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Old 20th November 2002, 11:15 PM   #1
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Default P3a Amplifier questions..plz help.

hi all,,
this's my 1st post with my first attemp to build an amp. and ive
found many knowlegable guys inhere recommends the P3Aproject
as its easy to build with a gr8 performance, if u plz ive 3 ques:

* whats the (BR,SIM1,SIM2) are used for?
* how to modify it to 2 channel amp. driving 4ohm speakers?
* anyone ever tried to make a car 12v PS for it ,or where can
i start searching to build such a PS??

thanks alot for any inputs..
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Old 20th November 2002, 11:22 PM   #2
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Quote:
* whats the (BR,SIM1,SIM2) are used for?
The SIM1 and SIM2 are takeoff points for connecting a sound impairment monitor (or SIM for short)

Read http://sound.westhost.com/project57.htm for more information.

BR allows you to use the other (inverting) input of the input stage, so that you can bridge the amplifier. To bridge it, you have one channel hooked up with BR as its input, and the other with IN as its input.

Quote:
* how to modify it to 2 channel amp. driving 4ohm speakers?
To make it a 2-channel amplifier, you simply build two of them as shown in the schematic. If you order the PCB from Rod, you already get a 2-channel (stereo) amp on one PCB. If you use good output transistors (and perhaps lower the supply voltage a little), the amp is perfectly happy with 4-ohm loads.

Quote:
* anyone ever tried to make a car 12v PS for it ,or where can i start searching to build such a PS??
http://sound.westhost.com/project89.htm

In short, all the information you needed was already on Rod's pages, you just needed to look a little harder.
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Old 21st November 2002, 12:48 AM   #3
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thanks alot man for ur reply,,
but one more ques. plzz
just how can i adjust the Gain in this amp.??
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Old 21st November 2002, 01:54 AM   #4
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Just like most power amplifiers, it's basically just a big op-amp.

The gain can be adjusted by changing the ratio of the feedback resistors R4 and R5, but unless you really know what you're doing, it's advisable not to play with it.

Raising the gain will increase distortion, and lowering the gain will possibly introduce stability problems.

Unless you have a really good reason for changing it, you should probably leave it alone. You don't get any more power or anything out of the amp by increasing the gain.
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