454Casull said:
I haven't put together a case yet. The piece of aluminum is just a scrap that I had in my basement. I marked the holes with a marker and drilled them. I used a larger little larger drill bit than necessary, and bolted it through. For a normal heatsink, I typically would measure much more carefully, and then center punch the hole, drill it and tap it.
The only issue that I found with the boards is that it is a bit tough to secure the chip to the heatsink on the left side. It is possible to do it, but there is room for improvement when I get around to get another batch of boards made. To make it a lot easier, one could not install the last decoupling capacitors until after the boards are mounted to the heat sink.
As for the boards, I had some extras made if anyone wants to be a beta tester for this new design. I can offer the boards for $9 each by themselves, or put together a kit with all parts needed to stuff the boards. Based on the feedback, I will revise the layout, and mail all that beta tested the board and provided feedback a board from the first production run. Drop me an e-mail if you are interested.
I will provide a BOM with the boards.
--
Brian
bmwman91 said:
As for LM4780 vs LM3886, according to National Semiconductor, the LM4780 is simply 2 LM3886 cores put into a single package. The only difference in the two packages is that the LM4780 doesn't have quite quite the heat dissipation abilities of the combined heat dissipation of two uninsulated LM3886 chips. Though, it still should be more than a pair of insulated chips.
As for the LM4780 board design, if you are bi-amping, it should be a great solution for that. There is a line on the bottom of the board for jumpering the input together, which would work great for a parallel amp, or a bi-amp setup, with both channels of one board running off the same signal.
--
Brian
Do you think you could drop the pitch of the signal holes to 0.1"? I'd like to use standard headers on these boards.
EDIT: Like these:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19423-ND
EDIT: Like these:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19423-ND
Hi Brian! I'm going to betatest your two boards..
a couple of open points:
I suppose C3,C4,C5,C6 are 100uF, C1, C2, C7, C8 are 100nF
but what about R1, R2, R3, R4 and R7, R8, R9?
My guesses for now:
R11 and R10 are 2.7ohm, 2w
R5 and R6 are 22kohm, 1/2w
which are now the 10k and 1k ones?
and the 680ohm?
and finally what is R9??
I also noticed no zobel so no couple of 47uF + 0.1uF cap, right? ok for me..
On the PS I guess:
R0 10k,
R12 and R13 are 1ohm
but I'm not able to spot 4 0.1uF to snubber a la CarlosFM way, right?
if I want usual 2.2kohm between the big 10000uF C9, c10, C11 and C12 (but I noticed that this usually inserts me some humm on the speakers... so probably won't do)
on this other board instead:
what is C7, c8, c9, c10, c11, c12? 1500uF??
and c3, c4, c5? 47uF? 22uF?
also most of the R resistors could be guessed but if you maybe already have a BOM or hint to give..
thanks in advance, and let you know how those protos will work (i'll use one to pilot a sub and one to pilot a center channell probably..)
tent:wq
a couple of open points:
BrianGT said:I received a small batch of boards, and will try them out soon.
LM4780
I suppose C3,C4,C5,C6 are 100uF, C1, C2, C7, C8 are 100nF
but what about R1, R2, R3, R4 and R7, R8, R9?
My guesses for now:
R11 and R10 are 2.7ohm, 2w
R5 and R6 are 22kohm, 1/2w
which are now the 10k and 1k ones?
and the 680ohm?and finally what is R9??
I also noticed no zobel so no couple of 47uF + 0.1uF cap, right? ok for me..
On the PS I guess:
R0 10k,
R12 and R13 are 1ohm
but I'm not able to spot 4 0.1uF to snubber a la CarlosFM way, right?
if I want usual 2.2kohm between the big 10000uF C9, c10, C11 and C12 (but I noticed that this usually inserts me some humm on the speakers...
so probably won't do)BrianGT said:
LM3886
on this other board instead:
what is C7, c8, c9, c10, c11, c12? 1500uF??
and c3, c4, c5? 47uF? 22uF?
also most of the R resistors could be guessed but if you maybe already have a BOM or hint to give..
thanks in advance, and let you know how those protos will work (i'll use one to pilot a sub and one to pilot a center channell probably..)
tent:wq
Tent, I don't think going higher than 10k will do anything too much for an amplifier with this current demands. Don't waste money on bigger caps.
Let's see .. C7 and C8 are the Zobel network caps, right ? That'll be 100nF ?
C9-12 are basically whatever high value you can fit in those positions, as mentioned above, going too high might prove of little benefit.
C3-6 are 100ish uF bypass caps.
C1-2 are 100nF bypass caps.
R12-13 are capacitor discharge resistors. They should be a large value, if you put 1ohm there, you'll literally vaporise them or just blow the fuses.
If you look at the schematics & guide from chipamp.com, you can see more or less all the values for the components, just identify them in the new layout.
No, there isn't a snubber on the PSU.
That's more or less it.
Let's see .. C7 and C8 are the Zobel network caps, right ? That'll be 100nF ?
C9-12 are basically whatever high value you can fit in those positions, as mentioned above, going too high might prove of little benefit.
C3-6 are 100ish uF bypass caps.
C1-2 are 100nF bypass caps.
R12-13 are capacitor discharge resistors. They should be a large value, if you put 1ohm there, you'll literally vaporise them or just blow the fuses.
