DIY Studio 50W RMS Channel LM3886 based Amplifier

We use passive speakers in our modest studio and so use a stereo amp to power them.  The 1970s Rotel Receiver we had been using for the last 8 years had recently died and we were using a stand in CLASS T amp, that even though it sounded good, has a reputation for an early death.

We also had all the bits and pieces from prototype things we have developed over the years and after seeing you can get the assembled guts of an amplifier, using the wonderful LM3886 IC on ebay for about the same as just buying the ICs , it seemed a useful exercise to make an amplifier using them.  All I really had to buy was a case to put it in. So I ordered a flat pack rack box and slowly set to work among the other paid projects I had going. 

This is the term to search for on ebay for what we ordered:

HIFI YJ LM3886 68W+68W stereo amplifier board 3pcs total  , 

US $23.20 free shipping.

For your money, you don't get any documentation or schematics of any kind. I had to reverse engineer the PCBs to see what I had.

Without going into all the details (may be I will write it all up later, and clean up all my hand drawn sketches), over a few months it is now finished.  Some pictures above of the initial test assembly.

We have the mains and transformers front left, and the signal inputs back right, as far away as possible.  The heatsinks with the modules run down the far right of the case, as the case top cover has ventilation slots in that area. 

I used two multi-tapped transformers to get the +/- 24VAC needed for the PSU board, as I had them.  I wired the primaries out of phase to each other, like a hum bucker. Does that make it hum less?   Not sure, but the resulting amp has no background hum.

The case is connected to mains earth. The audio electronics are only earthed via the RCA input ground connections. The RCA sockets are isolated from the case.  Possibly a 10R between audio ground and chassis would not go astray here....

I added 2A fuses in the 30V rails to the modules, and an old relay speaker protection unit I had. Modified it with a bigger relay and changed the 30V to 15V supply to include a 5W 56R series resistor and a 7815 regulator, instead of just a zener diode. Runs cooler that way.

We bought a Dremel grinding stone,  using it in our standard drill, to remove the powdercoat around all the case screw holes and any place an earth connection is needed.  This is required to actually make a completely earthed and shielded metal box.

During the initial testing of the assembled modules we found they worked, but there was a low level oscillation you call motor boating.  The modules don't have any stability components to roll of the HF amp gain, or any output zobel networks. The High pass around the feedback (the 1k and 22uF) is at a very low 7Hz and would be better off being a bit higher.  The data sheet suggests a cap across the differential input of the LM3886 helps too, but we have not done this.

Adding these fixed, or seems to at the moment, with normal RCA cables connected to the input, the issues and now it seems like a rock solid amp module.  If it was just an opamp, a capacitor across the feedback resistor would have been enough, but it isn't just like an opamp... 

I also reduced the input attenuation so the volume on my monitor controller has the range I'm used to.

The amp is way quieter then the Rotel amp was.  There is no audible hum or noise from the amp they way I use it.

The amp speaker outputs are connected to my studio speaker selector box, that also has a headphone output and additional PTC speaker protection. This connects to 4 sets of speakers and can mute the speakers for just headphone listening.

Our Megacurve music tracks can be found at SoundCloud.

Info on our DIY Auratone clone and monitor controller can be found here.

We can be contacted at Art & Technology.

DIY Album Production - Audio Technology Magazine

DIY Album Production Issue

The latest Audio Technology Magazine covers DIY Album Production. Interesting, as far as it goes.

They know what has really happened, but don't want to talk about it out loud. There isn't much money left in the recorded music business.

So they don't talk about those core issues, but instead the issues with doing it all yourself.  We all need editors and reviewers, or at least a good spell checker or friend to be objective.  All the same issues for writers, painters, illustrators, graphic designer, dancers and sculptors.  You could say the same for soccer players and other sports people too.

To quote Brian Eno:


"I think records were just a little bubble through time and those who made a living from them for a while were lucky. There is no reason why anyone should have made so much money from selling records except that everything was right for this period of time...
"It was a bit like if you had a source of whale blubber in the 1840s and it could be used as fuel. Before gas came along, if you traded in whale blubber, you were the richest man on Earth. Then gas came along and you'd be stuck with your whale blubber.
Sorry mate – history's moving along. Recorded music equals whale blubber. Eventually, something else will replace it."


And this interview with MOBY...

Are we moving back to a time were musicians are being realigned with other arts to  make a living, or not, from music art?  It seems so.   A key point in the MOBY video is that producing music isn't so special any more. What took 3 months in a well equipped commercial studio many years ago can take 30 minutes on a laptop for his genre today.

Biggest Australian Musical Instrument Chain closed Nov 25 2012

There are dramatic changes afoot. The biggest musical instrument store chain and wholesaler importer in Australia, with 25 stores and around 600 staff has also just closed up for good.  Nov 25 2012 was the last day the last stores were open.

So money to use on music of any type is tight and not enough to support retail outlets?  We will see.

Was told a story from a customer recently that there was a survey on facebook that found that people would pay $3 for a cup of coffee that took a minute to make and not much more to drink,  but would not pay much if anything at all for music, that took many years to master an instrument, create and produce.

Ok. Then recording music and getting paid for it, or breaking even on what it cost to produce is "problematic".  Sound On Sound  magazine has moved into promoting Live Sound, in addition to recording music.  The point about that is that you have to have built an audience, have supporting venues willing to let bands play instead of just having poker machines, and be touring all the time, in large enough venues, to be able to get anywhere near the income that you could have gotten from CD or Album sales in days gone by.    

Some months I put a blog post  on Music ROI on LinkedIn.  I had expected some type of comment. Got nothing at all. The wrong crowd.

What I implied, but didn't directly state using the sports scenario was:  the world of sport is supported by amateur teams and "clubs" that they pay to belong too.  Bigger pro clubs have gambling and generate more revenue to support their teams, competition prize money and facilities up keep  and have the clout to auction TV broadcast rights.

Maybe the music and arts worlds should form their own "clubs" for project funding.  Something more than random live performances. Something like Comedy Clubs maybe.....

Maybe too much like herding cats.....

Music production technology was the industry I was in for 25 years. See some of the details here. My original interest was for a system I could use myself.  The early systems I was involved with developing were very expensive, and not something I could own. It is only in recent years with PC based DAWs and software instruments and processors that I have what I set out to develop. And most of what I use now is actually free or shareware software, and we have and need very little supporting electronics.

It is now a whole new world and the best time ever for doing DIY projects.  Even if you don't make any money from them.

Some of our own tracks on SoundCloud:




Contact us at Art & Technology