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A few PIMETA build questions (New: troubleshooting questions) - Page 2

post #16 of 30
9/21/07 at 3:51am
I think most plastic-encapsulated devices (as opposed to ceramic or hermetic metal) will absorb moisture, but it's irrelevant to DIYers unless you live in a humid area. If you do, and you think your soldering job might build up enough heat inside the encapsulation to boil absorbed water and crack the thing open, you can put the chips in a 250 degree F or so oven for 10 minutes or so to desiccate the chips slowly.

These warnings have more to do with automated assembly, not just because of the difference in soldering methods, but also because most electronic assembly in the world happens in coastal Southeast Asia, which is pretty much universally humid.
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post #17 of 30
10/8/07 at 6:38pm
Thread Starter 
Quote:
Originally Posted by xmokshax View Post
so you just used the tube washers as standoffs, drilled holes in the bottom of the case, and threw some nuts on the outside ends? these specifics are what i was hoping to get at. i guess i'd like to avoid drilling through the case if possible, but it sounds like that's probably the best and most secure option, right?
bump... i've finally collected all the parts i need for my PIMETA, so the question of mounting the board in the case is becoming more immediate. as i said above, i don't want to ruin my $22 case by drilling holes in it unless that's the best way to mount the boards in the case. is this the best way? if so, how do you keep the ends of the screws from scraping up the surface that your amp is sitting on... are those little rubber feet supplied with the case tall enough?
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post #18 of 30
10/8/07 at 7:08pm
Quote:
as i said above, i don't want to ruin my $22 case by drilling holes in it unless that's the best way to mount the boards in the case. is this the best way?
You can always mount everything on a piece of sheet stock that fits between the rails of the enclosure.
Like I did for this alien DAC---->

[

I only did that because there was not an easy way to access the mounting screws (the enclosure did not have a removable top).


Do I need to suggest how much of a PITA that was?
Screws through the bottom is so much easier--->







Quote:
if so, how do you keep the ends of the screws from scraping up the surface that your amp is sitting on... are those little rubber feet supplied with the case tall enough?

Use flat head screws and countersink them.

Here is an example of a countersink bit---->
http://www.amazon.com/Irwin-12411-CO...880339&sr=1-40
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post #19 of 30
10/8/07 at 7:41pm
Thread Starter 
MisterX:

aha. excellent... i think i'll stick with screwing the PIMETA into the bottom of the case. as long as the screws are countersunk, that'll work perfectly well. thanks for the info.

out of curiosity, is there any common retail chain that will cut sheet metal stock to custom sizes, or is that something you need to have access to a machine shop to accomplish? i still need a "PCB extender" (per your suggestion) to keep my Alien DAC board stable inside the Hammond 1455C802 i bought for it.

one other thing: it looks like the little black piece in your PIMETA picture is a panel-mount LED holder. where does that part come from?
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post #20 of 30
10/8/07 at 8:17pm
Quote:
out of curiosity, is there any common retail chain that will cut sheet metal stock to custom sizes
Dunno but most of them sell tin snips.

Quote:
one other thing: it looks like the little black piece in your PIMETA picture is a panel-mount LED holder. where does that part come from?
Mouser page 135 iirc.
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post #21 of 30
10/8/07 at 10:14pm
Thread Starter 
Quote:
Originally Posted by MisterX View Post
Dunno but most of them sell tin snips.



Mouser page 135 iirc.
YRC. impressive. thanks again.
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post #22 of 30
10/17/07 at 8:39pm
Thread Starter 
so i've spent a bit of time the last couple of nights assembling my PIMETA and soldering the chips down to Brown Dog adapters. i finally took the power supply for a test-drive last night, which met with disappointing results. here are some specifics of my build:

-DIP sockets are installed, but i didn't drop any chips in before the power supply test.
-using a TREAD configured to output 22VDC. as mentioned in this thread, my meter measures very high VAC values even after filtering and regulation, but it was suggested that this is an artifact caused by my meter, not the circuit.
-using an ADAPTLE from Tangent's site for the rail splitter.
-no Class A bias yet - figured i'd get the circuit working correctly before installing those transistors.

