Welcome to the wonderful world of presbyopia...if you don't have them I strongly recommend getting a set of Donegan Optivisor headband mounted magnifying lenses. With a 3x lens set and 2.5x swing down loupe and add on LED lighting for maybe $60 they are a geezers best friend! I couldn't do board level electronics or 1/64" (0.4mm)woodworking without them!
Where I used to work we had a couple of dissecting microscopes at the soldering stations. That was a very cool setup. I think the magnification was about 7-10x.
I can solder 0603 SMD components without the microscope, but it tends to look like a bird just took a crap on the board. I wouldn't want to send that out to a customer. Do the work under a microscope and life becomes much easier and the end result much, much nicer.
Tom
I can solder 0603 SMD components without the microscope, but it tends to look like a bird just took a crap on the board. I wouldn't want to send that out to a customer. Do the work under a microscope and life becomes much easier and the end result much, much nicer.
Tom
It looks as though they charge 35 euros just for converting a sketch into a cad file.
That's not bad actually. That sounds like half an hour's worth of work. People don't work for free. I'm guessing you can avoid the fee by sending them the CAD file directly.
Tom
I think I might go for this case:
BZ4312A2 Aluminum amplifier chassis amp Enclosure Box 430*310*120mm L163-84 | eBay
I like the looks ( shame about the writing on the front panel) and the back panel is already partially ready. The volume knob will be redundant but who cares.
BZ4312A2 Aluminum amplifier chassis amp Enclosure Box 430*310*120mm L163-84 | eBay
I like the looks ( shame about the writing on the front panel) and the back panel is already partially ready. The volume knob will be redundant but who cares.
HI all,
Got a question about conformal coatings. I think i mentioned that I built some outboard xovers. While I was doing that and reading up on the subject I came across some folks recommending spraying PCBs and soldered and mechanical connections with VpCI coatings. I did some research and found, what seems to be, a very reputable company named Cortec Spray Technologies. I called them and they struck me as above board and willing to discuss things.
I bought a spray can of their Conformal Coating VpCI-286 and sprayed both pairs of the completed xovers. They have been working great for about 5 years.
I was wondering if it makes sense to spray the Mod86 and Power86 boards on top and bottom. Is there a downside to doing this. I don't have to spending any money because I've got plenty left.
Got a question about conformal coatings. I think i mentioned that I built some outboard xovers. While I was doing that and reading up on the subject I came across some folks recommending spraying PCBs and soldered and mechanical connections with VpCI coatings. I did some research and found, what seems to be, a very reputable company named Cortec Spray Technologies. I called them and they struck me as above board and willing to discuss things.
I bought a spray can of their Conformal Coating VpCI-286 and sprayed both pairs of the completed xovers. They have been working great for about 5 years.
I was wondering if it makes sense to spray the Mod86 and Power86 boards on top and bottom. Is there a downside to doing this. I don't have to spending any money because I've got plenty left.
Question on thermal grease. I sanded the surfaces of the heatsinks, where the LM3886s will be in contact, with 600, 800, 1,200 and 1,500 grit emery. Do I need only a very light coating of the grease, to fill any voids on the LM3886s, such that it doesn't even spread out beyond the edges of the LM3886s after tightening down?
Conformal coating. If you do this, the board must be antiseptically clean. You don't want to trap flux, oils, whatever under the coating. That said, unless you live on the ocean or within a mile or two of the ocean, or if you plan on sending the amps into space, there is no reason to conformally coat. You'll curse yourself if you ever have to rework the board.
Thermal grease: read the first few paragraphs of the Bill of Materials section. If you're using the LM3886 with exposed metal tab, you need an film insulator and won't need thermal grease. If you're using the insulated package version, then you need thermal grease. A small dab of thermal grease as it will squeeze out when you screw the amp chip to the heat sink. If the heat sink was flat there was no need to sand it. Likely you made the surface less flat by doing so. The goal is to have the heat sink surface as flat as possible to maximize direct contact to the amp chip's package. The thermal grease fills in the minute gaps in the surface. Its thermal conductivity is better than air, but no where near as good as surface-to-surface contact.
