help with LM3886 amp project

Bradford336 · 14th October 2012, 02:11 AM

I purchased this diy guitar amp kit and the instructions are direct translation and are horrible. The instructions say it needs a 15-0-15 to 25-0-25 5Amp power source. They say VAC but everything I have read including their sales ad says VDC. Any Ideas? Here is a link to the kit pic Chip Amplifier Sales, LM3886 Audio Chip Amplifiers Representatives, Sound System Supplies I can e-mail a copy of the schematic. My second question is where can I get a schematic for a power supply for it? I hope to add volume, tone and such on a separate board later so a flexible power supply would be nice. Would a simple rail splitter be best or should I stick to a toroidal transformer and filter board like this one? http://www.electronickits.com/kit/co.../powe/k114.pdf

ByronInLawrence · 14th October 2012, 03:44 AM

Hi Bradford.
My first amplifier was an LM3886 too. The learning curve is, indeed, steep on your first build.
Check out Texas Instrument's data sheet here http://www.ti.com/lit/ds/snas091b/snas091b.pdf
On the very first page is specifies +/-28V (that's DC) to get a max of 68watts into a 4ohm load, and +/-35V (again, DC) to get 50watts into an 8ohm load. These are maximum values, and assume excellent cooling, so don't skimp on the heatsink and thermal paste. If you're going to put this in a chassis, use one that's ventilated. Of course there's no harm is using lower voltages.

Linear, unregulated power supplies can be a bit confusing, because the VDC (rail voltages) you get out of the rectifier is actually 1.41 times more than the VAC (secondaries of your transformer) going into them, minus a little for inefficiencies. This means you'll want at most, a transformer with 20VAC secondaries for a 4 ohm, and 25VAC secondaries for an 8 ohm speaker. For a single LM3886, you only need about a 100VA to 150VA transformer. Keep in mind that a larger transformer will give you a little better sound. The power supply you linked seems just fine. Another good one is here: Chipamp Power Supply Kit | Chipamp.com
Here is a nice beginner's guide: Building a Gainclone chip amp power supply.
Good luck!

Bradford336 · 14th October 2012, 01:12 PM

Thank you very much! You were a lot of help.

Bradford336 · 15th October 2012, 01:45 AM

So for a transformer with 25 VAC secondaries and 150 VA would I use the 63V Caps and 100Vdiodes? Using the filter board that I posted.

14th October 2012, 02:11 AM	#1
Bradford336 diyAudio Member Join Date: Oct 2012 Location: North Carolina	help with LM3886 amp project I purchased this diy guitar amp kit and the instructions are direct translation and are horrible. The instructions say it needs a 15-0-15 to 25-0-25 5Amp power source. They say VAC but everything I have read including their sales ad says VDC. Any Ideas? Here is a link to the kit pic Chip Amplifier Sales, LM3886 Audio Chip Amplifiers Representatives, Sound System Supplies I can e-mail a copy of the schematic. My second question is where can I get a schematic for a power supply for it? I hope to add volume, tone and such on a separate board later so a flexible power supply would be nice. Would a simple rail splitter be best or should I stick to a toroidal transformer and filter board like this one? http://www.electronickits.com/kit/co.../powe/k114.pdf

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
My first project --> lm3886	Maxhax	Chip Amps	3	22nd September 2009 02:22 AM
My first LM3886 project (please help urgently!!)	Derfla	Chip Amps	13	20th March 2008 02:08 PM
lm3886 project	zafira1981	Chip Amps	9	23rd February 2007 09:06 AM
LM3886 PCB project and may be more	vasja	Chip Amps	9	8th October 2004 09:16 PM
How about our project of LM3886	AlivinCai	Chip Amps	6	4th January 2004 04:15 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

14th October 2012, 03:44 AM	#2
ByronInLawrence diyAudio Member Join Date: Nov 2010 Location: Lawrence, a nice little college town in Kansas	Hi Bradford. My first amplifier was an LM3886 too. The learning curve is, indeed, steep on your first build. Check out Texas Instrument's data sheet here http://www.ti.com/lit/ds/snas091b/snas091b.pdf On the very first page is specifies +/-28V (that's DC) to get a max of 68watts into a 4ohm load, and +/-35V (again, DC) to get 50watts into an 8ohm load. These are maximum values, and assume excellent cooling, so don't skimp on the heatsink and thermal paste. If you're going to put this in a chassis, use one that's ventilated. Of course there's no harm is using lower voltages. Linear, unregulated power supplies can be a bit confusing, because the VDC (rail voltages) you get out of the rectifier is actually 1.41 times more than the VAC (secondaries of your transformer) going into them, minus a little for inefficiencies. This means you'll want at most, a transformer with 20VAC secondaries for a 4 ohm, and 25VAC secondaries for an 8 ohm speaker. For a single LM3886, you only need about a 100VA to 150VA transformer. Keep in mind that a larger transformer will give you a little better sound. The power supply you linked seems just fine. Another good one is here: Chipamp Power Supply Kit \| Chipamp.com Here is a nice beginner's guide: Building a Gainclone chip amp power supply. Good luck!

14th October 2012, 01:12 PM	#3
Bradford336 diyAudio Member Join Date: Oct 2012 Location: North Carolina	Thank you very much! You were a lot of help.

15th October 2012, 01:45 AM	#4
Bradford336 diyAudio Member Join Date: Oct 2012 Location: North Carolina	So for a transformer with 25 VAC secondaries and 150 VA would I use the 63V Caps and 100Vdiodes? Using the filter board that I posted.