and now, the problem i encountered: i soldered the power leads from my TREAD to the outer + and - pads on the PIMETA board, and jumpered the switch position temporarily. when i plugged the TREAD in, it measured as expected - 22VDC from TP2 to TP3. however, when i measured from the supply pins of two of the DIP sockets to IG, i got readings of ~16 and ~20VDC or so. it was at this point that i smelled something hot, unplugged the amp, and realized that the TLE chip was rather warm. it wasn't burning up by the time i touched it a second after unplugging, but it was pretty hot. i've checked the board quickly for shorts/bridges, and nothing is immediately apparent... this evening i'll go through and reflow everything and de-flux the bottom of the board. i just figured i'd ask where on the board i should focus my attention if there seems to be a problem with the TLE chip. anyone know what could have fried it or made it spit out odd voltages like that?

EDIT: forgot to link to my other TREAD thread. fixed.
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post #23 of 30
10/17/07 at 8:44pm
Pics ...
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post #24 of 30
10/17/07 at 8:49pm
Quote:
anyone know what could have fried it or made it spit out odd voltages like that?
You mean besides having it installed backwards or shorted to the - rail from the tread (or AC adapter if this is in a case)?

And... did you install the buffers yet or no?
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post #25 of 30
10/17/07 at 8:57pm
Thread Starter 
Quote:
Originally Posted by tomb View Post
Pics ...
they're coming, as soon as i get home this evening. as i said, i will reflow everything and check stuff over very thoroughly. i just wanted to get an idea of what kinds of connectivity mistakes i should be looking for.

Quote:
Originally Posted by MisterX
You mean besides having it installed backwards or shorted to the - rail from the tread (or AC adapter if this is in a case)?

And... did you install the buffers yet or no?
i did check the orientation of the ADAPTLE before i installed it, but perhaps i still managed to reverse it - as i said above, pics will be coming in a bit, but i installed the ADAPTLE board such that the "top" side, onto which the chip and cap are soldered, face towards the edge of the PIMETA board that contains the volume pot. the amp isn't cased up yet, so there's no short to the AC adapter, and no, i haven't installed the buffers yet. none of the ICs are in place.

EDIT: $&%#, it appears that i DID install the TLE backwards. i suppose that'll do it. i thought i'd gotten it lined up correctly based on the pinouts on the TLE datasheet and the ADAPTLE board, but i apparently still managed to switch it. i didn't see that Tangent actually has the correct orientation posted on his ADAPTLE website. is it fair to assume that the TLE chip is extra crispy?
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post #26 of 30
10/17/07 at 9:28pm
Quote:
is it fair to assume that the TLE chip is extra crispy?
They are pretty durable but there is only one for sure way to find out.
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post #27 of 30
10/17/07 at 9:32pm
Thread Starter 
ok. well, i'll cross my fingers. i do have a TO-92 TLE lying around, but how much of a sonic difference does the presence of the noise reduction capacitor make? is it appreciable enough that i'd want to stick with the ADAPTLE over the TO-92 part for my PIMETA, in the long run?
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post #28 of 30
10/17/07 at 9:33pm
Quote:
Originally Posted by xmokshax View Post
<snip>is it fair to assume that the TLE chip is extra crispy?
Don't worry about the pics - sounds like you found your problem. I don't know if the TLE is damaged. From you description, it sounds like there's a chance that you may have gotten to it in time. I'm not familiar with the survivability of the TLE, though. Maybe you can solder it back in correctly and see what happens. You might give that a try before trashing it - unless you have an extra TLE just waiting.

EDIT: Looks Mister X answered in the meantime. I need to type faster.
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post #29 of 30
10/17/07 at 9:36pm
Quote:
is it appreciable enough that i'd want to stick with the ADAPTLE over the TO-92 part for my PIMETA, in the long run?
Nope, I benchmarked the same amp with one of each and found there was not enough difference to matter.
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post #30 of 30
10/19/07 at 4:57am
Thread Starter 
ok, i carved out a few minutes this evening to replace the ADAPTLE with a TO-92 TLE (decided not to even bother re-soldering the ADAPTLE in the right orientation, since there's a chance it's already fried). sure enough, i'm now getting 10.7V from each supply pin to IG (22V supply minus a diode drop). perfect!

now, if i could only listen to the damned thing... but audio testing is on hold until i get my hands on some molex connectors. don't want to solder and de-solder input and output jacks, and i'm not ready to do the final casework yet.
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