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Old 7th September 2013, 05:52 AM   #1
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Default First DIY solid state

Hello everybody,

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

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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Old 7th September 2013, 10:06 AM   #2
AndrewT is online now AndrewT  Scotland
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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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Last edited by AndrewT; 7th September 2013 at 10:20 AM.
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Old 7th September 2013, 01:04 PM   #3
djoffe is online now djoffe  United States
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A complete kit, like the GT-101, might be a good starting point. You could then save the parts you have for your next project!

Akitika GT-101 Audio Power Amplifier Kit
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Old 7th September 2013, 01:55 PM   #4
Spiny is offline Spiny  United Kingdom
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Remember you do not need a 100watts to power a 100 watt speaker. Plenty of sound with 1-5 watts

You need to know what the output voltage of the toroid is and from that you can decide a suitable amp.
Only one problem with DIY Audio - its addictive!
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Old 8th September 2013, 02:03 PM   #5
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Thanks for the great reply's guys!

Quote:
Build a fully loaded 3886 single channel.
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:

Quote:
A complete kit, like the GT-101
I like it but for that kind of money plus shipping to Australia I would want atleast three channels.

Quote:
Remember you do not need a 100watts to power a 100 watt speaker
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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Old 8th September 2013, 07:46 PM   #6
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Uhm, what is the secondary voltage of the 160VA toroidal?
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Old 9th September 2013, 02:39 AM   #7
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The transformer is the one in the link below, 15V+15V

Powertran 160VA Toroidal Transformer - 15+15V, Class B Insulation (M5315) | Techtronics Australia

Cheers
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Old 9th September 2013, 09:37 AM   #8
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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.

Last edited by ingenieus; 9th September 2013 at 09:46 AM.
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Old 9th September 2013, 11:32 PM   #9
jaycee is offline jaycee  United Kingdom
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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.
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Old 10th September 2013, 04:51 AM   #10
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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
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