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M³ Project Announcement - Page 25

post #361 of 565
1/25/05 at 12:13am
Wow! Looks great. Can't wait for the production boards to be released!
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post #362 of 565
1/25/05 at 12:19am
Same comment as for the PPA v2:

I just noticed something...

Shouldn't the bass boost pot area also have the twelve little square silkscreen areas on the volume pot area to protect the board when mounting an Alps Blue?

Or, that's what I always thought those twelve silkscreen squares are for...

Anyway, I thought it'd just make more sense, howmuchever difference it'll make, to have the same sort of silkscreening for both pots.
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post #363 of 565
1/25/05 at 12:20am
Quote:
Originally Posted by NeilPeart
Looks like the power was supplied using the crocodile clips to the tabs of the transistors?
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post #364 of 565
1/25/05 at 1:21am
Thread Starter 
doobooloo: I'm on it, thanks!

Quote:
Good catch, doobooloo! While the little silkscreen squares mostly cover the unsightly windows in the ground plane put there to prevent the sharp landing points on the pot legs from puncturing the soldermask and shorting to ground, the fact remains that the bass boost pot could theoretically short itself. I'll probably just move the traces so they don't cross the landing zone.
Dreamslacker: Yes, the MOSFETs are not electrically insulated from the heat sinks.
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post #365 of 565
1/25/05 at 2:04am
Quote:
Originally Posted by Dreamslacker
Looks like the power was supplied using the crocodile clips to the tabs of the transistors?
Yeah, I happened to be using an adjustable bench power supply in those photos, which came with banana-to-alligator-clips wires. It was convenient to simply clip them onto the heat sinks (which are tied to the drain pins of the MOSFETs) rather than make another cable.
Quote:
Originally Posted by doobooloo
Shouldn't the bass boost pot area also have the twelve little square silkscreen areas on the volume pot area to protect the board when mounting an Alps Blue?
As Morsel states, those little squares under the volume pot are actually cutouts on the ground plane to keep the sharp points around the Alps Blue pot pins from touching the ground plane. There are matching squares on the silkscreen layer to serve as markers. Since there is no ground plane under the bass boost pot the extra insulation is not necessary. I didn't have any problems with the layout as it was on the prototype, but I guess Morsel will move the traces slightly to make extra sure that no contact between pads (via the pot pins) would occur.
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post #366 of 565
1/25/05 at 2:23am
Quote:
Originally Posted by amb
The LM2937 is a 500mA negative regulator which would be operating near its limit with this amp. The LM2990 is also a negative regulator with max output of 1A. Its "complement" is the LM2940 positive regulator.

At any rate, this is a bit OT since the M³ pcb doesn't have any voltage regulators. If you want to design your own PSU for the M³, the LM2940 is probably ok, but I would feel a bit more comfortable with the LM317 which is rated at 1.5A or the LT1085 at 3A.
A frendly Correction the LM2990 is the Negitive complement to the LM2937 Both are fixed with 15 volts being the max output voltage Both are low dropout devices with 500mA for the 2937 and 1 amp for the 2990. These are might fine devices as far as Fixed voltage regulators go
Data Sheets>
http://cache.national.com/ds/LM/LM2990.pdf and http://cache.national.com/ds/LM/LM2937.pdf

My favorite IC voltage regulators are fromn LTC and the Best devices from them is The LT1185 for Negitive adj at 3 amps
http://www.linear.com/pc/downloadDoc...19,P1465,D2875

and the positive matching one is the LT1764
http://www.linear.com/pc/downloadDoc...55,P1820,D1316

also see the LT1085
http://www.linear.com/pc/downloadDoc...55,P1283,D3741

I also recomend reading this app not from LTC on Performance enhancements of three term Reg's AN2
http://www.linear.com/pc/downloadDoc...55,P1283,D4099
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post #367 of 565
1/25/05 at 3:17am
Thanks ppl. The info would be useful for those who want to design and build their own PSUs.
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post #368 of 565
1/25/05 at 5:07am
Thread Starter 
M³ v025

Quote:
Since there is no ground plane under the bass boost pot the extra insulation is not necessary.
Although the chance of it happening was remote, it was possible that the sharp pot landing leg could have pierced the left bass boost trace, shorting it to the center tap, thus disabling bass boost for that channel, which is why I moved the trace.

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post #369 of 565
1/25/05 at 5:32am
Is it possible to make the board 5.28" wide instead of 5"? Perhaps the extra 2 x 0.14" can go on both sides to allow for the board to slide in even with larger caps installed, and to make sure that the railings don't cover the input pads.

The Lansing MicroPak style cases can accommodate 5.28" x 5/6/7/8.5" PCBs.

I think the closest Hammond alternative is 6.319" x 8.661", a bit too big.

The Lansing enclosures look much nicer anyway...
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post #370 of 565
1/25/05 at 10:18am
doobooloo, the Lansing MicroPak series do not have any ventilation holes or slots, neither do the Hammond 1455 series. This makes the cases unsuitable for use with this amp. The MOSFET heatsinks get warm, and the heat need to escape.

I am working on enclosure solutions. Watch this thread for more info when I have more to share.
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post #371 of 565
1/25/05 at 11:40am
Quote:
Lansing MicroPak series do not have any ventilation holes or slots, neither do the Hammond 1455 series
That what you got the dremmel for...

During the test, how hot did the warmest heatsink become?
I guess it would be the heatsinks in the ground channel. An aproximate temperature would be enough. Just want it to base decision of using 1" or 2" heatsinks. I guess you never put the prototype in a box, but it might still be good as a guide.
Also would any other component on the board be over 1" high (counting from the PCB)?

It just came to my mind that in a chassi it will be easier to get air circulation near the edge of the board to cool the heatsink, and the warmest heatsinks happens to be the ones closest to the edge. Was it just luck that made it turn out like that?
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post #372 of 565
1/25/05 at 2:01pm
Thread Starter 
doobooloo: I think the issue of enlarging the board to fit one of those cases is worth exploring. Let's look at the thermal issues more closely. I think it is worth evaluating just how hot a closed box will get with all 3 channels biased at 80mA.

silvervarg: If you have a Dremel you can drill 4 mounting holes for pcb standoffs, however, it would be nice if there were an off the shelf case that fits M³.

I'm going to be out much of the next two days, and plan to wrap up PPA v2 tonight, so things will be a bit hectic until Thursday.
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post #373 of 565
1/25/05 at 2:37pm
Quote:
Originally Posted by morsel
doobooloo: I think the issue of enlarging the board to fit one of those cases is worth exploring. Let's look at the thermal issues more closely. I think it is worth evaluating just how hot a closed box will get with all 3 channels biased at 80mA.
Don't the Hammond and Lansing cases both have slide-off tops? If so, it might be interesting to replace those lids with something "airier" -- or just go topless
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post #374 of 565
1/25/05 at 5:30pm
Quote:
Originally Posted by Earwax
Don't the Hammond and Lansing cases both have slide-off tops? If so, it might be interesting to replace those lids with something "airier" -- or just go topless
My thoughts exactly. Those panels should be easy to machine, and it should also be pretty easy to make some substitute top cover as well.

Or Head-Fi can do a group buy on custom Lansing enclosures - or at least just a custom top panel?
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post #375 of 565
1/25/05 at 6:00pm
How about this?

http://www.audiokit.it/ITAENG/Cabine...000-Galaxy.htm

For european builders, off course (but I guess they ship to US).

Ciao
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