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Class D Switching Power Amplifiers and Power D/A conversion

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Old 16th April 2010, 05:40 PM   #521
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Buckapound, yeah you can use the input impedance resistor of the amplifer and the coupling cap to give you a desired 6dB rolloff, but it will only be a 6dB rolloff, which will save power but not as much as it could. A lot of these projects will be fed signal from devices designed to drive headphones, so you could easily make at least a 12dB passive system high-pass network with such a low source impedance. 4.7uF and 470 ohms gets you 72Hz for the first stage, for example, at a load an MP3 player wont mind at all.

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Old 16th April 2010, 05:40 PM   #522
ThokN is offline ThokN  Denmark
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I think I might actually have found the 4ohm version of HP10W here:
Strassacker: Lautsprecher - Boxen - Selbstbau
around the middle of the page!

Hope this helps those of you who are looking for it
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Old 16th April 2010, 05:43 PM   #523
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Amplfier bridging, as in full bridge, BTL, whatever, is pretty much a Series connected pair of amplifers, with the load between them. One amplifer is driven with an inverse signal, one way or another.
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Old 16th April 2010, 05:53 PM   #524
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If the Qms and Qes specs are correct for that HP10W, the Qts is .41, not .25
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Old 16th April 2010, 06:08 PM   #525
ThokN is offline ThokN  Denmark
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Hmm. I hope the 4ohm part isn't an error too. On the 8ohm drivers specsheet, it says a Qts of 0.44, so the two would need different enclosure volumes?
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Old 16th April 2010, 06:14 PM   #526
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A lower Qts yields a smaller box with a higher tuning frequency. I'm not familiar with those drivers at all so it would be best to try getting a datasheet straight from the manufacturer to work with.

You could try these calculators to give you a ballpark idea about box design:

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Old 16th April 2010, 06:21 PM   #527
ThokN is offline ThokN  Denmark
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Quote:
Originally Posted by Havoc08
The amp9 peaks at 11A as far as I remember but you will likely never see it happen as music signal does not contain all frequences at once. Does your SLAs really only deliver 2.1 amps? I use 12v 7aH gel lead batteries which are rated much much higher in short term power delivery (as engines crank). 2.1A is not enough and you might destroy the amp fairly quickly.
You can see the numbers here:
Click the image to open in full size.

It is a cheap battery (249kr). I can see these numbers are for charging, so maybe that doesn't comply with drawing power from it, but I can't find any info on that.
Do you have a link to your batteries?

Ps. sorry for mis-quoting you as someone else in my last reply.
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Old 16th April 2010, 06:37 PM   #528
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Yes that's charging current info. A fully charged generic 7AH lead acid battery in good shape will happily source the current peaks you need, though ideally average current would probably be more like an amp or less for that size battery.

Notice the standby versus cycle storage voltage ratings. For your application you want the cycle voltage. This will give you the maximum capacity of the battery.

What size supply filter capacitors are being used? Going a little generous here could help you stay on a more efficient portion of the impedance curve of the battery, while decreasing total supply impedance, especially at reduced charge.
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Old 16th April 2010, 06:52 PM   #529
ThokN is offline ThokN  Denmark
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Quote:
Originally Posted by Andrew Eckhardt View Post
Yes that's charging current info. A fully charged generic 7AH lead acid battery in good shape will happily source the current peaks you need, though ideally average current would probably be more like an amp or less for that size battery.

Notice the standby versus cycle storage voltage ratings. For your application you want the cycle voltage. This will give you the maximum capacity of the battery.
Nice, thanks! Now I don't need to worry about that anymore

Quote:
Originally Posted by Andrew Eckhardt View Post
What size supply filter capacitors are being used? Going a little generous here could help you stay on a more efficient portion of the impedance curve of the battery, while decreasing total supply impedance, especially at reduced charge.
Sorry, I don't know what you mean. If it requires changing components on the amplifier, I think we will pass. Hopefully we will have it build for us, and never touch it again with a soldering iron

The main concern is to get it to work without blowing anything up, and getting as much volume out of the boominator as possible.

I guess an easy solution would be to buy 4x 4ohm HP10W and connect each to it's own output of the Amp9, which would give us 4x100W as I understand.

However, if it's possible to parallel the 4ohm's into two pairs of 2ohms and thereby get even more wattage, it would be ideal. But I still haven't figured out whether it is possible or not, or which option is better.
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Old 16th April 2010, 07:04 PM   #530
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Well don't bother with the capacitors then, but if you're looking for max output power I would definitely suggest again looking at the high pass filter. A little algebra will translate into either less lead to carry or longer, louder running times.

7AH means 7 Amps for 1 Hour, but the ratings are typically given for a 20 hour cycle. So at 7 Amps you are likely to get much less than an hour, because at high current you start losing a lot more power in the battery's internal resistance.

That battery isn't going to cut it for more than "100 watts". RMS output power at that level probably wouldn't last more than 30 minutes with a brand new fully charged battery.
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