post #136 of 711
9/11/07 at 5:13am
Also, I've written to Justin about an optical line in:
No, there is no optical input. To have an optical input, it would have
to be larger to add a SPDIF receiver. Also, when using the optical,
DAC would have to run completely on battery power. With a DAC like
this, that would drain the battery in only about 3 hours. So, while I
may make a larger version that also has an optical input (at least a
year away), it will need to be quite a bit larger to fit a larger
battery. I'm only interested in sound quality and not 200+ hour
life, but I would still like the battery life to be at least 20 hours.
If this is the case, then what does Justin mean in saying that the Pico is "unique"?
I'm not sure what you mean by this, doesn't the iMod just bypass a bunch of stuff and replace others with higher quality parts after the DAC to the line out?
For those that don't know, SPDIF splits the data and clock signals, introducing jitter and whatnot. The music has to go through this twice, I2S to SPDIF -cable- and then SPDIF to I2S. An imod does the same thing, straight to DAC with no SPDIF. All other external DAC that I know of use SPDIF.
One of the advantages of the iMod vs.using an external dac is that there is no SPDIF involved. SPDIF is not all that great... the multiplexing of the clock and data signals is the worst thing about it. The I2S interface is what most actual dac chips use. So if an external dac has an SPDIF input, inside there is going to be an SPDIF receiver chip that is going to do conversion to I2S to pass to the internal dac chip. There is more jitter in this conversion process.
Keep in mind that the transport (e.g. CD player or any other source that generates the SPDIF output) has to also create the SPDIF signal. Then it must be transferred via a cable (coax or optical) to the external dac.
The beauty of the iMod is the simplicity of the circuit path, and the very small circuit design (very clean, short signal paths). The whole thing is battery powered as well, so the power source is nice and clean ;-)