PMA said:
I like capacitance multipliers as well. A couple of years ago I used MOSFET capacitance multipliers/pass transistors to provide input stage, driver and screen voltages for a vacuum tube power amp. In some applications like this you WANT the output voltage to track changes in the main power supply, so you don't really want precision regulation, you just want the great filtering and isolation afforded by the capacitance multiplier.
BJTs and MOSFETs each have their advantages in a capacitance multiplier application. One may have to give up a few more volts when using a MOSFET. Never forget to protect the gate from excessive gate-source voltages under turn-on, charge-up, or fault conditions.
Cheers,
Bob
With regard to cap multipliers. I have used them in all quality audio products since 1973, when I put a pair of cap multipliers as a buffer for the phono stage of the Levinson JC-2.
I have used 4 different types of cap multipliers: bipolar transistor, jfet, mosfet, and 'pseudo-zener' regulated.
The first, and most obvious is the bipolar multiplier. It appears to need a large electrolytic cap on its output to behave quietly. That is its problem.
The second is the jfet follower. This design is VERY quiet, but it has fairly high output resistance, limited current capacity, and is VERY sensitive to accidental shorts.
The third is the mosfet follower. It is relatively noisy at low frequencies, but it can drive high currents and is relatively immune from voltage or current overload.
The fourth is replacing the input resistor with a NORTON equivalent Zener by using a low noise current source, usually made by a selected n-channel jfet like the American part # j203, and a selected resistor connected to ground. This resistor must be bypassed with a large value cap, of 22uF or more, in order to work properly in order to bypass the resistor noise and to limit the noise gain of the current source jfet.
This controls both fixed voltage and noise, but it is not very accurate, with voltage, over temperature.
I have used 4 different types of cap multipliers: bipolar transistor, jfet, mosfet, and 'pseudo-zener' regulated.
The first, and most obvious is the bipolar multiplier. It appears to need a large electrolytic cap on its output to behave quietly. That is its problem.
The second is the jfet follower. This design is VERY quiet, but it has fairly high output resistance, limited current capacity, and is VERY sensitive to accidental shorts.
The third is the mosfet follower. It is relatively noisy at low frequencies, but it can drive high currents and is relatively immune from voltage or current overload.
The fourth is replacing the input resistor with a NORTON equivalent Zener by using a low noise current source, usually made by a selected n-channel jfet like the American part # j203, and a selected resistor connected to ground. This resistor must be bypassed with a large value cap, of 22uF or more, in order to work properly in order to bypass the resistor noise and to limit the noise gain of the current source jfet.
This controls both fixed voltage and noise, but it is not very accurate, with voltage, over temperature.
Bob Cordell said:
Sorry edit error.
Does it make sense to use capacitance multipliers to power the front end and Vas of a power amplifier.
Is it realistic to investigate the replacement by a capacitance multiplier of the large and expensive electrolytics of the output stage in a class AB amplifier.
What about the large pulses of current?
Will it sound better?
JPV
john curl said:
The BT thread will of course still have its own life, but a lot of the posts and a lot more posts could be implemented in the new thread:
The “John Curl Interview” thread is meant to be a discussion thread about all the topics “how to create the perfect sound”
Cheers
Stinius
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