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Old 28th September 2010, 06:03 PM   #281
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CeeVee,

I agree with your post above. Delete the holes under the part, they do not contribute all that much. The holes under the “wings” or finned area are the most important and should be made big enough that the entire finned area is exposed if possible to avoid hot spots in the completed product. Layout may dictate otherwise...

Qusp,

Just trying to contribute without distracting and am still very interested in the boards when you get there.

Dave
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Old 28th September 2010, 06:20 PM   #282
qusp is offline qusp  Australia
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no problem man, didnt mean anything by being short; even if it is a bit unusua for me :P
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Old 28th September 2010, 06:41 PM   #283
CeeVee is online now CeeVee  Portugal
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The holes to put in or not i think should be dependent on what pcb layout owen comes up with .

Some holes can be omitted and size can also change according to need.

Let's see first what owen produces and the discuss this...this is my sugestion.

Here is an illustration just to highlight the problems one would have in routing from the DAC to the IV and from the Transistors to the output if we put hole in all the fin areas.

after the layout is done we can reapreciate it to favour puting holes below the heatsinks that most need it.....and only those.

Another issue is that the PCB might just fall apart with so many holes. :-)
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Old 28th September 2010, 06:47 PM   #284
qusp is offline qusp  Australia
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Quote:
Originally Posted by CeeVee View Post
Hi qusp,

you just confirmed my liking for australians, love the plave, love the people.....
Cool , I'm glad we sorted it out painlessly, wasnt meant to cause conflict

Quote:
the main reason i posted the above rendering was exactly to ilustrate where we should or should not put holes.....as it is shown it's a ver holy board....pun intended.
right, well that makes sense

Quote:
but not very easy to route around as you say.
Realistically i think we should place holes only beneath the heatsink wings, this would ease the routing issue to the transistors and resistors while permiting better air flow to the heatsinks.
hmm see without some hole near the device in front of it roughly the mounting hole's height above the board in front of the part, my layout is not so clean and I have to think of whether I just leave it for the buff guys. I need to use the floor or wall for heatsinking, I cannot fit my dac + regs in the space afforded for the buff, it just wont happen. I need to mount the entire reg and dac assembly above the board, but preferably not as high as the height of heatsinks above the board.

I can mount them and then solder them in, but I would not be able to remove the IV board without destroying the sand (thats what the holes in front are for, removing the board with a screwdriver through the hole. so I guess we'll see what owen comes up with to that end.

although you could help there with your modeling software to see where the hole would have to be. thats a bit much to ask though, because if there being the heights of both to22 and to247. i'take some pics of my actual PSU tomorrow and show you what I mean. I suppose I could buy a large shallow finned flat sink from conrad and mount to that. but that would add about 100 to the build

night guys

Last edited by qusp; 28th September 2010 at 07:03 PM.
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Old 28th September 2010, 06:55 PM   #285
opc is offline opc  Canada
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Default Finally an update

Hi Guys,

Sorry for my absence over the past day and a bit... I've been hard at work on the layout, and trying my best not to get too distracted.

I think I've finally come up with something that will make everyone happy, and is smaller, cheaper, and doesn't require heatsinks on the board.

The resistors and fets are mounted between the bottom of the PCB and the bottom plate (or a heatsink if you prefer). The only on-board heatsinks are for the regs. I've upped the size of the PSU input and output caps to R18mm, and I've added an outline for the Ackodac with standoffs.

This layout will allow for either the Buffalo and the Acko DACs. It drops the board area from 50" sq to 36" sq, and generally provides a shorter circuit path for the critical connections between the DAC and I/V.

Now for the caveats:

- The Caddock resistors measure 0.127" high where the transistors measure 0.188" high. As a fun coincidence, the difference is about 0.062" which is exactly the height of normal FR4 PCB. In order to get things to clamp from the top of the board, I'll have to send shims made of old PCB material that will go between the top of the resistor, and the PCB to allow proper clamping force to be applied from the top of the board. This will be a bit of a PITA, but no more so than mounting 12 parts to board level heatsinks would be.

- The bottom of the enclosure will need to either be a heatsink, or at least a 1/4" plate to transfer heat properly. You'll need to get rid of about 42W from the DAC, excluding the regs. Bolting the parts to a flimsy 1/16" aluminum bottom will probably not be sufficient.

I've got the whole thing routed and ready to go, so all I need to do is check that my DAC fits correctly on it, and re-check the outline for the Ackodac. I still need to add tie-points for those who want to use different regs, and then I'll post the routed board up for comments on grounding and signal paths.

