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Class D Switching Power Amplifiers and Power D/A conversion

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Old 22nd June 2013, 06:41 PM   #141
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Can't wait for the next update. This project sounds really awesome!
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Old 1st July 2013, 02:00 AM   #142
gmarsh is offline gmarsh  Canada
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Update: well, not really an update. PCBs and parts are both ordered, gotta build a test jig and get started on the microcontroller code.

Figure I'll explain what the card looks like.

Card's designed to go in a Hammond 1590NFL case. You'll have to drill 4 holes in the bottom of the case to bolt down the card, and use 4mm spacers or 4mm worth of washers between the case and the PCB. There's a thermal pad on the underside of the card that's used to conduct heat out of the PCB and into the case.

To run wires in/out of the case, there's really no suitable chassis mount connector that can conduct the 15A of peak current this card might draw. Best suggestion I have is to drill a hole in the case, and use a cable gland to run wires in/out of the case, keep the moisture out, and keep the cable safe from sharp edges of the case.

User interface is a single switch (power on/off) and a RGB LED to indicate status. The LED will occasionally blink twice - once with the battery status, and once with the audio status (audio present, whether the amp is boosting or not, clipping, etc)

With the single switch turned off, the amp will draw very little power. With it switched on, the amp runs - but if it senses that no audio has been present for a while, it will shut down. In this mode it'll occasionally wake up and check for audio (every 5 seconds or so) which will give a low power shutdown mode, though not as low power as the switched-off state. I'll have to build/test the amp to give real current numbers.

There's 4 configuration DIP switches on the card, I haven't 100% nailed down what these are for yet.

For audio, there's currently a fixed analog highpass filter. No DSP on the prototype, but I'm still pondering including it in the production version. It'll cost a bit more, draw a bit more idle current but it might bring some interesting features to the table.

Audio input is a "ground loop breaker" circuit, which should hopefully mitigate major issues like loud buzzing when you're charging your MP3 player from a 12V->5V adapter. Can't guarantee it'll work in all cases, but it should be better than nothing.
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Old 1st July 2013, 11:51 AM   #143
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The Neutrik PowerCon connector supports 15A
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Old 1st July 2013, 10:43 PM   #144
gmarsh is offline gmarsh  Canada
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I've got my doubts that a Powercon will fit in the case without interfering with the PCB and terminal blocks. Bit of a spendy connector too, and you've still got 12 more wires to get in/out of the case.

Cable gland is probably the best way to do things. If you use dual wall heatshrink over the wire bundle where it goes through the gland and use the sealed 1590WN1FL case, you can probably make the whole assembly meet IP65 or better, sufficient to leave outdoors.
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Old 19th July 2013, 06:51 PM   #145
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Quote:
Originally Posted by PressureFM View Post
The Neutrik PowerCon connector supports 15A
A PowerCon connector has a larger diameter than the height of the case this amp fits in.
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Old 24th July 2013, 09:27 PM   #146
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Quote:
Originally Posted by Saturnus View Post
A PowerCon connector has a larger diameter than the height of the case this amp fits in.
I'm pretty certain that the Neutrik PowerCon TRUE1 connector is 31 mm high, needing a hole that is 23 mm in diameter. The 1590WN1FL case is 35 mm high.

Just saying ...
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Old 25th July 2013, 01:36 AM   #147
gmarsh is offline gmarsh  Canada
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You've got 33.5mm clearance inside the case, but only about 5mm of depth between the inside of the case and the edge of the terminal block inside, and the top of the terminal block is 22mm above the bottom of the case - not including wires sticking out the top of the terminal block.

Here's what you're up against (omg, secret prototype shot!):

Click the image to open in full size.

Best bet is probably to drill a row of holes across the top and use grommets.

Adding 40mm to the width of the Boominator (putting all the extra width in the battery compartment), using 12aH batteries instead of 7aH (100mm wide instead of 65mm wide) and using a 1590BBSFL case instead of the 1590N1FL will make piles of room for connectors.

Wish Hammond made a taller N1 case. Haven't looked at other manufacturers.
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Old 25th July 2013, 01:38 AM   #148
gmarsh is offline gmarsh  Canada
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Here's the cable gland I was originally proposing (but now I doubt will fit):

http://www.budind.com/pdf/hb9511.pdf
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Old 25th July 2013, 08:25 AM   #149
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I did something like that, except I stretched the normal design by 10 cm to fit two 12V batteries side-by-side and placed the AMP over them with Neutrik connectors facing downward.

Let me post a picture once I get near my computer
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Old 25th July 2013, 08:50 AM   #150
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Quote:
Originally Posted by gmarsh View Post
Here's the cable gland I was originally proposing (but now I doubt will fit):

http://www.budind.com/pdf/hb9511.pdf
I'd use a standard terminal block instead and just have the opening face towards the PCB, so you'd loop the cables over the top.
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