Here is a more detailed example of a side panel. I haven't given dimensions for the holes. You will select that based on the hardware you choose. I have left gaps at the coroners just as you may have in real life. The size of the gap will be determined by your skill at measuring and cutting. The example here is using 0.125" thickness for all stock. The second file is the same with a different perspective.
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Steve,
This tutorial is getting real nice.
Good work.
Magura
Thank you. Now on to some details of actually building a case.
Step 1: Decide what you need or want in the way of size.
Step 2: Sketch out all the parts you will have. For a case like we are discussing, you will have a top, bottom, two sides, back panel and a front panel. Give the panels dimensions. You will also have 12 pieces of angle to tie everything together.
Step 3: Decide how thick you must have or want to have for the flat panels. The sides will be the same thickness, but the rest of the pieces can be different. The bottom may need to be thicker (depending on what you choose for the sides) to support heavy objects like transformers. There is no rule that says all the flat pieces must be the same thickness. You may find that the top can be thinner stock than the bottom. The same is true for the back. The front will often be a cosmetic choice.
Step 4: If possible, make a cardboard model of your project to look for problems with sizing or interference between parts.
Step 5: Decide if you want to cut the angles yourself. Order the metal.
Step 6: When the metal arrives, check for size or defects. If you are cutting your own angels, do that first. If you don't have a band saw, there are other options. Google "cutting aluminum". If none of the other options are available to you, you can use a hacksaw and a miter box. Clamp the box to a solid surface and clamp the angel to the box.
Step 7: Do a test fitting with clamps. If the parts are cut correctly, it's time to start laying out the holes. Start with the four angels that will mount to the bottom. Using a combination square, mark the positions of the holes as closely as possible. Use an awl or an Exacto knife point to to make the marks so they will be more exact. Center punch the marked holes. Now you have a decision to make. The only place you really need threaded holes is where you can't reach the inside of the case, like when you put on the top. The rest of the holes can be drilled for machine screws of your choice using lock washers and nuts. If you want to thread the holes, that is your choice. After you drill an angel, clamp it to the panel where it will be fastened, line it up correctly and tighten the clamps. Now drill the panel through the holes in the angel so they will align perfectly. These pieces can be clamped first then drilled if you are shure you have the holes laid out correctly.
Step 8: If you are using flat sides you can repeat the steps above. If you are mounting heat sinks for the sides, you do pretty much the same thing using the heat sink instead of the flat panel. I have attached a drawing of a mounted heat sink. Doing it this way eliminates the need to cut out holes in the sides.
More latter.
Here is a drawing of the bottom with the bottom angles in place. Here I have used the square construction as it is both easier and there is less scrap. You will notice I have left a gap of 0.062" between the angle pieces to ensure clearance. You can reduce that gap if your cutting is very exact.
You will also notice that the bottom is 0.25" smaller than the case size of 12" X 17" X 3". This is so the completed case will be the correct size. This is based on 0.125" thickness sides, front and back. You may use other thickness material, just adjust the sizes accordingly.
As I mentioned earlier, you can drill the appropriate size holes for your chosen hardware. If you choose your hardware too large, you will need to move the holes further from the edges so the nuts have room to fit inside. Many times more than one size nut is offered for a given screw size, so you may be able to use one with smaller outer dimensions. I recommend lock washers also.
You will also notice that the bottom is 0.25" smaller than the case size of 12" X 17" X 3". This is so the completed case will be the correct size. This is based on 0.125" thickness sides, front and back. You may use other thickness material, just adjust the sizes accordingly.
As I mentioned earlier, you can drill the appropriate size holes for your chosen hardware. If you choose your hardware too large, you will need to move the holes further from the edges so the nuts have room to fit inside. Many times more than one size nut is offered for a given screw size, so you may be able to use one with smaller outer dimensions. I recommend lock washers also.
Here is the drawing of the side, back and top. I Zipped the top because the file was too large. If you have questions about why I have done anything the way I have, please ask. I probably had a reason, but it could be another mistake on my part.
I will give pointers for making holes and adding vents next, then move on to making your own heat sinks.
If I am leaving out something of interest to you, please ask about it.
I will give pointers for making holes and adding vents next, then move on to making your own heat sinks.
If I am leaving out something of interest to you, please ask about it.
In a typical preamp almost all of the holes are, or can be, round. They can be made by careful measurement, center punching and drilling. For larger round holes, the step bits work nicely. Another way I have laid out the hole patterns for the back of a preamp is to draw the back, from the inside view in a cad program, then print it. Draw the inside edges also and be sure to mark the hole centers. Now trim along the edge lines (I used a paper cutter) and tape the drawing to the inside of the back panel. You then use a center punch to mark all the round holes.
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Drilling works on many of the holes in an amp case also. There is no substitute for punching when it comes to the D shaped holes that many binding posts use. This is complicated even more by the fact that there is no standard hole sizes for input and output hardware. Fortunately, all of these can mount in round holes.
Ventilation holes for amps is another problem, but there is an answer for these also. Holes for fans can be cut using this tool.
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I have one of these that cuts up to 6.5" holes. It works great for small speaker mounting holes also.
For tube equipment or amps with internal heat sinks where fan cooling may be considered too noisy, there is an assortment of perforated Al sheets available in 0.062" and 0.125" thicknesses. The entire top could be made with this material, or you could make the top (or bottom) from more than one piece mixing solid plate and perforated plate to suit your needs.
