[daman]

I need an DAC AMP for listening music from laptop and smartphones.
 
Specs so far:
Inputs:

1. USB
2. line

Output:

1. headphone

Li-Ion batteries for portability. Build in charger charges from USB.
TI PCM2706 for USB receiver. TI PCM1794a/PCM1798 for DA conversion. I²S bus between chips. The external line out and DA chip line out connects to an OP-amp or a dedicated headphone amp chip. The DA chip got differential current output. So maybe differential output to headphones also?
 
Any good suggestions for a good amp chip?
Is there any good amps working from 3V?
 
I got Alessandro MS1 and may also buy ATH-M50.

 

[liamstrain]

what about adding a grub dac into an O2? 

 

[daman]

Quote:

what about adding a grub dac into an O2? 

Too large.
 
I did some home work and looks like I'm going to use MAX4410.

 

[tomb]

This has been done.  It's called the Carrie:
http://www.head-fi.org/t/387745/carrie-usb-powered-headphone-amplifier
 

 

[daman]

Quote:

This has been done.  It's called the Carrie:
http://www.head-fi.org/t/387745/carrie-usb-powered-headphone-amplifier
 

This does not have any battery.
 
Phew. I've been reading a lot about different amps. I try to keep my design simple and it's hard to not include all kind on fancy stuff.
 
Any other options for PCM2704? This chip is very easy to use but output specs could be better. Maybe an other DAC paired with this chip.

 

[liamstrain]

If you are using it as a USB Dac, it is self powered by the USB, and does not need a battery.

 

[daman]

Quote:

If you are using it as a USB Dac, it is self powered by the USB, and does not need a battery.

I'll use it for laptops and smart phones. USB for laptops and line in for phones.

 

[liamstrain]

Ah - my bad. I missed the smartphone requirement. 
 
Out of curiosity, why DIY? there are several good commercial offerings at various price points. Cost savings? Performance upgrade? Fun? 

 

[daman]

Quote:

Ah - my bad. I missed the smartphone requirement. 
 
Out of curiosity, why DIY? there are several good commercial offerings at various price points. Cost savings? Performance upgrade? Fun? 

Yes, it's faster and maybe even cheaper to buy a FiiO E7.
But designing and building it is fun.  And as a bonus you learn a lot.
 
PCM2704 got cross talk issues so I have to look for the older PCM2702 model or some other chip. Is there any other driver free USB DAC chips similar to PCM270x series? I found one (can't remember the brand) but it had very bad specs.

 

[daman]

I ordered the PCM2704 and PCM1798 for prototyping. For the final version the DA chip can be upgraded to PCM1794a. It is pin compatible with better specs.
I'm not going to use the MAX4410 chip. It would be an easy chip to use but specs could be better.

 

[Magsy]

I'm playing with something similar. Use LTC 4054 ( http://www.linear.com/product/LTC4054-4.2 ) for charging, works really well via USB as I've built a couple of standalone chargers and it follows a safe CC/CV charge curve. Tiny chip but really easy to implement.
 
 

 

[daman]

That is one chip I listed for potential charger chips.
 
The digital and charging part is easy for me. The hard part is the amp. stage.
Maybe something simple similar to Cmoy or something more advanced. The DA chip got differential current output. This could be used for balanced output.
 
I have designed DC-DC converters and I guess one is needed for most amps.

 

[daman]

The digital part now got PCM2704/PCM2706, DIR9001 and PCM1794a/PCM1798.
 
The DIR9001 part was added for S/PDIF input. I can feed better data for measurements and later use it if I got S/PDIF on the computer.
 
First I though about routing both PCM270x and DIR9001 with I²S to the DA chip. But the other option is to route PCM270x with S/PDIF to DIR9001 and DIR9001 with I²S to DA chip. This last option would make routing  easier since S/PDIF got only one wire. I was wondering if the last option would be better with jitter.
 
DIR9001 got very good jitter spec but can it fix S/PDIF input jitter? Or does the spec only mean it adds very little extra jitter?