lm3886 design

pingu · 3rd June 2009, 03:27 AM

I'm using a 2x 28v transformer salvaged from an old arcam alpha.

Is it Ok for me to use this with the typical application diagram on the lm3886 data sheet? I Just want to get this up and running ASAP and prehaps tweek it later. So as long as using this circuit isn't hi fi blasphemy ill go right ahead!

Also have some more noob questions-

Does it matter which way round i place the inductor?

Is the Lm3886 stereo capable?

Regards
Tim

ttan98 · 3rd June 2009, 04:04 AM

Using 28V ac is at the upper limit of operation for LM3886, it should work OK. Use adequate heatsink, CPU heatsink or preferably larger is adequate.

BTW I use 24V ac, the CPU heatsink is not even hot.

pacificblue · 3rd June 2009, 10:16 AM

Quote:

Originally posted by pingu
I'm using a 2x 28v transformer salvaged from an old arcam alpha.

You should use 8 Ohm speakers with that voltage.

Quote:

Originally posted by pingu
Is it Ok for me to use this with the typical application diagram on the lm3886 data sheet? I Just want to get this up and running ASAP

Read the datasheet. It explains, what you should do and why. Relax and take your time. Putting things together in a hurry is usually not a good way to work, especially for a first project.

Quote:

Originally posted by pingu
Does it matter which way round i place the inductor?

Can you detect any difference between both ends of the inductor?

Quote:

Originally posted by pingu
Is the Lm3886 stereo capable?

If you use two of them.

pingu · 3rd June 2009, 03:27 PM

ok im looking at the 'typical application' on the lm3886 data sheet:
http://www.google.co.uk/url?sa=t&sou...xVsZsIPWMxhvVg

will this circuit work with my power supply?

AndrewT · 3rd June 2009, 03:42 PM

Hi,
have you read the note at the bottom of Fig1?

I can count one optional component shown and seven other optional components that are missing.

The "optional components" are compulsory until you have sufficient design and assembly expertise and test equipment to prove to yourself that the circuit can operate reliably with a range of output transducers, without destroying itself and/or plain sounding bad.

Redshift187 · 4th June 2009, 02:03 PM

Keep in mind that CPU heatsinks are not designed for use without a fan (the fins are too close together for convection cooling).

ttan98 · 4th June 2009, 04:14 PM

Quote:

Originally posted by Redshift187
Keep in mind that CPU heatsinks are not designed for use without a fan (the fins are too close together for convection cooling).

not really, I use LM3875 and LM3886 mounted on cpu heatsink(*) without fan turned on on some occasions without problems. I even powered both of them using 34Vdc.

If you use low load(=<4ohm) and play at loud level then CPU fan should be turned on.

* I use PIII or PIV heatsink and I pay about $5 each, cheap and it works. I mount even 2*LM3886 on a single heatsink, this time I turn on the fan.

AndrewT · 4th June 2009, 06:49 PM

Quote:

Originally posted by ttan98

not really, I use LM3875 and LM3886 mounted on cpu heatsink(*) without fan turned on on some occasions without problems. I even powered both of them using 34Vdc.

If you use low load(=<4ohm) and play at loud level then CPU fan should be turned on.

* I use PIII or PIV heatsink and I pay about $5 each, cheap and it works. I mount even 2*LM3886 on a single heatsink, this time I turn on the fan.

that's most odd, uses a fanned sink as it's supposed to be used when required to dissipate some heat. Funny decision that.

ttan98 · 4th June 2009, 11:57 PM

Quote:

Originally posted by AndrewT
that's most odd, uses a fanned sink as it's supposed to be used when required to dissipate some heat. Funny decision that.

Not so if the amp is lightly loaded ie if playing at low level. The amp never gets hot. I built 2 amp one with fan turned on and the other with fan left off.

You must remember this is a hobby and there is no need to spend unnecessary money if you can get away with it. I am not building a Rolls Royce equivalent of an amp.

The left over money can be used for other projects.

garak · 5th June 2009, 12:06 AM

From the pictures I've seen of heatsinks used for LM3886 amps, and the resulting reports of how warm the heatsinks feel, I get the feeling that a CPU heatsink (designed for use with a fan) would be just fine, even if it's operating outside of its intended use and convection is lacking. It's still MUCH less heat than a CPU puts out.

I'm planning on using some Athlon heat sinks that I got for $2 each.

3rd June 2009, 03:27 AM	#1
pingu diyAudio Member Join Date: Oct 2007	lm3886 design I'm using a 2x 28v transformer salvaged from an old arcam alpha. Is it Ok for me to use this with the typical application diagram on the lm3886 data sheet? I Just want to get this up and running ASAP and prehaps tweek it later. So as long as using this circuit isn't hi fi blasphemy ill go right ahead! Also have some more noob questions- Does it matter which way round i place the inductor? Is the Lm3886 stereo capable? Regards Tim

3rd June 2009, 03:42 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, have you read the note at the bottom of Fig1? I can count one optional component shown and seven other optional components that are missing. The "optional components" are compulsory until you have sufficient design and assembly expertise and test equipment to prove to yourself that the circuit can operate reliably with a range of output transducers, without destroying itself and/or plain sounding bad. __________________ regards Andrew T.

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3rd June 2009, 04:04 AM	#2
ttan98 diyAudio Member Join Date: Apr 2006 Location: Melb	Using 28V ac is at the upper limit of operation for LM3886, it should work OK. Use adequate heatsink, CPU heatsink or preferably larger is adequate. BTW I use 24V ac, the CPU heatsink is not even hot.

3rd June 2009, 03:27 PM	#4
pingu diyAudio Member Join Date: Oct 2007	ok im looking at the 'typical application' on the lm3886 data sheet: http://www.google.co.uk/url?sa=t&sou...xVsZsIPWMxhvVg will this circuit work with my power supply?

4th June 2009, 02:03 PM	#6
Redshift187 diyAudio Member Join Date: Aug 2008	Keep in mind that CPU heatsinks are not designed for use without a fan (the fins are too close together for convection cooling).

5th June 2009, 12:06 AM	#10
garak diyAudio Member Join Date: Nov 2008	From the pictures I've seen of heatsinks used for LM3886 amps, and the resulting reports of how warm the heatsinks feel, I get the feeling that a CPU heatsink (designed for use with a fan) would be just fine, even if it's operating outside of its intended use and convection is lacking. It's still MUCH less heat than a CPU puts out. I'm planning on using some Athlon heat sinks that I got for $2 each.

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