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  #1  
Old 11-26-2009, 08:37 PM
hazim hazim is offline
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Default 30W 2N3055 Audio Amplifier circuit question

I want to build this simple audio amplifier and I need some information from you...
1)Are all the resistors 1/4W? What about R11?
2)What should be the loud speaker? will a 20W 4-8 Ohm works? and what's a best choice?
3)Is there any IC that outputs +20V 0V -20V from a 12V battery source and if available, handles the required power for the circuit? Any other idea how to feed this circuit from a 12V battery source?

Thanks

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Old 11-26-2009, 10:30 PM
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the TDA1562Q integrated circuit is an amplifier capable of delivering 36w rms to a 4 ohm load. Silicon chip magazine did a project with it called the 'mighty midget amplifier'.

The IC has a built in charge pump so it can get enough voltage out of a 12v supply to deliver this power.

Only problem is, the chip is out of production. It's easy to find on ebay as surplus stock though, and reasonably cheap too....
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Old 11-26-2009, 11:00 PM
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It is interesting to see what Pavel has made of the Z30. I attach the original circuit. This had a max supply of 35 volts single ended. However it did use better quality transistors and was pretty advanced for its time. Yes the original would work from a 12 volt car battery.

All amplifiers characteristics will be influenced by layout, and this one was pretty compact so you may have to adjust some capacitors on yours.

Yes 1/4 watt resistors for R7 & R8, the rest can be 1/8 watt.
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Old 11-27-2009, 12:12 AM
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The old Sinclair Z-30 amplifier had an output of 15W to 18W RMS into 8 ohms at 0.5% distortion per channel. My old store-bought stereo still works with the circuit. It is about 44 years old.
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Old 11-27-2009, 08:15 AM
hazim hazim is offline
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Using TDA1562Q to build such amplifier is a good idea.. but I'm sure this part isn't available here in Lebanon especially because it is out of production as you said... Any way the circuit I put is cheap, easy to build and simple too and I like to build it.

The only problem is with the voltage supply as I said... I want to know which IC I can use to obtain +/-20V from a 12V car battery source...
Also what loud speaker you advice me to use?
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Old 11-27-2009, 09:19 AM
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I'm sorry I bothered to post any sort of reply.

But I will warn you one fundamental difference between the original and revised circuit is the link between the base resistors of Q4 and Q9.

In the original there is no link, they are brought out to separate terminals (1 and 3) for very good reasons. This amplifier becomes unstable if they are combined. Also the distortion / noise characteristics are considerably worsened.
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Old 11-27-2009, 05:39 PM
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Well, a TDA7294 is a more modern amplifier IC that will be pretty compact, reliable, and has much lower distortion than the Z-30.

It's also in production. It may or may not be available in your country.

But it seems that your biggest problem is to create a power supply capable of generating the +/-20v rails.

If you want 30W output, you'll probably need 60W of power or more, as half (or more) will likely be dissipated in the amplifier itself. So, you will need some kind of boost-type switching supply.

Throwing some rough numbers out, if you can obtain a switching boost supply driver IC of the proper type, you might be able to get around 85% efficiency; providing it's really well-designed and laid out properly.

60W / 85% = 70.6 Watts. If the input for the supply is coming from an auto's alternator, figure on about 13.8v being available while the engine is running. 70.6 Watts / 13.8V = 5.1A.
If the engine were off, and you were running from straight battery voltage, you would get perhaps 12v; so 70.6W/12v=5.9A.

But this is all presuming that you've built a reasonably efficient power amplifier and a reasonably efficient boost converter, both of which require at least intermediate skills levels.

Also, both the amplifier you are considering and the TDA7294 are single ended. If instead, you used a pair of them with the input audio signal inverted to the 2nd amplifier, you would have a push-pull output arrangement, which would cut your rail voltage requirement in half.
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