[Alf]

Quote:

Originally Posted by guzzler 1) I personally liked the buffered ground, it was one of the most frequently asked questions about the old DAC for portable use.

I added an output ground capacitor CG. It resolves the conflict of different grounds. Also the DAC’s performance when USB powered is very good and it should be even better in the new release. An external PS is not really necessary. While the buffer was required in the previous revisions, I seriously doubt it is needed now.


Quote:

Originally Posted by guzzler 3) How's the availability and cost of the TPS30xx cf the REGs? At the end of the day, it's going to make a pretty marginal difference for this board.

Sorry, it was TPS973xx. I updated my original post.

TPS973xx is cheaper but its availability is poor. Changing the package allows both TPS973xx and REG102 to be used.

Quote:

Originally Posted by guzzler 4) Could the ground pads be moved directly next to the power inputs, makes life simpler for wiring, and shouldn't obstruct any current routing

The power input is supposed to be wired via S1. There is a ground pad next to it.

3V3, 5V, and G3 pads are meant for testing only.

 

[MASantos]

Alf, here are my opinions:
a)I think that removing the buffer is a good option, because if we can get good noise figures using USB then alternate power source shouldn't be necessary. regarding the LM317, I also agree that it is easy to implement outside the board.

b)I don't think 2 LED positions are needed. Just put one position and people can use some wire and redirect it to wherever they want it.

c) What is the purpose of the ground capacitor? Also, what are the differences between OG and G1?

d) I just read the datasheet for those TPS793XX and saw something about different grounds being needed? Do you know anything about this?

e) I think that the board could be made a little bit more compact.since he have all that empty space in the bottom, why not move the PCm2702 down and a bit to the left, the IC3 further to the left, and place the output holes more to the top? This could cut a few mils further. I think that 50,5 X 45 woudl be a great board size!
Regarding the USB receptacle holes, I too had some trouble placing it.

My 0,02 cents

Manuel

 

[.: ZMN :.]

Nice to see activity on this project.

The change in board size made me wonder about enclosure options a bit.

Can someone tell me what to expect for max height of components?
I wondered if the popular Serpac (H45) enclosures would now also be an option; there are plenty people using these for their portable amp, and might like a 'matching' DAC with it. With a decent bit of DIY (read cutting) on the board I think these colorful soap box enclosures could be used, if the height of board+components is max about 18mm.

Anyone?

 

[MASantos]

Quote:

Originally Posted by .: ZMN :. Nice to see activity on this project. The change in board size made me wonder about enclosure options a bit. Can someone tell me what to expect for max height of components? I wondered if the popular Serpac (H45) enclosures would now also be an option; there are plenty people using these for their portable amp, and might like a 'matching' DAC with it. With a decent bit of DIY (read cutting) on the board I think these colorful soap box enclosures could be used, if the height of board+components is max about 18mm. Anyone?

Well I'm actually going to put one inside a hammond 1455N1201 with a PIMETA, a batery pack and a charging circuit.

 

[.: ZMN :.]

Quote:

Well I'm actually going to put one inside a hammond 1455N1201 with a PIMETA, a batery pack and a charging circuit.

Nice! Dimensions 120x103x54mm, I quess that won't be your portable system

Anyway, if there is a need for compatibility, I *think* the current v1.0-r1 layout *could* also please the Serpac fans without much consideration - if height permits.

Just a thought ...

 

[Alf]

I played with SOT23-5 packages tonight and I did not like the result. The layout around the chips is too cramped. The package is tiny and may be difficult to solder for some people. Well the regulators stay SO8. It means no TPS793xx for now.



Quote:

Originally Posted by .: ZMN :. I wondered if the popular Serpac (H45) enclosures would now also be an option; there are plenty people using these for their portable amp, and might like a 'matching' DAC with it. With a decent bit of DIY (read cutting) on the board I think these colorful soap box enclosures could be used, if the height of board+components is max about 18mm.

The height of the board and components is about 18mm +/- 0.5mm. One of the problems that need to be solved is accessibility of the receptacle. I have never seen H45. Do you think the layout needs any modifications to please H45 fans?

