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Pico - USB DAC/Amplifier From HeadAmp - Page 10

post #136 of 711
Quote:
Originally Posted by justin w. View Post
the Pico is unique because it does not convert USB to SPDIF and then to I2S as most if not all multiple-input DACs do. It goes straight to I2S there is no SPDIF conversion
Justin, you have made clear the difficulties of adding an optical input to the Pico, but are you saying that the Pico will still have multiple digital inputs, i.e. USB and coax, and that the Pico is unique in its handling of these multiple digital signals, or will the Pico have only USB input like the MOVE, requiring in any case no SPDIF conversion?
post #137 of 711
As far as I understand, the Pico is USB input only, requiring no conversion to S/PDIF, ie USB signal straight to I2S of DAC. I'm no electrical engineer, but I think I can understand that going from USB to S/PDIF to I2S requires an additional receiver chip of some sort. Longer signal path = greater opportunity for signal degradation (eg jitter). Hence going straight to I2S is the best solution. Empirical Audio does something similar too...

Regarding a multiple digital input amp/dac, have a look at this:
Quote:
Originally Posted by antonyfirst View Post
Also, I've written to Justin about an optical line in:

Tony,

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,
the
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
battery
life, but I would still like the battery life to be at least 20 hours.

Thanks,
Justin
Hope that answers your question.
post #138 of 711
x 3 on interest in just the USB DAC.

I am after a quality USB DAC without amp and all the bells and whistles. I would never use a DAC for portable so wall power is fine for me.
post #139 of 711
I would have bought one too, previously. Now I would want the amp too but I'm sure there is a market for a simple DAC only. It would just have a plug to put in a mini usb cable, and a 3.5mm female jack. that's it, no switch, no light or anything. It would be cheap too, no need for wall power, wouldn't it run off the USB like the DAC in the Pico?
post #140 of 711
Quote:
Originally Posted by milkpowder View Post
As far as I understand, the Pico is USB input only, requiring no conversion to S/PDIF, ie USB signal straight to I2S of DAC.
If this is the case, then what does Justin mean in saying that the Pico is "unique"?
post #141 of 711
Thread Starter 
Quote:
Originally Posted by koto-in View Post
If this is the case, then what does Justin mean in saying that the Pico is "unique"?
Quote:
Originally Posted by justin w. View Post
...the Pico is unique because it does not convert USB to SPDIF and then to I2S as most if not all multiple-input DACs do. It goes straight to I2S there is no SPDIF conversion
Does that clear things up?
post #142 of 711
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.
post #143 of 711
Thread Starter 
Quote:
Originally Posted by stevenkelby View Post
An imod does the same thing, straight to DAC with no SPDIF.
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?
post #144 of 711
Quote:
Originally Posted by elnero View Post
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?
Yeah your right, I just meant that an imod is superior to an external DAC in as much as the sound doesn't go through SPDIF. That's true for all ipods and daps in general though.

Kind of OT I guess but I know people do wonder about why the imod is claimed to be so good and this contributes.
post #145 of 711
Quote:
Originally Posted by stevenkelby View Post
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.
sorry mate, but that post is incorrect in so many ways
post #146 of 711
Quote:
Originally Posted by d-cee View Post
sorry mate, but that post is incorrect in so many ways
Fair enough, I'm no genius. That's just how I remember Vinnie explaining it to me. I'll go find his email.

What's the correct info?
post #147 of 711
Here's what Vinnie wrote me, a few months ago now.

Quote:
Hi Steve,

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 ;-)

Best regards,

Vinnie
post #148 of 711
Quote:
Originally Posted by d-cee View Post
sorry mate, but that post is incorrect in so many ways
Constructive criticism please

iMod is probably better than an external DAC if we're talking about the quality of the signal going into the I2S interface of the DAC chip. What comes out the other side is dependent on a lot more other factors apart from the quality of the input signal. Anyhow, if jitter generated by the coaxial cable and S/PDIF chips is what we're most worried about, then there are currently a lot of DACs that clame to be very near jitter-proof. Elias claims the DAC1 is one such DAC and backs it up with numerous graphs and what-nots. Even the DAC in the Cambridge Audio 740c CD player is claimed to be more or less immune. I wonder how "jitter-proof" the Pico is.
post #149 of 711
Quote:
Originally Posted by elnero View Post
Does that clear things up?
No. If there is no optical/coax input, then there is no need for a multiple input DAC and thus no spdif conversion.

What it sounds like Justin is saying, and maybe he can pipe back in, is that because there is no 24-bit input, he can somehow use a 24-bit multiple-input DAC for 16-bit data without conversion to spdif. Since signal gain will presumably be applied by the analog amplification circuitry, I'm not clear what the advantage of this would be, but maybe Justin can shed some light on the matter.
post #150 of 711
Quote:
Originally Posted by stevenkelby View Post
Here's what Vinnie wrote me, a few months ago now.
What this means is that if you're listening to 16-bit data, then sound quality may be better with a 16-bit DAC because there will be no spdif conversion involved.
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