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Class D Switching Power Amplifiers and Power D/A conversion

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Old 10th December 2008, 12:09 PM   #211
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Are you sure? If you open the one that says BoominatorII.skp it should show all the panels assembled.

Anyways, yeah, sadly the bracing was the only part not to survive. It's pretty simple tough. It's 2 vertical panels of 12mm bircg ply running down the center following the grooves for them in the bottom, top, end, and center pieces.

Without CNC machinary to accurately cut it out from the start you should probably wait to cut out the holes in it until you have all pieces ready for assembly.

Or cut it into a large 0 shape 45-50mm wide on all sides except the port corner which is cut away.

Also get a sheet of 3-4 mm ply or masonite (or whatever you have handy), and use strips of that as guides. You'll need a piece for the bottom cover anyways.
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Old 10th December 2008, 12:31 PM   #212
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Quote:
Originally posted by Saturnus
I can't remember the exact size actually. I know it's between 22 and 24 liters. And I can remember that I worked with either 22.65 liters or 23.45 liters but I can't remember which it was settled on.
Btw, now I can remember it. The 22.65 liters was with the centre brace and the 23.45 was without it. That's because I made the first one without it but the testing showed that the top would vibrate too much under heavy loads if there was a full top solar panel on it. So the bracing was included on the next version. If you make it without the full top solar panel you don't need the bracing from a mechanical POW but I also think that version sounds better.

I calculated with 23 liters which is between the numbers for the with and without bracing. I figured that it wouldn't make a huge impact if it was slightly under- or over-tuned. And it don't.
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Old 18th December 2008, 11:20 PM   #213
tsnell is offline tsnell  Australia
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Hi Everybody,

Hope you are all doing well. Once again sorry for slow replies and lack of progress updates, deadlines seem to pile up leading into Christmas. Amp6 and Amp9 both arrived on Tuesday. Had a chance to get to building them last night. I figured I would start with the Amp6 to “get my eye in” because it’s been a little while since I’ve done much soldering. Amp6 went together and was playing music in about 2 hours! Absolutely fantastic, very impressed with everything. Was missing one of the 3.3uF low ESR caps but I temporarily stole it from the Amp9 kit to get it going.

I then started on the Amp9. There is an awfully big gap in the level of detail in the assembly instructions between these two amps. The 41Hz forums are critical, especially the diode soldering thread (thanks col!) because they are seriously fiddly to get right. Amp 9 is up to testing stage. It was very late in the night by the time that was finished so I left it for another time, I would hate to do something stupid when connecting the power because I was too tired to concentrate. Should get to it tonight and fingers crossed all will be good.

As for the rest of the construction... I have decided to make the overall length 1m as per the rev 2 of your Boominator Saturnus. The model posted above appears to be the 900mm long version. This will give that little bit of extra space and hopefully room for more air to circulate around the Amp9B. The cut-out for access to the battery compartment will be on the top of the enclosure and the solar panel will be fixed in place with wing nuts. This will allow it to be removed for hot air to vent away from the amp if necessary and/or will include enough cable to place panel remotely if required (i.e. Boominator in shade and panel in sun).

A few quick questions about connecting the source to the Amp9B. I have a few options available; iPod classic (current gen.), iPhone 3G or iPhone/iPod to Headamp Pico. Most likely will be just be using the iPod as I would rather leave the Pico at home (one less thing to lose, work days would really drag without it) but can take it if there is the possibility of any significant performance gains. The two channels of the source output will be paralleled across two inputs each. So, for the questions:
1. Will the iPod Classic have enough “grunt” to drive all four inputs of the Amp9B?
2. How do I optimise the input sensitivity to best suit?

Thanks again everybody.

PS. Will hopefully get some progress pics posted over the weekend.
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Old 19th December 2008, 01:19 AM   #214
col is offline col  Australia
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Hi Tsnell,

Glad you have managed to solder up the amps. Regarding the inputs, did you consider the "jaycar fader"? See post #194 Iv'e used it on several occasions with amp9b it works very well.

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Old 19th December 2008, 01:39 AM   #215
tsnell is offline tsnell  Australia
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Hi col,

Yes, I was planning to get one when I head to Jaycar over the weekend. I'm still planning to try the different wiring configurations so even if I don't end up using it for this it looks like a handy (and fairly cheap device) to have around.

It does not look powered though so will it help with input power levels at all?

Cheers,
Tim
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Old 19th December 2008, 04:05 AM   #216
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It a major problem with the amp9 that you can't adjust input sensitivity, thankfully it can be helped quite easy with a 1:4 input trafo.

Oh, and great work so far The amp6basic is a breeze to make, and the quality ... pure magic.
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Old 19th December 2008, 04:34 AM   #217
col is offline col  Australia
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There is nothing wrong with the amp9 input sensitivity, you only need to use a NTE4 trafo if you are using it with a PLLXO crossover.

Tsnell, you have the amp9 built do the tests for yourself.

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Old 19th December 2008, 07:51 AM   #218
v-bro is offline v-bro  Netherlands
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Hi Guys, I see some transformer pioneering around here and thought I'd let you know my last piece of pioneering with the Neutrik NTE-4.

If you have linear frequency response speakers and want to make the behaviour of the transformer linear too you should add a 470 or 680nF capacitor (ceramic quality is fine) and a resistor of 3,9 to 4,3Kohm in series and place this network in parallel with the secondary winding.

Some transformer datasheets show this type of correction, some not. Have a look:
http://www.farnell.com/datasheets/23903.pdf

(its at the bottom, but the correction they describe is NOT for the NTE-4)

I configured the network with a square wave generator and a scope and without the network you see terrible overshoots, with the network in place you get beautiful square waves!
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Old 19th December 2008, 08:24 AM   #219
col is offline col  Australia
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V-bro, does the same go for the Neutrik NTE-1?


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Old 19th December 2008, 08:37 AM   #220
v-bro is offline v-bro  Netherlands
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Yes, all transformers give such behaviour...

I must add that the input impedance of the amplifier dampens most of it, but not all. It is however not do-able without the proper equipment to tweak it exactly right...

Here's what the measurements look like in general:

Bare wire:
Click the image to open in full size.

Bare transformer:
Click the image to open in full size.

With the correction it's pretty close to the original square wave again:
Click the image to open in full size.

This provides a good starting point with nice flat response behaviour.

I can order a NTE1 myself and tweak a good working network and post my findings if you like Col?
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