help with LM3886 amp project

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Bradford336

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Joined 2012
I am building my first amp using a LM3886 simple design amp board for the heart of it. I will be using a 150VA 25-0-25VAC output toroidal transformer ran through this power supply http://www.electronickits.com/kit/complete/powe/k114.pdf . I am going to use the 63V capacitor. Is this right? I need a volume control and am looking at a NE5532 kit. NE5532 Volume Control Board Kit 10 Times Pre Amp DIY | eBay
My problem is that it needs 15-0-15VAC for its input. Is there a simple way of doing this without using another transformer? :confused:
http://www.ebay.com/itm/NE5532-volu...071&pid=100015&prg=1006&rk=1&sd=250803781526&
 
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CharlieLaub

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Bradford336 said:
I am building my first amp using a LM3886 simple design amp board for the heart of it. I will be using a 150VA 25-0-25VAC output toroidal transformer ran through this power supply http://www.electronickits.com/kit/complete/powe/k114.pdf . I am going to use the 63V capacitor. Is this right? I need a volume control and am looking at a NE5532 kit. NE5532 Volume Control Board Kit 10 Times Pre Amp DIY | eBay
My problem is that it needs 15-0-15VAC for its input. Is there a simple way of doing this without using another transformer? :confused:
http://www.ebay.com/itm/NE5532-volu...071&pid=100015&prg=1006&rk=1&sd=250803781526&
Click to expand...

That power supply is NOT good for this chip amp. The capacitors are too small in value (4x 2200uF)and the rectifiers are only 3A.

Here are my suggestions: The transformer is fine. Get a monolithic diode bridge rectifier, 25A or higher rated and having PIV of 400V or more. Model numbers are something like KBPC2504 or GBPC2504. You should use a MINIMUM of 20,000uF total capacitance per rail, per LM3886. For much better noise reduction and hum rejection, use two pairs of 10k uF capacitors per rail and connect an 0.47 to 1.0 ohm 5W power resistor on the rails in between. This created an RC low pass filter that attenuates all sorts of noise and will not waste much power. Definitely worth it.

The LM3886 can be used with a volume control pot on its inputs. Do some google searching and you will find info. You don't need to purchase an entire preamp board just to get a volume control, but you will need a well matched stereo log-taper potentiometer, I think around 20k ohms, 10k minimum.

-Charlie
 
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whizgeek

Member
Joined 2010
50v caps will be cheaper. maybe smaller. you can build this yourself without a pcb.
I'm pretty sure that preamp board has regulators onboard already, so as said already, you can just use the 35vdc from the power supply thro dropper resistors.
Try 100 ohm to start with 15-25volt zeners. check the max supply voltage to the preamp board, you might not even need the zeners.
 
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Bradford336

Member
Joined 2012
CharlieLaub said:
That power supply is NOT good for this chip amp. The capacitors are too small in value (4x 2200uF)and the rectifiers are only 3A.

Here are my suggestions: The transformer is fine. Get a monolithic diode bridge rectifier, 25A or higher rated and having PIV of 400V or more. Model numbers are something like KBPC2504 or GBPC2504. You should use a MINIMUM of 20,000uF total capacitance per rail, per LM3886. For much better noise reduction and hum rejection, use two pairs of 10k uF capacitors per rail and connect an 0.47 to 1.0 ohm 5W power resistor on the rails in between. This created an RC low pass filter that attenuates all sorts of noise and will not waste much power. Definitely worth it.

The LM3886 can be used with a volume control pot on its inputs. Do some google searching and you will find info. You don't need to purchase an entire preamp board just to get a volume control, but you will need a well matched stereo log-taper potentiometer, I think around 20k ohms, 10k minimum.

-Charlie
Click to expand...
Where would the power resistor go? Before, in between, or after, the capacitor pairs? I know it goes from one rail to the other. Does polarity matter on this resistor? Thank you for all the advice.
 
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