Iam a retired graduate lectrical engineer who
has been interested in
audio since high school.
A few years ago, I got
interested in solid-state
amplifiers and bought
some books on the
subject. Since then, I’ve
built a number of
amplifiers with superior
specifications and very
This simple amplifier
has very low distortion
and flat frequency
response well beyond the
audio frequency range.
Cost of parts for one
channel including the
power supply will be
about $30; a second
channel will only add
about another $15.
If you live in a large
metropolitan area, you
can find all the parts at a
local distributor. If not,
I’ve listed a number of
sources for parts here in
This project is rather
forgiving of beginner’s errors.
The design is simple and
straightforward, but its
performance is equal to or better than the best
commercially-available amplifiers in terms of low distortion
and noise, wide frequency response, and high damping
factor. I also added tone control.
A number of experimenters have little success with
constructing solid-state amplifiers. The reason is that a
short circuit or misconnection can result in instant
destruction of semiconductor devices. Miswiring a
vacuum tube will sometimes have no ill effect at all and
sometimes make the plate glow red hot. If you are
watching, you can cut the power and find the error.
A wiring error in a solid-state amplifier can result in
instant destruction. If you build this solid-state amplifier
carefully, however, it will be very reliable. When testing
the solid-state device using a probe for a voltmeter or
oscilloscope, a slip can cause a disaster, so be careful. If
you do slip, the transistors used here are quite
inexpensive, so no great harm will be done.
The most common error (I’ve done it myself more
than once) is to wire a transistor wrong. Small signal
transistors of the plastic case TO-92 type are usually wired
with the leads down and the flat of the case facing you;
the leads are from left to right, EBC. That is: emitter, base,
collector. The 2N5551 and 2N5401 used in this project
are wired in that order.
The output transistors are TO-126 style. With leads
downward and the label towards you, the leads are from
left to right ECB (Emitter, Collector, Base). These TO-126
transistors will have TO-220 style heatsinks attached (see
Figure 1). Get the type with a hole for mounting the
transistor with a screw and nut. Be sure these heatsinks
don’t touch each other since they have positive and
negative supply voltages on them. A dab of heatsink
compound between the transistor and the heatsink is
good, but probably not necessary at this point.
Another less common error in wiring is to reverse the
September 2013 29
■ FIGURE 1. One channel assembled on perfboard.