If you look at the schematics & guide from chipamp.com, you can see more or less all the values for the components, just identify them in the new layout.
No, there isn't a snubber on the PSU.
That's more or less it.
Atilla said:
Thanks a lot Atilla,
a pitty there is no snubber in the PSU.. anyway.. I got most of them now.. still some doubt on the resistors tough.. so those R12-13 are the ones usually I see on chipamp.com's PSU rated at 2.2kohm 2W+? I'll try to guess the other resistors now.. like R9..
What about that other board, the red mono 3886? Are those C8-11 all 1500uF also in your opinion? Any better value possible?
So basically another thing I understood, if I'm right, that the most important caps one should spend some money on should be those 100ish uF, and possibly the 10000 or 1500 uF ones, right? Is it also normal I do not see any 2.2uF or 3.3uF polipros on the input?
Thanks a lot,
tent:wq
On the red board, you can probably fit larger than 1500UF per position, depending on the voltage you'll be using. Just measure the diameter and find caps that are suitable. 6x2500uF should be quite allright, but you can probably fit bigger ones - check. it's a balance of capacitance, quality and price.
For R12-13 you can use the exact same resistors, yes. You can use larger values as well, but the discharge time will be longer. Shouldn't be a big issue.
I'd say don't go wild on the caps, but getting good quality 100uF caps and polyprops for the supply bypassing shouldn't cost you too much.
The caps in the input are for blocking DC and they're not present in this design. You should make sure that the source doesn't have high DC offset or you might run into trouble.
For R12-13 you can use the exact same resistors, yes. You can use larger values as well, but the discharge time will be longer. Shouldn't be a big issue.
I'd say don't go wild on the caps, but getting good quality 100uF caps and polyprops for the supply bypassing shouldn't cost you too much.
The caps in the input are for blocking DC and they're not present in this design. You should make sure that the source doesn't have high DC offset or you might run into trouble.
Great, thank you for your reply: now I have a clear picture!
Only on the first part about those six caps: that balance of capacitance and quality and price: let's simplify and price is no issue, would this mean that the higher the capacitance the better quality?
So, basically those are also the same thing that on the BLUE PCB is done by the four big 10000uF (or 15000uF still if price is no issue) ones?
But ok, now I can start building, will'lte you know my impressions.. will be going to compare it to my other stereo LM3886 based amp from chipamp.com
tent:wq
Only on the first part about those six caps: that balance of capacitance and quality and price: let's simplify and price is no issue, would this mean that the higher the capacitance the better quality?
So, basically those are also the same thing that on the BLUE PCB is done by the four big 10000uF (or 15000uF still if price is no issue) ones?
But ok, now I can start building, will'lte you know my impressions.. will be going to compare it to my other stereo LM3886 based amp from chipamp.com
tent:wq
Yes, it's just more caps in parallel, for lower ESR. There's many factors when choosing PSU caps, but in the end of the day I can't say it's something that will make a tremendous difference unless you do it really wrong.
More capacitance meas you'll have more headroom on dynamic peaks before your supply line sags. Then again the higher it is, the more it stresses the rectifiers upon charging. It seems a serious overkill to go over 2x10000uF per power line per channel for LMXXXX amp, at least to me.
Caps physical sizes grow with 2 factors - capacitance and voltage rating, if one of them goes up, the capacitor size must grow. Therefor there's just as much capacitance you can fit in a given diameter on the board.
There's other factors in a cap - ripple curent, ESR, ESL, temperature rating, expected lifetime, tolerance. For some of those to be better, you'd pay more than for other caps. Sometimes it might be better to fit a few thousand uF less, but with better specs, for the same price.
You can read a lot on that in the different forums here. If you don't want to deliberatelly spend money on some best-in-its range part, just follow the general advice and fit any cap that seems decent and you'll be fine. If you start figuring out the "best" cap, you'll never end up making the amp work.
BTW, I'm using the panasonic caps that come with brian's kits and it's more than good.
More capacitance meas you'll have more headroom on dynamic peaks before your supply line sags. Then again the higher it is, the more it stresses the rectifiers upon charging. It seems a serious overkill to go over 2x10000uF per power line per channel for LMXXXX amp, at least to me.
Caps physical sizes grow with 2 factors - capacitance and voltage rating, if one of them goes up, the capacitor size must grow. Therefor there's just as much capacitance you can fit in a given diameter on the board.
There's other factors in a cap - ripple curent, ESR, ESL, temperature rating, expected lifetime, tolerance. For some of those to be better, you'd pay more than for other caps. Sometimes it might be better to fit a few thousand uF less, but with better specs, for the same price.
You can read a lot on that in the different forums here. If you don't want to deliberatelly spend money on some best-in-its range part, just follow the general advice and fit any cap that seems decent and you'll be fine. If you start figuring out the "best" cap, you'll never end up making the amp work
. BTW, I'm using the panasonic caps that come with brian's kits and it's more than good.
AndrewT said:
Hi AndrewT!
er.. what was this 'device decoupling'?
something like putting an 1ohm, 2w resistor with a ten windings of copper around it? and what do you mean by "at chip" or "at output"?another thing I was trying to understand here in the forums, but still is not clear to me is that "bleeder resistors" usage? where should they usually be put (i.e. under one or all the PSU caps?), and what is the (sonic) advantage of using them?
thanks!
tent:wq
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.