Thermal grease: read the first few paragraphs of the Bill of Materials section. If you're using the LM3886 with exposed metal tab, you need an film insulator and won't need thermal grease. If you're using the insulated package version, then you need thermal grease. A small dab of thermal grease as it will squeeze out when you screw the amp chip to the heat sink. If the heat sink was flat there was no need to sand it. Likely you made the surface less flat by doing so. The goal is to have the heat sink surface as flat as possible to maximize direct contact to the amp chip's package. The thermal grease fills in the minute gaps in the surface. Its thermal conductivity is better than air, but no where near as good as surface-to-surface contact.
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You need just enough thermal grease to fill the voids. Apply a dab of thermal goop to the LM3886 with a finger and spread it to cover the entire back of the IC. You want the thinnest coat you can apply with a finger.
I usually slide the board back and forth a little as I tighten the mounting screw on the LM3886 to make sure any surface roughness on the heat sink gets covered as well. Do that, then loosen the mounting screw on the LM3886 a couple of turns before tightening the mounting screws on the board. Then finish up by tightening the screw on the LM3886. That way you avoid stress on the LM3886 pins.
Thermal grease is not all that thermally conductive, but it is more conductive than air. So the goal here is to have as thin a film of goop as you can get away with while filling all the voids. If you have a little bit of goop oozing out as you tighten the mounting screw the last quarter of a turn you're pretty close to optimum.
Without the goop, the LM3886 will deliver a bit over 30 W into 8 Ω on ±28 V supplies. With the goop, you'll get the full 38 W specified in the data sheet.
Tom
I usually slide the board back and forth a little as I tighten the mounting screw on the LM3886 to make sure any surface roughness on the heat sink gets covered as well. Do that, then loosen the mounting screw on the LM3886 a couple of turns before tightening the mounting screws on the board. Then finish up by tightening the screw on the LM3886. That way you avoid stress on the LM3886 pins.
Thermal grease is not all that thermally conductive, but it is more conductive than air. So the goal here is to have as thin a film of goop as you can get away with while filling all the voids. If you have a little bit of goop oozing out as you tighten the mounting screw the last quarter of a turn you're pretty close to optimum.
Without the goop, the LM3886 will deliver a bit over 30 W into 8 Ω on ±28 V supplies. With the goop, you'll get the full 38 W specified in the data sheet.
Tom
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Looks pretty good. I agree with your comment about the writing on the front. Now if the vendor allowed you to define your own text that would be pretty cool, though. You can always toss them a message and ask if they can deliver the enclosure without the writing, volume knob, etc.
You may also like ModuShop. They're in Italy.
Tom
I asked the vendor and he can supply it without the writing. However I've always liked the functional look of the old Quad 405 and the same vendor has this:
sep CLONE QUAD405 chassis Power amp box DIY amplifier case L155-45 | eBay
This would be big enough if I mount the PS PCB vertically on one of the side panels. I'm wondering though if did that whether the weight of the big caps would put too much strain on their solder joints and weaken them over time?
Out of curiosity, why a finger? Some of the grease I've bought over the years has come with spreader tools, which have all been light plastic cards of some sort. 30->38W is 2dB so potential for further improvement is probably dBGF. But it's kinda nice to do cleanup on the card rather than your finger and there's potentially a little less goop in the mounting.
The caps in the MOD86 are pretty small (16 mm diameter, 26 mm tall). As long as you get them inserted all the way to the PCB when you solder them you should be fine. Sometimes you see well-made commercial equipment where large components have been secured with a dab of some sort of glue. It appears to be some sort of silicone. Now, before you ask, I would not use regular silicone for this. Regular silicone contains acetic acid, which is why it smells like vinegar when you use it. I'm sure that can't be nice to the board and components. Maybe there's an acid-free silicone out there...
