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Old 17th August 2011, 10:50 AM   #1
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Question Simple sub amp a 10-year old could build?

Hi,

My son's little 2x40W Onkyo DR-645 stereo has a subwoofer output (full range, mono, post vol control), and he has expressed an interest in building a little amplifier and sub.

I've built a couple of gainclones, but power opamps hide the details.

Can anyone suggest a simple, discrete circuit we could build together?

Something simple enough to wire point to point would be great.

Any suggestions appreciated,
S
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Old 17th August 2011, 11:29 AM   #2
Mooly is online now Mooly  United Kingdom
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If it's for learning then maybe a simple AC coupled design (Single rail... speaker safe).

Something along the lines of the classic H.C. Lin circuits but maybe with a better bias scheme (vbe multiplier).
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Old 17th August 2011, 12:03 PM   #3
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How much power do you want that sub amp to put out? My guess would be 80W, and such things are not so easy to do simple.

One way to keep a power amp simple is to use the LME49830. It does hide some of the functionality, but the circuit is simple enough to wire point to point. Not sure if this method of construction is a good idea, haven't tried it myself. The datasheet for the LME49830 has a PCB layout.

Even simpler is to use the LME49810/LME49811 with Thermaltrak transistors - therefore no Vbe multiplier needed. The easiest way to do that is to get one of these kits. Very serendipitously, it puts out 80W.

Click the image to open in full size.

http://www.pansonaudio.com/Compact_Series.htm

Disclaimer: I am not affiliated with these guys, but I like what they do. And they hang out on this forum AFAIK.
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Last edited by ingenieus; 17th August 2011 at 12:28 PM.
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Old 17th August 2011, 12:30 PM   #4
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by autopoiesis View Post
I've built a couple of gainclones, but power opamps hide the details.

Can anyone suggest a simple, discrete circuit we could build together?

Something simple enough to wire point to point would be great.
Something of this kind:
2N3055 Power Amplifier
It's safe, proven and works well enough.

For a sub, increase the 1500µ output cap to 4700µ.

To simplify it further, you can replace the OP transistors+drivers by monolithic power darlingtons.

Or go for something really crude and nasty, like this one:
Cheap 100 to 150 Watt Amp
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Old 17th August 2011, 01:07 PM   #5
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Or the absolute simplest, but still with decent performances like this one:
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Old 17th August 2011, 02:23 PM   #6
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And finally, the darlington version: linearity is even better.

Q1/Q2 can be a single monolithic low power darlington like the BC517
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Old 17th August 2011, 02:51 PM   #7
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Quote:
Originally Posted by Elvee View Post
And finally, the darlington version: linearity is even better.

Q1/Q2 can be a single monolithic low power darlington like the BC517
I like this one - simple, cheap and easy to build with no bias to adjust.

If one is willing to make adjustments, a Vbe multiplier in place of the diode string would improve the THD a little.
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Old 17th August 2011, 05:24 PM   #8
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Quote:
Originally Posted by ingenieus View Post
I like this one - simple, cheap and easy to build with no bias to adjust.

If one is willing to make adjustments, a Vbe multiplier in place of the diode string would improve the THD a little.
Yes, and in practice, R6 should be made adjustable too, to set the output at mid-supply.

But it will work as it is, with a slightly reduced output dynamic.
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Old 17th August 2011, 08:32 PM   #9
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Thank you for your replies - the panson kit looks like a good one.

I'll post back when (prob in the autumn) when done...
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