First DIY solid state

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cjflis

Member
Joined 2013
Hello everybody,

This is my first post on here and my first foray into DIY audio so please be kind :p .

I decided to get the ball rolling by buying a 1U rackmount case second hand that had a 160VA toroidal in it and a heatsink mounted on the back and some other stuff inside (mostly empty) second hand. I also bought a small extruded aluminium heatsink case for whatever i use it for.

Anyway i was given two towers and a center speaker for free which are rated at 100 watt into 8 ohm and would like to get them powered. I realize the current transformer I purchased is not enough to power the three speakers and the case might not be big enough for the three amps but I would just like to get some sound atleast.

I have read that LM3886 are pretty good and simple to start with. I do not have much knowledge but understand basic electronics and would like to increase my soldering skills.

Eventually I would like to have 5 honey badger channels or F5 turbo V3 channels and then get a surround pre amp and have a go at building my own speakers......however i guess i should crawl before I run.

Anyways sorry for the essay, any recommendations apreciated.

Cheers,

CJ

TL;DR
Im a newbie, have a 1U case and three eight ohm tower speakers and would like to build my own amp so what should i do.
 
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AndrewT

R.I.P.
Joined 2004
Build a fully loaded 3886 single channel.
Learn how it works.
Learn how the component values affect performance.
Learn about the importance of good grounding.
Learn about soldering.
Learn how to wire up Mains Power safely.
Learn how to use your multimeter.
Learn what tests can easily be performed with very limited resources.

When all that has sunk in:
Work out how to fit two or three channels into your Chassis.
Learn about layout.
Learn about why twisted pairs of Flow and Return currents cancel many problems to insignificance.
 
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C

cjflis

Member
Joined 2013
Thanks for the great reply's guys!

Build a fully loaded 3886 single channel.
Click to expand...

Buy fully loaded you mean what exactly? (sorry for the stupid question haha)

And with the 3886 boards are they all the same? Or do some sound better then others? For example the ones on ebay vs the ones from a board website that is.

Also if I want to solder my own board components on is that gonna cost more to buy the components individually rather then get a pre-made 3886?

And is a 3886 still a good board for the money?

As for this suggestion djoffe:

A complete kit, like the GT-101
Click to expand...

I like it but for that kind of money plus shipping to Australia I would want atleast three channels.

Remember you do not need a 100watts to power a 100 watt speaker
Click to expand...

That is true, and i dont need something ridiculously loud...for my first project :)

Thanks for the help so far guys.
 
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ingenieus

Member
Joined 2011
The transformer will give you a DC output voltage of 21V. The LM3886 specifies a minimum of 20V, but this is not enough for a 100W amp. The good news is that you can bridge the LM3886 for more power. Here is the application note that explains how it is done:

http://www.ti.com/lit/an/snaa021b/snaa021b.pdf

Here is an example of such a project:

http://www.shine7.com/audio/bpa300.htm

It uses three LM3886 per board in parallel to increase the current capability. Two of these boards are then bridged. Doing this will probably exceed the 160VA that your transformer can deliver, but it goes to show that the LM3886 can be used in all sorts of ways.
 
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jaycee

jaycee

Member
Joined 2004
Don't worry about the 100W thing. I wanted to do this too, and have since built amps in the 30-50W range which are more than enough power :) The LM3886 is a pretty good amplifier IC which simplifies things immensely, and is suitable for a first time project. You will still learn plenty about building amps by doing this.

15VAC supplies will only get you about 21V supplies so youll get about 20-25W from that. However, it's enough to build a circuit with. If you want a little more power, you can easily get a new 2x18VAC or 2x22VAC transformer for a bit more power without changing the circuit.
 
Ian Finch

Ian Finch

Member
Joined 2010
Paid Member
If you decide at some point to use a higher voltage transformer, note that height restrictions of the 1U case will limit possibilities to custom (expensive) types. Follow jaycees's suggestions and stay with 160VA or less which, in some variants may fit in the likely ~42 mm max. internal height. Local supplies from retailers like Altronics though, are typically 57mm high.
This one, at 42 mm max, may just sandwich in.

Welcome to DIYAudio and good luck in your new adventures :)
 
C

cjflis

Member
Joined 2013
The case arrived today!!

The power supply is connected to a switch on the back and a power plug. There is also an LM388K adjustable regulator connected to some resistors and one big capacitor. There are three LEDS wired into that mess.

Anyway back on to what to do next, ingenius that is cool but i think i will just get one channel working for now so i dont have to get another Toroid.

Yeah Jaycee it doesnt look like i will be able to build something very powerful but thats ok i guess. If i can get an amp going with what I have got curently I will be happy, if not its not the end of the world.

Thanks Ian! Hopefully I dont get electrocuted at any stage :)

So guys with what i have got can I get one LM3886 up and running? And what should i do with the regulator and capacitor?

Thanks everybody :)
 
A

AudioSan

Member
Joined 2009
ingenieus said:
The transformer will give you a DC output voltage of 21V. The LM3886 specifies a minimum of 20V, but this is not enough for a 100W amp. The good news is that you can bridge the LM3886 for more power. Here is the application note that explains how it is done:

http://www.ti.com/lit/an/snaa021b/snaa021b.pdf

Here is an example of such a project:

DIY BPA300 6x LM3886 300W audio Amplifier

It uses three LM3886 per board in parallel to increase the current capability. Two of these boards are then bridged. Doing this will probably exceed the 160VA that your transformer can deliver, but it goes to show that the LM3886 can be used in all sorts of ways.
Click to expand...

the 20V minimum = +/-10V.
2*15V transformer will give you about +/-19-20V loaded.
 
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jaycee

jaycee

Member
Joined 2004
I wouldn't bother with bridging if this is your first amp. You will be surprised how loud 30-50W can go with good speakers. You need to have pretty inefficient speakers to justify 100W in a domestic listening environment.

Find a simple straightforward LM3886 kit (or make a PCB :) make 2 for stereo, and start there. If you find the 20-ish watts with a 2x15VAC transformer isnt enough, you can upgrade it to 2x18 or 2x25 later. Make sure you use 35V rated capacitors if you go up to 2x18VAC (will give +/-25VDC supplies), or 50V rated if you go up to 2x25VAC (will give +/-35VDC supplies)

You will still learn a lot, particularly about mechanical construction and power supply wiring.
 
jaycee

jaycee

Member
Joined 2004
cjflis said:
If i make one onto a PCB rather then buying pre soldered is it going to be far more expensive?

And can i go stereo? Wont i then be really, really short on power?
Click to expand...

If anything it will be cheaper buying a bare PCB or even a self-assemble kit rather than a finished board.

160VA of transformer is plenty of power for a stereo pair - this is what most off-the-shelf integrated amps use anyway. Back it up with a decent amount of power supply capacitors (I used 2x4700uF per voltage rail) and it'll be just fine.
 
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