A Foxx Upon Thee!
Analog Components in Complex Guitar‐Signal Processing
foxx Tone Machine
Circuit Schematic
What exactly does this thing do?
• Adds “fuzz” distortion to the input signal by means of soft diode clipping
• Allows independent tone/sustain/volume control
• Adds an octave to the input by means of phase‐splitter full wave rectification
• Spontaneously generates tomahawks ?
Fuzz Stage
Doped Semiconductors
P‐type
The polarization of the depletion region leads to an electric potential barrier that facilitates N‐type semiconductors have electron migration from the n‐
P‐type semiconductors have a an excess of electrons type side of the border to the p‐
deficiency of electrons type side and eventually stops (vacancies)
the diffusion process. The height of the potential barrier varies with the type of semiconductor. N‐type
Diode Function
An input signal (in the form of a sine wave) is incident on a forward biased diode.
If a diode is connected between the signal In theory, diodes conduct current in only one path and the ground, as in the foxx tone direction. But they don't operate perfectly. All machine, the signal won't be shunted to the diodes have a "forward voltage“ (they won't ground until it exceeds the forward voltage. conduct until that voltage is reached).
And even then, the whole signal isn't dissipated, only the portion of the signal above that forward voltage. So the signal’s peaks are simply "chopped off." Diode Function
Forward‐Biased Diode
Reverse‐Biased Diode
Both a forward and reverse‐biased diode connected to one another and connected to ground.
Symmetric Soft Clipping
Potentiometers
Colloquially known as pots
Their variable resistance allows the user to select how much current should be directed from the input towards each of the two outputs. No Resistance
Maximum (50kΩ)
They can be manufactured using a linear or log scale in any number of forms.
The Tone Control Stage
Low‐Pass Filter
The capacitor exhibits reactance (opposition to a change in current), and blocks low‐frequency signals, causing the lower frequencies to be routed through the 22K resistor. At higher frequencies the reactance drops, and they pass through to the tone control pot.
Let’s see how the potentiometer controls the flow of the signal by adding to the effective impedance.
Impedance Calculation
What does that mean?
Frequency Response
The Octave and Sustain Stage
Lovers
Phase‐Splitter
Start with a bipolar transistor with identical value resistors between collector and V+, and between emitter and ground (4.7k and 4.7k). This will yield equal amplitude signals at the emitter and collector that are in opposite phase ‐ whatever goes positive at the emitter goes negative at the collector.
Since the emitter and collector outputs are equal and opposite phase, if you run each of them through a diode that points in the same direction, you end up chopping the input signal into polarized complementary half‐
cycles. If you combine these two altered signals, you now have bump‐bump‐bump where each half might have had gap‐
bump‐gap or bump‐gap‐bump before being recombined.
You have effectively doubled the frequency of the input signal.
Back for the Sustain
1
A
2
B
C
3
Special Thanks to . . .
• Dr. Black – for all of the time and patience
• Steve Ridinger – the original designer of the foxx Tone Machine circuit (now president of Danelectro)
• The year 1971
• Bonnie Mattis
• You good people for sticking around