In article , wrote:

I'm just wondering if it is the Opamps or the ADC. I guess to find out I
could put a signal directly into the analog in pin on the ADC.

I'm betting it's a soft-limit inside the ADC chip. But if you are getting
that much distortion, you should see flat-topping on a scope. I see
flat-topping at about 3% distortion on a 1 KC tone, with my eyes and my
ancient Tek scope.

Just relax and keep your levels down. And save up for a decent set of
outboard converters. There is a reason the Prism costs more than the
Edirol.

It seems to distort anywhere above -3dB. I would be happy to run it at -6dB
and below, say, but the problem is there is a really nice "clip" light that
comes on at -3dB. I run this thing "standlone" (without a PC) and rely on the
clip light to set levels. (I set it so the clip light just flickers every now
and then.) I would be happy if I could find a way to make the clip light to
turn on earlier, say at -6 or -9dB. Does anyone know how this clip light
works? I'm thinking it might be reading right out a digital channel
somewhere.

The clip light is SUPPOSED to come on when a certain number of consecutive
full-scale samples appear. How many depends on the manufacturer... some
equipment has DIP switches inside so you can select it. I tend to set
things up for four consecutive FS to light the lamp, but some guys have it
set for as many as eight.

I'd set for peaks around -12dBFS or lower. Give yourself some headroom.
You have plenty of dynamic range, why not use some?

Oh yeah, one more question: What is the simplest ADC circuit I can make that
takes line in and outputs SPDIF optical? In particular, do I need this Cirrus
CS8402 to generate optical out? This does rate conversion and all kinds of
stuff, but can I just clock it at 44.1 and output 44.1/16 directly from the
AK4524? Again, I'm assuming that the AK4524 is really an OK chip. People
have told me the same chip is in reasonable prducts, like the "Apogee MiniME"
ADC box.

There are a bunch of chips that will give you SPDIF output.. check the
Crystal Semi databook (which I think is now the Cirrus). There are a couple
that don't do rate conversion or anything fancy. You can probably get
some of the Crystal Semi evaluation boards for cheap on Ebay if you look,
also, and they would be a good start toward homebrewing various ADC designs.

I'm not sure I'd call the MiniME reasonable, though... but use your ears
and eyes and see for yourself.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."