Perhaps the hardest hole to make in a case is the IEC power inlet. There are many variations on this and some take different size holes. The solution here is to have what you plan to use on hand and measure it. I suggest drilling four holes of the same radius as the rounded corners of the inlet, inset by the same radius. This gives you the four rounded corners in the correct location. Now use a metal cutting in a jig saw to finish cutting the hole. There are other options also. See the link I posted earlier about cutting square holes in Al.
Any questions or comments so far?
Enco - Guaranteed Lowest Prices on Machinery, Measuring Tools, Cutting Tools and Shop Supplies
Drilling works on many of the holes in an amp case also. There is no substitute for punching when it comes to the D shaped holes that many binding posts use. This is complicated even more by the fact that there is no standard hole sizes for input and output hardware. Fortunately, all of these can mount in round holes.
Ventilation holes for amps is another problem, but there is an answer for these also. Holes for fans can be cut using this tool.
Enco - Guaranteed Lowest Prices on Machinery, Measuring Tools, Cutting Tools and Shop Supplies
I have one of these that cuts up to 6.5" holes. It works great for small speaker mounting holes also.
For tube equipment or amps with internal heat sinks where fan cooling may be considered too noisy, there is an assortment of perforated Al sheets available in 0.062" and 0.125" thicknesses. The entire top could be made with this material, or you could make the top (or bottom) from more than one piece mixing solid plate and perforated plate to suit your needs.
Perhaps the hardest hole to make in a case is the IEC power inlet. There are many variations on this and some take different size holes. The solution here is to have what you plan to use on hand and measure it. I suggest drilling four holes of the same radius as the rounded corners of the inlet, inset by the same radius. This gives you the four rounded corners in the correct location. Now use a metal cutting in a jig saw to finish cutting the hole. There are other options also. See the link I posted earlier about cutting square holes in Al.
Any questions or comments so far?
Here is an example of a DIY heat sink. Drill the correct size hole for the tap you will be using through both the flat sheet and the rectangular extrusion while they are clamped together and aliened properly. Unclamp and drill the correct size holes in the flat plate. Tap the holes in the extrusion. You can also use machine screws and nuts if you prefer.
With no moving air, about 4 C/W. Not that great. The chimney effect will generate some moving air of course. At 10 LFM it drops to 1.2 C/W. With fan cooling it can go to 0.4 C/W or lower. It depends on fan speed.
Technical Information - Thermal Resistance Tool
I did a little on line research for better information on heat sink rating. The heat sink I used on my 100W amps was a 3" length of this:
Extrusion Profiles
It is rated at a thermal resistance of 1.23 C/W for a 3" length, or exactly what I used. I never had one of these amps shut down from over heating. Most people felt than ran pretty cool.
If I enter the data for this extrusion into the calculator I linked to in my last thread, it gives a much higher thermal resistance for no air flow. To get their rated thermal resistance, you must increase the air flow to 30 LFM. This sounds like a good number to use for unimpeded natural convection. I will assume here that Aavid Thermalloy did their homework on this. That is equivalent to a wind speed of 0.33 MPH. Not exactly a hurricane.
If I enter an air velocity of 30 LFM for the drawing of the DIY heat sink, I get a thermal resistance of 0.7 C/W. One of these on each side of the case we have been designing could easily make a 100W to 150W stereo amp, if the rest of the parts will fit inside. With fan cooling, it should be capable of 200W per channel with no problems.
I'm still waiting for comments or questions.
Extrusion Profiles
It is rated at a thermal resistance of 1.23 C/W for a 3" length, or exactly what I used. I never had one of these amps shut down from over heating. Most people felt than ran pretty cool.
If I enter the data for this extrusion into the calculator I linked to in my last thread, it gives a much higher thermal resistance for no air flow. To get their rated thermal resistance, you must increase the air flow to 30 LFM. This sounds like a good number to use for unimpeded natural convection. I will assume here that Aavid Thermalloy did their homework on this. That is equivalent to a wind speed of 0.33 MPH. Not exactly a hurricane.
If I enter an air velocity of 30 LFM for the drawing of the DIY heat sink, I get a thermal resistance of 0.7 C/W. One of these on each side of the case we have been designing could easily make a 100W to 150W stereo amp, if the rest of the parts will fit inside. With fan cooling, it should be capable of 200W per channel with no problems.
I'm still waiting for comments or questions.
My 100W amps put out 200W at 4 ohms and 300W at 2. They were frequently used with 4 ohm and lower loads and were especially good on electrostatics. I never heard of one over heating. I admit I would have preferred more heat sink, but these amps were designed to be sold very cheaply. I did a lot of testing on these heat sinks to determine their performance in actual use before I settled on them.
It has been pointed out that I haven't given sizes for machine screws to use. I would suggest 6-32 for most assembly. Some transistors will require 4-40 screws.
6-32 is 0.138" in diameter or 3.5mm.
4-40 is 0.112" in diameter or 2.85mm.
It is up to you to choose what to use. As long as it works and can be bought locally, that is about all that counts. Pick a head style that suits you also.
There are times larger screws may be needed, but I will address that when it is encountered.
6-32 is 0.138" in diameter or 3.5mm.
4-40 is 0.112" in diameter or 2.85mm.
It is up to you to choose what to use. As long as it works and can be bought locally, that is about all that counts. Pick a head style that suits you also.
There are times larger screws may be needed, but I will address that when it is encountered.
Here is a link to a thread about labeling front panels.
http://www.diyaudio.com/forums/solid-state/8189-diy-amps-front-panel-lettering.html#post89640
http://www.diyaudio.com/forums/solid-state/8189-diy-amps-front-panel-lettering.html#post89640
I was beginning to think I was talking to myself.
See post #4 of this thread, and check out this link.
http://www.ska-audio.com/resources/tapping.html
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