StewMac 57 MINI TWEED, Руководство по сборке

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Output
Gain
Negative feedback
Processing
Power
Mic level
Speaker level Line level Line level
You don’t need to read a schematic to build this kit . But it’s
fun to see how the circuit works, and to see the different
subcircuits that interact to shape your sound .
Working with the tiny signal from the guitar, the amp creates
the power needed to drive the speaker . The signal is affected
by the
gain , processing , output and power stages as it
passes through the circuit .
The gain circuit increases the signal
strength to line level (about 1 volt),
by passing it through 12AX7 preamp
tubes .
Inside the airless capsule of a tube,
electrons flow from a heated
cathode
to be received by the anode
plate
.
Between these two elements is a
grid
receiving the tiny voltage from
the guitar . The guitar’s
varying musical signal
controls the flow of
electrons to the plate .
This three-part component is called a
triode . The 12AX7 tubes are dual-tri-
ode tubes; combining the elements
of two tubes in one housing .
The negative feedback loop flattens
and extends the amp’s frequency re-
sponse, reducing distortion generat-
ed in the output stage . This makes the
amp’s sound cleaner and more hi-fi .
Some players disable this loop com-
pletely or add a potentiometer in
place of the resistor to create a “grit”
control . We don’t recommend doing
this, because it places stress on the
output transformer .
The processing stage shapes the tone
of the signal . Compared to most gui-
tar amplifiers, the 5F1 circuit design
has little in the way of processing,
because there’s no tone control on
the ’57 Tweed .
With this amp, players fine-tune their
tone by varying the volume and tone
controls on the guitar .
The power supply stage provides power to the other circuit stages, as well as the
tube heaters and pilot light .
This circuit receives the
AC power
from your wall and passes it through the power
transformer to create higher voltage . The electricity then goes to the rectifier,
which converts it to a pulsing
DC current
.
This then passes through a series of three large electrolytic capacitors which filter
out the pulsing to create a smooth current . As each cap smoothes a bit more, the
current is also passing through resistors that lower the voltage .
As the signal from the guitar becomes more amplified, the ripple of DC current
becomes less evident and the fully filtered current is sent to the most sensitive
part of the amplifier, the first pre-amp tube in the Gain stage .
The output stage increases the line
level signal to
speaker level
, which
is typically 8 volts or greater .
Amplifiers under 10 watts, like this
one, only need one power tube to
amplify the signal to the appropriate
voltage .
The output transformer adjusts the
impedance to
4 ohms to drive the
speaker . Amp output is typically 4, 8,
or 16 ohms .
A 4 ohm speaker is used in this amp .
cathode
plate
grid
We’ve color-coded these stages on our schematic, to show
how the parts work together . Symbols for components are
in the key at the bottom of the frame .
On the wiring diagram we build step-by-step in these
pages, the parts are easier to recognize . But studying these
color-coded stages will help you understand where each
component fits into the creation of your sound .
Learning more: secrets revealed in the schematic