I'm also going to add a quad of bi-directional 2.5V zeners across each of the DAC outputs. This will prevent destruction of the DAC in the even of someone hooking things up before adjustment. It will also protect the Buffalo in the even of a catastrophic failure of the I/V circuit. With no voltage swing at the output, I doubt they will have any sonic impact. Nonetheless, you're free to not populate them if you see fit.

Any comments are welcome!

Cheers,
Owen
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Old 28th September 2010, 07:03 PM   #286
opc is offline opc  Canada
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Forgot to mention:

CeeVee:

Those are some great renderings! I was hoping you could do me a favor and make another 3d render of the layout I just posted. It really does help to visualize things, and I am curious about the fit of the parts and any clearances my brain isn't catching in 2D

Sorry for changing everything and abandoning the previous design... I do appreciate the work you did.

qusp:

I got the ackodac stuff you sent, but I still don't know the location of the outputs relative to the edge of the PCB. If you can get me a drawing of that then I'll see if I can get the connectors to align for both boards.
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Old 28th September 2010, 07:29 PM   #287
igwt is offline igwt  United States
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There are some structural issues in CeeVee's last rendering the holes placed in line make for a delicate board . Smaller holes to screw the devices to the floor seems more feasible. Or two separate boards with devices on the sides with the option to mount separate sinks,large sinks,or case floor. Then spacing can be tweaked by each builder according to their needs. The space under the dac seems to be added real-estate in terms of board cost anyway. This option could actually give us shorter traces also. Sorry opc I didn't see your last post before submitting this the first time.

Last edited by igwt; 28th September 2010 at 07:37 PM.
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Old 28th September 2010, 07:41 PM   #288
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cool i'll have a look over that. I dont have an official spec for the placement of the outputs, but just measured it now and they are 29mm from the sides and 32mm from the 'top' they are 2mm pitch. which is a bit annoying as everything else is either 2.54 or 5.08 standard. TBH I doubt I will use a stacking headeras I need to have a layer of lexan for the regs to sit on. I will machine a hole where the outputs are so I can route wires through, but its unlikely I would use pin headers and 2mm pitch headers are not that available anyway.

most important for me are the mounting holes, you got that right? the dac is designed to have the IV stacked on it, not the other way around, but that wont work with this particular IV now will it, so I have to work with that. so I will bolt down through the lexan sheet and onto the board. sorry about no pics, had heaps on today and slipped my mind during the day as I didnt hear back.

will send pics tomorrow but its looking more workable. its a pity the linear tech regulators are more readily available, or I would suggest them as an alternative and would use the onboard supply, they are excellent and have some great HV SMD package linear regs, but yeah not all that available and at farnell where they are available, not all that cheap.

only thing is and i'm just asking your opinion here; are there some regs a bit far from the loads for low noise operation? or is the fact you are decoupling them with SMD caps making up for this? hard to see on this layout. can you have half of them on the top and the other half on the bottom?
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Old 28th September 2010, 08:25 PM   #289
CeeVee is online now CeeVee  Portugal
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Quote:
Originally Posted by opc View Post
Forgot to mention:

CeeVee:

Those are some great renderings! I was hoping you could do me a favor and make another 3d render of the layout I just posted. It really does help to visualize things, and I am curious about the fit of the parts and any clearances my brain isn't catching in 2D

Sorry for changing everything and abandoning the previous design... I do appreciate the work you did.

qusp:

I got the ackodac stuff you sent, but I still don't know the location of the outputs relative to the edge of the PCB. If you can get me a drawing of that then I'll see if I can get the connectors to align for both boards.
No i wont do you a favour opc.....it's my pleasure.

will post later...right now watching Real Madrid playing......
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Old 28th September 2010, 09:46 PM   #290
CeeVee is online now CeeVee  Portugal
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Ok game is ove and as i was multitasking i did the renders.....

Indeed opc if you intend to pressure the caddocks and transistors against bottom of case using the pcb you will need to fill space between cadock and pcb... the other solution would be to make holes on pcb for screws to hold caddocks and transistors....anyway here are the renders for your consideration.

Bottom plate is 5mm, standoffs are 10mm and top heatsinks are 38mm high (EA-T220-38E ohmite from mouser )

Seems to me that if the DAC is Buffalo then screws should allways be placed where the ackodac's standoffs should be for better thermal contact between transistors and bottom plate of case.
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File Type: jpg render2.jpg (115.8 KB, 526 views)
File Type: jpg render3.jpg (83.7 KB, 515 views)

Last edited by CeeVee; 28th September 2010 at 09:50 PM.
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