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Comments for my PCM2702 DAC layout? - Page 2

post #16 of 613
Redundant?!? I've seen you up to this stuff at the earliest hours of the morning, and not after waking up! For the basically non-profit work both you guys do, you're certainly very dedicated(Thanks!). And what too late? the prototypes haven't even been built yet :P
post #17 of 613
Quote:
Originally Posted by Citizen86 View Post
Would this board be easier to work on than the original Alien DAC? And if so... anyway some more people can get a hold of them?
It's probably a tradeoff. We hope some parts (REG or TPS chips) will be easier to get, but they will be smaller than the SOIC-8 of the Alien. Combined with the compactness of the layout, that could mean the actual soldering may be slightly more difficult.

Assuming the prototypes work out, we hope that a lot more people "can get a hold of them" shortly.

Quote:
Originally Posted by ruZZ.il
Redundant?!? I've seen you up to this stuff at the earliest hours of the morning, and not after waking up! For the basically non-profit work both you guys do, you're certainly very dedicated(Thanks!). And what too late? the prototypes haven't even been built yet :P
Thanks - I woke up again.
post #18 of 613
Thread Starter 
Noting the name overlap with error401's DAC project, tomb and I have been discussing possible new names, and have settled on calling this the BantamDAC.
post #19 of 613
A couple of updates -

1. I've got a rudimentary webpage started with the important files developed so far - most importantly, the first cut at a BantamDAC Bill Of Materials:

TooleAudio BantamDAC

2. Just to give you guys an idea of how small the BantamDAC really is, I did a little pic with a quarter for comparison:




Since they're fresh in my mind after just finishing the BOM, there are some important features about cetoole's design that deserve mention:

1. Note that the TPS79XXX series LDO's come in a TPS79475 version, with a fixed 4.75 regulated output. No ratioed resistor pair is needed.

2.Besides both Mouser and DigiKey having literally thousands of the TPS regs, they're only 88 cents each. That's about 1/3 the price of the former REG101's.

Mouser has over 27,000 of the 3.3V TPS's and 2,890 of the 4.75V.
DigiKey has over 2,100 of the 3.3V TPS's and 3,095 of the 4.75V.



EDIT: Looks like I was mistaken on the ceramic pads - I'll make the corrections.
post #20 of 613
Looks great guys! I'm looking to build a DAC/Amp for my laptop's audio out. This would be my first DIY project though, heh....

2 Questions:
1. How long before you think we can order the PCB? Also, price?
2. Are the alternatives of the TPS Regs, you think they are comparable quality, or is it worth it to spend 3x the price on the REGS used originally?

Thanks.
post #21 of 613
Sweet! Looking forward to it.
post #22 of 613
Quote:
Originally Posted by Citizen86 View Post
Looks great guys! I'm looking to build a DAC/Amp for my laptop's audio out. This would be my first DIY project though, heh....

2 Questions:
1. How long before you think we can order the PCB? Also, price?
2. Are the alternatives of the TPS Regs, you think they are comparable quality, or is it worth it to spend 3x the price on the REGS used originally?

Thanks.
1. This is highly variable and dependent on the prototypers' schedule, but I'm hoping it will go quickly. Colin has already done some pricing research and I think it will be safe to say under $5, perhaps less - but don't hold us to it, right now.
2. Just MHO, but I see no benefit to the REG101's, period.
post #23 of 613
Awesome! I'll keep an eye on this thread then. Maybe I'll try to put together a simple Cmoy in the meantime
post #24 of 613
Quote:
Originally Posted by Citizen86 View Post
2. Are the alternatives of the TPS Regs, you think they are comparable quality, or is it worth it to spend 3x the price on the REGS used originally?

Thanks.
These selected regulators seem to best REG101 in almost every specification, and they're considerably cheaper. They have better ripple rejection, especially at HF, and lower output noise. Just be careful with them, since the max input voltage is only 5.5V. I see no reason to want the REG101 other than for higher voltage input - but since the TPS793xx uses a standard SOT23 regulator pinout, you can substitute the REG101 or just about any other SOT23 regulator you want.

I missed them on my last 'regulator search' somehow. I don't know what it is about TI's site but I always seem to miss perfect parts when I search for things there.

I have been using LP2985 lately myself with good success, and I think I'll switch to these - they seem to spec better and they're a few cents cheaper. If you wanted to use something else, LP2985 make a good substitute as well - it's what's used on the Opus DAC which seems to have a good reputation. It also has a high-ish input max of 16V (REG101 is 10V, TPS793xx is 5.5V), which I have made use of to power directly from my bipolar 15V supply. But really I would stick to the TPS793xx, or if you must, the REG101, since this board is not set up to handle external power anyway.

cetoole/tomb
I know you mentioned it earlier in the thread, but in the interest of flexibility maybe it is worth adding a header and jumper to allow external power?
Actually, nevermind, you're right. It'd be tricky to add to your layout, and really you should have the logic gate to disable the chip when USB power is not connected anyway, which isn't appropriate to add here.
post #25 of 613
Is there any decent substitute for the soic8 reg101 that is used on the alien dac?
post #26 of 613
Thread Starter 
Quote:
Originally Posted by JamesL View Post
Is there any decent substitute for the soic8 reg101 that is used on the alien dac?
Not AFAIK, which is a large reason for the use of SOT23-5 regs on this board, and actually, a large reason Tom and I thought to finally do something with this layout.
post #27 of 613
Colin, have you thought of making these boards fit a case? I can see my self building a Pcm2702/mini3 in the same case. It would be nice if the DAC would be 54mm . they would both fit in the http://www.hammondmfg.com/pdf/1455C1201.pdf case. It would be great for listening to my headphones at class.

I will build one at any size though.
post #28 of 613
Thread Starter 
Its funny you mention that case, because it fits just fine. If you look at the datasheet again, 54mm is the exterior width of the Hammond 1455C cases, while 51mm is the maximum width of the PCB that can fit in the slots. The BantamDAC is 50mm wide, so it gives 0.5mm wiggle room each direction in that case. All you need to do is find some way to keep the board from sliding back, like had to be done on the Alien. You certainly could work up something to put it in a 1455C1201 with a mini3, though you would need to do something about the DC jack for charging the mini3.

Tom and I also have another different plan for where this could be used that we are working on.
post #29 of 613
So your waiting for the prototypers to build and test before releasing the pcb for a possible group buy or something?
This looks like a fun little build.
post #30 of 613
Quote:
Originally Posted by digger945 View Post
So your waiting for the prototypers to build and test before releasing the pcb for a possible group buy or something?
This looks like a fun little build.
Yes. FallenAngel has built one, but is troubleshooting a channel issue. I'm going to put one together Friday.

Colin has changed the layout slightly - based on FallenAngel's comments. It was only a slight re-arrangement, though - fairly trivial.
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