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Class D Switching Power Amplifiers and Power D/A conversion

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Old 8th December 2008, 09:31 PM   #191
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<shrugs> try both, see how they sound. pick what sounds best.

for reference:

Low Pass Filter and High Pass Filter theory.

or wikipedia even

which of these pictures looks like a resistor in series with a capacitive load?

for first order high and low pass RC filters:

cutoff freq in Hz = 1/(2*pi*R*C)

plug the values in and come to your own conclusions.

Col has built a lot of these 41Hz amps, and regularly runs small events with them.

In the spirit of the scientific method, try both configurations and see what works best. your finger on the heatsink is the best measure of whether you have sufficient cooling. report your findings so we can all benefit and mistakes arent replicated.

for my part, i'm quite happy to be shown i'm mistaken - so I'll set up my speaker testing rig and get some some real world response curve measurements on the piezos using a range of resistor values, and then we will have some hard data.

cheers,

Ben
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Old 8th December 2008, 11:11 PM   #192
tsnell is offline tsnell  Australia
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Thanks for all the help guys.

Saturnus Ė noted, will definitely mount the woofers so that the tabs face the tweeter cut out and wire any crossover components to be accessible at a later time.

But as for the crossover components... hey Iím willing do some testing and give some feedback if it will help. Iíve attached 2 jpegs showing the two different configurations as described by Saturnus and anomalous/col. Can you guys take a quick check and make sure that is what you described?

Any luck with the crashed hard disk Saturnus?
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Old 8th December 2008, 11:14 PM   #193
tsnell is offline tsnell  Australia
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And the next one.

How do you attach more than one image to a post?
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Old 8th December 2008, 11:45 PM   #194
col is offline col  Australia
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I prefer the first setup diagram. Also, with that one you can use a car rear/front fader to adjust the level between the woofers/piezo. This will also deal with your jack to RCA input dilemma. Iv'e used one of these for a few gigs and it works well. see jaycar CAT. NO. AA0485

http://jaycar.com.au/ShowLargephoto.asp?id=57&IMAGE=


The first amp9 I built I put a fan on the heatsink. I don't think it was needed though.

On the second amp I built I used a heatsink off of a Pentium II, It runs very cool, even flat out. I have a spare one if you are interested?

http://pix.minirig.org.au/main.php?g2_itemId=805


col.
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Old 9th December 2008, 12:24 AM   #195
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I agree with col (strangely enough).

what he says about surplus CPU heatsinks is good - i use them all the time as well. i often get given bung computers, and the heatsinks are good salvage. more recent cpu's often have fantastic copper cored monsters - incredibly efficient for their size.
Here is a pic of some that i have. I think the blue one is similar to what col is talking about.

Click the image to open in full size.
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Old 9th December 2008, 12:46 AM   #196
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The problem is that amp is inside the case with very little air coming in or out, and when you leave it out in the midday sun playing the amp case can become extremely hot. My guess is around 80 degrees celcius without having taking measurements. That's coming dangerously close to the termal envelope of many of the other components. And that's with an amp6basic.

I guess you could use a fan that only comes on when charging but you'll need extra circuitry for that. And everything extra means something more that can go wrong.
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Old 9th December 2008, 12:56 AM   #197
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i came in late on this thread, so forgive me if ive missed something. Saturnus, is the whole box a single chamber, or is it split in the middle?

i agree with you - mounting the amp modules inside may well result in heat issues.

I'd be tempted to mount them on a bit of 4mm aluminium plate which could be screwed (just like a plate amp ) into a recessed cutout on the box somewhere and if need be bolt some low profile heatsinks to the outside.

cheers,

ben
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Old 9th December 2008, 01:09 AM   #198
col is offline col  Australia
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I guess thats another good reason to keep modular. Although, I would have thought that the tuning port for the bass reflex would cause quite a bit of cooling. just make sure the amp heatsink is behind the tuning ports.

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Old 9th December 2008, 01:26 AM   #199
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It's 3 separate chambers actually. A left and a right speaker enclosure. And a middle enclosure for batteries and electronics.

I gotten the CAD files. Unfortunately not all could be recreated.

The thing to note is the 160mm wide 3mm deep grooves routed in the both sides of the middle compartment. They allow for the battery to slide in from the bottom because it becomes 66mm wide at that place but doesn't allow for the battery to slide around at all since they are 65mm wide and 150mm long (and about 200mm high when 2 are stacked on top of eachother).

I use a G111 case from Velleman. It's 65mm wide same as the batteries and 55mm high and 115mm long. The case is an aluminium case so it function perfectly as a heatsink as well, and the internal built-in PCB stand-offs fits the holes from the amp6basic perfectly. I use the remaining space on either side to hold cables, chargers (both battery and iPod charger) and the iPod itself. So there's no much left over room for cooling.
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Old 9th December 2008, 01:27 AM   #200
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hehe - i was going to suggest putting the heatsinks behind the ports as well

i wonder how effective it would be - ie is it causing enough air circulation or is it just pushing the same hot air back and forward...
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