about the lm4780 PCBs

[theChris]

i got a version of the layout done today, and I plan to get some boards printed this week. in anycase i took the schematics from the 4780 datasheet, except of course for their oversight on the inverted mode...

there is room for small bipolar capacitors for feedback stuff on the board. you can include something else if you are creative.

the schematic is something like the picture. obviously some components can be removed or shorted to give the desired results.

can be arranged as:
inverted x2
noninverted x2
bridged x1
parallel x1 (useing external 0.1ohm resistros or wire)
difference x2

i can include some screw terminals for the boards as well.

size looks like about 2.3" x 2" (5.8cm x 5cm)

works with lm4780 and lm4732.

[sangram]

$$ ??

And will you ship out to India? And shipping cost (ground is OK, but I prefer air)? I'll use western Union. Or something like that. My Paypal card has expired.

[tcpip]

Originally posted by sangram
And will you ship out to India? And shipping cost (ground is OK, but I prefer air)? I'll use western Union. Or something like that. My Paypal card has expired.

If theChris is willing to pass on the Gerber files to you, why don't you get the PCBs made in India? Won't that be far less expensive and bothersome?

[sangram]

Yes, you are right, but Chris has mentioned intent to sell earlier and he's also got like a minimum order qty which he needs to fulfil to keep order qtys low. I guess he will need to keep that commitment with the board maker, so I dunno if he'll send me the gerbers, but let him reply.

I also have pdf files of the board layout but am hesitant to use them post your feedback that pdfs aren't as good, the 4780 can be quite a pain to wire up as the distance between pins is very small. I don't even know how much he's asking for them, so if the price is decent I need 3 boards anyway plus one or two backups.

I'll hold a day.

[theChris]

i can give you the gerber files from autotrax if you want. while i do like money, shipping to india is a lot. just remember that these were intended for use on a milled PCB where the top layer is effectively a groundplane, with a few exceptions. so if your PCB designer etches off the top, which is likely a default, the board will not work correctly. the gnd terminals of the chip will not be connected, nor will the 100nF or 10uf caps (if used, they are listed on the datasheet, and thus included in the files).

what do you guys think is a reasonable price for milled PCBs. they are 2.3" by 2". Since i'm printing the boards myself, i am just using time. but it does take a lot of time. does this sound reasonable?
$10ea for 1-2 PCB
$9ea for 3-4
$8ea for 5-6
$7ea for 7-8

also, i don't have a minimum qty order, i'll ship just 1 PCB if that's all that's needed, but at some point shipping becomes much more expensive then the PCBs.

[theChris]

oh, you can email me for the gerbers. i'd rather not post them on the forum for everyone just yet.

the ICs are $9 each when purchaces in low quantities. thats kinda where i got the numbers from.

i'm also working on a dual 4780 board, well, 2 4780 boards in 1. though there is no reason for a discount, i may offer one on them.

[sangram]

Originally posted by theChris
i can give you the gerber files from autotrax if you want. while i do like money, shipping to india is a lot. just remember that these were intended for use on a milled PCB where the top layer is effectively a groundplane, with a few exceptions. so if your PCB designer etches off the top, which is likely a default, the board will not work correctly. the gnd terminals of the chip will not be connected, nor will the 100nF or 10uf caps (if used, they are listed on the datasheet, and thus included in the files).

what do you guys think is a reasonable price for milled PCBs. they are 2.3" by 2". Since i'm printing the boards myself, i am just using time. but it does take a lot of time. does this sound reasonable?
$10ea for 1-2 PCB
$9ea for 3-4
$8ea for 5-6
$7ea for 7-8

also, i don't have a minimum qty order, i'll ship just 1 PCB if that's all that's needed, but at some point shipping becomes much more expensive then the PCBs.

40 bucks for 5 PCBs sounds good to me. I have 3 chips (samples) right now, and 9$ per chip sounds good to me too - though I may not need them. You may have to mark packages as demo samples so I can minimise duty damages. I'll quickly figure out how many PCBs and/or chips I need for myself.

Unless, of course, Tarun feels that India is less trouble - since the suppliers are comfortable on email. I'm a bit of a loss beyond P2P (which is NOT a good idea for the 4780) but I also don't have any time to even breathe - it is quite miraculous that Tarun has been scouring the countryside for parts for quality DIY projects, and has actually found suppliers. I need to dig up the thread where all the contact details are buried. See ya.

[tcpip]

Originally posted by theChris
i can give you the gerber files from autotrax if you want. while i do like money, shipping to india is a lot. just remember that these were intended for use on a milled PCB where the top layer is effectively a groundplane, with a few exceptions. so if your PCB designer etches off the top, which is likely a default, the board will not work correctly. the gnd terminals of the chip will not be connected, nor will the 100nF or 10uf caps (if used, they are listed on the datasheet, and thus included in the files).

I'm lost here. Can you please explain how this is different from non-milled PCBs? I understand how a normal DSPTH PCB is made, and the PCB maker I'm dealing with regularly makes them. So, in DSPTH terms, if you give me a double-sided layout with the top layer as the ground plane, with vias and pads and thru-holes wherever needed, that's fine with this PCB maker... he can make it. Is a milled PCB very different? He can't make blind vias (but then they are not needed for DSPTH).

The rates for making DSPTH PCBs in quantities of, say, 50 or more, will not be more than two to three cents (US) per sq-cm, if made here. I'm talking about FR4 substrate, 1-ounce Cu on either side, and full plated through holes as per industry specs, with solder masking and legend printing. The only problem is that I wouldn't try tracks and clearances less than 12mil with this fab shop. If that's okay (which it should be for power amps of any kind), then this is the rate you'll get. I get small quantities made (two or three boards) for which rates are higher. But they're still less than the volume-purchase or group-buy rates I see among the European and US members.

[theChris]

etching - leaves traces unaffected, all other areas are removed.
milling - run a drill around traces, other areas are left. in my case the top is a peice of metal that is used for ground, but the files don't suggest this explicitly. with milling it works out, but with etching, i have doubts.

as for the PCB designs, i try not to have things closer then 12mils, as milling small areas needs very small bits and a lot more precision, though this makes the pads for the pins very small.

thats a great rate on the PCBs, makes me envious. my boards, being milled, don't have plated vias or silkscreen either. just solder to the metal.

[sangram]

I get the difference. It's a complete ground plane on which the non-ground traces are separated from the plane by thin areas of the laminate, like we see on a lot of peripheral cards - a LAN card I own is like this.

I will have to heavily modify the gerbers in order to do this, and I don't even own a PCB program.

Tarun: Chances of getting a good PCB from pdf?

theChris: to get these PCBs made here will cost about fifth, I guess, of what it would with S&H to India. I still might just decide to go for it.