[Syzygies]

What hasn't settled for me yet is how I'm going to secure the PIMETA board inside my (shortened) Hammond J16 case.

I'm not using the crossfeed mounting holes; is it enough to support the board by the pot and these holes? If so, how? I can imagine bolting to a board that slides down the Hammond board rails, but perhaps there's an easier way? I must have missed that class, what do you all do?

 

[Vadi]

I'll use the holes and drill a third one next to the pot.

 

[__redruM]

The mounted pot holds the board quite well. If you wanted to, you could add padding underneath the board or even extra screws, but they're not needed.

 

[knestle]

From my point of view (which is probably skewed and ignorant) this thread has gotten off point and deteriorated into esoterica involving battery types.

I have a Pimeta in a J case all but completed. My project has languished for a long time because I too want to use rechargables (dual 9V in my case) with minimal internal componants.

Can this be accomplished with just a jack in the back panel and connecting wires inside the case? Charger/regulator and whatever else outside, or in a seperate case? Or do I really NEED componants inside the case?

 

[Syzygies]

Quote:

Originally Posted by knestle deteriorated into esoterica involving battery types. ... Can this be accomplished with just a jack in the back panel? and connecting wires inside the case?

Yes. Also a standard idea for R/C, where weight and space also matters. RadioShack is closing out an "AA charger wall wart" for $5 right now that is intended exactly for this R/C application. Too bad it's the wrong current for AAA or 9V.

The battery pack is half the case problem, and unless you're etching your own board, the half you have the most control over. If by volume it's less than half your case problem (as dual 9V would be with a PIMETA), then I have to ask: Have you made the quiescent current draw computation, or measured this? Are you ok with the number of minutes of run time you'll get?

 

[Vadi]

Quote:

Originally Posted by Syzygies Actually, what you need is to provide access to the batteries for charging. That has generally been interpretted as easy removal, or an internal charging circuit. However, a simple jack that connects to the batteries, allowing an external charging circuit, is also fine.

Thanks a lot Syzygies! I'll do that and go for 8 rechargeable AA NiMh cells (2500 mAh).

 

[Voodoochile]

Quote:

Originally Posted by Porksoda Well, according to the BUF634 datasheet it draws 15 mA quiescent, plus 2.5 for the amp plus 2 for class a is about 20. Multiply by 3 (for 3 channels of course) and you have 60 mA, plus LED and whatever your headphones and any other misc. stuff might be drawing. Plus, I was planning on doing the 2-1-2 stacked buffer arrangement. Do you have the buffers running at less than full high bandwidth mode? EDIT: I checked the PIMETA schematic and with the 220 ohm resistor spec'd its about 8mA per buffer, which is pretty close to your estimate. I suppose I could play around with varying the bandwidth vs. stacking buffers and see how doubling the quiescent draw compares to just using twice as many buffers. Do you know if anyone has done this kind of testing with stacked buffers vs. variable bandwidth on the 634?

This may not exactly be what you are after, but I recalled it as being an excellent thread by KurtW. The information presented is pretty interesting.
Updated version here
Original thread here

 

[mono]

Quote:

Originally Posted by __redruM ... And a piece of antistatic bagging is between the back of the board and the Metal case.

FYI, many (most) types of anti-static bags conduct electricity and should not be used in this type of application. Anti-static bags are quite specifically designed to conduct electricity, albeit high resistance but in the computer field it's common to see someone put a new board on anti-static and get wierd symptoms.

 

[__redruM]

Quote:

Originally Posted by mono FYI, many (most) types of anti-static bags conduct electricity and should not be used in this type of application. Anti-static bags are quite specifically designed to conduct electricity, albeit high resistance but in the computer field it's common to see someone put a new board on anti-static and get wierd symptoms.

I did specifically test it with an Ohm meter before using it, and could not get it to conduct at amp voltage levels. And I haven't had an issue. I wouldn't trust it at high voltage levels. But I will keep you comments in mind.

 

[Quacker]

Just other questions.
Quote:

Originally Posted by Syzygies On the other hand, the RadioShack 2x2 AAA holders just fit the "J" case in one position, luckily the position where we don't have to worry about the batteries working loose. Moreover, the "J" case fits in a pocket. That was decisive for me.

.What is the part number for those battery holders that can fit in that "J" case?
Quote:

Originally Posted by Syzygies Actually, what you need is to provide access to the batteries for charging. That has generally been interpretted as easy removal, or an internal charging circuit. However, a simple jack that connects to the batteries, allowing an external charging circuit, is also fine.

.How would you wire a jack into the back pannel with what seems like a limitted amount of space with those radioshack battery holders?
.And if you didnt want to make your own external battery charger what kind would you need that would work in your set up?

 

[Syzygies]

RadioShack 270-413. They actually fit both ways, the way shown is a bit of a squeeze if you tape the AAA cells for security. The other way is easier, a bit loose.

If you leave out the 2 AAA holder I've squeezed in between, then there's room for a standard "N" type power jack on one side, taking advantage of the indent the batteries can't use. I opted for the extra volts instead. This is a J16 case, which I could cut down, or leave long and build in a charging circuit in back. The J12 case is a little bit too short, even if you start chopping the PIMETA board. As others have observed, easier to chop a case.

Outboard or inboard, you pretty much have to make a charger, but trickle chargers are easy compared to the amp you're making.

 

[Vadi]

Quote:

Originally Posted by __redruM I did specifically test it with an Ohm meter before using it, and could not get it to conduct at amp voltage levels. And I haven't had an issue. I wouldn't trust it at high voltage levels. But I will keep you comments in mind.

While shopping I found "hard paper" (Hartpapier in german). It's 1mm thick "plastic" and I'll use it because it's more durable.

 

[Porksoda]

Well, I'm almost done with my amp, and my conclusions are:

1) Height-wise, 8xAA batteries DO fit in the L series case, but only if you omit the holder and tape them together yourself. Also, you have to stagger the ones on top so that the whole thing sits as low as possible. Also you have to use extremely thin tape when taping them together. Electrical tape was too thick; I ended up using some Kapton tape we had laying around the dept. that is very thin and strong and worked perfectly. Even then, no more than 2 layers.

2) Unfortunately, the AAs in a 4x2 arrangement were too long to fit the whole thing in behind the PIMETA board, so I had to do a 6-battery arrangement along side the pimeta, and cram the last two in sideways behind the board. Otherwise, everything fits juuust barely. I think I might actually dremel some of the plastic off the top of the Alps to ease the fit. The power caps, Elna Cerafines, cut it extremely close, too. I was even able to cram a 1/4" output jack in between the alps and the power caps.

Only thing that remains to be done is squeeze the barrel power connector, rca jacks, and a fast charging board in the miniscule space that is left. I think I am gonna use a mint-style trick and sandwich two halves together, oriented upright. Then, I'm gonna screw the LM317 to the case to act as a heat sink and give the board support.

Hopefully, completed pics in a couple days!!!