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PA Amp schematic

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Hi all,
I want to make a sub unit for my dj gear and need a amp to supply 300w rms to my 18" 4ohm speaker.

Can someone supply a schematic, cheers
I think the L4702 high power one would be suitable, Im not a expert at schematics but know what 99% of it is, apart from the area in the rectangle, i would like this schematic to pump out about 80% max power, if anyone could sketch a schematic i would appreciate it., thanks


Most Helpful Member
The area in the big rectangle is the IC itself. Everything else is what is attached to it.
The four small rectanges are standard high wattage darlington transistors.

I dont know what more of a schematic you need other than a dual voltage power supply in the 40-60 volts per rail at perhaps 15 or more amps capacity.
That makes sense now thanks. One question i do have though is. is there another circuit i can add to control volume / bass amount? also this i need to connect to one 18" sub, how would i do that? i did rread about a resistor arrangement to create a bridge but looks shabby to me.

thanks for your help so far.


Most Helpful Member
I would just put a log pot on the inputs. That will give you a good simple volume control.
As far as crossovers just buy a good preamp crossover unit on eBay or from a local pawn shop or electronics store. They will give you far more control and function than you could ever build for the same price.
Building a good amplifier is easy and rather cheap. But crossovers can take up a lot of time and money. Factory made is easier and better for getting one of them.

As far as hook up just use it with one output. If you build it right and have a big enough power supply you can always just add a second speaker later. If you going to build your own amplifier do it all at once, Then you have a way to expand your system when you need to.


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Last edited:

Nigel Goodwin

Super Moderator
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Bear in mind for DJ use, and for a sub in particular, it will be run continually at high sustained powers - it needs to be very well built, and to have massive cooling capability.

300W is also pretty feeble for a sub-amp, I would suggest you try looking at the Behringer power amplifiers - you aren't going to build an amp anywhere near as good anywhere near as cheap.
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