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Class D Switching Power Amplifiers and Power D/A conversion

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Old 30th December 2009, 02:59 AM   #1
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Default Elementary Amp Building Questions

I'm gearing up to build a class D amp from kit.

I've been doing some studying, know how not to kill myself with electrical equipment, and get the gist of what is required for these kits. I'm looking at ones that do not involve soldering all the electronics together, as that is outside of my scope. I can manage a transformer, a rectifier, and perhaps a PSU (although I'm going to do this from kit, too().

But there are just a few basics that I think I'm missing, and appear to be hard to find online. First, are there good step-by-steps that talk about various choices and implementation options people choose in diy'ing an amp?

I've seen the pictures in the class D showcase, so I can get a pretty quick idea of things that way.

But here's what I can't figure out looking:

Mounting and case assembly. I looked around, and I see there are drill bits to help you make machine screw holes. Is that what people are doing to get the PCB's attached to the metal case bottoms? Case assembly is a mystery to me.

Anyway, is there a guide somewhere that would touch upon questions never asked?

Joe.
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Old 30th December 2009, 03:39 AM   #2
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I'm not sure of any guides per say, I'm sure people can answer any questions you might have around here. A little searching on the forum can bring up a lot of good stuff as well. As far as mounting a PCB to a metal case the most common approach is to use a standoff. Standoff are made from a non conductive material PCBs bolt onto one side and the other side bolts to the case. Here's a picture of a Standoff Good luck with your project!
Joe
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Old 30th December 2009, 03:51 AM   #3
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That was helpful. I've seen similar things made of metal for PC motherboards to space the mobo circuitry away from the PC case. But this begs the question: when I get a pc case, the standoff male pins already have female sockets to spin into. For a third party case and arbitrary set of amp boards, the holes won't be there.

Joe.
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Old 30th December 2009, 04:17 AM   #4
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Quote:
Originally Posted by joekraska View Post
....the holes won't be there...
Drill bit?
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Old 30th December 2009, 02:00 PM   #5
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Quote:
Originally Posted by joekraska View Post
That was helpful. I've seen similar things made of metal for PC motherboards to space the mobo circuitry away from the PC case. But this begs the question: when I get a pc case, the standoff male pins already have female sockets to spin into. For a third party case and arbitrary set of amp boards, the holes won't be there.

Joe.
I'm afraid I don't fully understand your question.... The standoffs are threaded on both sides. simply set the pcb on the case where you want it, mark where the mounts need to go on the case... then drill the small holes (usually 4) in your case.
Joe
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Old 30th December 2009, 02:29 PM   #6
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Quote:
Originally Posted by Josephjcole View Post
I'm afraid I don't fully understand your question.... The standoffs are threaded on both sides. simply set the pcb on the case where you want it, mark where the mounts need to go on the case... then drill the small holes (usually 4) in your case.
Joe
Well, I've never drilled for machine screws. So I guess this is how everyone does it. Thank you.

Joe.
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Old 30th December 2009, 03:54 PM   #7
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There is no "drilling for machine screws" all you need is a small hole. There is no threading involved if that's what you're thinking. Go to your local radio shack and pick up some standoffs and I think it will all be clear. It's quite easy as long as you own a drill.
Joe
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Old 30th December 2009, 05:01 PM   #8
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Outside of Googling, are there recommendations for where to pick up cases, and the like?
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Old 30th December 2009, 05:27 PM   #9
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You may be able to find old amp or other electronics cases cheap. It can be a fun a cheap way to do it. I've gotten them at thrift stores for a few bucks.

Otherwise cases are pretty expensive.
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Old 31st December 2009, 03:58 AM   #10
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Looking around at options, it appears that I can get wood of my choice, aluminum sheet metal from home depot, and make this work. Router lines can be run into the wood sides to slot the sheet metal in. Voila... I think. :-)

How does one size a toroidal transformer's output current vice an amp of a specific number of waited watts? I understand that the voltage of the toroidal transformer must be within tolerance of the power supply and AMP board, but I am uncertain about peak draws from an AMP. I.e., if an AMP is rated at 250W RMS, does it not require a transformer capable of doing better for the peaks, or is that all handled by transient discharge from the caps?

How do you appropriately size the fuse for a given amp build?

Does the potentiometer, for volume control, inline to the low level in?

Joe.
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