Hi to all, I'm building an audio amplifier with the TA202 chip (it's simple to solder at home and sounds great) for home use. I'd like to use a digital potentiometer as volume control and a digital switch to select the inputs (4 way will be enough).
My problem is that I'm a bit inexperienced, so I don't know how to put a pot like DS1802 (audio pot from Maxim) in the circuit Tripath shows in the datasheet.
I'll try to draw the circuit here, if it's not clear this is the link:
OUTSIDE | INSIDE | +- R2 --|OP-AMP OUT | | input --- C -- R1 -+-------|INV | | V \\______/ AC, maybe L---> high pass filter: no more DC with Dc bias
Inside the chip there is an opamp that takes INV and a constant signal as input, it's output is the OP-AMP OUT (obviously, OP-AMP OUT is only a feedback, not the only output).
OP-AMP OUT------+ |\\ | INV---| \\ | | \\ -----+---amplification
2,5V--| / |/
The TA2020 gain is: constant*R2/R1.
(I hope not to write obvious things).
The digital pot does not allow AC inputs/outputs, so I cannot put it instead of R2, since it is connected to R1 on one side and in R1 flows an AC signal.
How should I modify the circuit? I'd like not to put the digital pot simply after R1, since it would change the high-pass filter and it would attenuate the signal (less dynamic range), not set the gain.
As far as it concerns the audio input selection, I think I will read what is already available in sci.electronics.* before asking. However, I will probably have the same problem: the switch will accept DC inputs while I have AC inputs.
Thank in advance to anyone! I hope to be able to build my hi-fi soon! (I have already designed the circuit board, the gain and the switches are the only things left).
Olaf Marzocchi