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It is designed to mount on the flat surface of a heat sink with the output devices. Each
channel of the amplifier has its own switching power supply and draws about 1 amp of current
DC. The supply should be capable of delivering more than 2 amps of current short term. At
19 volts, the dissipation of the amplifier is about 20 watts, and the heat sink it is mounted on
should not be allowed to get more than about 25 degrees Centigrade above the ambient
temperature. This means that the rating of the sink should be around 1 deg C per watt.
The power transistors must be well attached to the heat sink since they dissipate about 10
watts each. As the cases of the transistors are electrically live, they must be insulated from
the heat sink by electrically non-conductive but thermally conductive material, either
commercial silicone TO-3P insulators or equivalent mica pads and thermal grease.
Here is a clear picture of the component placement:
A couple of notes about parts: Feel free to try different parts and different values, as there is
nothing that critical about much of this design. Remember that Mosfets are static sensitive,
so use a little common sense in handling them.
I chose the 10 uF caps as the Elna Silmics because they are cheap and very good. The 3300
uF cap will never see even 20 volts, but greater than 25 volts leaves margin for lower
If you can't find the Toshiba Jfets, you will find that the Linear Systems LSK170 is much more
than adequate as a replacement, and is not expensive.
You can substitute other Mosfets into this design, but keep in mind that they all must be
Enhancement mode parts requiring a Gate to Source bias of a least a volt (these are 4 volts)
or it will not work. Depletion mode parts won't work at all.
There is only one adjustment, assuming that you have built the circuit as described, and that
is to adjust P1 so that the Drain pin of Q1 is set at 10 volts DC. After you have set P1, you
need to let the amplifier spend some time warming up, say a half hour, and then adjust it to 10
volts again. Then do this one last time after another half hour.
While the amplifier is warming up, the cover should be set in place so as to simulate the
ventilation that the channel will experience under the same thermal conditions as normal
That all there is to it.