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Chip Amps Amplifiers based on integrated circuits

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Old 10th January 2013, 10:33 PM   #1
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Default Noob looking for advice

Hello all, first of all thank you for providing such a great resource. I've spent a lot of time just combing some threads and finding helpful bits to help put together a more full picture. However I can't help but get the feeling that I'm a missing a few pieces of the puzzle.

I have very limited experience, I had an electronics course in high school and a circuits course in college (3 years ago). My goal for this project is to have a mid range quality set up for my computer with a budget of about $200 for parts not including the case materials.

What I would like to do is basically copy these Ceramic Speakers designed by Joey Roth - simple, modern full range drivers for desktop or entire room | Joey Roth . I'm not so worried about the ceramic portion as I have experience with that. However learning amp design has been a bit overwhelming.

I was looking at getting a pair of these drivers:
Tang Band W4-1337SDF 4" Titanium Full Range Speaker 264-916

For the Amp I was looking at either
LM3886 Amplifier Kit | Chipamp.com (stereo kit).

Or perhaps a kit from 41hz.com Any come more highly recommended for this set up?

With the chipamp kit it looks like I'll need a transformer. I found this website which has a ton and from what other people were saying the 200-400va range and between 18-22A. Which would best suit my needs? Also I realize that it's kind of against the spirit of the whole thing but is there an easier way to do the power supply, like a laptop charger or something along those lines?


On the driver specs they go up to 50W, while the 3886 looks like it tops out at 25W, is that correct? Does that mean that the output of the drivers is going to be poor?

Also is it difficult to incorporate a headphone jack?

Any thing that I'm forgetting?

Last edited by CloverWS; 10th January 2013 at 11:41 PM. Reason: forgot link
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Old 11th January 2013, 01:05 AM   #2
zymurgn is offline zymurgn  United States
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http://chipamp.com/docs/lm3886-manual.pdf

That will give you more insight on the type of transformer you use if you decide to go with the chipamp.com kit. In fact, you can read the whole guide to see if it will suit your electronic building capabilities. Hope that helps.
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Old 11th January 2013, 10:18 AM   #3
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200VA is all you need really, and could probably get away with less. At 400VA you might have to start dealing with inrush current issues. And I think you mean 18-22V. For those speakers (6 ohm 50Watts) you will probably only need 18V-20V DC.

You need a split power supply. Those transformers give out two lots of 18VAC, which the circuitry turns into + AND - 25V DC roughly, and note the increase from 18VAC. A laptop charger, besides being possibly noisy and under current, gives out just +19V DC, say. There are single sided amplifier circuits, but they are typically around 50V or more.

You could build a very minimal power supply. You've said this isn't high end, so paying for those MUR860 diodes, etc. might not be necessary, you could just have transformer, 1 or 2 integrated bridge rectifiers, smoothing caps. This can easily be made on matrix board/point to point, and you could leave some room to add snubbers, small value bypass caps, etc, if and when you feel like it.

The LM3886 can give out enough power. Check out the datasheet http://www.ti.com/lit/ds/symlink/lm3886.pdf . On page 12 is an output power vs supply voltage graph. You'll see that for 6 ohm speakers you can supply about 40W at +/-25 or so volts. On the previous pages are some distortion figures. There isn't one for 6 ohms at 25V, but some interpolation suggests you could get up to 40W before it skyrockets (hence the 40W rating). This is good as it gives you some advance warning you are overloading your speakers.

I found this site very useful when building my first chip amp psu. Building a Gainclone chip amp power supply. . It's by a regular contributor to this site. There are also many pages on chip amps in general, which he calls gainclones, or GCs, though he uses a configuration different to typical datasheet schematics.

Last edited by Robert Kesh; 11th January 2013 at 10:27 AM.
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Old 11th January 2013, 03:40 PM   #4
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Thanks both of you for the info.

According to DecDungeon a 20v transformer will give 28v dc which then looking at the Vin Vs Wout graph would give about ~42 Watts. To me this looks ideal.

To be clear, as some of the verbiage is a little confusing to me, the transformer splits Vin into two Vout lines, which are the rails, correct? Is this the same as secondaries? Each of these rails would send the voltage to either the left or right speaker via the chipamp circuits correct?
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Old 11th January 2013, 04:27 PM   #5
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Hi there,

I built a chipamp.com 3886 kit as my first project. Had not soldered in 30 years and am no engineer either, but managed just fine to get it up and running in two evenings after work. Building a power supply was not such a big deal either. Just a few parts on a PCB. They deliver all the parts. For my first amp I used a 400va 24 volt toroid, single PSU. No inrush issues. ( on my second amp, a 3875 IC, I used 2 of those and then needed a softstart, as the house fuses blew :-). For some pictures check my blog (it's not much, but may give you an idea).

Have fun

Michael

Michael's Project Page
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Old 11th January 2013, 04:43 PM   #6
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Quote:
Originally Posted by CloverWS View Post
Thanks both of you for the info.

According to DecDungeon a 20v transformer will give 28v dc which then looking at the Vin Vs Wout graph would give about ~42 Watts. To me this looks ideal.

To be clear, as some of the verbiage is a little confusing to me, the transformer splits Vin into two Vout lines, which are the rails, correct? Is this the same as secondaries? Each of these rails would send the voltage to either the left or right speaker via the chipamp circuits correct?
There are two ways the transformers you will need come. Centre tap, or two secondaries.

The power supply will rectify and smooth and combine these to + and - DC, which are your rails, and also a 0V which you will connect to ground. There are various ways of doing this, depending on whether you have a centre tap or two secondaries. A picture is worth a thousand words, I find. First pic is centre tap, second pic is two secondaries. Just to complicate things, you can use a two secondary transformer as if it were a centre tap, but not vice versa.

Click the image to open in full size.

Both channels, left and right amps, need both + and - power. If you made only mono, you'd still need + and - power.
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Old 11th January 2013, 05:14 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

Oversized power supplies are a complete waste of time for chipamps.

160VA for 4 ohm stereo is more than adequate in the real world.

rgds, sreten.
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