PCB for PCM2902 (digital out)

[guzzler]

The problem (again) is the 5V supply; not many headphones will be driven effectively at that level, although it could easily be omitted if you didn't want it. 5V could drive 32R phones I suppose, which would be all you needed for portable use. edit: 2 x BUF634 would fit there as well? Or an LM6172 would provide a bit of current at low voltages, but we'd have to be careful with the ground plane there and bypassing.

Regards regulators, ST make two that are easily available in the UK. They are the LE33CZ, and LE50CZ. Annoyingly, the LE50 is available from DigiKey but not the LE33. They come in a TO-92 package. Dropout is .2V at 100mA; not fully read the datasheet though. They cost about 70p, cf REG102-AA £2.12. That said, I'd be happy with the REG102, as they're not too expensive.

With the output jacks, I like the idea of space on the board, as wiring inside the smallest Hammond would be a bit of a pain. AFAIK, the pin out is fairly standard, and if it's not, they're not expensive to include with the boards, or people could wire directly from the boards....

g

 

[individual6891]

Would analog out be that important with PCM2702 boards still available?

 

[Nisbeth]

My opinion on this is still that if the board is to remain the size of a Hammond 1455C, then the analog out should be included for flexibility (if you don't need it, leave the components out). If the idea is a simple USB-SPDIF converter without any extras, I would prefer to have the board made smaller (as small as possible actually).

As for the jacks-issue, from my point of view the disadvantage of board-mounted jacks is that drilling has to be that much more accurate to yield a decent-looking result and board mounted jacks can also reduce the flexibility of the design because it will be more difficult to integrate it into a bigger amp if you have board-mounted jacks on both ends of the board.


/U.

 

[00940]

Quote:

Originally Posted by guzzler The problem (again) is the 5V supply; not many headphones will be driven effectively at that level, although it could easily be omitted if you didn't want it. 5V could drive 32R phones I suppose, which would be all you needed for portable use. edit: 2 x BUF634 would fit there as well? Or an LM6172 would provide a bit of current at low voltages, but we'd have to be careful with the ground plane there and bypassing.

I considered the AD8606 because it delivers 80mA as output current, swings rail to rail and works out of 5V. http://www.analog.com/UploadedFiles/...8605_6_8_d.pdf

I'm quoting Tangent on the AD8606:

Quote:

AD8606: Similar to an OPA132, but better in most respects. Not quite as good as an AD823, but quite respectable. Also, it claims 80 mA output current. Not bad at all!

Nisbeth : my feelings exactly on the jacks.

 

[00940]

TI has a very interesting line of LDO regulators, less than half the price of reg102, the TPS793*** line. There is a wide range of fixed output, they give 200mA, drop only 112mV at full charge, have very low noise and cost 1.14$ at digikey, which stocks thousands of them. They come in sot23-5

 

[guzzler]

Yep, nice little regulator that one. Here's my version of the DAC using it, only coaxial output and not on the board as people have said. No optical option on it, but it wouldn't be hard to add, just need some rearrangement. I've included an inductor on the USB line as well... Board is 43mm x 29mm. All passive SMD passives are 0805, and the inductor is 1210. Just noticed I missed a via to ground from the 7404, oops. I still need to add the decoupling caps as well, but it's more to get the general idea.

Total cost for this one would be around £12 including tax. The boards would cost 2.40 euros per board for 50

g

 

[00940]

Nice little pcb.

I'm still completly reworking mine, the grounding of my previous doesn't satisfy me at all. The datasheet of the TPS793 also has very specific guidelines for the layout and I'm trying to see how to deal with those.

 

[Glassman]

maybe it would be better to use RS-422/485 line driver instead of 7404 gate..

this one looks good - 3.3V, 1.2mA, 20Mbps:
http://www.analog.com/en/prod/0,,767...485E%2C00.html

you should reconsider the usage of transformer, it is really benefical and since you are going to have a group buy of some sort, you can get good prices on them..

for example:
http://www.digikey.com/scripts/DkSea...115284&Site=US

 

[Nisbeth]

Very nice layout Gus, that'ss more what I had in mind (and probably also what the original poster had in mind

)


/U.

 

[dsavitsk]

Quote:

Originally Posted by Nisbeth ... and probably also what the original poster had in mind

Indeed.

 

[guzzler]

Bump with gratuitous Eagle 3D rendering

I've tidied up the regulator section and taken account of the grounding recommendations.... Silkscreen has component values on. The board is still the same size. If anyone's interested, I can get a batch run out; NO SUPPORT ON IT THOUGH!!

g

 

[Latexxx]

I'm sorry but your drawing doesn't look professional enough because it states "uH" instead of "µH".

 

[dsavitsk]

Quote:

Originally Posted by guzzler If anyone's interested, I can get a batch run out

I'd be in for a few.

Quote:

Originally Posted by guzzler NO SUPPORT ON IT THOUGH!!

Could you post a list of the parts? Is there anything particularly difficult to get?

-d

 

[guzzler]

Quote:

Originally Posted by Latexxx I'm sorry but your drawing doesn't look professional enough because it states "uH" instead of "µH".

Duly noted and corrected

I editted the ground plane as well, so you can drill through the two bottom corners without drilling into copper...

Parts:

1 x PCM2902 (SSOP28)
1 x 74HC04 (SO14)
1 x TPS793 4.75V (SOT23-5) <-- pain to solder!

1 x 560µF 6.3V Panasonic FC
2 x 22µF 10V OS-CON SC (or equivalent similar, FCs are fine)
4 x 1µF Wima MKS-02 (or similar, tantalum should be ok, 2.54mm pitch)
6 x 100nF 0805 ceramic capacitors
1 x 10nF 0805 ceramic capacitor
2 x 33pF 0805 ceramic capacitors

1 x 1M 0805 resistor
1 x 1K5 0805 resistor
1 x 360R 0805 resistor (higher quality, if possible)
1 x 91R 0805 resistor (higher quality, if possible)
2 x 22R 0805 resistor

1 x 12MHz HC49 crystal oscillator
1 x 10µH 1210 inductor
1 x USB B-type connector
1 x RCA socket
1 x case
1 x USB cable

Total cost, about £10 - £12 I'd say. Nothing hard to get; apart from Wima MKS-02 in the States, easy in Europe (for once

)

g

 

[Nisbeth]

Well, I can't see the rendering (server seems to be down atm), but I'm still interested in 3-4 boards

/U.