[dsavitsk]

The problem, for me, with the available portable amps is that they aren't really that portable. They all need batteries, and, even worse, they all need sources which also need batteries as well as cables to connect them. I wanted something that I could take to a coffee shop, connect to my computer, and listen without a pile of crap on the table.

That is, I wanted a usb dac with a built in headphone amp that was all powered via USB, and I wanted it to sound good. Now, Hagtech does make such a thing, but quite frankly it lacks the power to actually drive headphones, it uses a TI dac chip that does not sound that good, and it costs a fortune, all things considered.

So, this being DIY, I made my own (and of course spent way more than I would have on a hagtech one, but oh well.) It is a NOS USB DAC using the TDA1543 as a dac and a passive I/V. The amp stage is more or less ripped off from the Pint/Mini3. However, the really clever bit is the power supply. It uses a DC-DC converter to get a higher voltage out of the USB which is then regulated to what it needs to be for the amp and the DAC. I configured mine for 9V, but the chip can supply something like 24V if need be.

For the first experimental build I used the NJR4556 opamps, but the ad8397 is on deck for the next one. (Schematics and layout details will be on my site soon -- a couple of days probably.)

 

[MASantos]

I want one, I want one!!!

This is what I have spoken about some time ago, in the PCM2702 revision B DAC thread!

It looks really nice!!!!


it looks like it was build with the hammond 1455C801 enclosure in mind. can you confirm this?


THat's really nice!

 

[dsavitsk]

Quote:

Originally Posted by MASantos it looks like it was build with the hammond 1455C801 enclosure in mind. can you confirm this?

Indeed. However, I went a little closer to the edges that I should have and some of the parts (C11 and C12) touch the case. So, I may need to do another revision to pull the layout in a little tighter.

 

[joostoo]

It may not fit in that case. It was talked about in another thread about how the EVJ pot could be too tall to fit in it.

 

[MASantos]

This is funny! I was driving home today and was thinking about startting a new thread to convince someone to design exactly this! A usb dac with an amp powered form the usb. Strange coincidence. I'm in for a group buy if you decide to do one.

What's the estimate parts cost? Around 100$ including case and shipping costs?

 

[dsavitsk]

Quote:

Originally Posted by joostoo It may not fit in that case. It was talked about in another thread about how the EVJ pot could be too tall to fit in it.

I think that was my thread. It will fit, but you have to apply a little force. Also, the smoothing cap I used is a little tall, so I need to hunt around for a shortr one.

 

[Predator88]

Hmm, this could be extremely useful once I get a laptop. How much did this cost to build? Outstanding work. Another version of this that would be really sweet would be one that could bypass the amp so it could double as a regular desktop amp to be paired with something more powerful. Yet still be abel to use the built in when portability is a must.

 

[K2Grey]

nevermind.

 

[hanon]

Super conception and execution. I've been looking around for a long time for such a project for use with a notebook. My current proxy solution is rather primitive - use tbaam or esi u24 with an attenuator. Neither is very elegant nor very satisfying, so consider great interest expressed should a pcb or kit fs emerge.

 

[mrarroyo]

I want one too. Can you keep me in mind if there is a group buy? Hopefully I can buy one put together.

 

[ATAT]

a). what passive I/V network are you using?

b). what dc-dc converter are you running? and whats your current draw?
Im just shooting from the hip right now, but the usb runs at 0->5v, you have to up that to at least 9 volts for a useable pint config right? so you have some serious current draw if I'm not mistaken...

Looks like a great project =). good luck on that

 

[dsavitsk]

Quote:

Originally Posted by ATAT a). what passive I/V network are you using?

I used 1K for both I/V and for Vref. It is not necessarilly the optimum setup, but it actually does pretty well. It also keeps the output impedence of the DAC stage low enough that it works well into the 10K pot -- used because of the opamps used.

Quote:

Originally Posted by ATAT b). what dc-dc converter are you running? and whats your current draw? Im just shooting from the hip right now, but the usb runs at 0->5v, you have to up that to at least 9 volts for a useable pint config right? so you have some serious current draw if I'm not mistaken...

For the DC-DC converter I used a TPS61040. It is pretty efficient and current draw is not that bad. I converted the power to 9V which is reregulated to 8V by a LDO vreg for the amp and 5V for the DAC. The pcm2707 runs at 3.3V and for that there is a reg101 connected right to the usb supply.

I ran it off my laptop today which was on battery power and it ran comfprtably for about 5 hours that way. However, you are correct that this is the limiting factor. Oh well, it is almost the holy grail. Maybe it needs some solar power chips

 

[Fiola]

Im in for a group buy if anyone decides to do one!

looks awsome btw, great work!

 

[MASantos]

What would be the maximum voltage that could easily be pulled? WOuld there be any benefit it extracting something like 13v to have 12v after the reg? That could help the amp section a bit. The pint doesn't pull that much current anyway.

I am actually listening to a PINT 9volts only and it sound amazing liekt this!

Quote:

Originally Posted by dsavitsk I used 1K for both I/V and for Vref. It is not necessarilly the optimum setup, but it actually does pretty well. It also keeps the output impedence of the DAC stage low enough that it works well into the 10K pot -- used because of the opamps used. For the DC-DC converter I used a TPS61040. It is pretty efficient and current draw is not that bad. I converted the power to 9V which is reregulated to 8V by a LDO vreg for the amp and 5V for the DAC. The pcm2707 runs at 3.3V and for that there is a reg101 connected right to the usb supply. I ran it off my laptop today which was on battery power and it ran comfprtably for about 5 hours that way. However, you are correct that this is the limiting factor. Oh well, it is almost the holy grail. Maybe it needs some solar power chips

 

[ATAT]

dsavidsk very nice..

why not use a opamp i/v stage? it would be alot better (imho) and you could just waste one SOIC space..

by the way, any reason why you use the switcher for your 5v supply? you could just filter / tap that off straight USB and not strain your dc-dc converter..

My laptop doesnt run 5 hours stock

so that's that.

also.. one sided?