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  • Author Author: michaelkellett
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Audio Power Amplifier Silliness

michaelkellett

Recently I blogged about a little power amplifier that I had worked on with Shabaz 

 Two pre-amplifiers and a power amplifier. 

That design is pretty simple and adequate for his plans but I got to wondering just how much power you could get into a speaker with a linear power amplifier working with  a single DC supply in the range 6 - 8V.

I doodled around a bit and came up with this.

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It's not quite a ready to build design - because it still has some magic current sources which will need to be turned into real parts.

And the phase splitter looks a bit messy.

It can manage 4.83W into a 4 ohm load just below the clipping level. The distortion is about 0.3% at 1kHz at this level.

image

image

The key to the design is the output power transistors which were chosen to have very high gain which allows them to pull the load to within less than a 1V of the power rails with a current of up to 1.6A.

I've been wondering if it's worth building  - anyone have a use for it ?

Or better still any ideas for improvement ?

MK

  • in reply to michaelkellett

    No problem at all with these suggestions, they are still all very easy to do with limited equipment, and I'm very happy with 0603 too!  They are almost the same size as 0805 so I doubt anyone would struggle with 0603 if one was previously used to 0805. 

  • in reply to shabaz

    Hello Shabaz,

    My plan was to replace the current mirrors with dual transistors (for better matching) and to use current mirrors for the 4 x 2mA current sources. (Which will make 8 in total).

    The only readily obtainable matched dual transistors I know of are PMP4201Y.115 and PMP5201Y.115 (NPN and PNP) and they come in SOT363 packages.

    The power transistors in D-PAK packages so that kind of forces the board to be surface mount. The other transistors can easily be SOT23.

    I would normally use 0603 resistors which I keep in E24 + extras. 0805 would be possible.

    I don't have any issues hand soldering 0603  - do you think this would be a problem for you or many other home assemblers ?

    The current plan is to design the board so that it can be clamped to a heat sink via some suitable electrically  insulating and thermally conductive material.

    (I've just discovered that you can buy heat plates (like heat pipes but flat) from Aliexpress at the usual ultra cheap prices))

    I may need to ask for for tips ordering boards from JLPCB.

    MK

  • I probably will never use a LM386 ever again, because the discrete design was compact at 40x40mm, especially compared to the speaker that it usually drives, and would be fast to assemble with SMD resistors and transistors, plus it’s far better quality that the LM386.

    Although I don’t have a need for 5W, personally I’d still build it to try out if you did get enough interest to want to continue with it. I’ll think about it more, the only suggestion I currently had is that the design could be a SMD/through-hole hybrid, i.e. resistor and jellybean transistor footprints could be 0805/SOT-23, and the power transistors could be whatever is needed, and then it’s still easy-to-assemble and quick-to-assemble. I suspect it will be compact, since there are not many capacitors.