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Old 6th June 2013, 01:17 PM   #121
agdr is offline agdr  United States
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An update, I heard back from the Forum admins here and they say that the Vendors Bazaar would be the best spot for follow-on discussion of the 6 extra boards. I'll start a thread over there. I'll post the 4-layer Gerbers here when I have that design worked out.

I forgot to say that Seeed Studio has a small batch service for 50 - 300 quantity. At 50 pieces the price of a 4 layer board drops to just $3.50 or so, including shipping! Pretty amazing. I'll bet OSH Park's prices on quantity are similar.

Last edited by agdr; 6th June 2013 at 01:46 PM.
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Old 6th June 2013, 09:56 PM   #122
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Default Put me down for 4 ODA PCB's

Add my name to the list for four (4) ODA PCB's. How about doing the same
for the Massively parallel LME49990 headamp AMP. I would take four (4) of
these PCB's as well. You have been busy. Take care.
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Old 7th June 2013, 02:04 AM   #123
agdr is offline agdr  United States
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mrsavage - will do, I'll put you on the list for 4. I might finish the layout on that massively parallel LME49990 amp and fab it too. I'm just really curious how it would sound given those ridiculously low distortion numbers from the datasheet for the LME49990 chips.

I'm going to go ahead and allow any number of boards per person until the extras are gone. These relatively low 4 layer prices really have me jazzed, so I may very well do another larger run later if all works out with these first 10. Given that I'll make 8 of the 10 available, rather than 6, and keep one extra along with the test board I'm going to build up.

I've started a thread in the Vendor's Bazaar forum and I will post all subsequent status updates about the extra boards there:

Parallel NJM4556AL two stage amp

Also a correction on the small batch pricing I posted above. That was for 2 layer, and it is at iTead Studio. For 4 layer 8cm x16cm is around $7 per board with shipping. Still, pretty darn good for 4 layer.

Last edited by agdr; 7th June 2013 at 02:16 AM.
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Old 7th June 2013, 03:36 PM   #124
Tony72 is offline Tony72  United States
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Please add a second ODA pcb to my order if there are any left.
Thanks Tony
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Old 7th June 2013, 04:36 PM   #125
agdr is offline agdr  United States
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Quote:
Originally Posted by Tony72 View Post
Please add a second ODA pcb to my order if there are any left.
Thanks Tony
Added.
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Old 8th June 2013, 06:00 AM   #126
qusp is offline qusp  Australia
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so you arent going to prototype before offering for sale? I think thats unwise, especially for the massively parallel 49990 amp, which I think could be an oscillation risk. if I were you, I would also provide for some sort of BGA or similar heatsink for the 49990, they get rather toasty and with them in such close proximity ...
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Old 8th June 2013, 12:08 PM   #127
agdr is offline agdr  United States
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Hey qusp! You are right, this one wound up a bit backwards. I prototyped the two layer version with the posted Gerbers, except for a couple of minor changes. This one is just adding two more layers with ground plane and some more routing. These 10 boards are the proto of the 4 layer. That is why I've giving everyone the option of cancelling at any time - if I discover a major bug after I build one up I'll need to do another run of 10 before shipping anything, which will add a couple of more weeks. No $$ collected until anything ships.

If I do a board for that parallel LME49990 amp I will do that one the other way around and proto/test it first. I 100% agree on the need for heat sinking all those chips! Was thinking about that. Tell me more about your idea - a ball grid array heatsink for use with the VQFN LME49990 package? There might be a clever way to heat sink the SOIC version by putting the chips on the bottom of the board. That amp would use the same B2-080 case the O2 amp uses. There is about that much space (height of the SMD chip) between the bottom of the PC board and the aluminum case bottom. Then it would come down to how to close the small remaining thermal gap. I'll have to do some measuring.

Last edited by agdr; 8th June 2013 at 12:17 PM.
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Old 8th June 2013, 03:51 PM   #128
qusp is offline qusp  Australia
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hey mate!, I love how you always take my critique in the spirit its intended instead of getting all riled up like some of the more..erm.. philosophical members do. sounds like a decent plan to me, I didnt catch all those details, my apologies.

yep, something like these from Enzotech, the HCA series, preferrably with clip. especially now that itead (or is it seed) are offering slot cutting free as part of the standard cost.