By the way, Hammond 1533 seems to be a worthy contender too. It is a bit wider. No creative cutting should be required.



Quote:

Originally Posted by MASantos b)I don't think 2 LED positions are needed. Just put one position and people can use some wire and redirect it to wherever they want it.

I could not decide which one would be better.

Quote:

Originally Posted by MASantos c) What is the purpose of the ground capacitor? Also, what are the differences between OG and G1?

If you use the same PS for the DAC and a virtual ground amp, you have a conflict of grounds. You can find more details here. Using an output ground capacitor solves the problem.

G1 (also G2 and G3) – direct access to the DAC’s ground. Use it if you have no ground conflict.
OG – the DAC’s ground via the output ground capacitor. Use it if you have a shared PS.

Quote:

Originally Posted by MASantos e) I think that the board could be made a little bit more compact.since he have all that empty space in the bottom, why not move the PCm2702 down and a bit to the left, the IC3 further to the left, and place the output holes more to the top? This could cut a few mils further. I think that 50,5 X 45 woudl be a great board size!

C14 is a showstopper. I would not want it to be too close to the receptacle. Anyway 1mm-1.5mm could be gained by moving PCM2702 slightly to the left.

Additional 2mm-3mm millimetres can be gained by moving the receptacle to the left. However this would make the receptacle more prominent. It would stick out of the enclosure. I am not sure how this will look. Any thoughts?

 

[MASantos]

I would keep LED2, its nearer the receptacle and people can mount it directly to the panel without any extra wire.

Thanks for the explanation about the grounds.

Regarding the board size, if during the layout changes it can be made smaller that's great, if not, it's great anyway!

would there be any advantage if we move the PCM2702 down to place further away for the power regs? Would less noise go into the signal?(this just crossed my head, I always heard to keep the PS away from the amp, does this apply in this case?)

 

[.: ZMN :.]

Quote:

By the way, Hammond 1533 seems to be a worthy contender too. It is a bit wider. No creative cutting should be required.

Looks like a nice sollution too, good you mentioned.

Quote:

Do you think the layout needs any modifications to please H45 fans?

I don't think the layout needs changes, current setup will keep some H45 DIYers bussy.

Have a look yourself. If it will fit the H45, it will do so tightly. The usb-connector might be a problem.

 

[MASantos]

What program do you use to make those case drawings?

 

[Francis_Vaughan]

Looks a lot like Omnigraffle to me.

www.omnigroup.com

of course if you are stuck in the dark ages and don't have a Mac....

 

[Alf]

Quote:

Originally Posted by MASantos would there be any advantage if we move the PCM2702 down to place further away for the power regs? Would less noise go into the signal?

I don't think so.

Quote:

Originally Posted by MASantos this just crossed my head, I always heard to keep the PS away from the amp, does this apply in this case?

They mean the transformer, which is a source of noise.

 

[Alf]

The updated layout is just around the corner. However I feel that the layout can be improved if smaller vias are used. What is the smallest via size one can use with the PCB Shop? What are downsides of using smaller vias?

 

[Clutz]

I've got all of the resistors and capacitors I need to finish the second DAC board I have - fingers crossed. I'm going to power it by connecting S1 to AV+ as Alf described doing in http://www6.head-fi.org/forums/showp...&postcount=339. *Crosses fingers* I never managed to get the last one to work, unfortunately.

Any suggestions on how to get rid of the flux from the board? I can bring home some 95% ethanol home to use it and a toothbrush if that'll work...?

Thanks,
Clutz

 

[Sinbios]

99.99% isopropyl is probably your best bet. Those are like a buck a litre at the grocery store around here.

 

[MASantos]

Quote:

Originally Posted by Clutz I've got all of the resistors and capacitors I need to finish the second DAC board I have - fingers crossed. I'm going to power it by connecting S1 to AV+ as Alf described doing in http://www6.head-fi.org/forums/showp...&postcount=339. *Crosses fingers* I never managed to get the last one to work, unfortunately. Any suggestions on how to get rid of the flux from the board? I can bring home some 95% ethanol home to use it and a toothbrush if that'll work...? Thanks, Clutz

I've always used 96% medical alcool and an old toothbrush to clean the boards. Works fine for me!