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Old 18th December 2002, 10:40 AM   #1
hacknet is offline hacknet  Singapore
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Default cheap and dirty sub

i have been looking around but i cant find a cheap to build dirty sub... i intend to etch the PCB as i just bought 9 liters of consentrated ferric Chloride...

Cost is a big issue... quality is not...
i intend 150w sub...

thx...
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Old 18th December 2002, 10:55 AM   #2
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You could try the National class d overture chipset, they give you layouts and stuff, and bearing in mind most of the cost of the amp is in the trannie and heatsinks.
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Old 18th December 2002, 11:20 AM   #3
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...and the power supply....
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Old 18th December 2002, 02:54 PM   #4
hacknet is offline hacknet  Singapore
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ive had a thread on Class d amps... i dun find it usefull as it it so compilcated... the likely hood of it not working is very high due to lousy soldering and insufficient knowledge....

are class b amps that operate at 70% eff. any use to subs?
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Old 18th December 2002, 03:11 PM   #5
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Default national class D amp

I was going to build the national class D amp some time ago, but I was put off by the huge inductors on the output=$$$. Another diy-er said they filter the digital crap out of the signal above the listening range. I was wondering if there was any way to use smaller H inductors for a strictly subwoofer application?
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Old 18th December 2002, 03:51 PM   #6
hacknet is offline hacknet  Singapore
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that was the 1st point that put me off
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Old 18th December 2002, 03:53 PM   #7
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What inductance value did they have to be and what current capability ?

Regards

Charles
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Old 18th December 2002, 04:45 PM   #8
hacknet is offline hacknet  Singapore
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some unimaginable figure
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Old 18th December 2002, 04:54 PM   #9
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The app. notes give three options for different HF roll offs, 47uH- 5A, 50uH-5.6A, and 68uH-7.3A.

I must admit, I have had the chips for a while, but never used them because of this inductor problem. If there is a way of DIYing the the inductors then it might come off the back burner!
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Old 19th December 2002, 03:42 AM   #10
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Post stole this from the app note

Output Stage Filtering
As common with Class D amplifier design, there are many
trade-offs associated with different circuit values. The output
stage is not an exception. National has found good results
with a 50F inductor and a 5F Mylar capacitor (see Figure
1, Typical Audio Application Circuit) used as the output
LC filter. The two-pole filter contains three components; L1
and Cbyp because the LM4651 and LM4652 have a bridged
output. The design formula for a bridge output filter is fC =
1/[2pi(L1 2Cbyp )1/2].
A common mistake is to connect a large capacitor between
ground and each output. This applies only to single-ended applications. In bridge operation, each output sees Cbyp.
This causes the extra factor of 2 in the formula. The alternative
to Cbyp is a capacitor connected between each output,
V0 , and V02 , and ground. This alternative is, however, not
size or cost efficient because each capacitor must be twice
Cbyps value to achieve the same filter cutoff frequency. The
additional small value capacitors connected between each
output and ground (C1) help filter the high frequency from the
output to ground . The recommended value for C1 is 0.1F to
1F or 2% to 20% of Cbyp.

Hopefully someone can make sense of the formula, unfortunately I'm just a lowly LAS major, not an engineer.
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