A small DIY LM3886 Chip Amplifier

[tc]

I got the bug to build an amp to run the tweeters on a two-way that was using MiniDSP. I had a lot of misc parts laying around, so thought, what the heck. I think most everyone is familiar with the LM3886 chip amp or Gainclone Amp. I ordered a couple of boards from Chipamp.com and the parts from Mouser.

Mostly, this is about how simple it was to get a case together for it. I found a blown-out Marantz integrated at a local thrift store and scavenged a pair of heat sinks for it. Cost was $5. I used a 200VA toroid from Antek.com that was around $30, a PSU board from Bohemian Audio, and misc parts from Mouser. Add in the scrap wood and the sheet metal and it was an under-$100 amplifier that will play about 50Wpc or so into a 4r load without breaking a sweat on about +/-24Vdc rails. A neat, great-sounding amp. I will post a few pics and answer any questions I can. Neat project to try.

[tc]

Re: A small DIY LM3886 Chip Amplifier

[Silver1omo]

Re: A small DIY LM3886 Chip Amplifier

Nice, that is a lot of caps... How much per rail?

[---k---]

Re: A small DIY LM3886 Chip Amplifier

Nice.

[tc]

Re: A small DIY LM3886 Chip Amplifier

Nice, that is a lot of caps... How much per rail?

They are 2200uF caps, 22,000uF per rail. A bit overkill....but why not, amirite?

[DoubleTap]

Re: A small DIY LM3886 Chip Amplifier

Some of those chip amps can sound incredible ... not just good, but incredible. They flat out destroy the preconceived price to performance scale. I've been thinking about buying one, there are a few finished ones out there under $400 with beefy power supplies, nice cases, etc. But I might just build one myself. I have a bunch of big Pentium 3 heat sinks lying around that would work perfectly, and I have a torrid that's been on my shelf for years that would work.

[Silver1omo]

Re: A small DIY LM3886 Chip Amplifier

It looks like a lot more, I went with 20,000uF (2x10,000uF) per rail.
I want to try an audiosector kit...

They are 2200uF caps, 22,000uF per rail. A bit overkill....but why not, amirite?

[fdieck]

Re: A small DIY LM3886 Chip Amplifier

Very nice job. I think I may have been an influence on you but you put yours in a very nice box. I like the LM 1875 a little better but it is a lower power rating.

Fred

[hongrn]

Re: A small DIY LM3886 Chip Amplifier

tc, is that blue connector a Speakon?

[fastbike1]

Re: A small DIY LM3886 Chip Amplifier

I have an Audiosector LM4780 kit that I have yet to build. Based on the quality of the kit parts and the online support, I would expect you to be very happy with the kit.
Threads like these remind me to take a break from speaker building and build some of the amp kits I have "in stock".

It looks like a lot more, I went with 20,000uF (2x10,000uF) per rail.
I want to try an audiosector kit...

[Silver1omo]

Re: A small DIY LM3886 Chip Amplifier

tc, is that blue connector a Speakon?

That is a powercon

http://www.neutrik.com/en/audio/powercon/

[JasonP]

Re: A small DIY LM3886 Chip Amplifier

I have an Audiosector LM4780 kit that I have yet to build. Based on the quality of the kit parts and the online support, I would expect you to be very happy with the kit.
Threads like these remind me to take a break from speaker building and build some of the amp kits I have "in stock".

I have the pcb set for that same amp from Audiosector sitting here. I'll need to make that my winter project. The mouser cart is already built and loaded, just need to click the order button.

[donradick]

Re: A small DIY LM3886 Chip Amplifier

Very nice!
I like the overkill PS caps and overkill heat sinks.

[tc]

Re: A small DIY LM3886 Chip Amplifier

Thanks Don. I like beefy PSU's and heat sinks. I see so many of the gainclones with really flimsy heat sinks. Some with just a strip of AL. I just don't get it. I want my amps to survive the nuclear holocaust....

[Sydney]

Re: A small DIY LM3886 Chip Amplifier

...I like beefy PSU's and heat sinks. I see so many of the gainclones with really flimsy heat sinks. Some with just a strip of AL...

from a paper on Thermal management - ie the 10 degree rule
"In our world of electronic product design, we live by this rule of thumb: For every 10 degrees Centigrade rise in temperature, the average reliability is decreased by 50 percent. Or, from the quality assurance department's point of view, if we can lower the temperature by 10 degrees, we'll double the reliability. In other words, we will double the expected life within any predictable failure rate. Another way to look at this, for those interested in buying products with good MTBF (meantime between failures) ratings, is that MTBF will, on average, double if the operating temperature is lowered 10 degrees."