I in over my head and have no idea what I'm doing?