Yes you could also put the 49990 on the bottom, add a bunch of thermal vias to a clear solid copper area on the top, use some sekisui thermal tape or silver epoxy to provide low thermal impedance to the heatsink. I love the copper ones for extra bling factor too or you could go really mad and get one of their spread pin ones. I like the HCA though, as its nice and low profile. this will also help them act as one device with thermal coupling. the 37.5 x 37.5 x 6mm one should be a nice size.



btw yes, loving the itead and seeed options now, cheap 4 layer with cheap shipping, i've got some boards running with them next week as well as some flex PCB interconnects for power, input and output 'wiring' now if they up the ante to 6 layer and increase possible copper weight, i'll be in heaven.
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Old 11th June 2013, 01:48 AM   #129
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Default Heat Sink for the Massively Parallel Headphone AMP

In the Electronic Products Magazine (June 2013), I came across a heat sink aid
from CTS Corporation - EC, Sensors & Actuators, EMS!. It's about there low-profile thin-fin heat sinks that have
heights from 6.3mm to 32.6mm. They require no special tools to assemble on the
IC packages or any additional holes on the PCB. They suit large IC's or a
large number of IC's with heat dissipation needs. The BDN extruded heat sinks
have a pre-applied adhesive tape that peels off and sticks onto the component(s).
The adhesive shear strength at 100C is 36psi or so, hence, a one-inch square
heat sink would require a 36-lib force to remove. Take a look. They look like they
would work for the output driver chips. Take care.
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Old 11th June 2013, 03:25 AM   #130
agdr is offline agdr  United States
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mrsavage - hey I like that part you found! The LME49990 chip array on that amp measures about 40mm x 25mm on the layout, which is 1.6 inch x 0.98. The 1.6 x 1.6 heatsink might be the best, then just slice one side off at 0.98. Digikey has them:

BDN16-3CB/A01 CTS Thermal Management Products | 294-1103-ND | DigiKey (Digikey 294-1103-ND)

Or use two of the 0.91 x 0.91 sinks and cut one down slightly to make 1.6inch.

BDN09-3CB/A01 CTS Thermal Management Products | 294-1097-ND | DigiKey (Digikey 294-1097-ND)

The thermal adhesive tape on the sink solves another problem. The top of all those chips won't be exactly plane level of course and would leave tiny gaps if just in contact with a metal surface. The thermal adhesive tape would also act as a gap filler.

qusp - sorry about the delayed reply, I've haven't had a chance to look at the forum for a few days. I didn't know that those fab houses offered slot cutting! wowwww. Now that opens up a few possibilities. The vertical RCA jacks have rectangular plastic mounting tabs on each side that actually specify slots in the PCB footprint. I used holes since I didn't think I could do slotting. I'll have to go back and change that.

Although chips on the bottom seems like kind of an elegant solution, I think practically it would probably fail. The top and bottom of the aluminum case "warp" ever so slightly in the middle, making for a tricky thermal bond. Then there is the issue of sliding the board in. Silicon pad material (like those silicon TO-220 pads) would probably have a tacky surface that would bunch up under a sliding motion.

Those adhesive heatsinks mrsavage found sound like a good way to go. It also gets things turned around in the right direction - up - for convection. Even with a good thermal bond to the case I would probably worry that I was essentially creating an enclosed oven with the chips on the bottom.

Well in some 4-layer news, I've already come up with one slick change that makes use of the extra routing layer. I'm modifying the relay circuit to do away with the separate 24V regulator chip and instead just tap into the +/-18.5Vdc from the LM pre-regulator chips. The relay is then changed to the 48V coil unit of the same G6A Omron series. The relay has a "must operate" voltage of 70% of the rated coil voltage, so 18.5Vdc x 2 = 37Vdc should work. I wanted to do that originally, but without the extra routing layer there was no way to get the connections back to the pre-regulators made, at least without more jumper wires.

But the win isn't just getting rid of the regulator chip. The new arrangement will prevent the headphone relay from operating if someone accidentally plugs in a DC adapter rather than AC. That would "light up" only one rail, with a resulting rail-to-rail voltage a few volts less than the 48V relay's minimum pull-in voltage on Omron's datasheet graph. I've always thought that these dual rail half wave supplies need that particular protection.

So the change adds "accidental DC power adapter" protection to the relay circuit, while keeping the existing turn-on anti-thump delay and accelerated break at turn-off.

Last edited by agdr; 11th June 2013 at 03:44 AM.
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