I suppose you could use hot glue, but the glue likely won't stick very long. I'd also prefer something that remains flexible so it can handle thermal expansion and contraction.
Anyway. I think that's the longest "don't worry about it" I've written in a while.
I don't think I've ever bought thermal grease that came with a spreader. Besides, I was born with ten spreaders, five on each hand, so I tend to use them. I do make sure that I don't lick my fingers after, though.
Yeah. It's decidedly not rocket science, but getting it mostly right does make a difference. The used credit card or customer loyalty card spreader idea sounds like a winner.
Tom
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Probably worthwhile to be a little careful of the quality of the card edge. Just checked a few loyalty cards I've lying around and the side where the punch enters is pretty smooth with a reasonable radius but the exit sides are predictably flanged and hooky. Something similar happens when cutting up, say, plastic packaging or laminations. The credit and gift cards I have are rather better, though I suspect if I looked at the ones which ride round in my wallet all day in a microscope the edges would be pretty bunged up.
Fiddly details of minor effect. But if I'm going through the whole goop procedure the extra 500ms to use the better edge of the card's negligible.
More seriously, Intel's procedure doesn't use a spreader and relies instead on operating heat to complete gap filling. How to Apply Thermal Interface Material -> How to Apply TIM -> step 3. So optimal application may depend how engineered up one's goop is, its viscosity at application time, and working temperatures achieved.
Fiddly details of minor effect. But if I'm going through the whole goop procedure the extra 500ms to use the better edge of the card's negligible.
But it's a kitchen utensil!I do make sure that I don't lick my fingers after, though.
More seriously, Intel's procedure doesn't use a spreader and relies instead on operating heat to complete gap filling. How to Apply Thermal Interface Material -> How to Apply TIM -> step 3. So optimal application may depend how engineered up one's goop is, its viscosity at application time, and working temperatures achieved.
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My heat sinks came with a couple of light scratches in the LM3886 mounting area. The emery cloth was wrapped tightly around a precision size block. I have no doubt that the 1 1/2" square area is very likely flat <.0001" and it is scratch free.
I've noticed. The CPU heat sink comes with a square of thermal pad that's 1-2 mm thick. The heat from the CPU and the spring tension of the heat sink mounting spring clamps reduces the thickness to exactly what's needed to fill the gaps and voids. It's pretty clever.
I've also learned from practical experience that removing the CPU heatsink is nearly impossible and may dislodge the CPU from the socket if removal is attempted with the heat sink at room temperature. Nothing wakes you up in the morning like having to straighten 100 pins on a $300 CPU to make it fit in the socket.
All is well then.
Tom
Henry - sounds like you're OK then. I find I usually can make a surface like this less flat.
Tom -- I use a hot-melt glue gun to put little dabs of the glue at the base of tall-ish electrolytic caps that have only the two thin wire leads. As you mentioned this is common in commercial equipment such as PC power supplies. I'm not so much worried about vibration in use or shipment (much less any theory of sonic impairment due to the vibration) as I'm worried about continually bumping them due to handling during construction. The hot-melt glue, applied to a cleaned PCB tends to stay put unless you're really trying to break it loose by wiggling the caps.
Tom -- I use a hot-melt glue gun to put little dabs of the glue at the base of tall-ish electrolytic caps that have only the two thin wire leads. As you mentioned this is common in commercial equipment such as PC power supplies. I'm not so much worried about vibration in use or shipment (much less any theory of sonic impairment due to the vibration) as I'm worried about continually bumping them due to handling during construction. The hot-melt glue, applied to a cleaned PCB tends to stay put unless you're really trying to break it loose by wiggling the caps.
I find the best approach to obtaining a thin and consistent coating of heat sink compound and keeping that gooey stuff off my fingers is by using a latex glove. Get a small dab of compound on your gloved fingertip, the wipe the compound on a paper towel until you have a thin layer left on the gloved fingertip. It is then very easy to evenly wipe the compound onto the mating surface of the chip in a very thin and consistent layer without having gooey streamers hanging off.