Re: Audio Op Amp power

On Aug 9, 6:17 pm, "Jon Slaughter" <Jon_Slaugh...@xxxxxxxxxxx> wrote:
I need an amplifier front end for my dsp audio and I'm wondering what
exactly I should do.

I think the main use will be for a guitar effects processor but I think I'll
also want something that processes audio in general(not sure if I need to
make a distinction?).

I'll be using the PCM1804 for the ADC conversion and I'll be putting an
amplifier front end on it to try and get the max resolution. (So, say, it
will be calibrated to the input signal).

On the data*** for the ADC it says the analog input voltage is -0.3V to
(Vcc + 0.3V).

I'm not sure whats up with the -0.3V but in any case Vcc is from -0.3V to
6.5V.

I think because of convience I'll be using Vcc at 5V and I'll want to
minimize the power supply devices I'll need.

Now the op amps I've been looking at for audio say the min Vcc is 5V. I'm
wondering if its a good idea to run at the min voltages?

Right now I need a power supplies of 3.3V for the DSP, ADC, and DAC; 5V for
ADC and DAC and then the supplies with for the op amps(buffers, filters, and
amplifiers). I'd like to use the same power supplies instead of creating a
new one. I will of course need a negative rail also so I was hoping that all
I need is 3.3V and +-5V but I'm a little worried about using the +-5V on the
op amp since its the min supply voltage. Not sure if it will cause any
problems?

Also, would there be any special considers I need to worry about for
different types of inputs into the op amps? Are there better configurations
than just the simple stuff you learn in any basic text book? (I was thinking
of just using a fully differential op amp configured as an inverting amp)

Ultimately I rather not use the op amps if possible because it causes me to
need to have a negative supply but maybe this isn't difficult with with some
of the ic's available now days?

Is there any good books on audio circuits with mainly practical knowledge?
I'm just really afraid of using some of the stuff I've learned from basic EE
books and it not cutting it in the real world. (I do have the AOE which I
need to re read again).

Thanks,
Jon

It is really hard to hand wire the SSOP package. Not impossible, but I
don't think I ever did a dead bug on a chip with so many pins.

A good trick if you can do it is to get the evaluation board for the
part. I don't know about TI, but Crystal sells them, and they
occasionally end up on the surplus market.

Looking at the TI design, I cringe at the 10uF polarized caps in the
audio chain. Assuming you are willing to waste some space, you can go
non-polarized.

I suspect you could just take an eval board and tweak it a bit (better
components) and get better performance than some Creative or M-Audio
box. But certainly at a higher price.

Just the fact that you don't use the USB port for a power supply would
be an improvement.

.

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