Mute System Volume on Shutting Down

1. Download NirCmd,then extract to C:\Program Files\NirCmd


2. Click Start -> Run, then type gpedit.msc


3. Go to Computer Configuration -> Windows Settings -> Scripts (Startup/Shutdown), then double click on Shutdown


4. Click Add button, type C:\Program Files\NirCmd\nircmd.exe into Script Name.
And type mutesysvolume 1 into Script Parameters.
Click OK and close the Group Policy window.


To unmute system volume, click on Volume at System Tray, then uncheck the Mute.
Or you can also press a Mute/Unmute function key on your laptop.

Mini Pre-microphone

Have you ever tried to use dynamic microphone with PC?
If you have, you'll know that it won't work.
So a microphone amplifier is needed.
And I've found one at Baanmooh, it's 200 BHT, very small.
The sensitivity can be adjusted.
It can operate at 0.9 Volt 0.8 mA.
If you use a 1.5 Volt 800 mAh button cell battery,
it'll last for 1000 hours, or 41 days!!!












[See all photos]

Power Amp Class-D

Today I got a power amp from NPE.
It's Class-D Power Amp 20W, 665 BHT

20 WATTS CLASS D Specifications 1. 20W at 8 ohms 16 Vcc 2. No Heatsink 3. Short Circuit Protection 4. Vcc 9-18 V 5. Imax 1.3 A at Po 20 W 6. Shutdown 1 uA

Can't believe that it requires no heat sink.
I used to do 2W power amp, it's very hot and have to use heat sink.
And also can't believe that it requires only 1.5A transformer.
Most 30W power amp requires 5-6A transformer.

But when I tested it to drive a subwoofer speaker, powered by very cheap 1A transformer.
It's soooo amazing!!!
After continuous using about 4 hours, no heat generated at all. Like it's not operating.
This very cheap 1A transformer is not enought to supply the AA battery charger.
But this power amp powered by that transformer can shake my door!

Class	Efficiency
A	25% (theoretical)
AB	less than 78.5% (theoretical)
D	80-95% (practical)

(Credit http://en.wikipedia.org/wiki/Electronic_amplifier)

[Sat 11 Oct 2008]
Finally, I put my power amp class-D in an (antiquated) box.
Althought it's looked uninterested, but it can shake the room, no heat generated.





If you want a subwoofer filter, try this. Subwoofer Filter

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