Metaxas Audio Systems Ikarus, User Manual

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K O S T A S M E T A X A S D E S I G N
D e s i g n P h i l o s o p h y
07
LOW NOISE, HIGH SPEED VOLTAGE
REGULATOR DESIGN.
The most significant difference between VALVE and TRANSISTOR circuits
is the amplifier/power supply interaction.
In VALVE amplifier, the high voltages (from 200-400 Volts DC) result in a
50,000 to 100,000 Ohms value for resistor R. The equivalent transistor
amplifier using much lower voltages (from 12-30 Volts) would have a
substantially lower value of R between 200 Ohms-100 Ohms. Therefore a
normal power supply in a transistor amplifier is more likely to affect the
transistor amplifier circuit compared to a Valve amplifier circuit.
If we assume that the regulator impedance at V+ is around 2 Ohms just for
the purpose of this illustration, then let us study the amplitude of the 10
VOLT sine wave as it goes through R and returns back to the OUTPUT of
the TRANSISTOR circuit and VALVE circuit.
In the VALVE circuit, when 10 VOLTS travels across the 50,000 Ohms R towards
the power supply impedance of 2 Ohms , the 10V signal is attenuated
50,000/2 = 25,000 times. Therefore 10V/25,000 = 0.0004 Volts of 1,0kHz sine
wave.
On its way back to the OUTPUT of the circuit it is attenuated by the
impedance of the amplifier (say 100 Ohms): 0.0004 Volts/50,000/1,000 =
0.000008 Volts. Therefore, 0.000008 VOLTS of out of phase sine wave
accompanies the 10 Volts sine wave as out-of-phase distortion in the VALVE
CIRCUIT.
In a normal TRANSISTOR circuit, the 10 VOLTS going across the 200 Ohms
resistor R would be attenuated only 10/200/2 = 0.1 VOLTS. On the way back
to the output, the voltage is attenuated by: 0.1V/200/1000 = 0.05 VOLTS of
out-of-phase sine wave added to the 10 VOLT output sine wave.
V1
12AX7
R1
47K
R2
1.82k
RL
300k
C2
0.1uF
V+
Vin
VSIN
IN
OUT
V1
1kHz R1
47K
RL
7.75k
R2
1.8K
Q1
2N2222A
VCC
IN
C2
0.1uF
OUT